19-1899; Rev 1; 5/04
12-Bit, 20Msps, 3.3V, Low-Power ADC with
Internal Reference
General Description
The MAX1422 3.3V, 12-bit analog-to-digital converter
(ADC) features a fully differential input, pipelined, 12-
stage ADC architecture with wideband track-and-hold
(T/H) and digital error correction incorporating a fully-dif-
ferential signal path. The MAX1422 is optimized for low-
power, high dynamic performance applications in
imaging and digital communications. The converter
operates from a single 3.3V supply, consuming only
137mW while delivering a 67dB (typ) signal-to-noise
ratio (SNR) at a 5MHz input frequency and a 20Msps
sampling frequency. The fully-differential input stage
has a small signal -3dB bandwidth of 400MHz and may
be operated with single-ended inputs.
An internal 2.048V precision bandgap reference sets
the ADCs full-scale range. A flexible reference structure
accommodates an internally or externally applied
buffered or unbuffered reference for applications
requiring increased accuracy or a different input volt-
age range.
In addition to low operating power, the MAX1422 features
two power-down modes, a reference power-down, and a
shutdown mode. In reference power-down, the internal
bandgap reference is deactivated, resulting in a 2mA
(typ) supply current reduction. For idle periods, a full
shutdown mode is available to maximize power savings.
The MAX1422 provides parallel, offset binary, CMOS-
compatible three-state outputs.
The MAX1422 is available in a 7mm
✕
7mm
✕
1.4mm,
48-pin TQFP package and is specified over the com-
mercial (0°C to +70°C) and extended industrial (-40°C
to +85°C) temperature ranges.
Pin-compatible higher-speed versions of the MAX1422
are also available. Please refer to the MAX1421 data
sheet for 40Msps and the MAX1420 data sheet for
60Msps.
♦
Single 3.3V Power Supply
♦
67dB SNR at f
IN
= 5MHz
♦
Internal 2.048V Precision Bandgap Reference
♦
Differential Wideband Input T/H Amplifier
♦
Power-Down Modes
130mW (Reference Shutdown Mode)
10µW (Shutdown Mode)
♦
Space-Saving 48-Pin TQFP Package
Features
MAX1422
Ordering Information
PART
MAX1422CCM
MAX1422ECM
TEMP RANGE
0°C to +70°C
-40°C to +85°C
PIN-PACKAGE
48 TQFP
48 TQFP
Pin Configuration
AGND
AV
DD
CML
REFN
REFP
REFIN
AV
DD
AGND
PD
OE
D11
D10
48
47
46
45
44
43
42
41
40
39
38
________________________Applications
Medical Ultrasound Imaging
CCD Pixel Processing
Data Acquisition
Radar
IF and Baseband Digitization
AGND
AV
DD
AV
DD
AGND
AGND
INP
INN
AGND
AGND
AV
DD
AV
DD
AGND
37
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
36
35
34
33
32
31
30
29
28
27
26
25
D9
D8
D7
D6
DV
DD
DV
DD
DGND
DGND
D5
D4
D3
D2
MAX1422
AGND
AV
DD
AV
DD
AGND
CLK
Functional Diagram appears at end of data sheet.
TQFP
________________________________________________________________
Maxim Integrated Products
CLK
AGND
AV
DD
DV
DD
DGND
D0
D1
1
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.
12-Bit, 20Msps, 3.3V, Low-Power ADC with
Internal Reference
MAX1422
ABSOLUTE MAXIMUM RATINGS
AV
DD
, DV
DD
to AGND ..............................................-0.3V to +4V
DV
DD
, AV
DD
to DGND..............................................-0.3V to +4V
DGND to AGND.....................................................-0.3V to +0.3V
INP, INN, REFP, REFN, REFIN,
CML,CLK,
CLK,
....................(AGND - 0.3V) to (AV
DD
+ 0.3V)
D0–D11,
OE,
PD .......................(DGND - 0.3V) to (DV
DD
+ 0.3V)
Continuous Power Dissipation (T
A
= +70°C)
48-Pin TQFP (derate 21.7mW/°C above +70°C)........1739mW
Operating Temperature Ranges
MAX1422CCM ....................................................0°C to +70°C
MAX1422ECM .................................................-40°C to +85°C
Maximum Junction Temperature .....................................+150°C
Storage Temperature Range .............................-65°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
(V
AVDD
= V
DVDD
= 3.3V, AGND = DGND = 0, V
IN
= ±1.024V, differential input voltage at -0.5dBFS, internal reference, f
CLK
= 20MHz (50%
duty cycle); digital output load C
L
= 10pF,
≥+25°C
guaranteed by production test, <+25°C guaranteed by design and characterization.
Typical values are at T
A
= +25°C.)
PARAMETER
DC ACCURACY
Resolution
Differential Nonlinearity
Integral Nonlinearity
Mid-scale Offset
Mid-scale Offset Temperature
Coefficient
RES
DNL
INL
MSO
MSOTC
Internal reference (Note 1)
Gain Error
GE
External reference applied to REFIN, (Note 2)
External reference applied to REFP, CML,
and REFN (Note 3)
Gain Error Temperature
Coefficient
Signal-to-Noise Ratio
Spurious-Free Dynamic Range
Total Harmonic Distortion
Signal-to-Noise and Distortion
Effective Number of Bits
Two-Tone Intermodulation
Distortion
Differential Gain
Differential Phase
ANALOG INPUTS
(INP, INN, CML)
Input Resistance
Input Capacitance
Common-Mode Input Level
(Note 5)
R
IN
C
IN
V
CML
Either input to ground
Either input to ground
61
4
V
AVDD
✕
0.5
kΩ
pF
V
GETC
External reference applied to REFP, CML,
and REFN (Note 3)
f
IN
= 5MHz, T
A
= +25°C
f
IN
= 5MHz, T
A
= +25°C
f
IN
= 5MHz, T
A
= +25°C
f
IN
= 5MHz, T
A
= +25°C
f
IN
= 5MHz
f
IN1
= 7.028MHz, f
IN2
= 8.093MHz (Note 4)
60
63
64
-5
-5
-1.5
15
✕
10
-6
T
A
= +25°C, no missing codes
T
A
= T
MIN
to T
MAX
T
A
= T
MIN
to T
MAX
-3
-1
±0.5
±2
±.75
3
✕
10
-4
±0.1
±0.2
5
5
1.5
%/°C
%FSR
3
12
1
Bits
LSB
LSB
%FSR
%/°C
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
DYNAMIC PERFORMANCE
(f
CLK
= 20MHz, 4096-point FFT)
SNR
SFDR
THD
SINAD
ENOB
IMD
DG
DP
67
74
-72
65
10.5
-77
±1
±0.25
-63
dB
dBc
dBc
dB
Bits
dBc
%
Degrees
2
_______________________________________________________________________________________
12-Bit, 20Msps, 3.3V, Low-Power ADC with
Internal Reference
ELECTRICAL CHARACTERISTICS (continued)
(V
AVDD
= V
DVDD
= 3.3V, AGND = DGND = 0, V
IN
= ±1.024V, differential input voltage at -0.5dBFS, internal reference, f
CLK
= 20MHz (50%
duty cycle); digital output load C
L
= 10pF,
≥+25°C
guaranteed by production test, <+25°C guaranteed by design and characterization.
Typical values are at T
A
= +25°C.)
PARAMETER
Common-Mode Input Voltage
Range (Note 5)
Differential Input Range
Small-Signal Bandwidth
Large-Signal Bandwidth
Overvoltage Recovery
SYMBOL
V
CMVR
V
IN
BW
-3dB
FPBW
-3dB
OVR
V
INP
- V
INN
(Note 6)
(Note 7)
(Note 7)
1.5
✕
FS input
CONDITIONS
MIN
TYP
V
CML
±5%
±V
DIFF
400
150
1
MAX
UNITS
V
V
MHz
MHz
Clock
cycles
MAX1422
INTERNAL REFERENCE
(REFIN bypassed with 0.22µF in parallel with 1nF)
Common-Mode Reference
Voltage
Positive Reference Voltage
Negative Reference Voltage
Differential Reference Voltage
V
CML
V
REFP
V
REFN
V
DIFF
At CML
At REFP
At REFN
(Note 6)
V
AVDD
✕
0.5
V
CML
+ 0.512
V
CML
- 0.512
1.024
±5%
±100
V
V
V
V
ppm/°C
Differential Reference
REFTC
Temperature Coefficient
EXTERNAL REFERENCE
(V
REFIN
= 2.048V)
REFIN Input Resistance
REFIN Input Capacitance
REFIN Reference Input Voltage
Range
Differential Reference Voltage
Range
REFP, REFN, CML Input Current
REFP, REFN, CML Input
Capacitance
Differential Reference Voltage
Range
CML Input Voltage Range
REFP Input Voltage Range
REFN Input Voltage Range
R
IN
C
IN
V
REFIN
V
DIFF
(Note 6)
(Note 8)
5
kΩ
10
2.048
±10%
pF
V
V
0.92
✕
1.08
✕
V
REFIN
/2
V
REFIN
/2
V
REFIN
/2
-200
15
200
EXTERNAL REFERENCE
(V
REFIN
= 0, reference voltage applied to REFP, REFN, and CML)
I
IN
C
IN
V
DIFF
V
CML
V
REFP
V
REFN
(Note 6)
µA
pF
V
V
V
V
1.024
±10%
1.65
±10%
V
CML
+
V
DIFF
/2
V
CML
-
V
DIFF
/2
0.7
✕
V
DVDD
0.3
✕
V
DVD
DIGITAL INPUTS
(CLK,
CLK,
PD,
OE)
Input Logic High
Input Logic Low
V
IH
V
IL
V
V
_______________________________________________________________________________________
3
12-Bit, 20Msps, 3.3V, Low-Power ADC with
Internal Reference
MAX1422
ELECTRICAL CHARACTERISTICS (continued)
(V
AVDD
= V
DVDD
= 3.3V, AGND = DGND = 0, V
IN
= ±1.024V, differential input voltage at -0.5dBFS, internal reference, f
CLK
= 20MHz (50%
duty cycle); digital output load C
L
= 10pF,
≥+25°C
guaranteed by production test, <+25°C guaranteed by design and characterization.
Typical values are at T
A
= +25°C.)
PARAMETER
Input Current
Input Capacitance
DIGITAL OUTPUTS
(D0–D11)
Output Logic High
Output Logic Low
Three-State Leakage
Three-State Capacitance
POWER REQUIREMENTS
Analog Supply Voltage
Digital Supply Voltage
Analog Supply Current
Analog Supply Current with
Internal Reference in Shutdown
Analog Shutdown Current
Digital Supply Current
Digital Shutdown Current
Power Dissipation
Power-Supply Rejection Ratio
TIMING CHARACTERISTICS
Maximum Clock Frequency
Clock High
Clock Low
Pipeline Delay (Latency)
Aperture Delay
Aperture Jitter
Data Output Delay
Bus Enable Time
Bus Disable Time
t
AD
t
AJ
t
OD
t
BE
t
BD
f
CLK
t
CH
t
CL
Figure 6
Figure 6, clock period 50ns
Figure 6, clock period 50ns
Figure 6
Figure 10
Figure 10
Figure 6
Figure 5
Figure 5
5
20
25
25
7
2
2
10
5
5
14
MHz
ns
ns
Clock
cycles
ns
ps
ns
ns
ns
P
DISS
PSRR
I
DVDD
PD = DV
DD
Analog power dissipation
(Note 9)
137
±1
V
AVDD
V
DVDD
I
AVDD
V
REFIN
= 0
PD = DV
DD
3
20
152
3.138
2.7
3.3
3.3
39
37
3.465
3.63
46
44
20
V
V
mA
mA
µA
mA
µA
mW
mV/V
V
OH
V
OL
I
OH
= 200µA
I
OL
= -200µA
V
DVDD
- 0.5
0
-10
2
V
DVDD
0.5
10
V
V
µA
pF
SYMBOL
CLK,
CLK
PD
OE
-20
-20
10
CONDITIONS
MIN
TYP
±330
20
20
pF
µA
MAX
UNITS
Note 1:
Note 2:
Note 3:
Note 4:
Note 5:
Note 6:
Note 7:
Note 8:
Note 9:
4
Internal reference, REFIN bypassed to AGND with a combination of 0.22µF in parallel with 1nF capacitor.
External 2.048V reference applied to REFIN.
Internal reference disabled. VREFIN = 0, VREFP = 2.162V, VCML = 1.65V, and VREFN = 1.138V.
IMD is measured with respect to either of the fundamental tones.
Specifies the common-mode range of the differential input signal supplied to the MAX1422.
VDIFF = VREFP - VREFN.
Input bandwidth is measured at a 3dB level.
VREFIN is internally biased to 2.048V through a 10kΩ resistor.
Measured as the ratio of the change in mid-scale offset voltage for a ±5% change in VAVDD, using the internal reference.
_______________________________________________________________________________________
12-Bit, 20Msps, 3.3V, Low-Power ADC with
Internal Reference
MAX1422
Typical Operating Characteristics
(V
AVDD
= V
DVDD
= 3.3V, AGND = DGND = 0, V
IN
= ±1.024V, differential input drive, A
IN
= -0.5dBFS, f
CLK
= 20MHz (50% duty
cycle) digital output load C
L
= 10pF, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25
°C.)
FFT PLOT (4096-POINT DATA RECORD)
MAX1422 toc01
FFT PLOT (4096-POINT DATA RECORD)
MAX1422 toc02
FFT PLOT (4096-POINT DATA RECORD)
f
IN
= 19.8051MHz
MAX1422 toc03
0
-20
AMPLITUDE (dB)
-40
-60
-80
-100
-120
0
f
IN
= 5.2235MHz
0
-20
AMPLITUDE (dB)
-40
-60
-80
-100
-120
f
IN
= 8.1637MHz
0
-20
AMPLITUDE (dB)
-40
-60
-80
-100
-120
HD2
HD3
HD3
HD2
HD2
HD3
1
2
3
4
5
6
7
8
9
10
0
1
2
3
4
5
6
7
8
9
10
0
1
2
3
4
5
6
7
8
9
10
ANALOG INPUT FREQUENCY (MHz)
ANALOG INPUT FREQUENCY (MHz)
ANALOG INPUT FREQUENCY (MHz)
TWO-TONE IMD PLOT
(4096-POINT DATA RECORD)
MAX1422 toc04
SPURIOUS-FREE DYNAMIC RANGE vs.
ANALOG INPUT FREQUENCY
MAX1422 toc05
SIGNAL-TO-NOISE RATIO vs.
ANALOG INPUT FREQUENCY
MAX1422 toc06
0
-20
AMPLITUDE (dB)
-40
-60
-80
-100
-120
0
f
IN1
= 7.0283MHz
f
IN2
= 8.0931MHz
f
CLK
= 20.0056MHz
A
IN1
= A
IN2
= -6.5dB FS
f
IN1
IMD2
IMD3
85
70
f
IN2
SFDR (dBc)
77
66
61
SNR (dB)
1
10
ANALOG INPUT FREQUENCY (MHz)
100
69
62
58
53
54
45
1
2
3
4
5
6
7
8
9
10
ANALOG INPUT FREQUENCY (MHz)
50
1
10
ANALOG INPUT FREQUENCY (MHz)
100
TOTAL HARMONIC DISTORTION vs.
ANALOG INPUT FREQUENCY
MAX1422 toc07
SIGNAL-TO-NOISE PLUS DISTORTION
vs. ANALOG INPUT FREQUENCY
MAX1422 toc08
SPURIOUS-FREE DYNAMIC RANGE
vs. ANALOG INPUT POWER (f
IN
= 5MHz)
70
60
SFDR (dBc)
50
40
30
20
MAX1422 toc09
-50
70
80
-56
66
SINAD (dB)
THD (dBc)
-62
62
-68
58
-74
54
10
0
1
10
ANALOG INPUT FREQUENCY (MHz)
100
-60
-50
-40
-30
-20
-10
0
ANALOG INPUT POWER (dB FS)
-80
1
10
ANALOG INPUT FREQUENCY (MHz)
100
50
_______________________________________________________________________________________
5
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