AD6659: Dual IF Receiver Data Sheet (Rev. A) PDF

Dual IF Receiver
AD6659
FEATURES
APPLICATIONS
Communications
Diversity radio systems
Multimode digital receivers
3G, W-CDMA, LTE, CDMA2000, TD-SCDMA, MC-GSM
I/Q demodulation systems
Smart antenna systems
Battery-powered instruments
General-purpose software radios
FUNCTIONAL BLOCK DIAGRAM
AVDD
AGND
SDIO
SCLK
CSB
QUADRATURE
ERROR AND
DC OFFSET
CORRECTION
12
NOISE
SHAPING
REQUANTIZER
VREF
SENSE
VCM
RBIAS
AD6659
REF
SELECT
16
VIN+B
VIN–B
ADC
QUADRATURE
ERROR AND
DC OFFSET
CORRECTION
DIVIDE
1 TO 6
CLK+ CLK–
12
NOISE
SHAPING
REQUANTIZER
D11A (MSB)
D0A (LSB)
DCOA
DRVDD
DUTY CYCLE
STABILIZER
MODE
CONTROLS
DCS
PDWN DFS OEB
SYNC
ORA
ORB
D11B (MSB)
D0B (LSB)
DCOB
08701-001
VIN–A
ADC
CMOS OUTPUT BUFFER
16
VIN+A
CMOS OUTPUT BUFFER
SPI
PROGRAMMING DATA
MUX OPTION
12-bit, 80 MSPS output data rate per channel
1.8 V analog supply operation (AVDD)
1.8 V to 3.3 V output supply (DRVDD)
Integrated noise shaping requantizer (NSR)
Integrated quadrature error correction (QEC)
Performance with NSR enabled
SNR = 81 dBFS in 16 MHz band up to 30 MHz at 80 MSPS
Performance with NSR disabled
SNR = 72 dBFS up to 70 MHz at 80 MSPS
SFDR = 90 dBc up to 70 MHz input at 80 MSPS
Low power: 98 mW per channel at 80 MSPS
Differential input with 700 MHz bandwidth
On-chip voltage reference and sample-and-hold circuit
2 V p-p differential analog input
Serial port control options
Offset binary, gray code, or twos complement data format
Optional clock duty cycle stabilizer
Integer 1-to-6 input clock divider
Data output multiplex option
Built-in selectable digital test pattern generation
Energy-saving power-down modes
Data clock out with programmable clock and data alignment
Figure 1.
PRODUCT HIGHLIGHTS
1.
2.
3.
4.
5.
The AD6659 operates from a single 1.8 V analog power
supply and features a separate digital output driver supply
to accommodate 1.8 V to 3.3 V logic families.
SPI-selectable noise shaping requantizer (NSR) function
that allows for improved SNR within a reduced bandwidth
of up to 70 MHz at 80 MSPS.
SPI-selectable dc correction and quadrature error
correction (QEC) that corrects for dc offset, gain, and
phase mismatches between the two channels.
A standard serial port interface supports various product
features and functions, such as data output formatting,
internal clock divider, power-down, DCO/data timing,
offset adjustments, and voltage reference modes.
The AD6659 is packaged in a 64-lead RoHS-compliant
LFCSP that is pin compatible with the AD9269 16-bit
ADC, the AD9268 16-bit ADC, the AD9258 14-bit ADC,
the AD9251 14-bit ADC, the AD9231 12-bit ADC, and the
AD9204 10-bit ADC, enabling a simple migration path
between 10-bit and 16-bit converters sampling from
20 MSPS to 125 MSPS.
Rev. A
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
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Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113
©2010 Analog Devices, Inc. All rights reserved.
AD6659
TABLE OF CONTENTS
Features .............................................................................................. 1 Digital Outputs ........................................................................... 22 Applications ....................................................................................... 1 Timing ......................................................................................... 22 Functional Block Diagram .............................................................. 1 Built-In Self-Test and Output Test ............................................... 24 Product Highlights ........................................................................... 1 BIST .............................................................................................. 24 Revision History ............................................................................... 2 Output Test Modes ..................................................................... 24 General Description ......................................................................... 3 Channel/Chip Synchronization .................................................... 25 Specifications..................................................................................... 4 Noise Shaping Requantizer (NSR) ............................................... 26 DC Specifications ......................................................................... 4 20% BW NSR Mode (16 MHz BW at 80 MSPS) .................... 26 AC Specifications.......................................................................... 5 DC and Quadrature Error Correction (QEC) ............................ 27 Digital Specifications ................................................................... 6 Serial Port Interface (SPI) .............................................................. 29 Switching Specifications .............................................................. 7 Configuration Using the SPI ..................................................... 29 Timing Specifications .................................................................. 8 Hardware Interface..................................................................... 30 Absolute Maximum Ratings............................................................ 9 Configuration Without the SPI ................................................ 30 Thermal Characteristics .............................................................. 9 SPI Accessible Features .............................................................. 30 ESD Caution .................................................................................. 9 Memory Map .................................................................................. 31 Pin Configuration and Function Descriptions ........................... 10 Reading the Memory Map Register Table............................... 31 Typical Performance Characteristics ........................................... 12 Open Locations .......................................................................... 31 Equivalent Circuits ......................................................................... 14 Default Values ............................................................................. 31 Theory of Operation ...................................................................... 16 Memory Map Register Table ..................................................... 32 ADC Architecture ...................................................................... 16 Memory Map Register Descriptions ........................................ 35 Analog Input Considerations.................................................... 16 Applications Information .............................................................. 37 Voltage Reference ....................................................................... 19 Design Guidelines ...................................................................... 37 Clock Input Considerations ...................................................... 20 Outline Dimensions ....................................................................... 38 Power Dissipation and Standby Mode ..................................... 21 Ordering Guide .......................................................................... 38 REVISION HISTORY
2/10―Rev. 0 to Rev. A
Changes to Title ................................................................................ 1
Changes to Features Section............................................................ 1
Changes to General Description Section ...................................... 3
1/10—Revision 0: Initial Version
Rev. A | Page 2 of 40
AD6659
GENERAL DESCRIPTION
The AD6659 is a mixed-signal, dual-channel IF receiver supporting radio topologies requiring two receiver signal paths, such as
in main/diversity or direct conversion. This communications
systems processor consists of two high performance analog-todigital converters (ADCs) and noise shaping requantizer (NSR)
digital blocks. It is designed to support various communications
applications where high dynamic range performance and small size
are desired.
The high dynamic range ADC core features a multistage differential pipelined architecture with integrated output error correction
logic. Each ADC features a wide bandwidth switch capacitor
sampling network within the first stage of the differential pipeline. An integrated voltage reference eases design considerations.
Each ADC output is connected internally to an NSR block. The
integrated NSR circuitry allows for improved SNR performance
in a smaller frequency band within the Nyquist region. The
device supports two different output modes selectable via the
serial port interface (SPI).
With the NSR feature enabled, the outputs of the ADCs are
processed such that the AD6659 supports enhanced SNR
performance within a limited region of the Nyquist bandwidth
while maintaining a 12-bit output resolution. The NSR block is
programmed to provide a bandwidth of 20% of the sample
clock. For example, with a sample clock rate of 80 MSPS, the
AD6659 can achieve up to 81.5 dBFS SNR for a 16 MHz
bandwidth at 9.7 MHz AIN.
With the NSR block disabled, the ADC data is provided directly
to the output with an output resolution of 12 bits. The AD6659
can achieve up to 72 dBFS SNR for the entire Nyquist
bandwidth when operated in this mode.
After digital processing, output data is routed into two 12-bit
output ports that support 1.8 V or 3.3 V CMOS levels.
The AD6659 receiver digitizes a wide spectrum of IF frequencies.
Each receiver is designed for simultaneous reception of the
main and diversity channel. This IF sampling architecture
greatly reduces component cost and complexity compared with
traditional analog techniques or less integrated digital methods.
The AD6659 also incorporates an optional integrated dc offset
correction and quadrature error correction (QEC) block that
corrects for gain and phase mismatch between the two channels.
This functional block proves invaluable in complex signal
processing applications such as direct conversion receivers.
The ADC contains several features designed to maximize
flexibility and minimize system cost, such as programmable
clock and data alignment and programmable digital test pattern
generation. The available digital test patterns include built-in
deterministic and pseudorandom patterns, along with custom
user-defined test patterns entered via the serial port interface (SPI).
A differential clock input controls all internal conversion cycles.
An optional duty cycle stabilizer (DCS) compensates for wide
variations in the clock duty cycle while maintaining excellent
overall ADC performance.
The digital output data is presented in offset binary, gray code, or
twos complement format. A data clock output (DCO) is provided
for each ADC channel to ensure proper latch timing with
receiving logic. Both 1.8 V and 3.3 V CMOS levels are supported,
and output data can be multiplexed onto a single output bus.
The AD6659 is available in a 64-lead, RoHS-compliant LFCSP,
and it is specified over the industrial temperature range
(−40°C to +85°C).
Rev. A | Page 3 of 40
AD6659
SPECIFICATIONS
DC SPECIFICATIONS
AVDD = 1.8 V; DRVDD = 1.8 V, maximum sample rate, 2 V p-p differential input, 1.0 V internal reference; AIN = −1.0 dBFS,
DCS disabled, unless otherwise noted.
Table 1.
Parameter
RESOLUTION
ACCURACY
No Missing Codes
Offset Error
Gain Error 1
Differential Nonlinearity (DNL) 2
Integral Nonlinearity (INL)2
MATCHING CHARACTERISTICS
Offset Error
Gain Error1
TEMPERATURE DRIFT
Offset Error
INTERNAL VOLTAGE REFERENCE
Output Voltage (1 V Mode)
Load Regulation Error at 1.0 mA
INPUT REFERRED NOISE
VREF = 1.0 V
ANALOG INPUT
Input Span, VREF = 1.0 V
Input Capacitance 3
Input Common-Mode Voltage
Input Common-Mode Range
REFERENCE INPUT RESISTANCE
POWER SUPPLIES
Supply Voltage
AVDD
DRVDD
Supply Current
IAVDD2
IDRVDD2 (1.8 V)
IDRVDD2 (3.3 V)
POWER CONSUMPTION
DC Input
Sine Wave Input2 (DRVDD = 1.8 V)
Sine Wave Input2 (DRVDD = 3.3 V)
Standby Power 4
Power-Down Power
Temp
Full
Min
12
Full
Full
Full
Full
25°C
Full
25°C
Typ
Max
Unit
Bits
Guaranteed
±0.05
−1.9
±0.5
% FSR
% FSR
LSB
LSB
LSB
LSB
±0.30
±0.13
±0.40
±0.17
25°C
25°C
±0.0
0.4
Full
±2
Full
Full
0.981
0.993
2
±0.65
% FSR
% FSR
ppm/°C
1.005
V
mV
25°C
0.25
LSB rms
Full
Full
Full
Full
Full
2
6.5
0.9
V p-p
pF
V
V
kΩ
Full
Full
0.5
1.3
7.5
1.8
1.9
3.6
V
V
Full
Full
Full
113
9.3
18.5
119
mA
mA
mA
Full
Full
Full
Full
Full
196
220
264
37
1.0
1
1.7
1.7
240
Measured with 1.0 V external reference.
Measured with a 10 MHz input frequency at rated sample rate, full-scale sine wave, with approximately 5 pF loading on each output bit.
3
Input capacitance refers to the effective capacitance between one differential input pin and AGND.
4
Standby power is measured with a dc input and the CLK active.
2
Rev. " | Page 4 of 40
mW
mW
mW
mW
mW
AD6659
AC SPECIFICATIONS
AVDD = 1.8 V; DRVDD = 1.8 V, maximum sample rate, 2 V p-p differential input, 1.0 V internal reference; AIN = −1.0 dBFS,
DCS disabled, unless otherwise noted.
Table 2.
Parameter 1
SIGNAL-TO-NOISE RATIO (SNR)—NSR DISABLED
fIN = 9.7 MHz
fIN = 30.5 MHz
fIN = 70 MHz
SIGNAL-TO-NOISE RATIO (SNR)—NSR ENABLED
20% Bandwidth (16 MHz @ 80 MSPS)
fIN = 9.7 MHz
fIN = 30.5 MHz
fIN = 70 MHz
SIGNAL-TO-NOISE-AND-DISTORTION (SINAD)
fIN = 9.7 MHz
fIN = 30.5 MHz
fIN = 70 MHz
EFFECTIVE NUMBER OF BITS (ENOB)
fIN = 9.7 MHz
fIN = 30.5 MHz
fIN = 70 MHz
WORST SECOND OR THIRD HARMONIC
fIN = 9.7 MHz
fIN = 30.5 MHz
fIN = 70 MHz
SPURIOUS-FREE DYNAMIC RANGE (SFDR)
fIN = 9.7 MHz
fIN = 30.5 MHz
fIN = 70 MHz
WORST OTHER (HARMONIC OR SPUR)
fIN = 9.7 MHz
fIN = 30.5 MHz
fIN = 70 MHz
TWO-TONE SFDR
fIN = 28.3 MHz (−7 dBFS), 30.6 MHz (−7 dBFS)
CROSSTALK 2
ANALOG INPUT BANDWIDTH
1
2
Temp
25°C
25°C
25°C
Full
Min
Typ
Max
Unit
72.4
72.3
72.0
dBFS
dBFS
dBFS
dBFS
25°C
25°C
25°C
81.5
81.2
80.3
dBFS
dBFS
dBFS
25°C
25°C
25°C
Full
72.4
72.2
71.9
dBFS
dBFS
dBFS
dBFS
25°C
25°C
25°C
11.7
11.7
11.7
Bits
Bits
Bits
25°C
25°C
25°C
Full
−93
−92
−90
dBc
dBc
dBc
dBc
25°C
25°C
25°C
Full
93
92
90
dBc
dBc
dBc
dBc
25°C
25°C
25°C
Full
−99
−99
−98
dBc
dBc
dBc
dBc
25°C
Full
25°C
90
−110
700
71.4
71.5
−80
80
See the AN-835 Application Note, Understanding High Speed ADC Testing and Evaluation, for a complete set of definitions.
Crosstalk is measured at 100 MHz with −1.0 dBFS on one channel and no input on the alternate channel.
Rev. " | Page 5 of 40
−91
dBc
dBc
MHz
AD6659
DIGITAL SPECIFICATIONS
AVDD = 1.8 V; DRVDD = 1.8 V, maximum sample rate, 2 V p-p differential input, 1.0 V internal reference; AIN = −1.0 dBFS,
DCS disabled, unless otherwise noted.
Table 3.
Parameter
DIFFERENTIAL CLOCK INPUTS (CLK+, CLK−)
Logic Compliance
Internal Common-Mode Bias
Differential Input Voltage
Input Voltage Range
High Level Input Current
Low Level Input Current
Input Resistance
Input Capacitance
LOGIC INPUTS (SCLK/DFS, SYNC, PDWN) 1
High Level Input Voltage
Low Level Input Voltage
High Level Input Current
Low Level Input Current
Input Resistance
Input Capacitance
LOGIC INPUTS (CSB) 2
High Level Input Voltage
Low Level Input Voltage
High Level Input Current
Low Level Input Current
Input Resistance
Input Capacitance
LOGIC INPUTS (SDIO1/DCS2)
High Level Input Voltage
Low Level Input Voltage
High Level Input Current
Low Level Input Current
Input Resistance
Input Capacitance
DIGITAL OUTPUTS
DRVDD = 3.3 V
High Level Output Voltage, IOH = 50 μA
High Level Output Voltage, IOH = 0.5 mA
Low Level Output Voltage, IOL = 1.6 mA
Low Level Output Voltage, IOL = 50 μA
DRVDD = 1.8 V
High Level Output Voltage, IOH = 50 μA
High Level Output Voltage, IOH = 0.5 mA
Low Level Output Voltage, IOL = 1.6 mA
Low Level Output Voltage, IOL = 50 μA
1
2
Temp
Full
Full
Full
Full
Full
Full
Full
Min
Typ
Max
Unit
3.6
AVDD + 0.2
+10
+10
12
V
V p-p
V
μA
μA
kΩ
pF
CMOS/LVDS/LVPECL
0.9
0.2
GND − 0.3
−10
−10
8
Full
Full
Full
Full
Full
Full
1.2
0
−50
−10
Full
Full
Full
Full
Full
Full
1.2
0
−10
40
Full
Full
Full
Full
Full
Full
1.2
0
−10
40
Full
Full
Full
Full
3.29
3.25
Full
Full
Full
Full
1.79
1.75
10
4
DRVDD + 0.3
0.8
−75
+10
V
V
μA
μA
kΩ
pF
DRVDD + 0.3
0.8
+10
135
V
V
μA
μA
kΩ
pF
DRVDD + 0.3
0.8
+10
130
V
V
μA
μA
kΩ
pF
30
2
26
2
26
5
Internal 30 kΩ pull-down.
Internal 30 kΩ pull-up.
Rev. " | Page 6 of 40
0.2
0.05
V
V
V
V
0.2
0.05
V
V
V
V
AD6659
SWITCHING SPECIFICATIONS
AVDD = 1.8 V; DRVDD = 1.8 V, maximum sample rate, 2 V p-p differential input, 1.0 V internal reference; AIN = −1.0 dBFS,
DCS disabled, unless otherwise noted.
Table 4.
Parameter
CLOCK INPUT PARAMETERS
Input Clock Rate
Conversion Rate 1
CLK Period—Divide-by-1 Mode (tCLK)
CLK Pulse Width High (tCH)
Aperture Delay (tA)
Aperture Uncertainty (Jitter, tJ)
DATA OUTPUT PARAMETERS
Data Propagation Delay (tPD)
DCO Propagation Delay (tDCO)
DCO to Data Skew (tSKEW)
Pipeline Delay (Latency)
With NSR Enabled
With QEC Enabled
Wake-Up Time 2
Standby
OUT-OF-RANGE RECOVERY TIME
2
Min
Full
Full
Full
Full
Full
Full
Typ
Max
Unit
480
80
6.25
1.0
0.1
MHz
MSPS
ns
ns
ns
ps rms
3
3
0.1
9
10
11
350
260
2
ns
ns
ns
Cycles
Cycles
Cycles
μs
ns
Cycles
3
12.5
Full
Full
Full
Full
Full
Full
Full
Full
Full
Conversion rate is the clock rate after the CLK divider.
Wake-up time is dependent on the value of the decoupling capacitors.
N–1
N+4
tA
N+5
N
N+3
VIN
N+1
tCH
N+2
tCLK
CLK+
CLK–
tDCO
DCOA/DCOB
tSKEW
CH A/CH B DATA
N–9
N–8
tPD
Figure 2. CMOS Output Data Timing
Rev. " | Page 7 of 40
N–7
N–6
N–5
08701-002
1
Temp
AD6659
N–1
N+4
tA
N+5
N
N+3
VIN
N+1
tCH
N+2
tCLK
CLK+
CLK–
tDCO
DCOA/DCOB
CH A/CH B DATA
CH B
N–9
CH A
N–8
CH B
N–8
CH A
N–7
CH B
N–7
CH A
N–6
CH B
N–6
CH A
N–5
tPD
08701-003
tSKEW
CH A
N–9
Figure 3. CMOS Interleaved Output Timing
TIMING SPECIFICATIONS
Table 5.
Parameter
SYNC TIMING REQUIREMENTS
tSSYNC
tHSYNC
SPI TIMING REQUIREMENTS
tDS
tDH
tCLK
tS
tH
tHIGH
tLOW
tEN_SDIO
tDIS_SDIO
Test Conditions/Comments
Min
SYNC to rising edge of CLK setup time (see Figure 4)
SYNC to rising edge of CLK hold time (see Figure 4)
0.24
0.40
Setup time between the data and the rising edge of SCLK (see Figure 50)
Hold time between the data and the rising edge of SCLK (see Figure 50)
Period of the SCLK (see Figure 50)
Setup time between CSB and SCLK (see Figure 50)
Hold time between CSB and SCLK (see Figure 50)
SCLK pulse width high (see Figure 50)
SCLK pulse width low (see Figure 50)
Time required for the SDIO pin to switch from an input to an output relative
to the SCLK falling edge
Time required for the SDIO pin to switch from an output to an input relative
to the SCLK rising edge
Timing Diagram
CLK+
tHSYNC
08701-004
tSSYNC
SYNC
Figure 4. SYNC Input Timing Requirements
Rev. " | Page 8 of 40
Typ
Max
Unit
ns
ns
2
2
40
2
2
10
10
10
ns
ns
ns
ns
ns
ns
ns
ns
10
ns
AD6659
ABSOLUTE MAXIMUM RATINGS
THERMAL CHARACTERISTICS
Table 6.
Parameter
AVDD to AGND
DRVDD to AGND
VIN+A, VIN+B, VIN−A, VIN−B to AGND
CLK+, CLK− to AGND
SYNC to AGND
VREF to AGND
SENSE to AGND
VCM to AGND
RBIAS to AGND
CSB to AGND
SCLK/DFS to AGND
SDIO/DCS to AGND
OEB to AGND
PDWN to AGND
D0x through D11x to AGND
DCOx to AGND
Operating Temperature Range
(Ambient)
Maximum Junction Temperature
Under Bias
Storage Temperature Range
(Ambient)
Rating
−0.3 V to +2.0 V
−0.3 V to +3.9 V
−0.3 V to AVDD + 0.2 V
−0.3 V to AVDD + 0.2 V
−0.3 V to DRVDD + 0.3 V
−0.3 V to AVDD + 0.2 V
−0.3 V to AVDD + 0.2 V
−0.3 V to AVDD + 0.2 V
−0.3 V to AVDD + 0.2 V
−0.3 V to DRVDD + 0.3 V
−0.3 V to DRVDD + 0.3 V
−0.3 V to DRVDD + 0.3 V
−0.3 V to DRVDD + 0.3 V
−0.3 V to DRVDD + 0.3 V
−0.3 V to DRVDD + 0.3 V
−0.3 V to DRVDD + 0.3 V
−40°C to +85°C
The exposed paddle is the only ground connection for the chip.
The exposed paddle must be soldered to the AGND plane of the
user’s circuit board. Soldering the exposed paddle to the user’s
board also increases the reliability of the solder joints and
maximizes the thermal capability of the package.
Typical θJA is specified for a 4-layer PCB with a solid ground
plane. As listed in Table 7, airflow improves heat dissipation,
which reduces θJA. In addition, metal in direct contact with the
package leads from metal traces, through holes, ground, and
power planes, reduces the θJA.
Table 7. Thermal Resistance
Package Type
64-Lead LFCSP
9 mm × 9 mm
(CP-64-4)
1
Airflow
Velocity
(m/sec)
0
1.0
2.5
θJA1, 2
23°C/W
20°C/W
18°C/W
θJC1, 3
2.0°C/W
Per JEDEC 51-7, plus JEDEC 25-5 2S2P test board.
Per JEDEC JESD51-2 (still air) or JEDEC JESD51-6 (moving air).
3
Per MIL-STD 883, Method 1012.1.
4
Per JEDEC JESD51-8 (still air).
2
150°C
−65°C to +150°C
ESD CAUTION
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
Rev. " | Page 9 of 40
θJB1, 4
12°C/W
AD6659
64
63
62
61
60
59
58
57
56
55
54
53
52
51
50
49
AVDD
AVDD
VIN+B
VIN–B
AVDD
AVDD
RBIAS
VCM
SENSE
VREF
AVDD
AVDD
VIN–A
VIN+A
AVDD
AVDD
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
PIN 1
INDICATOR
AD6659
TOP VIEW
(Not to Scale)
48
47
46
45
44
43
42
41
40
39
38
37
36
35
34
33
PDWN
OEB
CSB
SCLK/DFS
SDIO/DCS
ORA
D11A (MSB)
D10A
D9A
D8A
D7A
DRVDD
D6A
D5A
D4A
D3A
NOTES
1. NC = NO CONNECT.
2. THE EXPOSED PADDLE MUST BE SOLDERED TO THE PCB GROUND TO
ENSURE PROPER HEAT DISSIPATION, NOISE, AND MECHANICAL
STRENGTH BENEFITS.
08701-005
D8B
D9B
DRVDD
D10B
(MSB) D11B
ORB
DCOB
DCOA
NC
NC
NC
DRVDD
NC
(LSB) D0A
D1A
D2A
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
CLK+
CLK–
SYNC
NC
NC
NC
NC
(LSB) D0B
D1B
DRVDD
D2B
D3B
D4B
D5B
D6B
D7B
Figure 5. Pin Configuration
Table 8. Pin Function Descriptions
Pin No.
0, EP
Mnemonic
AGND
1, 2
3
4 to 7, 25 to 27, 29
8, 9, 11 to 18, 20, 21
10, 19, 28, 37
22
23
24
30 to 36, 38 to 42
43
44
CLK+, CLK−
SYNC
NC
D0B to D11B
DRVDD
ORB
DCOB
DCOA
D0A to D11A
ORA
SDIO/DCS
45
SCLK/DFS
46
47
CSB
OEB
48
PDWN
Description
Exposed paddle is the only ground connection for the chip. It must be connected to
the printed circuit board (PCB) AGND.
Differential Encode Clock. PECL, LVDS, or 1.8 V CMOS inputs.
Digital Input. SYNC input to clock divider. 30 kΩ internal pull-down.
Do Not Connect.
Channel B Digital Outputs. D11B is the MSB and D0B is the LSB.
Digital Output Driver Supply (1.8 V to 3.3 V).
Channel B Out-of-Range Digital Output.
Channel B Data Clock Digital Output.
Channel A Data Clock Digital Output.
Channel A Digital Outputs. D11A is the MSB and D0A is the LSB.
Channel A Out-of-Range Digital Output.
SPI Data Input/Output (SDIO). The SDIO function provides bidirectional SPI data I/O in
SPI mode with a 30 kΩ internal pull-down in SPI mode. The duty cycle stabilizer (DCS pin
function) is the static enable input for the duty cycle stabilizer in non-SPI mode with a
30 kΩ internal pull-up in non-SPI (DCS) mode.
SPI Clock (SCLK) Input in SPI Mode/Data Format Select (DFS). 30 kΩ internal pull-down for both
SCLK and DFS. The DFS function provides static control of data output format in non-SPI mode.
When DFS is high, it equals twos complement output. When DFS is low, it equals offset binary
output.
SPI Chip Select. Active low enable; 30 kΩ internal pull-up.
Digital Input. When OEB is low, it enables the Channel A and Channel B digital outputs; when
OEB is high, the outputs are tristated. 30 kΩ internal pull-down.
Digital Input. 30 kΩ internal pull-down. When PDWN is high, it powers down the device.
When PDWN is low, the device runs in normal operation.
Rev. " | Page 10 of 40
AD6659
Pin No.
49, 50, 53, 54, 59, 60, 63, 64
51, 52
55
56
57
58
61, 62
Mnemonic
AVDD
VIN+A, VIN−A
VREF
SENSE
VCM
RBIAS
VIN−B, VIN+B
Description
1.8 V Analog Supply Pins.
Channel A Analog Inputs.
Voltage Reference Input/Output.
Reference Mode Selection.
Analog output voltage at midsupply to set common mode of the analog inputs.
Sets Analog Current Bias. Connect to a 10 kΩ (1% tolerance) resistor to ground.
Channel B Analog Inputs.
Rev. " | Page 11 of 40
AD6659
TYPICAL PERFORMANCE CHARACTERISTICS
AVDD = 1.8 V; DRVDD = 1.8 V, maximum sample rate, 2 V p-p differential input, 1.0 V internal reference; AIN = −1.0 dBFS,
DCS disabled, unless otherwise noted.
0
0
80MSPS
9.7MHz @ –1dBFS
SNR = 70.2dB (71.2dBFS)
SFDR = 93.6dBc
80MSPS
100.3MHz @ –1dBFS
SNR = 70.5dB (71.5dBFS)
SFDR = 83.5dBc
–15
–30
–40
AMPLITUDE (dBFS)
AMPLITUDE (dBFS)
–20
–60
–80
–100
–45
–60
–75
–90
–105
–120
0
5
10
15
20
25
FREQUENCY (MHz)
30
35
40
–135
08701-054
–140
0
4
Figure 6. Single-Tone FFT with fIN = 9.7 MHz
12
16
20
24
28
FREQUENCY (MHz)
32
36
40
Figure 9. Single-Tone FFT with fIN = 100.3 MHz
0
0
80MSPS
30.6MHz @ –1dBFS
SNR = 71.4 dB (72.4dBFS)
SFDR = 94.4dBc
–20
–40
80MSPS
28.3MHz @ –7dBFS
30.6MHz @ –7dBFS
SFDR = 87.9dBc
–15
–30
AMPLITUDE (dBFS)
AMPLITUDE (dBFS)
8
08701-057
–120
–60
–80
–100
–45
–60
–75
–90
F2 – F1 2F2 – F1
2F1 + F2
F1 + F2
2F2 – F1
2F1 – F2
–105
–120
0
5
10
15
20
25
FREQUENCY (MHz)
30
35
40
–135
08701-055
–140
0
8
12
16
20
24
28
FREQUENCY (MHz)
32
36
40
Figure 10. Two-Tone FFT with fIN1 = 28.3 MHz and fIN2 = 30.6 MHz
Figure 7. Single-Tone FFT with fIN = 30.6 MHz
0
0
80MSPS
69MHz @ –1dBFS
SNR = 70dB (71dBFS)
SFDR = 88.9dBc
–20
SFDR/IMD3 (dBc AND dBFS)
–20
–40
–60
–80
–100
SFDR (dBc)
–40
–60
IMD3 (dBc)
–80
SFDR (dBFS)
–100
–140
0
5
10
15
20
25
FREQUENCY (MHz)
30
35
40
–120
–70
IMD3 (dBFS)
–60
–50
–40
–30
–20
INPUT AMPLITUDE (dBFS)
–10
Figure 11. Two-Tone SFDR/IMD3 vs. Input Amplitude (AIN) with
fIN1 = 28.3 MHz and fIN2 = 30.6 MHz
Figure 8. Single-Tone FFT with fIN = 69 MHz
Rev. " | Page 12 of 40
08701-060
–120
08701-056
AMPLITUDE (dBFS)
4
08701-059
–120
AD6659
AVDD = 1.8 V; DRVDD = 1.8 V, maximum sample rate, 2 V p-p differential input, 1.0 V internal reference; AIN = −1.0 dBFS,
DCS disabled, unless otherwise noted.
100
120
SFDR
100
80
SNR/SFDR (dBFS AND dBc)
SNR/SFDR (dBFS AND dBc)
90
SNR
70
60
50
40
30
20
SFDRFS
80
SNRFS
60
SFDR
SNR
40
20
0
50
100
150
INPUT FREQUENCY (MHz)
0
–70
08701-061
0
200
Figure 12. SNR/SFDR vs. Input Frequency (AIN) with
2 V p-p Full Scale
–60
–50
–40
–30
–20
INPUT AMPLITUDE (dBc)
–10
0
08701-064
10
Figure 15. SNR/SFDR vs. Input Amplitude (AIN) with fIN = 9.7 MHz
0.4
0.3
0.2
INL ERROR (LSB)
DNL ERROR (LSB)
0.2
0.1
0
–0.1
0
–0.2
0
500
1000
1500 2000 2500
OUTPUT CODE
3000
3500
4000
–0.4
08701-063
–0.3
0
Figure 13. DNL Error with fIN = 9.7 MHz
SFDR
SNRFS
70
60
50
40
30
20
10
0
20
30
40
50
60
70
SAMPLE RATE (MHz)
80
08701-062
SNRFS/SFDR (dBFS/dBc)
80
10
1000
1500 2000 2500
OUTPUT CODE
3000
Figure 16. INL Error with fIN = 9.7 MHz
100
90
500
Figure 14. SNR/SFDR vs. Sample Rate with AIN = 9.7 MHz
Rev. A | Page 13 of 40
3500
4000
08701-066
–0.2
AD6659
EQUIVALENT CIRCUITS
DRVDD
AVDD
350Ω
SCLK/DFS, SYNC,
OEB, AND PDWN
VIN±x
08701-043
08701-039
30kΩ
Figure 21. Equivalent SCLK/DFS, SYNC, OEB, and PDWN Input Circuit
Figure 17. Equivalent Analog Input Circuit
AVDD
5Ω
CLK+
AVDD
15kΩ
0.9V
AVDD
15kΩ
375Ω
RBIAS
AND VCM
5Ω
08701-040
08701-044
CLK–
Figure 22. Equivalent RBIAS and VCM Circuit
Figure 18. Equivalent Clock Input Circuit
AVDD
DRVDD
DRVDD
30kΩ
SDIO/DCS
AVDD
350Ω
350Ω
30kΩ
CSB
08701-041
08701-045
30kΩ
Figure 23. Equivalent CSB Input Circuit
Figure 19. Equivalent SDIO/DCS Input Circuit
AVDD
DRVDD
375Ω
08701-046
08701-042
SENSE
Figure 20. Equivalent Digital Output Circuit
Figure 24. Equivalent SENSE Circuit
Rev. " | Page 14 of 40
AD6659
AVDD
375Ω
7.5kΩ
08701-047
VREF
Figure 25. Equivalent VREF Circuit
Rev. " | Page 15 of 40
AD6659
THEORY OF OPERATION
The AD6659 dual ADC design can be used for diversity reception of signals, where the ADCs are operating identically on the
same carrier but from two separate antennae. The ADCs can be
operated with independent analog inputs. The user can sample
any fS/2 frequency segment from dc to 200 MHz, using appropriate
low-pass or band-pass filtering at the ADC inputs with little loss
in ADC performance. Operation to 300 MHz analog input is
permitted but occurs at the expense of increased ADC noise
and distortion.
In nondiversity applications, the AD6659 can be used as a baseband or direct downconversion receiver, where one ADC is used
for I input data and the other ADC is used for Q input data.
Synchronization capability is provided to allow synchronized
timing between multiple channels or multiple devices.
The AD6659 features a noise shaping requantizer (NSR) to
allow higher than 12-bit SNR to be maintained in a subset of
the Nyquist band.
The AD6659 also incorporates an optional integrated dc offset
correction and quadrature error correction (QEC) block that
can correct for dc offset, gain, and phase mismatch between the
two channels. This functional block can be very beneficial to
complex signal processing applications such as direct conversion
receivers.
Each ADC output is connected internally to an NSR block. The
integrated NSR circuitry allows for improved SNR performance
in a smaller frequency band within the Nyquist region. The
device supports two different output modes selectable via the
SPI. With the NSR feature enabled, the outputs of the ADCs are
processed such that the AD6659 supports enhanced SNR
performance within a limited region of the Nyquist bandwidth
while maintaining a 12-bit output resolution. With the NSR
block disabled, the ADC data is provided directly to the output
with an output resolution of 12 bits. The output staging block
aligns the data, corrects errors, and passes the data to the
CMOS output buffers. The output buffers are powered from a
separate (DRVDD) supply, allowing adjustment of the output
voltage swing. During power-down, the output buffers go into a
high impedance state.
ANALOG INPUT CONSIDERATIONS
The analog input to the AD6659 is a differential switched capacitor
circuit designed for processing differential input signals. This
circuit can support a wide common-mode range while maintaining
excellent performance. By using an input common-mode voltage
of midsupply, users can minimize signal dependent errors and
achieve optimum performance.
H
Programming and control of the AD6659 is accomplished using
a 3-wire, SPI-compatible serial interface.
CPAR
H
VIN+x
CSAMPLE
ADC ARCHITECTURE
S
The pipelined architecture permits the first stage to operate
with a new input sample while the remaining stages operate
with preceding samples. Sampling occurs on the rising edge
of the clock.
Each stage of the pipeline, excluding the last, consists of a low
resolution flash ADC connected to a switched capacitor DAC
and an interstage residue amplifier (for example, a multiplying
digital-to-analog converter (MDAC)). The residue amplifier
magnifies the difference between the reconstructed DAC output
and the flash input for the next stage in the pipeline. One bit of
redundancy is used in each stage to facilitate digital correction
of flash errors. The last stage simply consists of a flash ADC.
S
S
S
CSAMPLE
VIN–x
H
CPAR
H
08701-006
The AD6659 architecture consists of a multistage, pipelined ADC.
Each stage provides sufficient overlap to correct for flash errors
in the preceding stage. The quantized outputs from each stage
are combined into a final 12-bit result in the digital correction
logic. Alternately, the 12-bit result can be processed through the
noise shaping requantizer (NSR) block before it is sent to the
digital correction logic.
Figure 26. Switched Capacitor Input Circuit
The clock signal alternately switches the input circuit between
sample and hold mode (see Figure 26). When the input circuit
is switched to sample mode, the signal source must be capable
of charging the sample capacitors and settling within one-half
of a clock cycle. A small resistor in series with each input can
help reduce the peak transient current injected from the output
stage of the driving source. In addition, low Q inductors or ferrite
beads can be placed on each leg of the input to reduce high
differential capacitance at the analog inputs and, therefore, achieve
the maximum bandwidth of the ADC. Such use of low Q
inductors or ferrite beads is required when driving the converter
front end at high IF frequencies. Either a shunt capacitor or two
single-ended capacitors can be placed on the inputs to provide a
matching passive network. This ultimately creates a low-pass
filter at the input to limit unwanted broadband noise. See the
Rev. " | Page 16 of 40
AD6659
AN-742 Application Note, the AN-827 Application Note, and the
Analog Dialogue article “Transformer-Coupled Front-End for
Wideband A/D Converters” (Volume 39, April 2005) for more
information. In general, the precise values depend on the
application.
the analog input, the VCM voltage can be connected to the
center tap of the secondary winding of the transformer.
VIN+x
R
2V p-p
49.9Ω
Input Common Mode
An on-board, common-mode voltage reference is included in
the design and is available from the VCM pin. The VCM pin
must be decoupled to ground by a 0.1 μF capacitor, as described
in the Applications Information section.
100
SFDR (dBc)
0.1µF
Figure 29. Differential Transformer-Coupled Configuration
The signal characteristics must be considered when selecting
a transformer. Most RF transformers saturate at frequencies
below a few megahertz (MHz). Excessive signal power can also
cause core saturation, which leads to distortion.
At input frequencies in the second Nyquist zone and above, the
noise performance of most amplifiers is not adequate to achieve
the true SNR performance of the AD6659. For applications above
~10 MHz where SNR is a key parameter, differential double balun
coupling is the recommended input configuration (see Figure 31).
An alternative to using a transformer-coupled input at frequencies
in the second Nyquist zone is to use the AD8352 differential driver.
An example is shown in Figure 32. See the AD8352 data sheet
for more information.
90
80
SNR (dBFS)
In any configuration, the value of Shunt Capacitor C is dependent
on the input frequency and source impedance and may need to
be reduced or removed. Table 9 displays the suggested values to set
the RC network. However, these values are dependent on the
input signal and should be used only as a starting guide.
70
50
0.5
0.6
0.7
0.8
0.9
1.0
1.1
INPUT COMMON-MODE VOLTAGE (V)
1.2
1.3
08701-149
60
Table 9. Example RC Network
Figure 27. SNR/SFDR vs. Input Common-Mode Voltage,
fIN = 30.5 MHz, fS = 80 MSPS
Differential Input Configurations
Optimum performance is achieved while driving the AD6659 in a
differential input configuration. For baseband applications, the
AD8138, ADA4937-2, and ADA4938-2 differential drivers provide
excellent performance and a flexible interface to the ADC.
The output common-mode voltage of the ADA4938-2 is easily
set with the VCM pin of the AD6659 (see Figure 28), and the
driver can be configured in a Sallen-Key filter topology to
provide band limiting of the input signal.
200Ω
33Ω
76.8Ω
VIN–x
A single-ended input can provide adequate performance in
cost-sensitive applications. In this configuration, SFDR and
distortion performance degrade due to the large input commonmode swing. If the source impedances on each input are matched,
there should be little effect on SNR performance. Figure 30
shows a typical single-ended input configuration.
10µF
AVDD
AVDD
1kΩ
ADA4938
10pF
ADC
33Ω
VIN+x
VCM
200Ω
49.9Ω
08701-007
1V p-p
120Ω
C Differential (pF)
22
Open
Single-Ended Input Configuration
90Ω
0.1µF
R Series
(Ω Each)
33
125
Frequency Range (MHz)
0 to 70
70 to 200
Figure 28. Differential Input Configuration Using the ADA4938
Rev. " | Page 17 of 40
R
VIN+x
1kΩ
AVDD
1kΩ
10µF
For baseband applications below ~10 MHz where SNR is a key
parameter, differential transformer coupling is the recommended
input configuration. An example is shown in Figure 29. To bias
0.1µF
C
ADC
R
VIN–x
0.1µF
1kΩ
Figure 30. Single-Ended Input Configuration
08701-009
SNR/SFDR (dBFS/dBc)
VCM
08701-008
VIN–x
The analog inputs of the AD6659 are not internally dc-biased.
Therefore, in ac-coupled applications, the user must provide a
dc bias externally. Setting the device so that VCM = AVDD/2 is
recommended for optimum performance, but the device can
function over a wider range with reasonable performance, as
shown in Figure 27.
VIN
ADC
C
R
AD6659
0.1µF
0.1µF
R
VIN+x
2V p-p
25Ω
S
S
P
ADC
C
0.1µF
25Ω
0.1µF
R
VIN–x
VCM
08701-010
PA
Figure 31. Differential Double Balun Input Configuration
VCC
0Ω
ANALOG INPUT
16
1
8, 13
11
2
CD
RD
RG
3
ANALOG INPUT
0.1µF 0Ω
R
VIN+x
200Ω
10
ADC
C
AD8352
4
5
0.1µF
0.1µF
0.1µF
200Ω
R
VIN–x
14
0.1µF
0.1µF
Figure 32. Differential Input Configuration Using the AD8352
Rev. " | Page 18 of 40
VCM
08701-011
0.1µF
AD6659
0
Internal Reference Connection
A comparator within the AD6659 detects the potential at the
SENSE pin and configures the reference in one of two possible
modes, which are summarized in Table 10. If SENSE is grounded,
the reference amplifier switch is connected to the internal resistor
divider (see Figure 33), setting VREF to 1.0 V.
–0.5
–1.0
INTERNAL VREF = 0.993V
–1.5
–2.0
–2.5
–3.0
0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
LOAD CURRENT (mA)
08701-014
A stable and accurate 1.0 V voltage reference is built into the
AD6659. The VREF can be configured using either the internal
1.0 V reference or an externally applied 1.0 V reference voltage.
The various reference modes are summarized in the sections
that follow. The Reference Decoupling section describes best
practices for PCB layout of the reference.
REFERENCE VOLTAGE ERROR (%)
VOLTAGE REFERENCE
Figure 34. VREF Accuracy vs. Load Current
External Reference Operation
VIN+A/VIN+B
The use of an external reference may be necessary to enhance
the gain accuracy of the ADC or improve thermal drift characteristics. Figure 35 shows the typical drift characteristics of the
internal reference in 1.0 V mode.
VIN–A/VIN–B
ADC
CORE
4
VREF
3
0.1µF
2
SELECT
LOGIC
VREF ERROR (mV)
VREF ERROR (mV)
1
SENSE
ADC
08701-012
0.5V
Figure 33. Internal Reference Configuration
0
–1
–2
–3
–4
If the internal reference of the AD6659 is used to drive multiple
converters to improve gain matching, the loading of the reference
by the other converters must be considered. Figure 34 shows
how the internal reference voltage is affected by loading.
–5
–6
–40
–20
0
20
40
TEMPERATURE (°C)
60
80
08701-052
1.0µF
Figure 35. Typical VREF Drift
When the SENSE pin is tied to AVDD, the internal reference is
disabled, allowing the use of an external reference. An internal
reference buffer loads the external reference with an equivalent
7.5 kΩ load (see Figure 25). The internal buffer generates the
positive and negative full-scale references for the ADC core.
Therefore, the external reference must be limited to a maximum
of 1.0 V.
Table 10. Reference Configuration Summary
Selected Mode
Fixed Internal Reference
Fixed External Reference
SENSE Voltage (V)
AGND to 0.2
AVDD
Resulting VREF (V)
1.0 internal
1.0 applied to external VREF pin
Rev. " | Page 19 of 40
Resulting Differential Span (V p-p)
2.0
2.0
AD6659
CLOCK INPUT CONSIDERATIONS
1nF
CLOCK
INPUT
0.1µF
CLK+
50Ω
ADC
0.1µF
1nF
CLK–
SCHOTTKY
DIODES:
HSMS2822
AVDD
08701-018
For optimum performance, clock the AD6659 sample clock inputs,
CLK+ and CLK−, with a differential signal. The signal is typically
ac-coupled into the CLK+ and CLK− pins via a transformer or
capacitors. These pins are biased internally (see Figure 36) and
require no external bias.
Figure 38. Balun-Coupled Differential Clock (Up to 480 MHz)
If a low jitter clock source is not available, another option is to
ac couple a differential PECL signal to the sample clock input
pins, as shown in Figure 39. The AD9510/AD9511/AD9512/
AD9513/AD9514/AD9515/AD9516/AD9517 clock drivers offer
excellent jitter performance.
0.9V
CLK+
CLK–
2pF
08701-016
2pF
Figure 36. Equivalent Clock Input Circuit
0.1µF
0.1µF
CLOCK
INPUT
The AD6659 has a very flexible clock input structure. The clock
input can be a CMOS, LVDS, LVPECL, or sine wave signal.
Regardless of the type of signal being used, clock source jitter
is of the most concern, as described in the Jitter Considerations
section.
Figure 37 and Figure 38 show two preferred methods for clocking
the AD6659 (at clock rates up to 480 MHz before the internal
CLK divider). A low jitter clock source is converted from a
single-ended signal to a differential signal using either an RF
transformer or an RF balun.
CLK+
0.1µF
AD951x
PECL DRIVER
CLOCK
INPUT
100Ω
ADC
0.1µF
CLK–
50kΩ
240Ω
50kΩ
08701-019
Clock Input Options
240Ω
Figure 39. Differential PECL Sample Clock (Up to 480 MHz)
Another option is to ac couple a differential LVDS signal to the
sample clock input pins, as shown in Figure 40. The AD9510/
AD9511/AD9512/AD9513/AD9514/AD9515/AD9516/AD9517
clock drivers offer excellent jitter performance.
0.1µF
0.1µF
The RF balun configuration is recommended for clock frequencies
between 125 MHz and 480 MHz, and the RF transformer is
recommended for clock frequencies from 10 MHz to 200 MHz.
The back-to-back Schottky diodes across the transformer/balun
secondary limit clock excursions into the AD6659 to approximately
0.8 V p-p differential.
CLOCK
INPUT
This limit helps prevent the large voltage swings of the clock from
feeding through to other portions of the AD6659 while preserving
the fast rise and fall times of the signal that are critical to a low
jitter performance.
In some applications, it may be acceptable to drive the sample
clock inputs with a single-ended 1.8 V CMOS signal. In such
applications, drive the CLK+ pin directly from a CMOS gate and
bypass the CLK− pin to ground with a 0.1 μF capacitor (see
Figure 41).
CLK+
0.1µF
CLOCK
INPUT
50Ω
XFMR
08701-020
50kΩ
Figure 40. Differential LVDS Sample Clock (Up to 480 MHz)
VCC
0.1µF
0.1µF
CLK+
100Ω
CLOCK
INPUT
ADC
0.1µF
50Ω 1
SCHOTTKY
DIODES:
HSMS2822
1kΩ
AD951x
CMOS DRIVER
OPTIONAL
0.1µF
100Ω
1kΩ
08701-017
CLK–
0.1µF
ADC
0.1µF
CLK+
ADC
CLK–
0.1µF
Figure 37. Transformer-Coupled Differential Clock (Up to 200 MHz)
150Ω
RESISTOR IS OPTIONAL.
Figure 41. Single-Ended 1.8 V CMOS Input Clock (Up to 200 MHz)
Rev. " | Page 20 of 40
08701-021
0.1µF
100Ω
CLK–
50kΩ
Mini-Circuits®
ADT1-1WT, 1:1 Z
CLOCK
INPUT
AD951x
LVDS DRIVER
AD6659
Input Clock Divider
Jitter Considerations
The AD6659 contains an input clock divider with the ability
to divide the input clock by integer values from 1 to 6.
Optimum performance is obtained by enabling the internal
DCS when using divide ratios other than 1, 2, or 4.
High speed, high resolution ADCs are sensitive to the quality of the
clock input. The degradation in SNR from the low frequency
SNR (SNRLF) at a given input frequency (fINPUT) due to jitter
(tJRMS) can be calculated by
The AD6659 clock divider can be synchronized using the
external SYNC input. Bit 1 and Bit 2 of Register 0x100 allow
the clock divider to be resynchronized on every SYNC signal
or only on the first SYNC signal after the register is written. A
valid SYNC causes the clock divider to reset to its initial state.
This synchronization feature allows multiple parts to have
their clock dividers aligned to guarantee simultaneous input
sampling.
SNRHF = −10 log[(2π × fINPUT × tJRMS)2 + 10 ( − SNRLF /10) ]
In the previous equation, the rms aperture jitter represents the
clock input jitter specification. IF undersampling applications
are particularly sensitive to jitter, as illustrated in Figure 43.
80
75
0.05ps
70
Clock Duty Cycle
0.5ps
60
55
1.0ps
1.5ps
50
The AD6659 contains a DCS that retimes the nonsampling
(falling) edge, providing an internal clock signal with a nominal
50% duty cycle. This allows the user to provide a wide range of
clock input duty cycles without affecting the performance of the
AD6659. Noise and distortion performance are nearly flat for a
wide range of duty cycles with the DCS on, as shown in Figure 42.
80
75
DCS ON
70
SNR (dBFS)
65
65
60
3.0ps
45
1
10
2.0ps
2.5ps
100
1k
FREQUENCY (MHz)
08701-022
SNR (dBFS)
0.2ps
Typical high speed ADCs use both clock edges to generate
a variety of internal timing signals and, as a result, may be
sensitive to clock duty cycle. Commonly, a ±5% tolerance
is required on the clock duty cycle to maintain dynamic
performance characteristics.
Figure 43. SNR vs. Input Frequency and Jitter
Treat the clock input as an analog signal in cases in which
aperture jitter may affect the dynamic range of the AD6659. To
avoid modulating the clock signal with digital noise, keep
power supplies for clock drivers separate from the ADC output
driver supplies. Low jitter, crystal controlled oscillators make
the best clock sources. If the clock is generated from another
type of source (by gating, dividing, or another method), it
should be retimed by the original clock at the last step.
DCS OFF
For more information, see the AN-501 Application Note and the
AN-756 Application Note, available at www.analog.com.
55
50
POWER DISSIPATION AND STANDBY MODE
08701-078
45
40
10
20
30
40
50
60
POSITIVE DUTY CYCLE (%)
70
As shown in Figure 44, the analog core power dissipated by the
AD6659 is proportional to its sample rate. The digital power
dissipation of the CMOS outputs is determined primarily by the
strength of the digital drivers and the load on each output bit.
80
Figure 42. SNR vs. DCS On/Off
Jitter in the rising edge of the input is still of concern and is not
easily reduced by the internal stabilization circuit. The duty
cycle control loop does not function for clock rates less than
20 MHz nominal. The loop has a time constant associated with
it that must be considered in applications in which the clock
rate can change dynamically. A wait time of 1.5 μs to 5 μs
is required after the dynamic clock frequency increases or decreases
before the DCS loop is relocked to the input signal.
The maximum DRVDD current (IDRVDD) can be calculated as
IDRVDD = VDRVDD × CLOAD × fCLK × N
where N is the number of output bits (26 bits, in the case of the
AD6659).
This maximum current occurs when every output bit switches
on every clock cycle, that is, a full-scale square wave at the
Nyquist frequency of fCLK/2. In practice, the DRVDD current
is established by the average number of output bits switching,
Rev. " | Page 21 of 40
AD6659
which is determined by the sample rate and the characteristics
of the analog input signal.
Reducing the capacitive load presented to the output drivers
can minimize digital power consumption. The data in Figure 44
was taken using the same operating conditions as those used for the
Typical Performance Characteristics, with a 5 pF load on each
output driver.
210
ANALOG CORE POWER (mW)
190
170
The CMOS output drivers are sized to provide sufficient output
current to drive a wide variety of logic families. However, large
drive currents tend to cause current glitches on the supplies and
may affect converter performance.
Applications that require the ADC to drive large capacitive
loads or large fanouts may require external buffers or latches.
The output data format can be selected to be either offset binary
or twos complement by setting the SCLK/DFS pin when operating
in the external pin mode (see Table 11). Output codings for the
respective data formats are shown in Table 12.
As detailed in the AN-877 Application Note, Interfacing to High
Speed ADCs via SPI, the data format can be selected for offset
binary, twos complement, or gray code when using the SPI control.
150
130
Table 11. SCLK/DFS Mode Selection (External Pin Mode)
110
Voltage at Pin
AGND
DRVDD
70
10
20
30
40
50
60
70
CLOCK RATE (MSPS)
80
08701-152
90
Figure 44. Analog Core Power vs. Clock Rate
The AD6659 is placed in power-down mode either by the SPI
port or by asserting the PDWN pin high. In this state, the ADC
typically dissipates 1.0 mW. During power-down, the output
drivers are placed in a high impedance state. By asserting the
PDWN pin low returns the AD6659 to its normal operating
mode. Note that PDWN is referenced to the digital output driver
supply (DRVDD) and should not exceed that supply voltage.
Low power dissipation in power-down mode is achieved by
shutting down the reference, reference buffer, biasing networks,
and clock. Internal capacitors are discharged when entering powerdown mode and must then be recharged when returning to normal
operation. As a result, wake-up time is related to the time spent
in power-down mode, and shorter power-down cycles result in
proportionally shorter wake-up times.
When using the SPI port interface, the user can place the ADC
in power-down mode or standby mode. Standby mode allows
the user to keep the internal reference circuitry powered when
faster wake-up times are required. See the Memory Map section
for more details.
DIGITAL OUTPUTS
The AD6659 output drivers can be configured to interface with
1.8 V to 3.3 V CMOS logic families. Output data can also be
multiplexed onto a single output bus to reduce the total number
of traces required.
SCLK/DFS
Offset binary (default)
Twos complement
SDIO/DCS
DCS disabled (default)
DCS enabled
Digital Output Enable Function (OEB)
The AD6659 has a flexible three-state ability for the digital output
pins. The three-state mode is enabled using the OEB pin or
through the SPI interface. If the OEB pin is low, the output data
drivers and DCOs are enabled. If the OEB pin is high, the output
data drivers and DCOs are placed in a high impedance state.
This OEB function is not intended for rapid access to the data
bus. Note that OEB is referenced to the digital output driver
supply (DRVDD) and should not exceed that supply voltage.
When using the SPI interface, the data outputs and DCO of
each channel can be independently three-stated by using the
output disable (OEB) bit (Bit 4) in Register 0x14.
TIMING
The AD6659 provides latched data with a pipeline delay of nine
clock cycles. Data outputs are available one propagation delay
(tPD) after the rising edge of the clock signal.
Minimize the length of the output data lines and loads placed
on them to reduce transients within the AD6659. These transients
can degrade converter dynamic performance.
The lowest typical conversion rate of the AD6659 is 3 MSPS. At
clock rates below 3 MSPS, dynamic performance can degrade.
Data Clock Output (DCOx)
The AD6659 provides two data clock output (DCOx) signals
intended for capturing the data in an external register. The
CMOS data outputs are valid on the rising edge of DCOx, unless
the DCOx clock polarity was changed via the SPI. See Figure 2 and
Figure 3 for graphical timing descriptions.
Rev. " | Page 22 of 40
AD6659
Table 12. Output Data Format
Input (V)
VIN+ − VIN−
VIN+ − VIN−
VIN+ − VIN−
VIN+ − VIN−
VIN+ − VIN−
Condition (V)
< −VREF − 0.5 LSB
= −VREF
=0
= +VREF − 1.0 LSB
> +VREF − 0.5 LSB
Offset Binary Output Mode
0000 0000 0000
0000 0000 0000
1000 0000 0000
1111 1111 1111
1111 1111 1111
Rev. " | Page 23 of 40
Twos Complement Mode
1000 0000 0000
1000 0000 0000
0000 0000 0000
0111 1111 1111
0111 1111 1111
OR
1
0
0
0
1
AD6659
BUILT-IN SELF-TEST AND OUTPUT TEST
The AD6659 includes a built-in self-test (BIST) feature designed to
enable verification of the integrity of each channel as well as to
facilitate board level debugging. A BIST feature that verifies the
integrity of the digital datapath of the AD6659 is included.
Various output test options are also provided to place predictable
values on the outputs of the AD6659.
BIST
The BIST is a thorough test of the digital portion of the selected
AD6659 signal path. Perform the BIST test after a reset to ensure
that the part is in a known state. During BIST, data from an internal
pseudorandom noise (PN) source is driven through the digital
datapath of both channels, starting at the ADC block output. At
the datapath output, CRC logic calculates a signature from the
data. The BIST sequence runs for 512 cycles and then stops.
When completed, the BIST compares the signature results with a
predetermined value. If the signatures match, the BIST sets Bit 0
of Register 0x24, signifying that the test passed. If the BIST test
failed, Bit 0 of Register 0x24 is cleared. The outputs are
connected during this test so that the PN sequence can be
observed as it runs. Writing the value of 0x05 to Register 0x0E
runs the BIST. This enables Bit 0 (BIST enable) of Register 0x0E
and resets the PN sequence generator, Bit 2 (BIST INIT) of Register
0x0E. At the completion of the BIST, Bit 0 of Register 0x24
automatically clears. The PN sequence can be continued from its
last value by writing a 0 in Bit 2 of Register 0x0E. However, if the
PN sequence is not reset, the signature calculation does not
equal the predetermined value at the end of the test. At that point,
the user must rely on verifying the output data.
OUTPUT TEST MODES
The output test options are described in Table 17 at Address 0x0D.
When an output test mode is enabled, the analog section of the
ADC is disconnected from the digital back end blocks and the
test pattern is run through the output formatting block. Some of
the test patterns are subject to output formatting, and some of
the test patterns are not. The PN generators from the PN sequence
tests can be reset by setting Bit 4 or Bit 5 of Register 0x0D.
These tests can be performed with or without an analog signal
(if present, the analog signal is ignored), but they do require
an encode clock. For more information, see the AN-877
Application Note, Interfacing to High Speed ADCs via SPI.
Rev. " | Page 24 of 40
AD6659
CHANNEL/CHIP SYNCHRONIZATION
The AD6659 has a SYNC input that offers the user flexible
synchronization options for synchronizing sample clocks
across multiple ADCs. The input clock divider can be enabled to
synchronize on a single occurrence of the SYNC signal or on every
occurrence. The SYNC input is internally synchronized to the
sample clock; however, to ensure that there is no timing
uncertainty exists between multiple parts, the SYNC input
signal should be externally synchronized to the input clock
signal, meeting the setup and hold times shown in Table 5.
Drive the SYNC input using a single-ended CMOS-type signal.
Rev. " | Page 25 of 40
AD6659
NOISE SHAPING REQUANTIZER
NSR mode offers excellent noise performance over 20% of the
ADC sample rate (40% of Nyquist). The fundamental can be
tuned using a low-pass, band-pass, or high-pass filter by setting
the NSR Mode Bits[2:1] in the 0x11E SPI register.
80MSPS
19.7MHz @ –1dBFS
NSR BAND-PASS MODE
SNR = 80.3dB (81.3dBFS)
(IN-BAND)
SFDR = 93.8dBc (IN-BAND)
–15
–30
–45
–60
–90
5 +
–120
–135
–45
–60
–75
6
4
5
12
16
20
24
28
FREQUENCY (MHz)
+
36
40
–45
–60
–75
5 +
3
2
–90
6
4
3
–90
32
80MSPS
32MHz @ –1dBFS
NSR HIGH PASS MODE
SNR = 80.4dB (81.4dBFS) (IN-BAND)
SFDR = 96.8dBc (IN-BAND)
–30
AMPLITUDE (dBFS)
AMPLITUDE (dBFS)
–30
8
0
–15
–15
4
Figure 46. Band-Pass NSR Mode: 19.7 MHz AIN @ 80 MSPS (16 MHz BW)
0
80MSPS
7.5MHz @ –1dBFS
NSR LOW PASS MODE
SNR = 80.4dB (81.4dBFS) (IN-BAND)
SFDR = 96.5dBc (IN-BAND)
3
–105
0
Figure 45 to Figure 47 shows the typical spectrum that can be
expected from the AD6659 with the 20% BW NSR mode
enabled for the three different filter settings.
62
4
–75
08701-154
20% BW NSR MODE (16 MHZ BW AT 80 MSPS)
0
AMPLITUDE (dBFS)
The AD6659 features a noise shaping requantizer (NSR) to
allow higher than 12-bit SNR to be maintained in a subset of
the Nyquist band. Enabling and disabling the NSR mode is
controlled via Bit 0 in the 0x11E SPI register. In NSR mode,
the band of interest can be tuned using a low-pass, band-pass,
or high-pass filter setting via Bits[2:1] in the 0x11E SPI register.
–105
2
–105
–120
–135
0
4
8
12
16
20
24
28
FREQUENCY (MHz)
32
36
40
08701-153
0
–135
4
8
12
16
20
24
28
FREQUENCY (MHz)
32
36
40
08701-155
–120
Figure 47. High Pass NSR Mode: 32 MHz AIN @ 80 MSPS (16 MHz BW)
Figure 45. Low Pass NSR Mode: 7.5 MHz AIN @ 80 MSPS (16 MHz BW)
Rev. " | Page 26 of 40
AD6659
DC AND QUADRATURE ERROR CORRECTION (QEC)
In direct conversion or other quadrature systems, mismatches
between the real (I) and imaginary (Q) signal paths cause
frequencies in the positive spectrum to image into the negative
spectrum and vice versa. From an RF point of view, this is
equivalent to information above the LO frequency interfering
with information below the LO frequency, and vice versa. These
mismatches may occur from gain and/or phase mismatches in
the analog quadrature demodulator or in any other mismatches
between the I and Q signal chains. In a single-carrier zero-IF
system where the carrier has been placed symmetrically around
dc, this causes self-distortion of the carrier as the two sidebands
fold onto one another and degrade the EVM of the signal.
In a multicarrier communication system, this mismatch can be
even more problematic because carriers of widely different
power levels can interfere with one another. For example, a large
carrier centered at +f1 can have an image appear at –f1 that is
much larger than the desired carrier at –f1.
The integrated quadrature error correction (QEC) algorithm of
the AD6659 attempts to measure and correct the amplitude and
phase imbalances of the I and Q signal paths to achieve higher
levels of image suppression than is achievable by analog means
alone. These errors can be corrected in an adapted manner,
where the I and Q gain and quadrature phase mismatches are
constantly estimated and corrected, allowing slow changes in
mismatches due to supply and temperature to be constantly
tracked.
The quadrature errors are corrected in a frequency independent
manner on the AD6659; therefore, systems with significant
mismatch in the baseband I and Q signal chains may have
reduced image suppression. The AD6659 QEC still corrects the
systematic imbalances.
The convergence time of the QEC algorithm is dependent on
the statistics of the input signal. For large signals and large
imbalance errors, this convergence time is typically less than
2M samples of the AD6659 data rate.
LO Leakage (DC) Correction
In a direct conversion receiver subsystem, LO to RF leakage of
the quadrature modulator shows up as dc offsets at baseband.
These offsets are added to dc offsets in the baseband signal
paths and both contribute to a carrier at dc. In a zero-IF receiver,
this dc energy can cause problems because it appears in the
band of a desired channel. As part of the AD6659 QEC
function, the dc offset is suppressed by applying a low
frequency notch filter to form a null around dc. In applications
where constant tracking of the dc offsets and quadrature errors
is not needed, the algorithms can be independently frozen to save
power. When frozen, the image and LO leakage (dc) correction are
still performed, but changes are no longer tracked. Bits[5:3] in
Register 0x110 disable the respective correction when frozen.
The default configuration of the AD6659 has the QEC and dc
correction blocks disabled, and Bits[2:0] in Register 0x110 must
be pulled high to enable the correction blocks. The quadrature
gain, quadrature phase, and dc correction algorithms can also
be disabled independently for system debugging or to save
power by pulling Bits[2:0] low in Register 0x110.
When the QEC is enabled and a correction value has been
calculated, the value remains active as long as any of the QEC
functions (dc, gain, or phase correction) are used.
QEC and DC Correction Range
Table 13 gives the minimum and maximum correction ranges
of the QEC algorithms on the AD6659; if the mismatches are
greater than these ranges, an imperfect correction results.
Table 13. QEC and DC Correction Range
Parameter
Gain
Phase
DC
Rev." | Page 27 of 40
Minimum
−1.1 dB
−1.79°
−6%
Maximum
+1.0 dB
+1.79°
+6%
AD6659
0
0
–15
–15
–30
–30
–90
FREQUENCY (MHz)
FREQUENCY (MHz)
Figure 49. QEC Mode On
Figure 48. QEC Mode Off
Rev. " | Page 28 of 40
37.5
30.0
22.5
08701-157
4
15.0
7.5
08701-156
37.5
30.0
22.5
15.0
7.5
0
–7.5
–15.0
–135
–22.5
–135
–30.0
–120
6
0
–105
–120
IMAGE
2
5
3
–7.5
–105
4
5
3
–15.0
2
6
–75
–22.5
–90
DC
–60
–30.0
–75
–45
–37.5
AMPLITUDE (dBFS)
–60
–37.5
AMPLITUDE (dBFS)
IMAGE
DC
–45
AD6659
SERIAL PORT INTERFACE (SPI)
The AD6659 SPI allows the user to configure the converter for
specific functions or operations through a structured register
space provided inside the ADC. The SPI gives the user added
flexibility and customization, depending on the application.
Addresses are accessed via the serial port and can be written to
or read from the port. Memory is organized into bytes that can
be further divided into fields, which are documented in the
Memory Map section. For detailed operational information, see
the AN-877 Application Note, Interfacing to High Speed ADCs
via SPI.
The falling edge of CSB, in conjunction with the rising edge of
SCLK, determines the start of the framing. An example of the
serial timing and its definitions can be found in Figure 50 and
Table 5.
CONFIGURATION USING THE SPI
During an instruction phase, a 16-bit instruction is transmitted.
Data follows the instruction phase, and its length is determined
by the W1 and W0 bits, as shown in Figure 50.
Other modes involving CSB are available. CSB can be held low
indefinitely, which permanently enables the device; this is called
streaming. CSB can stall high between bytes to allow for additional
external timing. When CSB is tied high, SPI functions are placed
in high impedance mode. This mode turns on any SPI pin
secondary functions.
Three pins define the SPI of this ADC: SCLK, SDIO, and CSB
(see Table 14). SCLK (a serial clock) is used to synchronize the
read and write data presented from and to the ADC. SDIO (serial
data input/output) is a dual-purpose pin that allows data to be
sent to and read from the internal ADC memory map registers.
CSB (chip select bar) is an active low control that enables or
disables the read and write cycles.
All data is composed of 8-bit words. The first bit of the first byte
in a multibyte serial data transfer frame indicates whether a read
command or a write command is issued. This allows the serial
data input/output (SDIO) pin to change direction from an input
to an output at the appropriate point in the serial frame.
In addition to word length, the instruction phase determines
whether the serial frame is a read or write operation, allowing
the serial port to be used both to program the chip and to read
the contents of the on-chip memory. If the instruction is a readback
operation, performing a readback causes the serial data input/
output (SDIO) pin to change direction from an input to an output
at the appropriate point in the serial frame.
Table 14. Serial Port Interface Pins
Pin
SCLK
SDIO
tHIGH
tDS
tS
tDH
Data can be sent in MSB-first mode or LSB-first mode. MSBfirst mode is the default on power-up and can be changed via
the SPI port configuration register. For more information about
this and other features, see the AN-877 Application Note,
Interfacing to High Speed ADCs via SPI.
tCLK
tH
tLOW
CSB
SCLK
DON’T
CARE
SDIO
DON’T
CARE
DON’T
CARE
R/W
W1
W0
A12
A11
A10
A9
A8
A7
D5
Figure 50. Serial Port Interface Timing Diagram
Rev. " | Page 29 of 40
D4
D3
D2
D1
D0
DON’T
CARE
08701-023
CSB
Description
Serial Clock. The serial shift clock input, which is used
to synchronize serial interface reads and writes.
Serial Data Input/Output. A dual-purpose pin that typically
serves as an input or an output, depending on the
instruction being sent and the relative position in the
timing frame.
Chip Select Bar. An active low control that gates the
read and write cycles.
AD6659
HARDWARE INTERFACE
Table 15. Mode Selection
The pins described in Table 14 constitute the physical interface
between the programming device of the user and the serial port
of the AD6659. When using the SPI interface, SCLK and CSB
function as inputs. SDIO is bidirectional, functioning as an input
during write phases and as an output during readback.
Pin
SDIO/DCS
The SPI interface is flexible enough to be controlled by either
FPGAs or microcontrollers. One method for SPI configuration
is described in detail in the AN-812 Application Note,
Microcontroller-Based Serial Port Interface (SPI) Boot Circuit.
The SPI port should not be active during periods when the full
dynamic performance of the converter is required. Because the
SCLK signal, the CSB signal, and the SDIO signal are typically
asynchronous to the ADC clock, noise from these signals can
degrade converter performance. If the on-board SPI bus is used for
other devices, it may be necessary to provide buffers between
this bus and the AD6659 to prevent these signals from transitioning at the converter inputs during critical sampling periods.
SDIO/DCS and SCLK/DFS serve a dual function when the SPI
interface is not being used. When the pins are strapped to DRVDD
or ground during device power-on, they are associated with a
specific function. The Digital Outputs section describes the
strappable functions supported on the AD6659.
CONFIGURATION WITHOUT THE SPI
SCLK/DFS
OEB
PDWN
External Voltage
DRVDD
AGND (default)
DRVDD
AGND (default)
DRVDD
AGND (default)
DRVDD
AGND (default)
SPI ACCESSIBLE FEATURES
Table 16 provides a brief description of the general features that
are accessible via the SPI. These features are described in detail
in the AN-877 Application Note, Interfacing to High Speed ADCs
via SPI. The AD6659 part-specific features are described in
detail in Table 17.
Table 16. Features Accessible Using the SPI
Feature
Mode
Clock
Offset
Test I/O
In applications that do not interface to the SPI control registers,
SDIO/DCS, SCLK/DFS, OEB, and PDWN serve as standalone
CMOS-compatible control pins. When the device is powered
up, it is assumed that the user intends to use the pins as static
control lines for the duty cycle stabilizer, output data format,
output enable, and power-down feature control. In this mode,
connect the CSB pin to DRVDD, which disables the serial port
interface.
Configuration
Duty cycle stabilizer enabled
Duty cycle stabilizer disabled
Twos complement enabled
Offset binary enabled
Outputs in high impedance
Outputs enabled
Chip in power-down or standby
Normal operation
Output Mode
Output Phase
Output Delay
Rev. " | Page 30 of 40
Description
Allows the user to set either power-down mode
or standby mode
Allows the user to access the DCS via the SPI
Allows the user to digitally adjust the converter
offset
Allows the user to set test modes to place
known data on output bits
Allows the user to set up outputs
Allows the user to set the output clock polarity
Allows the user to vary the DCO delay
AD6659
MEMORY MAP
READING THE MEMORY MAP REGISTER TABLE
Logic Levels
Each row in the memory map register table (see Table 17) has
eight bit locations. The memory map is roughly divided into
four sections: the chip configuration registers (Address 0x00 to
Address 0x02); the device index and transfer registers (Address 0x05
and Address 0xFF); the program registers, including setup, control,
and test (Address 0x08 to Address 0x2E); and the digital feature
control registers (Address 0x100 to Address 0x11E).
An explanation of logic level terminology follows:
Table 17 documents the default hexadecimal value for each
hexadecimal address shown. The column with the heading
Bit 7 (MSB) is the start of the default hexadecimal value given.
For example, Address 0x05, the channel index register, has a hexadecimal default value of 0x03. This means that in Address 0x05
Bits[7:2] = 0, and the remaining Bits[1:0] = 1. This setting is the
default channel index setting. The default value results in both
ADC channels receiving the next write command. For more
information on this function and others, see the AN-877
Application Note, Interfacing to High Speed ADCs via SPI. This
application note details the functions controlled by Register 0x00
to Register 0xFF. The remaining AD6659 specific registers,
Register 0x100 through Register 0x11E, are documented in the
Memory Map Register Descriptions section following Table 17.
Address 0x08 to Address 0x18 are shadowed. Writes to these
addresses do not affect part operation until a transfer command
is issued by writing 0x01 to Address 0xFF, setting the transfer bit.
This allows these registers to be updated internally and simultaneously when the transfer bit is set. The internal update takes
place when the transfer bit is set, and then the bit autoclears.
OPEN LOCATIONS
All address and bit locations excluded in the SPI map are not
currently supported for this device. Unused bits of a valid
address location should be written with 0s. Writing to these
locations is required only when part of an address location is
open (for example, Address 0x05). If the entire address location
is open, it is omitted from the SPI map (for example, Address 0x13)
and should not be written.
•
•
“Bit is set” is synonymous with “bit is set to Logic 1” or
“writing Logic 1 for the bit.”
“Bit is cleared” is synonymous with “bit is set to Logic 0” or
“writing Logic 0 for the bit.”
Transfer Register Map
Channel-Specific Registers
Some channel setup functions can be programmed differently
for each channel. In these cases, channel address locations are
internally duplicated for each channel. These registers and bits
are designated in the memory map register table as local. These
local registers and bits can be accessed by setting the appropriate
Channel A (Bit 0) or Channel B (Bit 1) bit in Register 0x05.
If both bits are set, the subsequent write affects the registers of both
channels. In a read cycle, set only Channel A or Channel B to read
one of the two registers. If both bits are set during an SPI read
cycle, the part returns the value for Channel A. Registers and
bits designated as global in the memory map register table (see
Table 17) affect the entire part or the channel features for which
independent settings are not allowed between channels. The
settings in Register 0x05 do not affect the global registers and bits.
DEFAULT VALUES
After the AD6659 is reset, critical registers are loaded with default
values. The default values for the registers are given in the
memory map register table (see Table 17).
Rev. " | Page 31 of 40
AD6659
MEMORY MAP REGISTER TABLE
All address and bit locations excluded from Table 17 are not currently supported for this device.
Table 17.
Addr
(Hex)
Register Name
Bit 7
(MSB)
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
(LSB)
LSB
first
Soft reset
1
1
Soft
reset
LSB first
0
Default
Value
(Hex)
0x18
Comments
Chip Configuration Registers
0x00
SPI port
configuration
(global)
0x01
Chip ID (global)
0x02
Chip grade
(global)
0
8-bit Chip ID Bits[7:0]
AD6659 = 0x76
Open
The nibbles are
mirrored so that
LSB- or MSB-first
mode registers
correctly, regardless
of shift mode
Unique chip ID
used to
differentiate
devices; read only
Speed Grade ID[6:4]
80 MSPS = 011
Open
Unique speed
grade ID used to
differentiate
devices; read only
Device Index and Transfer Registers
0x05
Channel index
Open
Open
Open
Open
Open
Open
ADC B
default
ADC A
default
0x03
Bits are set to
determine which
device on chip
receives the next
write command;
the default is all
devices on chip
0xFF
Transfer
Open
Open
Open
Open
Open
Open
Open
Transfer
0x00
Synchronously
transfers data from
the master shift
register to the slave
0x80
Determines various
generic modes of
chip operation
0x00
Enables or disables
theDCS
0x00
The divide ratio is
the value plus 1
Program Registers (May or May Not Be Indexed by Device Index)
0x08
Modes
0x09
Clock (global)
0x0B
Clock divide
(global)
External
powerdown
enable
(local)
External pin function
Open
Open
Open
Open
0x00 full power-down
00 = chip run
01 = full power-down
0x01 standby (local)
10 = standby
11 = chip wide digital
reset (local)
Open
Open
Open
Open
Duty
cycle
stabilize
Clock Divider[2:0]
Clock divide ratio
000 = divide by 1
001 = divide by 2
010 = divide by 3
011 = divide by 4
100 = divide by 5
101 = divide by 6
Rev. " | Page 32 of 40
AD6659
Addr
(Hex)
Register Name
0x0D
Test mode (local)
Bit 7
(MSB)
Bit 6
User test mode
(local)
Bit 5
Bit 4
Reset PN
long gen
Reset
PN
short
gen
00 = single
01 = alternate
Bit 3
Bit 2
Bit 1
Bit 0
(LSB)
Output test mode [3:0] (local)
Default
Value
(Hex)
When set, the test
data is placed on
the output pins in
place of normal
data
0x00
When Bit 0 is set,
the BIST function is
initiated
0x00
Device offset trim
0x00
Configures the
outputs and the
format of the data
0x22
Determines CMOS
output drive
strength properties
0000 = off (default)
0001 = midscale short
10 = single once
0010 = positive FS
11 = alternate
once
0011 = negative FS
Comments
0x00
0100 = alternating checkerboard
0101 = PN 23 sequence
0110 = PN 9 sequence
0111 = 1-/0-word toggle
1000 = user input
1001 = 1-/0-bit toggle
1010 = 1× sync
1011 = one bit high
1100 = mixed bit frequency
0x0E
BIST enable
0x10
Offset adjust
(local)
0x14
Output mode
Open
Open
Open
Open
Open
BIST
INIT
Open
BIST
enable
8-bit Device Offset Adjustment[7:0] (local)
Offset adjust in LSBs from +127 to −128 (twos complement format)
00 = 3.3 V CMOS
10 = 1.8 V CMOS
Output mux
enable
(interleaved)
Output
disable
(local)
Open
Output
invert
(local)
00 = offset binary
01 = twos
complement
10 = gray code
11 = offset binary
(local)
0x15
Output adjust
3.3 V DCO drive
strength
1.8 V DCO drive
strength
3.3 V data drive
strength
1.8 V data drive
strength
00 = 1 stripe
(default)
00 = 1 stripe
00 = 1 stripe
(default)
00 = 1 stripe
01 = 2 stripes
01 = 2 stripes
01 = 2 stripes
01 = 2 stripes
10 = 3 stripes
10 = 3 stripes (default)
10 = 3 stripes
10 = 3 stripes
(default)
11 = 4 stripes
11 = 4 stripes
11 = 4 stripes
11 = 4 stripes
0x16
Output phase
DCO
output
polarity
0=
normal
1=
inverted
(local)
Open
Open
Open
Open
Input Clock Phase Adjust[2:0]
(Value is number of input
clock cycles of phase delay)
000 = no delay
001 = 1 input clock cycle
010 = 2 input clock cycles
011 = 3 input clock cycles
100 = 4 input clock cycles
101 = 5 input clock cycles
110 = 6 input clock cycles
111 = 7 input clock cycles
0x00
On devices that use
global clock divide,
this register
determines which
phase of the
divider output is
used to supply the
output clock;
internal latching is
unaffected
0x17
Output delay
Enable
DCO
delay
Open
Enable data
delay
Open
Open
DCO/Data Delay[2:0]
000 = 0.56 ns
001 = 1.12 ns
010 = 1.68 ns
011 = 2.24 ns
100 = 2.80 ns
101 = 3.36 ns
110 = 3.92 ns
111 = 4.48 ns
0x00
Sets the fine output
delay of the output
clock but does not
change internal
timing
0x19
USER_PATT1_LSB
B7
B6
B5
B4
B3
0x00
User-defined
Pattern 1, LSB
Rev. " | Page 33 of 40
B2
B1
B0
AD6659
Addr
(Hex)
0x1A
Bit 1
Bit 0
(LSB)
Default
Value
(Hex)
B9
B8
0x00
User-defined
Pattern 1, MSB
B2
B1
B0
0x00
User-defined
Pattern 2, LSB
B10
B9
B8
0x00
User-defined
Pattern 2, MSB
0x00
Least significant
byte of BIST
signature, read
only
OR OE
(local)
0x01
Disable the ORx pin
for the indexed
channel
0 = ADC A
Ch A =
0x00
Assigns an ADC to
an output channel
1 = ADC B
(local)
Ch B =
0x01
Register Name
Bit 7
(MSB)
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
USER_PATT1_MSB
B15
B14
B13
B12
B11
B10
0x1B
USER_PATT2_LSB
B7
B6
B5
B4
B3
0x1C
USER_PATT2_MSB
B15
B14
B13
B12
B11
0x24
BIST signature LSB
0x2A
Features
Open
Open
Open
Open
Open
Open
Open
0x2E
Output assign
Open
Open
Open
Open
Open
Open
Open
BIST signature [7:0]
Comments
Digital Feature Control Registers
0x100
Sync control
(global)
Open
Open
Open
Open
Open
Clock
divider
next
sync
only
Clock
divider
sync
enable
Master
sync
enable
0x01
0x101
USR2
Enable
OEB
Pin 47
(local)
Open
Open
Open
Enable
GCLK
detect
Run
GCLK
Open
Disable
SDIO pulldown
0x88
0x110
QEC Control 0
Open
Open
Freeze dc
Freeze
phase
Freeze
gain
DC
enable
Phase
enable
Gain
enable
0x00
0x111
QEC Control 1
Open
Open
Open
Open
Open
Force
dc
Force
phase
Force
gain
0x00
0x112
QEC gain bandwidth control
Open
Kexp_gain, Bits[4:0]
0x02
0x113
QEC phase bandwidth control
Open
Kexp_phase, Bits[4:0]
0x02
0x114
QEC dc bandwidth control
Open
Kexp_DC, Bits[4:0]
0x02
0x116
QEC Initial Gain 0
0x117
QEC Initial Gain 1
0x118
QEC Initial Phase 0
0x119
QEC Initial Phase 1
0x11A
QEC Initial DC I 0
0x11B
QEC Initial DC I 1
0x11C
QEC Initial DC Q 0
0x11D
QEC Initial DC Q 1
0x11E
NSR Control
Initial gain, Bits[7:0]
Open
0x00
Initial gain, Bits[14:8]
0x00
Initial phase, Bits[7:0]
Open
0x00
Initial phase, Bits[12:8]
0x00
Initial DC I, Bits[7:0]
Open
0x00
Initial DC I, Bits[13:8]
0x00
Initial DC Q, Bits[7:0]
Open
0x00
Initial DC Q, Bits[13:8]
Open
Noise shaping mode:
00 = low pass
01 = high pass
1x = band-pass
Rev. " | Page 34 of 40
Enables internal
oscillator for clock
rates < 5 MHz
0x00
Enable
NSR
0x00
AD6659
MEMORY MAP REGISTER DESCRIPTIONS
QEC Control 0 (Register 0x110)
For additional information about functions controlled in
Register 0x00 to Register 0xFF, see the AN-877 Application
Note, Interfacing to High Speed ADCs via SPI.
Bits[7:6]—Open
Bits[5:3]—Freeze DC/Freeze Phase/Freeze Gain
Sync Control (Register 0x100)
Bits[7:3]—Open
Bit 2—Clock Divider Next Sync Only
If the master sync enable bit (Address 0x100, Bit 0) and the clock
divider sync enable bit (Address 0x100, Bit 1) are high, Bit 2
allows the clock divider to sync to the first sync pulse that it
receives and to ignore the rest. The clock divider sync enable
bit (Address 0x100, Bit 1) resets after it syncs.
These bits can be used to freeze the corresponding dc, phase,
and gain offset corrections of the quadrature error correction
(QEC) independently. When asserted high, QEC is applied
using frozen values, and the estimation of the quadrature errors
is halted.
Bits[2:0]—DC Enable/Phase Enable/Gain Enable
These bits allow the corresponding dc, phase, and gain offset
corrections to be enabled independently.
QEC Control 1 (Register 0x111)
Bit 1—Clock Divider Sync Enable
Bits[7:3]—Open
Bit 1 gates the sync pulse to the clock divider. The sync signal
is enabled when Bit 1 and Bit 0 are high and the device is operating
in continuous sync mode as long as Bit 2 of the sync control
register is low.
Bit 2—Force DC
Bit 0—Master Sync Enable
When set high, this bit forces the initial static correction values
from Register 0x11A and Register 0x11B for the I data and
Register 0x11C and Register 0x11D for the Q data.
Bit 1—Force Phase
Bit 0 must be high to enable any of the sync functions.
USR2 (Register 0x101)
When set high, this bit forces the initial static correction values
from Register 0x118 and Register 0x119.
Bit 7—Enable OEB Pin 47 (Local)
Bit 0—Force Gain
Normally set high, this bit allows Pin 47 to function as the
output enable. If it is set low, it disables Pin 47.
When set high, this bit forces the initial static correction values
from Register 0x116 and Register 0x117.
Bits[6:4]—Open
QEC Gain Bandwidth Control (Register 0x112)
Bit 3—Enable GCLK Detect
Bits[7:5]—Open
Normally set high, this bit enables a circuit that detects encode
rates below approximately 5 MSPS. When a low encode rate is
detected, an internal oscillator, GCLK, is enabled ensuring the
proper operation of several circuits. If set low, the detector is
disabled.
Bits[4:0]—Kexp_Gain[4:0]
Bit 2—Run GCLK
Bits[7:5]—Open
This bit enables the GCLK oscillator. For some applications
with encode rates below 10 MSPS, it may be preferable to set
this bit high to supersede the GCLK detector (Bit 3).
Bits[4:0]—Kexp_Phase[4:0]
Bit 1—Open
QEC DC Bandwidth Control (Register 0x114)
Bit 0—Disable SDIO Pull-Down
Bits[7:5]—Open
This bit can be set high to disable the internal 30 kΩ pull-down
on the SDIO pin, which can be used to limit the loading when
many devices are connected to the SPI bus.
Bits[4:0]—Kexp_DC[4:0]
These bits adjust the time constants of the gain control feedback
loop for quadrature error correction.
QEC Phase Bandwidth Control (Register 0x113)
These bits adjust the time constants of the phase control
feedback loop for quadrature error correction.
These bits adjust the time constants of the dc control feedback
loop for quadrature error correction.
Rev. " | Page 35 of 40
AD6659
QEC Initial Gain 0 and QEC Initial Gain 1 (Register 0x116
and Register 0x117)
When the force dc bit (Register 0x111, Bit 2) is set high, these
values are used for dc error correction.
Bits[14:0]—Initial Gain[14:0]
NSR Control (Register 0x11E)
When the force gain bit (Register 0x111, Bit 0) is set high, these
values are used for gain error correction.
Bits[7:3]—Open
QEC Initial Phase 0 and QEC Initial Phase 1 (Register 0x118
and Register 0x119)
Bits[12:0]—Initial Phase[12:0]
Bits[2:1]—Noise Shaping Mode
These bits select the mode of the noise shaping requantizer as
shown in Table 18.
Bit 0—NSR On and Off Control
When the force phase bit (Register 0x111, Bit 1) is set high,
these values are used for phase error correction.
When set high, this bit enables the NSR function.
QEC Initial DC I (Register 0x11A and Register 0x11B)
Table 18.
Bits[13:0]—Initial DC I[13:0]
Setting
00
01
1x
When the force dc bit (Register 0x111, Bit 2) is set high, these
values are used for dc error correction.
QEC Initial DC Q (Register 0x11C and Register 0x11D)
Bits[13:0]—Initial DC Q[13:0]
Rev. " | Page 36 of 40
Mode
Low pass mode
High pass mode
Band-pass mode
AD6659
APPLICATIONS INFORMATION
DESIGN GUIDELINES
Before starting design and layout of the AD6659 as a system, it
is recommended that the designer become familiar with these
guidelines, which discuss the special circuit connections and
layout requirements needed for certain pins.
Power and Ground Recommendations
When connecting power to the AD6659, it is strongly
recommended that two separate supplies be used. Use one 1.8 V
supply for analog (AVDD); use a separate 1.8 V to 3.3 V supply for
the digital output supply (DRVDD). If a common 1.8 V AVDD
and DRVDD supply must be used, the AVDD and DRVDD
domains must be isolated with a ferrite bead or filter choke and
separate decoupling capacitors. Several different decoupling
capacitors can be used to cover both high and low frequencies.
Locate these capacitors close to the point of entry at the PCB
level and close to the pins of the part, with minimal trace length.
A single PCB ground plane should be sufficient when using the
AD6659. With proper decoupling and smart partitioning of the
PCB analog, digital, and clock sections, optimum performance
is easily achieved.
Exposed Paddle Thermal Heat Sink Recommendations
The exposed paddle (Pin 0) is the only ground connection for
the AD6659; therefore, it must be connected to analog ground
(AGND) on the customer’s PCB. To achieve the best electrical
and thermal performance, mate an exposed (no solder mask)
continuous copper plane on the PCB to the AD6659 exposed
paddle, Pin 0.
The copper plane should have several vias to achieve the
lowest possible resistive thermal path for heat dissipation to
flow through the bottom of the PCB. Fill or plug these vias
with nonconductive epoxy.
To maximize the coverage and adhesion between the ADC and
the PCB, a silkscreen should be overlaid to partition the continuous
plane on the PCB into several uniform sections. This provides
several tie points between the ADC and the PCB during the reflow
process. Using one continuous plane with no partitions guarantees
only one tie point between the ADC and the PCB. For detailed
information about packaging and PCB layout of chip scale
packages, see the AN-772 Application Note, A Design and
Manufacturing Guide for the Lead Frame Chip Scale Package
(LFCSP), at www.analog.com.
VCM
The VCM pin should be decoupled to ground with a 0.1 μF
capacitor, as shown in Figure 29.
RBIAS
The AD6659 requires that a 10 kΩ resistor be placed between
the RBIAS pin and ground. This resistor sets the master current
reference of the ADC core and should have at least a 1% tolerance.
Reference Decoupling
Externally decouple the VREF pin to ground with a low ESR,
1.0 μF capacitor in parallel with a low ESR, 0.1 μF ceramic
capacitor.
SPI Port
The SPI port should not be active during periods when the full
dynamic performance of the converter is required. Because the
SCLK, CSB, and SDIO signals are typically asynchronous to the
ADC clock, noise from these signals can degrade converter
performance. If the on-board SPI bus is used for other devices,
it may be necessary to provide buffers between this bus and the
AD6659 to keep these signals from transitioning at the converter
inputs during critical sampling periods.
Rev. " | Page 37 of 40
AD6659
OUTLINE DIMENSIONS
0.60 MAX
9.00
BSC SQ
0.60
MAX
64
49
48
PIN 1
INDICATOR
1
PIN 1
INDICATOR
8.75
BSC SQ
0.50
BSC
0.50
0.40
0.30
1.00
0.85
0.80
SEATING
PLANE
33
32
16
17
0.25 MIN
7.50
REF
0.80 MAX
0.65 TYP
12° MAX
0.05 MAX
0.02 NOM
0.30
0.23
0.18
6.35
6.20 SQ
6.05
EXPOSED PAD
(BOTTOM VIEW)
0.20 REF
FOR PROPER CONNECTION OF
THE EXPOSED PAD, REFER TO
THE PIN CONFIGURATION AND
FUNCTION DESCRIPTIONS
SECTION OF THIS DATA SHEET.
COMPLIANT TO JEDEC STANDARDS MO-220-VMMD-4
091707-C
TOP VIEW
Figure 51. 64-Lead Lead Frame Chip Scale Package [LFCSP_VQ]
9 mm × 9 mm Body, Very Thin Quad (CP-64-4)
Dimensions shown in millimeters
ORDERING GUIDE
Model1
AD6659BCPZ-80
AD6659BCPZRL7-80
AD6659-80EBZ
1
2
Temperature Range
–40°C to +85°C
–40°C to +85°C
Package Description
64-Lead Lead Frame Chip Scale Package [LFCSP_VQ] 2
64-Lead Lead Frame Chip Scale Package [LFCSP_VQ]2
Evaluation Board
Z = RoHS Compliant Part.
The exposed paddle (Pin 0) is the only ground connection on the chip and must be connected to the PCB AGND.
Rev. A | Page 38 of 40
Package Option
CP-64-4
CP-64-4
AD6659
NOTES
Rev. " | Page 39 of 40
AD6659
NOTES
©2010 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D08701-0-/10(0)
Rev. " | Page 40 of 40
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