Exar CDK1308CILP40 Ultra low power, 20/40/65/80msps, 10-bit analog-to-digital converters (adcs) Datasheet

Data Sheet
CDK1308
Ultra Low Power, 20/40/65/80MSPS,
10-bit Analog-to-Digital Converters (ADCs)
n
10-bit resolution
n
20/40/65/80MSPS max sampling rate
n
The CDK1308 is a high performance ultra low power analog-to-digital
converter (ADC). The ADC employs internal reference circuitry, a CMOS
control interface and CMOS output data, and is based on a proprietary
structure. Digital error correction is employed to ensure no missing codes in
the complete full scale range.
Ultra-Low Power Dissipation:
15/25/38/46mW
n
61.6dB SNR at 80MSPS and 8MHz FIN
n
Internal reference circuitry
n
1.8V core supply voltage
n
1.7 – 3.6V I/O supply voltage
n
Parallel CMOS output
n
40-pin QFN package
n
Pin compatible with CDK1307
Two idle modes with fast startup times exist. The entire chip can either be
put in Standby Mode or Power Down mode. The two modes are optimized to
allow the user to select the mode resulting in the smallest possible energy
consumption during idle mode and startup.
The CDK1308 has a highly linear THA optimized for frequencies up to Nyquist.
The differential clock interface is optimized for low jitter clock sources and
supports LVDS, LVPECL, sine wave, and CMOS clock inputs.
APPLICATIONS
n
Medical Imaging
n
Portable Test Equipment
n
Digital Oscilloscopes
n
IF Communication
n
Video Conferencing
n
Video Distribution
Functional Block Diagram
Rev 1B
10
Ordering Information
Part Number
Speed
Package
Pb-Free
RoHS Compliant
Operating Temperature Range
Packaging Method
CDK1308AILP40
20MSPS
QFN-40
Yes
Yes
-40°C to +85°C
Tray
CDK1308BILP40
40MSPS
QFN-40
Yes
Yes
-40°C to +85°C
Tray
CDK1308CILP40
65MSPS
QFN-40
Yes
Yes
-40°C to +85°C
Tray
CDK1308DILP40
80MSPS
QFN-40
Yes
Yes
-40°C to +85°C
Tray
Moisture sensitivity level for all parts is MSL-2A.
Exar Corporation
48720 Kato Road, Fremont CA 94538, USA
CDK1308 Ultra Low Power, 20/40/65/80MSPS, 10-bit ADCs
General Description
FEATURES
www.exar.com
Tel. +1 510 668-7000 - Fax. +1 510 668-7001
Data Sheet
Pin Configuration
SLP_N
CM_EXTBC_0
CM_EXTBC_1
OVDD
OVDD
D_9
D_8
D_7
D_6
D_5
39
38
37
36
35
34
33
32
31
DVDD
1
30
D_4
CM_EXT
2
29
D_3
AVDD
3
28
D_2
AVDD
4
27
CLK_EXT
IP
5
26
OVDD
IN
6
25
OVDD
AVDD
7
24
ORNG
DVDDCLK
8
23
D_1
CLKP
9
22
D_0
CLKN
10
21
NC
CDK1308
11
12
13
14
15
16
17
18
19
20
DVDD
CLK_EXT_EN
DFRMT
PD_N
OE_N
DVDD
OVDD
OVDD
NC
NC
QFN-40
CDK1308 Ultra Low Power, 20/40/65/80MSPS, 10-bit ADCs
40
QFN-40
Pin Assignments
Pin No.
Pin Name
Description
0
VSS
1, 11, 16
DVDD
2
CM_EXT
3, 4, 7
AVDD
Analog supply voltage, 1.8V
5, 6
IP, IN
Analog input (non-inverting, inverting)
8
DVDDCLK
9
CLKP
Clock input, non-inverting (format: LVDS, LVPECL, CMOS/TTL, Sine Wave)
10
CLKN
Clock input, inverting. For CMOS input on CLKP, connect CLKN to ground
12
CLK_EXT_EN
CLK_EXT signal enabled when low (zero). Tristate when high.
13
DFRMT
Data format selection. 0: Offset Binary, 1: Two's Complement
14
PD_N
Full chip Power Down mode when Low. All digital outputs reset to zero. After chip power up
always apply Power Down mode before using Active Mode to reset chip.
15
OE_N
Output Enable. Tristate when high
17, 18, 25,
26, 36, 37
OVDD
I/O ring post-driver supply voltage. Voltage range 1.7 to 3.6V
19
NC
20
NC
21
NC
22
D_0
Ground connection for all power domains. Exposed pad
Digital and I/O-ring pre driver supply voltage, 1.8V
Common Mode voltage output
Rev 1B
Clock circuitry supply voltage, 1.8V
Output Data (LSB)
©2009-2013 Exar Corporation 2/14
Rev 1B
Data Sheet
Pin Assignments (Continued)
Pin No.
Description
23
D_1
Output Data
24
ORNG
Out of Range flag. High when input signal is out of range
27
CLK_EXT
Output clock signal for data synchronization. CMOS levels
28
D_2
Output Data
29
D_3
Output Data
30
D_4
Output Data
31
D_5
Output Data
32
D_6
Output Data
33
D_7
Output Data
34
D_8
Output Data
35
D_9
Output Data (MSB)
38, 39
CM_EXTBC_1,
CM_EXTBC_0
40
SLP_N
CDK1308 Ultra Low Power, 20/40/65/80MSPS, 10-bit ADCs
Pin Name
Bias control bits for the buffer driving pin CM_EXT
00: OFF
01: 50μA
10: 500μA
11: 1mA
Sleep Mode when low
Rev 1B
©2009-2013 Exar Corporation 3/14
Rev 1B
Data Sheet
Absolute Maximum Ratings
The safety of the device is not guaranteed when it is operated above the “Absolute Maximum Ratings”. The device
should not be operated at these “absolute” limits. Adhere to the “Recommended Operating Conditions” for proper device
function. The information contained in the Electrical Characteristics tables and Typical Performance plots reflect the
operating conditions noted on the tables and plots.
Min
Max
Unit
AVDD
DVDD
AVSS, DVSSCK, DVSS, OVSS
OVDD
CLKP, CLKN
Analog inputs and outpts (IPx, INx)
Digital inputs
Digital outputs
-0.3
-0.3
-0.3
-0.3
-0.3
-0.3
-0.3
-0.3
+2.3
+2.3
+0.3
+3.9
+3.9
+2.3
+3.9
+3.9
V
V
V
V
V
V
V
V
CDK1308 Ultra Low Power, 20/40/65/80MSPS, 10-bit ADCs
Parameter
Reliability Information
Parameter
Min
Storage Temperature Range
Lead Temperature (Soldering, 10s)
-60
Typ
Max
Unit
+150
°C
J-STD-20
ESD Protection
Product
QFN-40
Human Body Model (HBM)
2kV
Recommended Operating Conditions
Parameter
Min
Operating Temperature Range
-40
Typ
Max
Unit
+85
°C
Rev 1B
©2009-2013 Exar Corporation 4/14
Rev 1B
Data Sheet
Electrical Characteristics
(AVDD = 1.8V, DVDD = 1.8V, DVDDCLK = 1.8V, OVDD = 2.5V, 20/40/65/80MSPS clock, 50% clock duty cycle,
-1dBFS 8MHz input signal, unless otherwise noted)
Symbol
Parameter
Conditions
Min
Typ
Max
Units
DC Accuracy
Guaranteed
Offset Error
Midscale offset
Gain Error
Full scale range deviation from typical
1
-6
LSB
6
%FS
DNL
Differential Non-Linearity
±0.15
LSB
INL
Integral Non-Linearity
±0.2
LSB
VCMO
Common Mode Voltage Output
VAVDD/2
V
Analog Input
VCMI
Input Common Mode
Analog input common mode voltage
VCM -0.1
VCM +0.2
V
VFSR
Full Scale Range
Differential input voltage range
2.0
Input Capacitance
Differential input capacitance
2.0
Bandwidth
Input bandwidth, full power
500
AVDD,
DVDD
Core Supply Voltage
Supply voltage to all 1.8V domain pins.
See Pin Configuration and Description
1.7
1.8
2.0
V
2.5
3.6
V
I/O Supply Voltage
Output driver supply voltage (OVDD).
Must be higher than or equal to Core Supply
Voltage (VOVDD ≥ VDVDD)
1.7
OVDD
Vpp
pF
MHz
Power Supply
CDK1308 Ultra Low Power, 20/40/65/80MSPS, 10-bit ADCs
No Missing Codes
Rev 1B
©2009-2013 Exar Corporation 5/14
Rev 1B
Data Sheet
Electrical Characteristics - CDK1308A
(AVDD = 1.8V, DVDD = 1.8V, DVDDCLK = 1.8V, OVDD = 2.5V, 20MSPS clock, 50% clock duty cycle,
-1dBFS 8MHz input signal, unless otherwise noted)
Symbol
Parameter
Conditions
Min
Typ
Max
Units
61.7
dBFS
60
61.6
dBFS
FIN ≃ FS/2
61.6
dBFS
FIN = 20MHz
61.6
dBFS
FIN = 2MHz
61.7
dBFS
Performance
SNR
SINAD
Signal to Noise Ratio
Signal to Noise and Distortion Ratio
FIN = 8MHz
FIN = 8MHz
61.6
dBFS
FIN ≃ FS/2
60
60.5
dBFS
FIN = 20MHz
61.6
dBFS
80
dBc
81
dBc
70
dBc
FIN = 20MHz
80
dBc
FIN = 2MHz
-90
dBc
-90
dBc
FIN ≃ FS/2
-90
dBc
FIN = 20MHz
-90
dBc
FIN = 2MHz
-80
dBc
-81
dBc
FIN ≃ FS/2
-70
dBc
FIN = 20MHz
-80
dBc
FIN = 2MHz
10.0
bits
FIN = 2MHz
SFDR
HD2
HD3
ENOB
Spurious Free Dynamic Range
Second order Harmonic Distortion
Third order Harmonic Distortion
Effective number of Bits
FIN = 8MHz
70
FIN ≃ FS/2
FIN = 8MHz
-80
FIN = 8MHz
-70
FIN = 8MHz
9.7
bits
9.8
bits
FIN = 20MHz
9.9
bits
5.7
mA
Digital core supply
1.0
mA
2.5V output driver supply, sine wave input,
FIN = 1MHz, CLK_EXT enabled
1.7
mA
2.5V output driver supply, sine wave input,
FIN = 1MHz, CLK_EXT disabled
1.2
mA
Power Supply
AIDD
Analog Supply Current
DIDD
Digital Supply Current
OIDD
Output Driver Supply
Analog Power Dissipation
10.3
mW
Digital Power Dissipation
OVDD = 2.5V, 5pF load on output bits,
FIN = 1MHz, CLK_EXT disabled
4.8
mW
Total Power Dissipation
OVDD = 2.5V, 5pF load on output bits,
FIN = 1MHz, CLK_EXT disabled
15.1
mW
Power Down Dissipation
Sleep Mode
Power Dissipation, Sleep mode
9.9
µW
7.7
mW
Clock Inputs
Max. Conversion Rate
20
Min. Conversion Rate
©2009-2013 Exar Corporation MSPS
15
6/14
MSPS
Rev 1B
Rev 1B
9.9
FIN ≃ FS/2
CDK1308 Ultra Low Power, 20/40/65/80MSPS, 10-bit ADCs
FIN = 2MHz
Data Sheet
Electrical Characteristics - CDK1308B
(AVDD = 1.8V, DVDD = 1.8V, DVDDCLK = 1.8V, OVDD = 2.5V, 40MSPS clock, 50% clock duty cycle,
-1dBFS 8MHz input signal, unless otherwise noted)
Symbol
Parameter
Conditions
Min
Typ
Max
Units
Performance
SNR
SINAD
Signal to Noise Ratio
Signal to Noise and Distortion Ratio
61.6
dBFS
61.6
dBFS
FIN ≃ FS/2
61.6
dBFS
FIN = 30MHz
61.5
dBFS
FIN = 2MHz
61.6
dBFS
FIN = 8MHz
60
FIN = 8MHz
61.6
dBFS
FIN ≃ FS/2
60
61.2
dBFS
FIN = 30MHz
61.4
dBFS
80
dBc
81
dBc
72.0
dBc
FIN = 30MHz
80
dBc
FIN = 2MHz
-90
dBc
-90
dBc
FIN ≃ FS/2
-85
dBc
FIN = 30MHz
-85
dBc
FIN = 2MHz
-80
dBc
-81
dBc
FIN = 2MHz
SFDR
HD2
HD3
ENOB
Spurious Free Dynamic Range
Second order Harmonic Distortion
Third order Harmonic Distortion
Effective number of Bits
FIN = 8MHz
70
FIN ≃ FS/2
FIN = 8MHz
-80
FIN = 8MHz
-70
FIN ≃ FS/2
-72.0
dBc
FIN = 30MHz
-80
dBc
FIN = 2MHz
9.9
bits
FIN = 8MHz
9.9
bits
FIN ≃ FS/2
9.7
9.9
bits
FIN = 30MHz
9.9
bits
Power Supply
AIDD
Analog Supply Current
DIDD
Digital Supply Current
Output Driver Supply
mA
1.7
mA
2.5V output driver supply, sine wave input,
FIN = 1MHz, CLK_EXT enabled
3.1
mA
2.5V output driver supply, sine wave input,
FIN = 1MHz, CLK_EXT disabled
2.2
mA
Analog Power Dissipation
16.7
mW
Digital Power Dissipation
OVDD = 2.5V, 5pF load on output bits,
FIN = 1MHz, CLK_EXT disabled
8.6
mW
Total Power Dissipation
OVDD = 2.5V, 5pF load on output bits,
FIN = 1MHz, CLK_EXT disabled
25.3
mW
9.7
µW
Power Dissipation, Sleep mode
11.3
mW
Power Down Dissipation
Sleep Mode
Clock Inputs
Max. Conversion Rate
40
Min. Conversion Rate
©2009-2013 Exar Corporation MSPS
20
7/14
MSPS
Rev 1B
Rev 1B
OIDD
9.3
Digital core supply
CDK1308 Ultra Low Power, 20/40/65/80MSPS, 10-bit ADCs
FIN = 2MHz
Data Sheet
Electrical Characteristics - CDK1308C
(AVDD = 1.8V, DVDD = 1.8V, DVDDCLK = 1.8V, OVDD = 2.5V, 65MSPS clock, 50% clock duty cycle,
-1dBFS 8MHz input signal, unless otherwise noted)
Symbol
Parameter
Conditions
Min
Typ
FIN = 8MHz
60
Max
Units
Performance
Signal to Noise Ratio
dBFS
61.6
dBFS
FIN ≃ FS/2
61.5
dBFS
FIN = 40MHz
61.3
dBFS
61.6
dBFS
FIN = 20MHz
61.6
dBFS
FIN ≃ FS/2
60.4
dBFS
FIN = 40MHz
61.1
dBFS
FIN = 8MHz
SINAD
Signal to Noise and Distortion Ratio
60
FIN = 8MHz
SFDR
Spurious Free Dynamic Range
77
dBc
FIN = 20MHz
70
77
dBc
FIN ≃ FS/2
70
dBc
FIN = 40MHz
75
dBc
-90
dBc
FIN = 20MHz
-95
dBc
FIN ≃ FS/2
-85
dBc
FIN = 40MHz
-90
dBc
-77
dBc
FIN = 20MHz
-77
dBc
FIN ≃ FS/2
-70
dBc
FIN = 40MHz
-75
dBc
9.9
bits
FIN = 20MHz
9.9
bits
FIN ≃ FS/2
9.7
bits
FIN = 40MHz
9.9
bits
FIN = 8MHz
HD2
Second order Harmonic Distortion
-80
FIN = 8MHz
HD3
Third order Harmonic Distortion
-70
FIN = 8MHz
ENOB
Effective number of Bits
9.7
Power Supply
AIDD
Analog Supply Current
DIDD
Digital Supply Current
mA
2.6
mA
2.5V output driver supply, sine wave input,
FIN = 1MHz, CLK_EXT enabled
4.9
mA
2.5V output driver supply, sine wave input,
FIN = 1MHz, CLK_EXT disabled
3.4
mA
24.8
mW
Digital Power Dissipation
OVDD = 2.5V, 5pF load on output bits,
FIN = 1MHz, CLK_EXT disabled
13.2
mW
Total Power Dissipation
OVDD = 2.5V, 5pF load on output bits,
FIN = 1MHz, CLK_EXT disabled
38.0
mW
9.3
µW
Power Dissipation, Sleep mode
15.7
mW
Output Driver Supply
Analog Power Dissipation
Power Down Dissipation
Sleep Mode
Clock Inputs
Max. Conversion Rate
65
Min. Conversion Rate
©2009-2013 Exar Corporation MSPS
40
8/14
MSPS
Rev 1B
Rev 1B
OIDD
13.8
Digital core supply
CDK1308 Ultra Low Power, 20/40/65/80MSPS, 10-bit ADCs
SNR
61.6
FIN = 20MHz
Data Sheet
Electrical Characteristics - CDK1308D
(AVDD = 1.8V, DVDD = 1.8V, DVDDCLK = 1.8V, OVDD = 2.5V, 80MSPS clock, 50% clock duty cycle,
-1dBFS 8MHz input signal, unless otherwise noted)
Symbol
Parameter
Conditions
Min
Typ
FIN = 8MHz
60
Max
Units
Performance
Signal to Noise Ratio
dBFS
61.2
dBFS
FIN = 30MHz
61.3
dBFS
FIN ≃ FS/2
61.3
dBFS
61.3
dBFS
FIN = 20MHz
60.7
dBFS
FIN = 30MHz
61.0
dBFS
59
dBFS
FIN = 8MHz
SINAD
Signal to Noise and Distortion Ratio
60
FIN ≃ FS/2
FIN = 8MHz
SFDR
Spurious Free Dynamic Range
75
dBc
FIN = 20MHz
70
75
dBc
FIN = 30MHz
75
dBc
FIN ≃ FS/2
65
dBc
-90
dBc
FIN = 20MHz
-95.0
dBc
FIN = 30MHz
-90
dBc
FIN ≃ FS/2
-80
dBc
-75
dBc
FIN = 20MHz
-75.0
dBc
FIN = 30MHz
-75
dBc
FIN ≃ FS/2
-65
dBc
9.9
bits
FIN = 20MHz
9.8
bits
FIN = 30MHz
9.8
bits
FIN ≃ FS/2
9.5
bits
FIN = 8MHz
HD2
Second order Harmonic Distortion
-80
FIN = 8MHz
HD3
Third order Harmonic Distortion
-70
FIN = 8MHz
ENOB
Effective number of Bits
9.7
Power Supply
AIDD
Analog Supply Current
DIDD
Digital Supply Current
mA
3.3
mA
2.5V output driver supply, sine wave input,
FIN = 1MHz, CLK_EXT enabled
5.9
mA
2.5V output driver supply, sine wave input,
FIN = 1MHz, CLK_EXT disabled
4.1
mA
29.7
mW
Digital Power Dissipation
OVDD = 2.5V, 5pF load on output bits,
FIN = 1MHz, CLK_EXT disabled
16.2
mW
Total Power Dissipation
OVDD = 2.5V, 5pF load on output bits,
FIN = 1MHz, CLK_EXT disabled
45.9
mW
9.1
µW
Power Dissipation, Sleep mode
18.3
mW
Output Driver Supply
Analog Power Dissipation
Power Down Dissipation
Sleep Mode
Clock Inputs
Max. Conversion Rate
80
Min. Conversion Rate
©2009-2013 Exar Corporation MSPS
65
9/14
MSPS
Rev 1B
Rev 1B
OIDD
16.5
Digital core supply
CDK1308 Ultra Low Power, 20/40/65/80MSPS, 10-bit ADCs
SNR
61.6
FIN = 20MHz
Data Sheet
Digital and Timing Electrical Characteristics
(AVDD = 1.8V, DVDD = 1.8V, DVDDCLK = 1.8V, OVDD = 2.5V, 20/40/65/80MSPS clock, 50% clock duty cycle,
-1 dBFS input signal, 5pF capacitive load, unless otherwise noted)
Symbol
Parameter
Conditions
Min
Typ
Max
Units
80
% high
Clock Inputs
20
Compliance
CMOS, LVDS, LVPECL, Sine Wave
Differential input swing
400
Differential input swing, sine wave clock input
1.6
Input Common Mode Voltage
Keep voltages within ground and voltage of OVDD
0.3
Input Capacitance
Differential
Input Range
mVpp
Vpp
VOVDD -0.3
2
V
pF
Timing
TPD
Start Up Time from Power Down
TSLP
Start Up Time from Sleep
TOVR
Out Of Range Recovery Time
TAP
From Power Down Mode to Active Mode
From Sleep Mode to Active Mode
900
clk cycles
20
clk cycles
1
clk cycles
ns
Aperture Delay
0.8
εRMS
Aperture Jitter
<0.5
ps
TLAT
Pipeline Delay
12
clk cycles
TD
Output Delay
5pF load on output bits (see timing diagram)
3
10
ns
TDC
Output Delay Relative to CLK_EXT
See timing diagram
1
6
ns
VOVDD ≥ 3.0V
2
Logic Inputs
VIH
High Level Input Voltage
VOVDD = 1.7V – 3.0V
V
0.8 • VOVDD
V
VOVDD ≥ 3.0V
0
0.8
V
VOVDD = 1.7V – 3.0V
0
0.2 • VOVDD
V
VIL
Low Level Input Voltage
IIH
High Level Input Leakage Current
-10
10
µA
IIL
Low Level Input Leakage Current
-10
10
µA
CI
Input Capacitance
3
pF
Logic Outputs
High Level Output Voltage
VOL
Low Level Output Voltage
CL
Max Capacitive Load
VOVDD -0.1
V
Post-driver supply voltage equal to pre-driver
supply voltage VOVDD = VOCVDD
Post-driver supply voltage above 2.25V (1)
10
0.1
V
5
pF
pF
Note:
(1) The outputs will be functional with higher loads. However, it is recommended to keep the load on output data bits as low as possible to keep dynamic currents
and resulting switching noise at a minimum.
©2009-2013 Exar Corporation 10/14
Rev 1B
Rev 1B
VOH
CDK1308 Ultra Low Power, 20/40/65/80MSPS, 10-bit ADCs
Duty Cycle
Data Sheet
N+3
N+4
N+5
N+2
N
N+1
CLK_EXT
Figure 1. Timing Diagram
Recommended Usage
DC-Coupling
Analog Input
Figure 3 shows a recommended configuration for DCcoupling. Note that the common mode input voltage must
be controlled according to specified values. Preferably, the
CM_EXT output should be used as a reference to set the
common mode voltage.
The analog inputs to the CDK1308 is a switched capacitor
track-and-hold amplifier optimized for differential operation. Operation at common mode voltages at mid supply
is recommended even if performance will be good for the
ranges specified. The CM_EXT pin provides a voltage suitable as common mode voltage reference. The internal
buffer for the CM_EXT voltage can be switched off, and
driving capabilities can be changed by using the CM_EXTBC control input.
43Ω
Rev 1B
Figure 2 shows a simplified drawing of the input network. The signal source must have sufficiently low output
impedance to charge the sampling capacitors within one
clock cycle. A small external resistor (e.g. 22Ω) in series
with each input is recommended as it helps reducing transient currents and dampens ringing behavior. A small differential shunt capacitor at the chip side of the resistors
may be used to provide dynamic charging currents and
may improve performance. The resistors form a low pass
filter with the capacitor, and values must therefore be determined by requirements for the application.
The input amplifier could be inside a companion chip or
it could be a dedicated amplifier. Several suitable single
ended to differential driver amplifiers exist in the market.
The system designer should make sure the specifications
of the selected amplifier is adequate for the total system,
and that driving capabilities comply with the CDK1308
input specifications.
33pF
43Ω
Figure 3. DC-Coupled Input
Detailed configuration and usage instructions must be
found in the documentation of the selected driver, and
the values given in Figure 3 must be varied according to
the recommendations for the driver.
AC-Coupling
Figure 2. Input Configuration
©2009-2013 Exar Corporation A signal transformer or series capacitors can be used
to make an AC-coupled input network. Figure 4 shows
11/14
CDK1308 Ultra Low Power, 20/40/65/80MSPS, 10-bit ADCs
N-13
Rev 1B
Data Sheet
Note that startup time from Sleep Mode and Power Down
Mode will be affected by this filter as the time required
to charge the series capacitors is dependent on the filter
cut-off frequency.
If the input signal has a long traveling distance, and the kickbacks from the ADC not are effectively terminated at the
signal source, the input network of Figure 6 can be used.
The configuration is designed to attenuate the kickback
from the ADC and to provide an input impedance that looks
as resistive as possible for frequencies below Nyquist.
Values of the series inductor will however depend on board
design and conversion rate. In some instances a shunt
capacitor in parallel with the termination resistor (e.g. 33pF)
may improve ADC performance further. This capacitor
attenuate the ADC kick-back even more, and minimize the
kicks traveling towards the source. However, the impedance match seen into the transformer becomes worse.
120nH 33Ω
1:1
33Ω
RT
47Ω
optional
RT
68Ω
220Ω
pF
120nH
33Ω
33Ω
Figure 4. Transformer-Coupled Input
Ω
pF
Ω
Figure 5. AC-Coupled Input
©2009-2013 Exar Corporation Figure 6. Alternative Input Network
Rev 1B
Figure 5 shows AC-coupling using capacitors. Resistors
from the CM_EXT output, RCM, should be used to bias the
differential input signals to the correct voltage. The series
capacitor, CI, form the high-pass pole with these resistors,
and the values must therefore be determined based on
the requirement to the high-pass cut-off frequency.
Clock Input And Jitter Considerations
Typically high-speed ADCs use both clock edges to generate internal timing signals. In the CDK1308 only the rising
edge of the clock is used. Hence, input clock duty cycles
between 20% and 80% is acceptable.
The input clock can be supplied in a variety of formats.
The clock pins are AC-coupled internally, and hence a wide
common mode voltage range is accepted. Differential
clock sources as LVDS, LVPECL or differential sine wave
can be connected directly to the input pins. For CMOS
inputs, the CLKN pin should be connected to ground, and
the CMOS clock signal should be connected to CLKP. For
differential sine wave clock input the amplitude must be
at least ±800mVpp.
12/14
CDK1308 Ultra Low Power, 20/40/65/80MSPS, 10-bit ADCs
a recommended configuration using a transformer. Make
sure that a transformer with sufficient linearity is selected,
and that the bandwidth of the transformer is appropriate.
The bandwidth should exceed the sampling rate of the
ADC with at least a factor of 10. It is also important to
keep phase mismatch between the differential ADC inputs
small for good HD2 performance. This type of transformer
coupled input is the preferred configuration for high frequency signals as most differential amplifiers do not have
adequate performance at high frequencies. If the input
signal is traveling a long physical distance from the signal
source to the transformer (for example a long cable), kickbacks from the ADC will also travel along this distance. If
these kick-backs are not terminated properly at the source
side, they are reflected and will add to the input signal at
the ADC input. This could reduce the ADC performance.
To avoid this effect, the source must effectively terminate
the ADC kick-backs, or the traveling distance should be
very short. If this problem could not be avoided, the circuit in Figure 6 can be used.
Rev 1B
Data Sheet
The quality of the input clock is extremely important for
high-speed, high-resolution ADCs. The contribution to SNR
from clock jitter with a full scale signal at a given frequency
is shown in the equation below:
•
π • FIN • εt)
where FIN is the signal frequency, and εt is the total rms
jitter measured in seconds. The rms jitter is the total of all
jitter sources including the clock generation circuitry, clock
distribution and internal ADC circuitry.
For applications where jitter may limit the obtainable performance, it is of utmost importance to limit the clock
jitter. This can be obtained by using precise and stable
clock references (e.g. crystal oscillators with good jitter
specifications) and make sure the clock distribution is
well controlled. It might be advantageous to use analog
power and ground planes to ensure low noise on the supplies to all circuitry in the clock distribution. It is of utmost
importance to avoid crosstalk between the ADC output bits
and the clock and between the analog input signal and
the clock since such crosstalk often results in harmonic
distortion.
The jitter performance is improved with reduced rise and
fall times of the input clock. Hence, optimum jitter performance is obtained with LVDS or LVPECL clock with fast
edges. CMOS and sine wave clock inputs will result in
slightly degraded jitter performance.
Digital Outputs
Digital output data are presented on parallel CMOS form.
The digital outputs can be set in tristate mode by setting
the OE_N signal high.
The CDK1308 employs digital offset correction. This means
that the output code will be 4096 with shorted inputs.
However, small mismatches in parasitics at the input
can cause this to alter slightly. The offset correction also
results in possible loss of codes at the edges of the full
scale range. With no offset correction, the ADC would clip
in one end before the other, in practice resulting in code
loss at the opposite end. With the output being centered
digitally, the output will clip, and the out of range flags will
be set, before max code is reached. When out of range
flags are set, the code is forced to all ones for over-range
and all zeros for under-range.
Data Format Selection
The output data are presented on offset binary form
when DFRMT is low (connect to OVSS). Setting DFRMT
high (connect to OVDD) results in 2’s complement output
format. Details are shown in Table 1 below.
Table 1: Data Format Description for 2Vpp Full Scale Range
Differential Input Voltage (IP - IN)
Output data: D_9 : D_0
Output Data: D_9 : D_0
(DFRMT = 0, offset binary)
(DFRMT = 1, 2’s complement)
1.0 V
11 1111 1111
01 1111 1111
+0.24mV
10 0000 0000
00 0000 0000
-0.24mV
01 1111 1111
11 1111 1111
-1.0V
00 0000 0000
10 0000 0000
©2009-2013 Exar Corporation 13/14
Rev 1B
Rev 1B
If the clock is generated by other circuitry, it should be retimed with a low jitter master clock as the last operation
before it is applied to the ADC clock input.
The timing is described in the Timing Diagram section.
Note that the load or equivalent delay on CK_EXT always
should be lower than the load on data outputs to ensure
sufficient timing margins.
CDK1308 Ultra Low Power, 20/40/65/80MSPS, 10-bit ADCs
SNRjitter = 20 • log (2
The voltage on the OVDD pin set the levels of the CMOS
outputs. The output drivers are dimensioned to drive a
wide range of loads for OVDD above 2.25V, but it is recommended to minimize the load to ensure as low transient
switching currents and resulting noise as possible. In applications with a large fanout or large capacitive loads, it
is recommended to add external buffers located close to
the ADC chip.
Data Sheet
Reference Voltages
tributes to the Power Down Dissipation. The startup time
from this mode is longer than for Sleep Mode as all references need to settle to their final values before normal
operation can resume.
The SLP_N signal can be used to set the full chip in Sleep
Mode. In this mode internal clocking is disabled, but some
low bandwidth circuitry is kept on to allow for a short
startup time. However, Sleep Mode represents a significant reduction in supply current, and it can be used to
save power even for short idle periods.
Operational Modes
The operational modes are controlled with the PD_N and
SLP_N pins. If PD_N is set low, all other control pins are
overridden and the chip is set in Power Down mode. In
this mode all circuitry is completely turned off and the internal clock is disabled. Hence, only leakage current con-
The input clock should be kept running in all idle modes.
However, even lower power dissipation is possible in Power
Down mode if the input clock is stopped. In this case it is
important to start the input clock prior to enabling active mode.
Mechanical Dimensions
QFN-40 Package
D
D2
Pin 1 ID - Dia. 0.5
(Top Side)
1.14
Pin 1 ID - Dia. R
F
A
G
A3
0.45
A1
Pin 0 Exposed Pad
Symbol
A
A1
A2
A3
b
D
D1
D2
L
e
θ1
F
G
R
Min
–
0.001
–
0.008
0.156
0.012
0°
0.008
0.0096
0.004
Inches
Typ
–
0.0004
0.023
0.008 REF
0.010
0.236 BSC
0.226 BSC
0.162
0.016
0.020 BSC
–
–
0.0168
0.008
Max
0.035
0.002
0.028
Min
–
0.00
–
0.013
0.2
0.167
0.020
3.95
0.3
12°
–
0.024
–
0°
0.2
0.24
0.1
Millimeters
Typ
–
0.01
0.65
0.2 REF
0.25
6.00 BSC
5.75 BSC
4.10
0.4
0.50 BSC
–
–
0.42
0.2
Max
0.9
0.05
0.7
0.32
4.25
0.5
12°
–
0.6
–
NOTE:
D
D2
D1
Package dimensions in millimeter unless otherwise noted.
CDK1308 Ultra Low Power, 20/40/65/80MSPS, 10-bit ADCs
The reference voltages are internally generated and buffered based on a bandgap voltage reference. No external
decoupling is necessary, and the reference voltages are
not available externally. This simplifies usage of the ADC
since two extremely sensitive pins, otherwise needed, are
removed from the interface.
Rev 1B
θ1
L
e
b
A2
For Further Assistance:
Exar Corporation Headquarters and Sales Offices
48720 Kato Road
Tel.: +1 (510) 668-7000
Fremont, CA 94538 - USA
Fax: +1 (510) 668-7001
www.exar.com
NOTICE
EXAR Corporation reserves the right to make changes to the products contained in this publication in order to improve design, performance or reliability. EXAR Corporation assumes no responsibility for the use of any
circuits described herein, conveys no license under any patent or other right, and makes no representation that the circuits are free of patent infringement. Charts and schedules contained here in are only for illustration
purposes and may vary depending upon a user’s specific application. While the information in this publication has been carefully checked; no responsibility, however, is assumed for inaccuracies.
EXAR Corporation does not recommend the use of any of its products in life support applications where the failure or malfunction of the product can reasonably be expected to cause failure of the life support system or
to significantly affect its safety or effectiveness. Products are not authorized for use in such applications unless EXAR Corporation receives, in writing, assurances to its satisfaction that: (a) the risk of injury or damage
has been minimized; (b) the user assumes all such risks; (c) potential liability of EXAR Corporation is adequately protected under the circumstances.
Reproduction, in part or whole, without the prior written consent of EXAR Corporation is prohibited.
©2009-2013 Exar Corporation 14/14
Rev 1B
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