MAXIM MAX1195ECM

19-2410; Rev 0; 4/02
Dual, 8-Bit, 40Msps, 3V, Low-Power ADC with
Internal Reference and Parallel Outputs
♦ Low Power
87mW (Normal Operation)
9mW (Sleep Mode)
0.3µW (Shutdown Mode)
♦ 0.05dB Gain and ±0.05° Phase Matching
♦ Wide ±1VP-P Differential Analog Input Voltage
Range
♦ 400MHz -3dB Input Bandwidth
♦ On-Chip 2.048V Precision Bandgap Reference
♦ User-Selectable Output Format—Two’s
Complement or Offset Binary
♦ Pin-Compatible 8-Bit and 10-Bit Upgrades
Available
Ordering Information
PART
MAX1195ECM
TEMP RANGE
-40°C to +85°C
PIN-PACKAGE
48 TQFP-EP*
*EP = Exposed paddle
Functional Diagram and Pin Compatible Upgrades table
appear at end of data sheet.
37
38
39
40
41
42
43
44
45
46
47
48
REFN
REFP
REFIN
REFOUT
D7A
D6A
D5A
D4A
D3A
D2A
D1A
D0A
Pin Configuration
COM
VDD
GND
INA+
INA-
1
36
2
35
3
34
4
33
5
32
VDD
GND
INBINB+
GND
VDD
CLK
6
31
MAX1195
7
30
N.C.
N.C.
OGND
OVDD
OVDD
OGND
N.C.
N.C.
D0B
D1B
D2B
D3B
24
23
22
21
25
20
12
19
26
18
27
11
17
28
10
16
29
9
15
8
14
WLAN, WWAN, WLL,
MMDS Modems
Set-Top Boxes
VSAT Terminals
♦ Excellent Dynamic Performance
48.5dB/46.7dB SINAD at fIN = 20MHz/200MHz
68.7dBc/55.7dBc SFDR at fIN = 20MHz/200MHz
♦ -72dB Interchannel Crosstalk at fIN = 20MHz
GND
VDD
VDD
GND
T/B
SLEEP
PD
OE
D7B
D6B
D5B
D4B
Baseband I/Q Sampling
Multichannel IF Sampling
Ultrasound and Medical
Imaging
Battery-Powered
Instrumentation
♦ Single 2.7V to 3.6V Operation
13
Applications
Features
TQFP-EP
________________________________________________________________ Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
1
MAX1195
General Description
The MAX1195 is a 3V, dual, 8-bit analog-to-digital converter (ADC) featuring fully differential wideband trackand-hold (T/H) inputs, driving two ADCs. The MAX1195
is optimized for low-power, small size, and high-dynamic
performance for applications in imaging, instrumentation
and digital communications. This ADC operates from a
single 2.7V to 3.6V supply, consuming only 87mW while
delivering a typical signal-to-noise and distortion (SINAD)
of 48.5dB at an input frequency of 20MHz and a sampling rate of 40Msps. The T/H-driven input stages incorporate 400MHz (-3dB) input amplifiers. The converters
may also be operated with single-ended inputs. In addition to low operating power, the MAX1195 features a
3mA sleep mode as well as a 0.1µA power-down mode
to conserve power during idle periods.
An internal 2.048V precision bandgap reference sets
the full-scale range of the ADC. A flexible reference
structure allows the use of this internal or an externally
applied reference, if desired, for applications requiring
increased accuracy or a different input voltage range.
The MAX1195 features parallel, CMOS-compatible threestate outputs. The digital output format can be set to two’s
complement or straight offset binary through a single control pin. The device provides for a separate output power
supply of 1.7V to 3.6V for flexible interfacing with various
logic families. The MAX1195 is available in a 7mm x 7mm,
48-pin TQFP package, and is specified for the extended
industrial (-40°C to +85°C) temperature range.
Pin-compatible higher speed versions of the MAX1195
are also available. Refer to the MAX1197 data sheet for
60Msps and the MAX1198 data sheet for 100Msps. In
addition to these speed grades, this family will include a
multiplexed output version (MAX1196, 40Msps), for
which digital data is presented time interleaved and on
a single, parallel 8-bit output port.
For a 10-bit, pin-compatible upgrade, refer to the
MAX1183 data sheet. With the N.C. pins of the MAX1195
internally pulled down to ground, this ADC becomes a
drop-in replacement for the MAX1183.
MAX1195
Dual, 8-Bit, 40Msps, 3V, Low-Power ADC with
Internal Reference and Parallel Outputs
ABSOLUTE MAXIMUM RATINGS
VDD, OVDD to GND ...............................................-0.3V to +3.6V
OGND to GND.......................................................-0.3V to +0.3V
INA+, INA-, INB+, INB- to GND ...............................-0.3V to VDD
REFIN, REFOUT, REFP, REFN,
COM, CLK to GND .................................-0.3V to (VDD + 0.3V)
OE, PD, SLEEP, T/B, D7A–D0A,
D7B–D0B to OGND .............................-0.3V to (OVDD + 0.3V)
Continuous Power Dissipation (TA = +70°C)
48-Pin TQFP (derate 12.5mW/°C above +70°C).........1000mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-60°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VDD = OVDD = 3V, 0.1µF and 2.2µF capacitors from REFP, REFN, and COM to GND; REFOUT connected to REFIN through a 10kΩ
resistor, VIN = 2VP-P (differential with respect to COM), CL = 10pF at digital outputs, fCLK = 40MHz, TA = TMIN to TMAX, unless
otherwise noted. ≥+25°C guaranteed by production test, <+25°C guaranteed by design and characerization. Typical values are at
TA = +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
DC ACCURACY
Resolution
8
Bits
Integral Nonlinearity
INL
fIN = 7.51MHz (Note 1)
±0.3
±1
LSB
Differential Nonlinearity
DNL
fIN = 7.51MHz, no missing codes
guaranteed (Note 1)
±0.15
±1
LSB
Offset Error
±4
%FS
Gain Error
±4
Gain Temperature Coefficient
%FS
±100
ppm/°C
ANALOG INPUT
Differential Input Voltage Range
Common-Mode Input Voltage
Range
VDIFF
Differential or single-ended inputs
VCM
Input Resistance
RIN
Input Capacitance
CIN
Switched capacitor load
±1.0
V
VDD / 2
±0.2
V
140
kΩ
5
pF
5
Clock
Cycles
CONVERSION RATE
Maximum Clock Frequency
fCLK
40
Data Latency
MHz
DYNAMIC CHARACTERISTICS (fCLK = 40MHz, 4096-point FFT)
Signal-to-Noise Ratio
SNR
fINA or B = 1MHz at -1dB FS
48.7
fINA or B = 7.5MHz at -1dB FS
48.7
fINA or B = 20MHz at -1dB FS
fINA or B = 115.1MHz at -1dB FS
2
47.5
48.6
48.0
_______________________________________________________________________________________
dB
Dual, 8-Bit, 40Msps, 3V, Low-Power ADC with
Internal Reference and Parallel Outputs
(VDD = OVDD = 3V, 0.1µF and 2.2µF capacitors from REFP, REFN, and COM to GND; REFOUT connected to REFIN through a 10kΩ
resistor, VIN = 2VP-P (differential with respect to COM), CL = 10pF at digital outputs, fCLK = 40MHz, TA = TMIN to TMAX, unless
otherwise noted. ≥+25°C guaranteed by production test, <+25°C guaranteed by design and characerization. Typical values are at
TA = +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
fINA or B = 1MHz at -1dB FS
Signal-to-Noise
and Distortion
SINAD
48.5
47
fINA or B = 115.1MHz at -1dB FS
Spurious-Free
Dynamic Range
SFDR
Third-Harmonic
Distortion
HD3
47.8
73
fINA or B = 7.5MHz at -1dB FS
69
fINA or B = 115.1MHz at -1dB FS
UNITS
dB
48.5
fINA or B = 1MHz at -1dB FS
fINA or B = 20MHz at -1dB FS
MAX
48.6
fINA or B = 7.5MHz at -1dB FS
fINA or B = 20MHz at -1dB FS
TYP
60
dBc
68.7
63
fINA or B = 1MHz at -1dB FS
-75
fINA or B = 7.5MHz at -1dB FS
-73
fINA or B = 20MHz at -1dB FS
-70
fINA or B = 115.1MHz at -1dB FS
-63
dBc
Intermodulation Distortion
(First Five Odd-Order IMDs)
IMD
fIN1(A or B) = 1.997MHz at -7dB FS
fIN2(A or B) = 2.046MHz at -7dB FS
(Note 2)
-69.5
dBc
Third-Order Intermodulation
Distortion
IM3
fIN1(A or B) = 1.997MHz at -7dB FS
fIN2(A or B) = 2.046 MHz at -7dB FS
(Note 2)
-71.7
dBc
Total Harmonic Distortion
(First Four Harmonics)
THD
Small-Signal Bandwidth
Full-Power Bandwidth
FPBW
Gain Flatness
(12MHz Spacing)
fINA or B = 1MHz at -1dB FS
-70
fINA or B = 7.5MHz at -1dB FS
-69
fINA or B = 20MHz at -1dB FS
-69
-57
dBc
fINA or B = 115.1MHz at -1dB FS
-62
Input at -20dB FS, differential inputs
500
MHz
Input at -1dB FS, differential inputs
400
MHz
fIN1(A or B) = 106 MHz at -1dB FS
fIN2(A or B) = 118 MHz at -1dB FS
(Note 3)
0.05
dB
Aperture Delay
tAD
(Note 1)
1
ns
Aperture Jitter
tAJ
1dB SNR degradation at Nyquist
2
psRMS
For 1.5 × full-scale input
2
ns
Overdrive Recovery Time
INTERNAL REFERENCE (REFIN = REFOUT through 10kΩ resistor; REFP, REFN, and COM levels are generated internally.)
Reference Output Voltage
VREFOUT
(Note 4)
2.048
±3%
V
Positive Reference Output
Voltage
VREFP
(Note 5)
2.012
V
Negative Reference Output
Voltage
VREFN
(Note 5)
0.988
V
_______________________________________________________________________________________
3
MAX1195
ELECTRICAL CHARACTERISTICS (continued)
MAX1195
Dual, 8-Bit, 40Msps, 3V, Low-Power ADC with
Internal Reference and Parallel Outputs
ELECTRICAL CHARACTERISTICS (continued)
(VDD = OVDD = 3V, 0.1µF and 2.2µF capacitors from REFP, REFN, and COM to GND; REFOUT connected to REFIN through a 10kΩ
resistor, VIN = 2VP-P (differential with respect to COM), CL = 10pF at digital outputs, fCLK = 40MHz, TA = TMIN to TMAX, unless
otherwise noted. ≥+25°C guaranteed by production test, <+25°C guaranteed by design and characerization. Typical values are at
TA = +25°C.)
PARAMETER
SYMBOL
CONDITIONS
Common-Mode Level
VCOM
(Note 5)
Differential Reference Output
Voltage Range
∆VREF
∆VREF = VREFP - VREFN
Reference Temperature
Coefficient
TCREF
MIN
TYP
MAX
UNITS
VDD / 2
±0.1
V
1.024
±3%
V
±100
ppm/°C
BUFFERED EXTERNAL REFERENCE (VREFIN = 2.048V)
Positive Reference Output
Voltage
VREFP
(Note 5)
2.012
V
Negative Reference Output
Voltage
VREFN
(Note 5)
0.988
V
Common-Mode Level
VCOM
(Note 5)
VDD / 2
±0.1
V
Differential Reference Output
Voltage Range
∆VREF
∆VREF = VREFP - VREFN
1.024
±2%
V
REFIN Resistance
RREFIN
>50
MΩ
ISOURCE
5
mA
ISINK
-250
µA
ISOURCE
250
µA
ISINK
-5
mA
Maximum REFP, COM Source
Current
Maximum REFP, COM Sink
Current
Maximum REFN Source Current
Maximum REFN Sink Current
UNBUFFERED EXTERNAL REFERENCE (VREFIN = AGND, reference voltage applied to REFP, REFN, and COM)
REFP, REFN Input Resistance
REFP, REFN, COM Input
Capacitance
4
RREFP,
RREFN
Measured between REFP, COM, REFN,
and COM
CIN
4
kΩ
15
pF
1.024
±10%
V
Differential Reference Input
Voltage Range
∆VREF
COM Input Voltage Range
VCOM
VDD / 2
±5%
V
REFP Input Voltage
VREFP
VCOM +
∆VREF / 2
V
REFN Input Voltage
VREFN
VCOM –
∆VREF / 2
V
∆VREF = VREFP - VREFN
_______________________________________________________________________________________
Dual, 8-Bit, 40Msps, 3V, Low-Power ADC with
Internal Reference and Parallel Outputs
(VDD = OVDD = 3V, 0.1µF and 2.2µF capacitors from REFP, REFN, and COM to GND; REFOUT connected to REFIN through a 10kΩ
resistor, VIN = 2VP-P (differential with respect to COM), CL = 10pF at digital outputs, fCLK = 40MHz, TA = TMIN to TMAX, unless
otherwise noted. ≥+25°C guaranteed by production test, <+25°C guaranteed by design and characerization. Typical values are at
TA = +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
DIGITAL INPUTS (CLK, PD, OE, SLEEP, T/B)
Input High Threshold
Input Low Threshold
Input Hysteresis
CLK
0.8 ×
VDD
PD, OE, SLEEP, T/B
0.8 ×
OVDD
VIH
CLK
0.2 ×
VDD
PD, OE, SLEEP, T/B
0.2 ×
OVDD
VIL
VHYST
Input Leakage
Input Capacitance
V
0.15
V
IIH
VIH = VDD = OVDD
±20
IIL
VIL = 0
±20
CIN
V
5
µA
pF
DIGITAL OUTPUTS ( D7A–D0A, D7B–D0B)
Output Voltage Low
VOL
ISINK = -200µA
Output Voltage High
VOH
ISOURCE = 200µA
Three-State Leakage Current
ILEAK
OE = OVDD
Three-State Output Capacitance
COUT
OE = OVDD
0.2
OVDD
- 0.2
V
V
±10
5
µA
pF
POWER REQUIREMENTS
Analog Supply Voltage Range
VDD
Output Supply Voltage Range
OVDD
CL = 15pF
Operating, fINA & B = 20MHz at
-1dB FS applied to both channels
Analog Supply Current
IVDD
Sleep mode
Shutdown, clock idle, PD = OE = OVDD
Output Supply Current
Analog Power Dissipation
Power-Supply
Rejection
IOVDD
PDISS
PSRR
2.7
3
3.6
V
1.7
3
3.6
V
29
36
mA
3
0.1
20
Operating, fINA & B = 20MHz at
-1dB FS applied to both channels (Note 6)
8
Sleep mode
3
Shutdown, clock idle, PD = OE = OVDD
3
10
Operating, fINA & B = 20MHz at
-1dB FS applied to both channels
87
108
Sleep mode
9
Shutdown, clock idle, PD = OE = OVDD
0.3
Offset, VDD ±5%
±3
Gain, VDD ±5%
±3
µA
mA
60
µA
mW
µW
mV/V
_______________________________________________________________________________________
5
MAX1195
ELECTRICAL CHARACTERISTICS (continued)
MAX1195
Dual, 8-Bit, 40Msps, 3V, Low-Power ADC with
Internal Reference and Parallel Outputs
ELECTRICAL CHARACTERISTICS (continued)
(VDD = OVDD = 3V, 0.1µF and 2.2µF capacitors from REFP, REFN, and COM to GND; REFOUT connected to REFIN through a 10kΩ
resistor, VIN = 2VP-P (differential with respect to COM), CL = 10pF at digital outputs, fCLK = 40MHz, TA = TMIN to TMAX, unless
otherwise noted. ≥+25°C guaranteed by production test, <+25°C guaranteed by design and characerization. Typical values are at
TA = +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
6
9
ns
TIMING CHARACTERISTICS
CLK Rise to Output Data Valid
Time
tDO
OE Fall to Output Enable Time
tENABLE
OE Rise to Output Disable Time
CL = 20pF (Notes 1, 7)
5
ns
tDISABLE
5
ns
CLK Pulse Width High
tCH
Clock period: 25ns (Note 7)
12.5
±1.5
ns
CLK Pulse Width Low
tCL
Clock period: 25ns (Note 7)
12.5
±1.5
ns
Wake-Up Time
tWAKE
Wake up from sleep mode
1
Wake up from shutdown mode (Note 11)
20
µs
CHANNEL-TO-CHANNEL MATCHING
Crosstalk
fINA or B = 20MHz at -1dB FS (Note 8)
-72
dB
Gain Matching
fINA or B = 20MHz at -1dB FS (Note 9)
0.05
dB
Phase Matching
fINA or B = 20MHz at -1dB FS (Note 10)
±0.05
Degrees
Note 1: Guaranteed by design. Not subject to production testing.
Note 2: Intermodulation distortion is the total power of the intermodulation products relative to the total input power.
Note 3: Analog attenuation is defined as the amount of attenuation of the fundamental bin from a converted FFT between two
applied input signals with the same magnitude (peak-to-peak) at fIN1 and fIN2.
Note 4: REFIN and REFOUT should be bypassed to GND with a 0.1µF (min) and 2.2µF (typ) capacitor.
Note 5: REFP, REFN, and COM should be bypassed to GND with a 0.1µF (min) and 2.2µF (typ) capacitor.
Note 6: Typical analog output current at fINA&B = 20MHz. For digital output currents vs. analog input frequency,
see Typical Operating Characteristics.
Note 7: See Figure 3 for detailed system timing diagrams. Clock to data valid timing is measured from 50% of the clock
level to 50% of the data output level.
Note 8: Crosstalk rejection is tested by applying a test tone to one channel and holding the other channel at DC level.
Crosstalk is measured by calculating the power ratio of the fundamental of each channel’s FFT.
Note 9: Amplitude matching is measured by applying the same signal to each channel and comparing the magnitude of the fundamental of the calculated FFT.
Note 10: Phase matching is measured by applying the same signal to each channel and comparing the phase of the fundamental
of the calculated FFT. The data from both ADC channels must be captured simultaneously during this test.
Note 11: SINAD settles to within 0.5dB of its typical value in unbuffered external reference mode.
6
_______________________________________________________________________________________
Dual, 8-Bit, 40Msps, 3V, Low-Power ADC with
Internal Reference and Parallel Outputs
-40
-50
fINB
-40
-50
-60
HD2
-50
-80
-80
-90
-90
-90
4
6
8
10 12 14 16 18 20
0
2
4
6
10 12 14 16 18 20
8
fIN1
-20
fIN2
-60
-30
-40
-50
-70
-80
-80
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
10 12 14 16 18 20
49
CHA
48
CHB
47
fIN2
46
45
5
6
7
8
0
10 11 12 13 14 15
9
40
80
120
160
ANALOG INPUT FREQUENCY (MHz)
ANALOG INPUT FREQUENCY (MHz)
ANALOG INPUT FREQUENCY (MHz)
SIGNAL-TO-NOISE + DISTORTION
vs. ANALOG INPUT FREQUENCY
TOTAL HARMONIC DISTORTION
vs. ANALOG INPUT FREQUENCY
SPURIOUS-FREE DYNAMIC RANGE
vs. ANALOG INPUT FREQUENCY
49
-50
CHB
47
-60
CHA
-70
-80
46
120
160
ANALOG INPUT FREQUENCY (MHz)
200
70
CHA
60
50
-90
45
200
CHB
SFDR (dBc)
THD (dBc)
48
80
80
CHB
CHA
40
90
MAX1195 toc08
-40
MAX1195 toc07
50
0
8
50
-90
0
6
-60
-70
-90
fIN1
4
SIGNAL-TO-NOISE RATIO
vs. ANALOG INPUT FREQUENCY
SNR (dB)
-40
-50
-10
AMPLITUDE (dB)
-30
MAX1195 toc04
0
fCLK = 40.001536MHz
fIN1 = 10.024799MHz
fIN2 = 9.956437MHz
AIN = -7dB FS
COHERENT SAMPLING
2
ANALOG INPUT FREQUENCY (MHz)
0
-20
0
ANALOG INPUT FREQUENCY (MHz)
TWO-TONE IMD PLOT (DIFFERENTIAL INPUT,
8192-POINT DATA RECORD)
-10
fINB
HD2
-70
TWO-TONE IMD PLOT (DIFFERENTIAL INPUT,
8192-POINT DATA RECORD)
fCLK = 40.001536MHz
fIN1 = 1.997147MHz
fIN2 = 2.045977MHz
AIN = -7dB FS
COHERENT SAMPLING
HD3
-60
-70
2
MAX1195 toc03
-40
-80
ANALOG INPUT FREQUENCY (MHz)
AMPLITUDE (dB)
HD3 fINB
fINA
-30
-70
0
SINAD (dB)
-20
MAX1195 toc06
HD2 HD3
fINA
-30
fCLK = 40.056789MHz
fINA = 115.0665837MHz
fINB = 99.9512724MHz
AIN = -1dB FS
COHERENT SAMPLING
MAX1195 toc09
-60
-20
0
-10
AMPLITUDE (dB)
fINA
-30
fCLK = 40.056789MHz
fINA = 7.4861992MHz
fINB = 19.9159303MHz
AIN = -1dB FS
COHERENT SAMPLING
FFT PLOT CHA (DIFFERENTIAL INPUT,
8192-POINT DATA RECORD)
MAX1195 toc05
AMPLITUDE (dB)
-20
0
-10
AMPLITUDE (dB)
fCLK = 40.056789MHz
fINA = 1.0317361MHz
fINB = 7.4861992MHz
AIN = -1dB FS
COHERENT SAMPLING
MAX1195 toc01
0
-10
FFT PLOT CHA (DIFFERENTIAL INPUT,
8192-POINT DATA RECORD)
MAX1195 toc02
FFT PLOT CHA (DIFFERENTIAL INPUT,
8192-POINT DATA RECORD)
40
0
40
80
120
160
ANALOG INPUT FREQUENCY (MHz)
200
0
40
80
120
160
200
ANALOG INPUT FREQUENCY (MHz)
_______________________________________________________________________________________
7
MAX1195
Typical Operating Characteristics
(VDD = 3V, OVDD = 3V, VREFIN = 2.048V, differential input at -1dB FS, fCLK = 40MHz, CL ≈ 10pF TA = +25°C, unless otherwise
noted.)
Typical Operating Characteristics (continued)
(VDD = 3V, OVDD = 3V, VREFIN = 2.048V, differential input at -1dB FS, fCLK = 40MHz, CL ≈ 10pF TA = +25°C, unless otherwise
noted.)
FULL-POWER INPUT BANDWIDTH
vs. ANALOG INPUT FREQUENCY
1
1
SNR
50
40
SINAD
0
GAIN (dB)
SFDR
60
-1
-15
10
35
60
-1
-2
-2
-3
-3
-4
-40
85
-4
1
10
1000
100
1
10
1000
100
TEMPERATURE (°C)
ANALOG INPUT FREQUENCY (MHz)
ANALOG INPUT FREQUENCY (MHz)
SIGNAL-TO-NOISE RATIO vs. INPUT POWER
(fIN = 19.9159303MHz)
SIGNAL-TO-NOISE + DISTORTION
vs. INPUT POWER (fIN = 19.9159303MHz)
TOTAL HARMONIC DISTORTION
vs. INPUT POWER (fIN = 19.9159303MHz)
50
-50
40
-55
THD (dBc)
45
SINAD (dB)
45
40
-60
35
35
-65
30
30
-70
25
25
-20
-16
-12
-8
-4
0
MAX1195 toc15
50
-45
MAX1195 toc14
55
MAX1195 toc13
55
-75
-20
-16
-12
-8
-4
0
-20
-16
-12
-8
-4
INPUT POWER (dB FS)
INPUT POWER (dB FS)
INPUT POWER (dB FS)
SPURIOUS-FREE DYNAMIC RANGE
vs. INPUT POWER (fIN = 19.9159303MHz)
INTEGRAL NONLINEARITY
(262144-POINT DATA RECORD)
DIFFERENTIAL NONLINEARITY
(262144-POINT DATA RECORD)
0.3
INL (LSB)
65
60
55
50
-20
-16
-12
-8
INPUT POWER (dB FS)
-4
0
0.4
0.3
0.2
0.2
0.1
0.1
0
-0.1
0
-0.1
-0.2
-0.2
-0.3
-0.3
-0.4
-0.4
-0.5
45
0.5
DNL (LSB)
70
0.4
0
MAX1195 toc18
0.5
MAX1195 toc16
75
MAX1195 toc17
SNR (dB)
VIN = 100mVP-P
0
70
30
8
2
MAX1195 toc11
THD
GAIN (dB)
SNR/SINAD, THD/SFDR, (dB, dBc)
fIN = 19.9159303MHz
80
2
MAX1195 toc10
90
SMALL-SIGNAL INPUT BANDWIDTH
vs. ANALOG INPUT FREQUENCY
MAX1195 toc12
SNR/SINAD, THD/SFDR
vs. TEMPERATURE
SFDR (dBc)
MAX1195
Dual, 8-Bit, 40Msps, 3V, Low-Power ADC with
Internal Reference and Parallel Outputs
-0.5
0
32
64
98
128 160 192 224 256
DIGITAL OUTPUT CODE
0
32
64
98
128 160 192 224 256
DIGITAL OUTPUT CODE
_______________________________________________________________________________________
Dual, 8-Bit, 40Msps, 3V, Low-Power ADC with
Internal Reference and Parallel Outputs
0.2
0.1
CHA
-0.4
CHB
CHA
-0.6
0
SFDR
80
60
40
SNR
20
-20
-40
THD
-60
-15
10
35
60
85
-40
-15
10
35
0
85
60
40
60
80
TEMPERATURE (°C)
SAMPLING SPEED (Msps)
ANALOG SUPPLY CURRENT
vs. TEMPERATURE
DIGITAL SUPPLY CURRENT
vs. ANALOG INPUT FREQUENCY
SNR/SINAD, THD/SFDR
vs. CLOCK DUTY CYCLE
32
8
31
IOVDD (mA)
30
29
28
27
6
4
2
80
fIN = 19.9159303MHz
SNR/SINAD, THD/SFDR (dB, dBc)
10
MAX1195 toc22
33
SFDR
70
100
THD
60
SNR
50
SINAD
40
26
0
25
-15
10
35
60
30
0
85
4
8
12
20
16
30
40
ANALOG INPUT FREQUENCY (MHz)
TEMPERATURE (°C)
2.0320
60
70
INTERNAL REFERENCE VOLTAGE
vs. TEMPERATURE
2.040
MAX1195 toc26
2.0324
50
CLOCK DUTY CYCLE (%)
INTERNAL REFERENCE VOLTAGE
vs. ANALOG SUPPLY VOLTAGE
MAX1195 toc25
2.036
2.0316
VREFOUT (V)
-40
VREFOUT (V)
IVDD (mA)
20
TEMPERATURE (°C)
MAX1195 toc23
-40
fIN = 19.9159303MHz
-100
-0.8
SINAD
0
-80
-0.1
MAX1195 toc21
MAX1195 toc20
-0.2
100
MAX1195 toc24
CHB
0.3
0
OFFSET ERROR (%FS)
0.4
GAIN ERROR (%FS)
0.2
MAX1195 toc19
0.5
SNR/SINAD, THD/SFDR
vs. SAMPLING SPEED
OFFSET ERROR vs. TEMPERATURE, EXTERNAL
REFERENCE VREFIN = 2.048V
SNR/SINAD, THD/SFDR (dB, dBc)
GAIN ERROR vs. TEMPERATURE, EXTERNAL
REFERENCE VREFIN = 2.048V
2.0312
2.032
2.028
2.0308
2.024
2.0304
2.0300
2.020
2.70
2.85
3.00
3.15
VDD (V)
3.30
3.45
3.60
-40
-15
10
35
60
85
TEMPERATURE (°C)
_______________________________________________________________________________________
9
MAX1195
Typical Operating Characteristics (continued)
(VDD = 3V, OVDD = 3V, VREFIN = 2.048V, differential input at -1dB FS, fCLK = 40MHz, CL ≈ 10pF TA = +25°C, unless otherwise
noted.)
MAX1195
Dual, 8-Bit, 40Msps, 3V, Low-Power ADC with
Internal Reference and Parallel Outputs
Pin Description
PIN
NAME
1
COM
Common-Mode Voltage I/O. Bypass to GND with a ≥ 0.1µF capacitor.
FUNCTION
2, 6, 11, 14, 15
VDD
Analog Supply Voltage. Bypass to GND with a capacitor combination of 2.2µF in parallel with
0.1µF.
3, 7, 10, 13, 16
GND
Analog Ground
4
INA+
Channel A Positive Analog Input. For single-ended operation connect signal source to INA+.
5
INA-
Channel A Negative Analog Input. For single-ended operation connect INA- to COM.
8
INB-
Channel B Negative Analog Input. For single-ended operation connect INB- to COM.
9
INB+
Channel B Positive Analog Input. For single-ended operation connect signal source to INB+.
12
CLK
Converter Clock Input
17
T/B
T/B Selects the ADC Digital Output Format
High: Two’s complement
Low: Straight offset binary
18
SLEEP
19
PD
High-Active Power Down Input
High: Power-down mode
Low: Normal operation
20
OE
Low-Active Output Enable Input
High: Digital outputs disabled
Low: Digital outputs enabled
21
D7B
Three-State Digital Output, Bit 7 (MSB), Channel B
22
D6B
Three-State Digital Output, Bit 6, Channel B
23
D5B
Three-State Digital Output, Bit 5, Channel B
24
D4B
Three-State Digital Output, Bit 4, Channel B
25
D3B
Three-State Digital Output, Bit 3, Channel B
26
D2B
Three-State Digital Output, Bit 2, Channel B
27
D1B
Three-State Digital Output, Bit 1, Channel B
28
D0B
Three-State Digital Output, Bit 0, Channel B
29, 30, 35, 36
N.C.
No Connect
31, 34
OGND
Output Driver Ground
32, 33
OVDD
Output Driver Supply Voltage. Bypass to OGND with a capacitor combination of 2.2µF in parallel
with 0.1µF.
37
D0A
Three-State Digital Output, Bit 0, Channel A
38
D1A
Three-State Digital Output, Bit 1, Channel A
39
D2A
Three-State Digital Output, Bit 2, Channel A
40
D3A
Three-State Digital Output, Bit 3, Channel A
41
D4A
Three-State Digital Output, Bit 4, Channel A
10
Sleep Mode Input
High: Disables both quantizers, but leaves the reference bias circuit active
Low: Normal operation
______________________________________________________________________________________
Dual, 8-Bit, 40Msps, 3V, Low-Power ADC with
Internal Reference and Parallel Outputs
PIN
NAME
FUNCTION
42
D5A
Three-State Digital Output, Bit 5, Channel A
43
D6A
Three-State Digital Output, Bit 6, Channel A
44
D7A
Three-State Digital Output, Bit 7 (MSB), Channel A
45
REFOUT
46
REFIN
Reference Input. VREFIN = 2 x (VREFP – VREFN).
Bypass to GND with a > 0.1µF capacitor.
47
REFP
Positive Reference I/O. Conversion range is ±(VREFP – VREFN).
Bypass to GND with a > 0.1µF capacitor.
48
REFN
Negative Reference I/O. Conversion range is ±(VREFP – VREFN).
Bypass to GND with a > 0.1µF capacitor.
Internal Reference Voltage Output. May be connected to REFIN through a resistor or a resistor
divider.
2-BIT FLASH
ADC
STAGE 1
STAGE 2
STAGE 6
2-BIT FLASH
ADC
STAGE 7
STAGE 1
VINA
8
D7A–D0A
STAGE 6
STAGE 7
DIGITAL ALIGNMENT LOGIC
DIGITAL ALIGNMENT LOGIC
T/H
STAGE 2
T/H
VINB
8
D7B–D0B
VINA = INPUT VOLTAGE BETWEEN INA+ AND INA- (DIFFERENTIAL OR SINGLE ENDED)
VINB = INPUT VOLTAGE BETWEEN INB+ AND INB- (DIFFERENTIAL OR SINGLE ENDED)
Figure 1. Pipelined Architecture—Stage Blocks
Detailed Description
The MAX1195 uses a seven-stage, fully differential,
pipelined architecture (Figure 1) that allows for highspeed conversion while minimizing power consumption. Samples taken at the inputs move progressively
through the pipeline stages every half-clock cycle.
Including the delay through the output latch, the total
clock-cycle latency is five clock cycles.
Flash ADCs convert the held input voltages into a digital code. Internal MDACs convert the digitized results
back into analog voltages, which are then subtracted
from the original held input signals. The resulting error
signals are then multiplied by two, and the residues are
passed along to the next pipeline stages where the
process is repeated until the signals have been
processed by all seven stages.
Input Track-and-Hold Circuits
Figure 2 displays a simplified functional diagram of the
input T/H circuits in both track and hold mode. In track
mode, switches S1, S2a, S2b, S4a, S4b, S5a, and S5b
are closed. The fully differential circuits sample the
input signals onto the two capacitors (C2a and C2b)
through switches S4a and S4b. S2a and S2b set the
common mode for the amplifier input, and open simul-
______________________________________________________________________________________
11
MAX1195
Pin Description (continued)
MAX1195
Dual, 8-Bit, 40Msps, 3V, Low-Power ADC with
Internal Reference and Parallel Outputs
INTERNAL
BIAS
COM
S5a
S2a
C1a
S3a
S4a
INA+
OUT
C2a
S4c
S1
OUT
INAS4b
C2b
C1b
S3b
S5b
S2b
INTERNAL
BIAS
COM
HOLD
INTERNAL
BIAS
TRACK
COM
CLK
HOLD
TRACK
INTERNAL
NONOVERLAPPING
CLOCK SIGNALS
S5a
S2a
C1a
S3a
S4a
INB+
OUT
C2a
S4c
S1
OUT
INBS4b
MAX1195
C2b
C1b
S3b
S2b
INTERNAL
BIAS
S5b
COM
Figure 2. MAX1195 T/H Amplifiers
taneously with S1 sampling the input waveform.
Switches S4a, S4b, S5a, and S5b are then opened
before switches S3a and S3b connects capacitors C1a
and C1b to the output of the amplifier and switch S4c is
closed. The resulting differential voltages are held on
capacitors C2a and C2b. The amplifiers are used to
charge capacitors C1a and C1b to the same values
originally held on C2a and C2b. These values are then
presented to the first-stage quantizers and isolate the
12
pipelines from the fast-changing inputs. The wide input
bandwidth T/H amplifiers allow the MAX1195 to track
and sample/hold analog inputs of high frequencies
(>Nyquist). Both ADC inputs (INA+, INB+ and INA-,
INB-) can be driven either differentially or single-ended.
Match the impedance of INA+ and INA-, as well as
INB+ and INB-, and set the common-mode voltage to
mid-supply (VDD/2) for optimum performance.
______________________________________________________________________________________
Dual, 8-Bit, 40Msps, 3V, Low-Power ADC with
Internal Reference and Parallel Outputs
MAX1195
5-CLOCK-CYCLE LATENCY
N
ANALOG INPUT
N+1
N+2
N+3
N+4
N+5
N+6
tAD
CLOCK INPUT
tDO
tCH
tCL
DATA OUTPUT
D7A–D0A
N-6
N-5
N-4
N-3
N-2
N-1
N
N+1
DATA OUTPUT
D7B–D0B
N-6
N-5
N-4
N-3
N-2
N-1
N
N+1
Figure 3. System Timing Diagram
Analog Inputs and Reference
Configurations
and REFN are outputs. REFOUT can be left open or
connected to REFIN through a >10kΩ resistor.
The full-scale range of the MAX1195 is determined by
the internally generated voltage difference between
REFP (VDD/2 + VREFIN/4) and REFN (VDD/2 - VREFIN/4).
The full-scale range for both on-chip ADCs is
adjustable through the REFIN pin, which provides high
input impedance is provided for this purpose.
The MAX1195 provides three modes of reference operation:
• Internal reference mode
• Buffered external reference mode
• Unbuffered external reference mode
In internal reference mode, connect the internal reference output REFOUT to REFIN through a resistor (e.g.,
10kΩ) or resistor divider, if an application requires a
reduced full-scale range. For stability and noise-filtering
purposes, bypass REFIN with a >10nF capacitor to
GND. In internal reference mode, REFOUT, COM,
REFP, and REFN become low-impedance outputs.
In unbuffered external reference mode, connect REFIN
to GND. This deactivates the on-chip reference buffers
for REFP, COM, and REFN. With their buffers shut
down, these nodes become high-impedance inputs
and can be driven through separate, external reference
sources.
For detailed circuit suggestions and how to drive this
dual ADC in buffered/unbuffered external reference
mode, see the Applications Information section.
In buffered external reference mode, adjust the reference voltage levels externally by applying a stable and
accurate voltage at REFIN. In this mode, COM, REFP,
Clock Input (CLK)
The MAX1195’s CLK input accepts a CMOS-compatible clock signal. Since the interstage conversion of the
device depends on the repeatability of the rising and
falling edges of the external clock, use a clock with low
jitter and fast rise and fall times (<2ns). In particular,
sampling occurs on the rising edge of the clock signal,
requiring this edge to provide lowest possible jitter. Any
significant aperture jitter would limit the SNR performance of the on-chip ADCs as follows:
SNR = 20 × log
1
2 × π × f IN × t AJ
______________________________________________________________________________________
13
MAX1195
Dual, 8-Bit, 40Msps, 3V, Low-Power ADC with
Internal Reference and Parallel Outputs
Table 1. MAX1195 Output Codes For
Differential Inputs
OE
tENABLE
OUTPUT
D7A–D0A
HIGH-Z
OUTPUT
D7B–D0B
HIGH-Z
tDISABLE
VALID DATA
VALID DATA
HIGH-Z
HIGH-Z
VREF x 255/256
+Full Scale
-1LSB
1111 1111
0111 1111
VREF x 1/256
+1LSB
1000 0001
0000 0001
Figure 4. Output Timing Diagram
where fIN represents the analog input frequency and
tAJ is the time of the aperture jitter.
Clock jitter is especially critical for undersampling
applications. The clock input should always be considered as an analog input and routed away from any analog input or other digital signal lines.
The MAX1195 clock input operates with a voltage threshold set to VDD/2. Clock inputs with a duty cycle other
than 50% must meet the specifications for high and low
periods as stated in the Electrical Characteristics table.
System Timing Requirements
Figure 3 depicts the relationship between the clock
input, analog input, and data output. The MAX1195
samples at the rising edge of the input clock. Output
data for channels A and B is valid on the next rising
edge of the input clock. The output data has an internal
latency of five clock cycles. Figure 3 also determines
the relationship between the input clock parameters
and the valid output data on channels A and B.
Digital Output Data (D0A/B–D7A/B), Output
Data Format Selection (T/B), Output
Enable (OE)
All digital outputs, D0A–D7A (channel A) and D0B–D7B
(channel B), are TTL/CMOS-logic compatible. There is
a five-clock-cycle latency between any particular sample and its corresponding output data. The output coding
can either be straight offset binary or two’s complement
(Table 1) controlled by a single pin (T/B). Pull T/B low to
select offset binary and high to activate two’s complement output coding. The capacitive load on the digital
outputs D0A–D7A and D0B–D7B should be kept as low
as possible (<15pF), to avoid large digital currents that
could feed back into the analog portion of the
MAX1195, thereby degrading its dynamic performance.
Using buffers on the digital outputs of the ADCs can
further isolate the digital outputs from heavy capacitive
loads. To further improve the dynamic performance of
14
STRAIGHT
TWO’S
OFFSET
COMPLEMENT
BINARY
T/B = 0
T/B = 1
DIFFERENTIAL
DIFFERENTIAL
INPUT
INPUT
VOLTAGE*
0
Bipolar zero
1000 0000
0000 0000
-VREF x 1/256
-1LSB
0111 1111
1111 1111
-VREF x 255/256
-Full Scale
+1LSB
0000 0001
1000 0001
-VREF x 256/256
-Full Scale
0000 0000
1000 0000
*VREF = VREFP – VREFN
the MAX1195, small series resistors (e.g., 100Ω) can
be added to the digital output paths close to the
MAX1195.
Figure 4 displays the timing relationship between output enable and data output valid, as well as powerdown/wake-up and data output valid.
Power-Down and Sleep Modes
The MAX1195 offers two power-save modes—sleep
mode (SLEEP) and full power-down (PD) mode. In
sleep mode (SLEEP = 1), only the reference bias circuit
is active (both ADCs are disabled), and current consumption is reduced to 3mA.
To enter full power-down mode, pull PD high. With OE
simultaneously low, all outputs are latched at the last
value prior to the power down. Pulling OE high forces
the digital outputs into a high-impedance state.
Applications Information
Figure 5 depicts a typical application circuit containing
two single-ended-to-differential converters. The internal
reference provides a VDD/2 output voltage for levelshifting purposes. The input is buffered and then split
to a voltage follower and inverter. One lowpass filter per
amplifier suppresses some of the wideband noise
associated with high-speed operational amplifiers. The
user can select the RISO and CIN values to optimize the
filter performance, to suit a particular application. For
the application in Figure 5, a RISO of 50Ω is placed
before the capacitive load to prevent ringing and oscillation. The 22pF CIN capacitor acts as a small filter
capacitor.
______________________________________________________________________________________
Dual, 8-Bit, 40Msps, 3V, Low-Power ADC with
Internal Reference and Parallel Outputs
MAX1195
+5V
0.1µF
LOWPASS FILTER
INA-
MAX4108
RIS0
50Ω
0.1µF
300Ω
CIN
22pF
0.1µF
-5V
600Ω
600Ω
300Ω
+5V
COM
0.1µF
+5V
0.1µF
600Ω
INPUT
0.1µF
LOWPASS FILTER
MAX4108
300Ω
-5V
0.1µF
INA+
MAX4108
RIS0
50Ω
300Ω
CIN
22pF
0.1µF
-5V
300Ω
300Ω
+5V
600Ω
MAX1195
0.1µF
LOWPASS FILTER
INB-
MAX4108
RIS0
50Ω
0.1µF
300Ω
0.1µF
-5V
+5V
CIN
22pF
600Ω
600Ω
300Ω
0.1µF
+5V
0.1µF
INPUT
600Ω
0.1µF
LOWPASS FILTER
MAX4108
300Ω
-5V
0.1µF
INB+
MAX4108
RIS0
50Ω
300Ω
CIN
22pF
0.1µF
-5V
300Ω
300Ω
600Ω
Figure 5. Typical Application for Single-Ended-to-Differential Conversion
______________________________________________________________________________________
15
MAX1195
Dual, 8-Bit, 40Msps, 3V, Low-Power ADC with
Internal Reference and Parallel Outputs
REFP
25Ω
INA+
22pF
VIN
0.1µF
0.1µF
1
VIN
T1
6
INA+
MAX4108
100Ω
N.C.
2
5
3
4
1kΩ RISO
50Ω
1kΩ
CIN
22pF
COM
2.2µF
COM
0.1µF
REFN
0.1µF
MINICIRCUITS
TT1–6-KK81
25Ω
INA-
100Ω
INA-
RISO
50Ω
CIN
22pF
22pF
REFP
MAX1195
MAX1195
25Ω
INB+
VIN
22pF
0.1µF
1
VIN
N.C.
T1
5
3
4
1kΩ RISO
50Ω
INB+
MAX4108
6
2
0.1µF
100Ω
2.2µF
1kΩ
REFN
0.1µF
MINICIRCUITS
TT1–6-KK81
100Ω
25Ω
INB-
0.1µF
CIN
22pF
RISO
50Ω
INBCIN
22pF
22pF
Figure 6. Transformer-Coupled Input Drive
Figure 7. Using an Op Amp for Single-Ended, AC-Coupled
Input Drive
Using Transformer Coupling
Single-Ended AC-Coupled Input Signal
An RF transformer (Figure 6) provides an excellent
solution to convert a single-ended source signal to a
fully differential signal, required by the MAX1195 for
optimum performance. Connecting the center tap of the
transformer to COM provides a VDD/2 DC level shift to
the input. Although a 1:1 transformer is shown, a stepup transformer can be selected to reduce the drive
requirements. A reduced signal swing from the input
driver, such as an op amp, can also improve the overall
distortion.
Figure 7 shows an AC-coupled, single-ended application. Amplifiers like the MAX4108 provide high speed,
high bandwidth, low noise, and low distortion to maintain the integrity of the input signal.
In general, the MAX1195 provides better SFDR and
THD with fully differential input signals than singleended drive, especially for very high input frequencies.
In differential input mode, even-order harmonics are
lower as both inputs (INA+, INA- and/or INB+, INB-) are
balanced, and each of the ADC inputs only requires
half the signal swing compared to single-ended mode.
16
Buffered External Reference Drives
Multiple ADCs
Multiple-converter systems based on the MAX1195 are
well suited for use with a common reference voltage.
The REFIN pin of those converters can be connected
directly to an external reference source.
A precision bandgap reference like the MAX6062 generates an external DC level of 2.048V (Figure 8), and
exhibits a noise voltage density of 150nV/√Hz. Its output passes through a 1-pole lowpass filter (with 10Hz
cutoff frequency) to the MAX4250, which buffers the
reference before its output is applied to a second 10Hz
lowpass filter. The MAX4250 provides a low offset voltage (for high gain accuracy) and a low noise level. The
______________________________________________________________________________________
Dual, 8-Bit, 40Msps, 3V, Low-Power ADC with
Internal Reference and Parallel Outputs
MAX1195
3.3V
3.3V
0.1µF
2.048V
0.1µF
N.C.
31
1
2
16.2kΩ
3
REFIN
REFP
1 REFN
2
COM
5
MAX4250
1µF
1
162Ω
4
3
REFOUT
32
0.1µF
MAX6062
29
10Hz LOWPASS
FILTER
N=1
MAX1195
100µF
2
0.1µF 0.1µF 0.1µF
10Hz LOWPASS
FILTER
NOTE: ONE FRONT-END REFERENCE CIRCUIT DESIGN MAY BE USED WITH UP TO 1000 ADCs.
0.1µF
N.C.
29
31
32
0.1µF
1
2
2.2µF
10V
REFOUT
REFIN
REFP
N = 1000
REFN
MAX1195
COM
0.1µF 0.1µF 0.1µF
Figure 8. External Buffered (MAX4250) Reference Drive Using a MAX6062 Bandgap Reference
passive 10Hz filter following the buffer attenuates noise
produced in the voltage reference and buffer stages.
This filtered noise density, which decreases for higher
frequencies, meets the noise levels specified for precision ADC operation.
Unbuffered External Reference Drives
Multiple ADCs
Connecting each REFIN to analog ground disables the
internal reference of each device, allowing the internal
reference ladders to be driven directly by a set of
external reference sources. Followed by a 10Hz lowpass filter and precision voltage divider, the MAX6066
generates a DC level of 2.500V. The buffered outputs
of this divider are set to 2.0V, 1.5V, and 1.0V, with an
accuracy that depends on the tolerance of the divider
resistors. The three voltages are buffered by the
MAX4252, which provides low noise and low DC offset.
The individual voltage followers are connected to 10Hz
lowpass filters, which filter both the reference voltage
and amplifier noise to a level of 3nV/√Hz. The 2.0V and
1.0V reference voltages set the differential full-scale
range of the associated ADCs at 2VP-P. The 2.0V and
1.0V buffers drive the ADC’s internal ladder resistances
between them.
Note that the common power supply for all active components removes any concern regarding power-supply
sequencing when powering up or down. With the outputs of the MAX4252 matching better than 0.1%, the
buffers and subsequent lowpass filters can be replicated to support as many as 32 ADCs. For applications
that require more than 32 matched ADCs, a voltage
reference and divider string common to all converters
is highly recommended.
Typical QAM Demodulation Application
A frequently used modulation technique in digital communications applications is quadrature amplitude
modulation (QAM). Typically found in spread-spectrum-based systems, a QAM signal represents a carrier
frequency modulated in both amplitude and phase. At
the transmitter, modulating the baseband signal with
______________________________________________________________________________________
17
MAX1195
Dual, 8-Bit, 40Msps, 3V, Low-Power ADC with
Internal Reference and Parallel Outputs
3.3V
0.1µF
N.C.
29
31
1
2.0V
2
MAX6066
32
3.3V
21.5kΩ
3
4
1/4 MAX4252
1
1
2.0V AT 8mA
2
10µF
6V
1.47kΩ
11
21.5kΩ
1.5V
REFIN
REFP
REFN
47kΩ
2
3
REFOUT
N=1
MAX1195
COM
330µF
6V
0.1µF 0.1µF 0.1µF
3.3V
5
4
1.5V AT 0mA
1/4 MAX4252
7
47kΩ
6
1µF
10µF
6V
1.47kΩ
11
21.5kΩ
3.3V
1.0V
0.1µF
4
47kΩ
9
11
21.5kΩ
2.2µF
10V
1.0V AT -8mA
1/4 MAX4252
8
MAX4254 POWER SUPPLY
BYPASSING. PLACE CAPACITOR
AS CLOSE AS POSSIBLE TO
THE OP AMP.
0.1µF
3.3V
10
21.5kΩ
330µF
6V
10µF
6V
1.47kΩ
330µF
6V
N.C.
29
31
32
1
2
REFOUT
REFIN
REFP
N = 32
REFN
MAX1195
COM
0.1µF 0.1µF 0.1µF
NOTE: ONE FRONT-END REFERENCE CIRCUIT DESIGN MAY BE USED WITH UP TO 32 ADCs.
Figure 9. External Unbuffered Reference Drive with MAX4252 and MAX6066
quadrature outputs, a local oscillator followed by subsequent upconversion can generate the QAM signal.
The result is an in-phase (I) and a quadrature (Q) carrier component, where the Q component is 90° phase
shifted with respect to the in-phase component. At the
receiver, the QAM signal is divided down into its I and
Q components, essentially representing the modulation
process reversed. Figure 10 displays the demodulation
process performed in the analog domain, using the
dual matched 3V, 8-bit ADC MAX1195 and the
MAX2451 quadrature demodulator to recover and digi-
18
tize the I and Q baseband signals. Before being digitized by the MAX1195, the mixed-down signal components may be filtered by matched analog filters, such
as Nyquist or pulse-shaping filters which remove
unwanted images from the mixing process, thereby
enhancing the overall signal-to-noise (SNR) performance and minimizing intersymbol interference.
______________________________________________________________________________________
Dual, 8-Bit, 40Msps, 3V, Low-Power ADC with
Internal Reference and Parallel Outputs
MAX1195
MAX2451
INA+
INA0°
90°
MAX1195
DSP
POSTPROCESSING
INB+
INBDOWNCONVERTER
÷8
Figure 10. Typical QAM Application Using the MAX1195
CLK
ANALOG
INPUT
tAD
tAJ
SAMPLED
DATA (T/H)
T/H
TRACK
HOLD
TRACK
Figure 11. T/H Aperture Timing
Grounding, Bypassing,
and Board Layout
The MAX1195 requires high-speed board layout design
techniques. Locate all bypass capacitors as close to
the device as possible, preferably on the same side as
the ADC, using surface-mount devices for minimum
inductance. Bypass VDD, REFP, REFN, and COM with
two parallel 0.1µF ceramic capacitors and a 2.2µF
bipolar capacitor to GND. Follow the same rules to
bypass the digital supply (OVDD) to OGND. Multilayer
boards with separated ground and power planes produce the highest level of signal integrity. Consider the
use of a split ground plane arranged to match the
physical location of the analog ground (GND) and the
digital output driver ground (OGND) on the ADC’s
package. The two ground planes should be joined at a
single point so the noisy digital ground currents do not
interfere with the analog ground plane. The ideal location for this connection can be determined experimentally at a point along the gap between the two ground
planes, which produces optimum results. Make this
connection with a low-value, surface-mount resistor (1Ω
to 5Ω), a ferrite bead, or a direct short.
Alternatively, all ground pins could share the same
ground plane, if the ground plane is sufficiently isolated
from any noisy, digital systems ground plane (e.g.,
downstream output buffer or DSP ground plane). Route
high-speed digital signal traces away from the sensitive
analog traces of either channel. Make sure to isolate
the analog input lines to each respective converter to
minimize channel-to-channel crosstalk. Keep all signal
lines short and free of 90° turns.
Static Parameter Definitions
Integral Nonlinearity
Integral nonlinearity (INL) is the deviation of the values
on an actual transfer function from a straight line. This
straight line can be either a best-straight-line fit or a line
drawn between the endpoints of the transfer function,
once offset and gain errors have been nullified. The
static linearity parameters for the MAX1195 are measured using the best-straight-line-fit method.
Differential Nonlinearity
Differential nonlinearity (DNL) is the difference between
an actual step width and the ideal value of 1LSB. A
DNL error specification of less than 1LSB guarantees
no missing codes and a monotonic transfer function.
______________________________________________________________________________________
19
MAX1195
Dual, 8-Bit, 40Msps, 3V, Low-Power ADC with
Internal Reference and Parallel Outputs
Dynamic Parameter Definitions
quantization noise only. ENOB for a full-scale sinusoidal
input waveform is computed from:
Aperture Jitter
Figure 11 depicts the aperture jitter (tAJ), which is the
sample-to-sample variation in the aperture delay.
ENOB =
SINAD −1.76
6.02
Aperture Delay
Aperture delay (tAD) is the time defined between the
rising edge of the sampling clock and the instant when
an actual sample is taken (Figure 11).
Signal-to-Noise Ratio
For a waveform perfectly reconstructed from digital
samples, the theoretical maximum SNR is the ratio of
the full-scale analog input (RMS value) to the RMS
quantization error (residual error). The ideal, theoretical
minimum analog-to-digital noise is caused by quantization error only and results directly from the ADC’s resolution (N-bits):
SNRdB[max] = 6.02dB ✕ N + 1.76dB
In reality, there are other noise sources besides quantization noise: thermal noise, reference noise, clock jitter,
etc. SNR is computed by taking the ratio of the RMS
signal to the RMS noise, which includes all spectral
components minus the fundamental, the first five harmonics, and the DC offset.
Signal-to-Noise Plus Distortion
SINAD is computed by taking the ratio of the RMS signal to all spectral components minus the fundamental
and the DC offset.
Effective Number of Bits
Effective number of bits (ENOB) specifies the dynamic
performance of an ADC at a specific input frequency
and sampling rate. An ideal ADC’s error consists of
20
Total Harmonic Distortion
THD is typically the ratio of the RMS sum of the first four
harmonics of the input signal to the fundamental itself.
This is expressed as:
2
THD = 20 × log
2
2
V2 + V3 + V4 + V5
V1
2
where V1 is the fundamental amplitude, and V2 through
V5 are the amplitudes of the 2nd- through 5th-order
harmonics.
Spurious-Free Dynamic Range
Spurious-free dynamic range (SFDR) is the ratio
expressed in decibels of the RMS amplitude of the fundamental (maximum signal component) to the RMS
value of the next largest spurious component, excluding DC offset.
Intermodulation Distortion
The two-tone intermodulation distortion (IMD) is the
ratio expressed in decibels of either input tone to the
worst third-order (or higher) intermodulation products.
The individual input tone levels are at -7dB full scale
and their envelope is at -1dB full scale.
Chip Information
TRANSISTOR COUNT: 11,601
PROCESS: CMOS
______________________________________________________________________________________
Dual, 8-Bit, 40Msps, 3V, Low-Power ADC with
Internal Reference and Parallel Outputs
VDD
OGND
OVDD
GND
INA+
8
ADC
T/H
DEC
OUTPUT
DRIVERS
8
D7A–D0A
INA-
CONTROL
CLK
OE
INB+
8
ADC
T/H
DEC
OUTPUT
DRIVERS
8
D7B–D0B
INB-
REFERENCE
MAX1195
T/B
PD
SLEEP
REFOUT
REFN COM REFP
REFIN
Pin-Compatible Upgrades
(Sampling Speed and Resolution)
SAMPLING SPEED
(Msps)
8-BIT PART
10-BIT PART
MAX1195
MAX1183
40
MAX1197
MAX1182
60
MAX1198
MAX1180
100
MAX1196*
MAX1186
40, multiplexed
*Future product, please contact factory for availability.
______________________________________________________________________________________
21
MAX1195
Functional Diagram
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
48L,TQFP.EPS
MAX1195
Dual, 8-Bit, 40Msps, 3V, Low-Power ADC with
Internal Reference and Parallel Outputs
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
22 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2002 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.