19-1597; Rev 1; 7/11
10-Bit, 20Msps ADC
General Description
The MAX1425 10-bit, monolithic analog-to-digital con-
verter (ADC) is capable of a 20Msps sampling rate. This
device features an internal track-and-hold (T/H) amplifier
for excellent dynamic performance; at the same time, it
minimizes the number of external components. Low
input capacitance of only 8pF minimizes input drive
requirements. A wide input bandwidth (up to 150MHz)
makes this device suitable for digital RF/IF downconvert-
er applications employing undersampling techniques.
The MAX1425 employs a differential pipelined architec-
ture with a wideband T/H amplifier to maximize through-
put while limiting power consumption to only 172mW.
The MAX1425 generates an internal +2.5V reference
that supplies three additional reference voltages
(+3.25V, +2.25V, and +1.25V). These reference volt-
ages provide a differential input range of +2V to -2V.
The analog inputs are biased internally to correct the
DC level, eliminating the need for external biasing on
AC-coupled applications.
A separate +3V digital logic supply input allows for
separation of digital and analog circuitry. The output
data is in two’s complement format. The MAX1425 is
available in the space-saving 28-pin SSOP package.
For a pin-compatible version at a lower data rate, refer
to the MAX1426 data sheet. For a higher data rate, refer
to the MAX1424 data sheet.
Features
o
Differential Inputs for High Common-Mode
Noise Rejection
o
Signal-to-Noise Ratio
61dB (at f
IN
= 2MHz)
59.3dB (at f
IN
= 10MHz)
o
Internal +2.5V Reference
o
150MHz Input Bandwidth
o
Wide ±2V Input Range
o
Low Power Consumption: 172mW
o
Separate Digital Supply Input for 3V Logic
Compatibility
o
Single +5V Supply Operation Possible
MAX1425
Ordering Information
PART
MAX1425CAI+
MAX1425EAI+
TEMP. RANGE
0°C to +70°C
-40°C to +85°C
PIN-PACKAGE
28 SSOP
28 SSOP
+Denotes
a lead(Pb)-free/RoHS-compliant package.
Devices are also available in a tape-and-reel packaging.
Specify tape and reel by adding “T” to the number when order-
ing.
Applications
Medical Ultrasound Imaging
CCD Pixel Processing
IR Focal Plane Array
Radar
IF and Baseband Digitization
Set-Top Boxes
TOP VIEW
+
AGND 1
AV
DD
2
REFP 3
REFIN 4
REFN 5
Pin Configuration
28 D0
27 D1
26 D2
25 D3
24 D4
Functional Diagram
CLK
INTERFACE
INP
T/H
INN
REF SYSTEM +
BIAS
PIPELINE ADC
MAX1425
AV
DD
AGND
CML 6
AGND 7
AV
DD
8
INP 9
INN 10
MAX1425
23 DGND
22 DV
DD
21 DGND
20 DV
DD
19 D5
18 D6
17 D7
16 D8
15 D9
OUTPUT
DRIVERS
D9–D0
DV
DD
DGND
CMLP 11
CMLN 12
CLK 13
OE/PD 14
REF
REFIN REFP
CML REFN
OE/PD
SSOP
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
10-Bit, 20Msps ADC
MAX1425
ABSOLUTE MAXIMUM RATINGS
AV
DD
to AGND ........................................................ -0.3V to +6V
DV
DD
to DGND ....................................................... -0.3V to +6V
AV
DD
to DGND ........................................................ -0.3V to +6V
DGND to AGND ................................................................. ±0.3V
REFP, REFIN, REFN, CMLN, CMLP,
CML, INP, INN ....................(V
AGND
- 0.3V) to (V
AVDD
+ 0.3V)
CLK,
OE/PD,
D0–D9 ...............(V
DGND
- 0.3V) to (V
DVDD
+ 0.3V)
Continuous Power Dissipation (T
A
= +70°C)
28-Pin SSOP (derated 9.5mW/°C above +70°C) .........762mW
Operating Temperature Ranges
MAX1425CAI ..................................................... 0°C to +70°C
MAX1425EAI................................................... -40°C to +85°C
Junction Temperature ..................................................... +150°C
Storage Temperature Range ............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Soldering Temperature (reflow) .......................................+260°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
CMLP
= +5V, V
DVDD
= +3.3V, V
CMLN
= V
AGND
= V
DGND
= 0V, internal reference, digital output load = 35pF, f
CLK
= 20MHz
(50% duty cycle), T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
ACCURACY
Resolution
Differential Nonlinearity
Integral Nonlinearity
No Missing Codes
Midscale Offset
MSO
RES
DNL
INL
Guaranteed monotonic
(Note 1)
Internal reference (Note 1)
Gain Error
GE
External reference (REFIN) (Note 2)
External reference (REFP, CML, REFN)
(Note 3)
Power-Supply Rejection Ratio
PSRR
(Note 4)
f = 2MHz
f = 10MHz
f = 2MHz
f = 10MHz
f = 2MHz
f = 10MHz
f = 2MHz
f = 10MHz
f = 2MHz
f = 10MHz
f1 = 10.17MHz, f2 = 10.19MHz
(-7dB FS, each tone) (Note 5)
59
55
9.3
8.8
DYNAMIC PERFORMANCE
(A
IN
= -1.0dBFS)
Signal-to-Noise Ratio
SNR
60
56
70
64
61
59
72
69
-70
-69
61
59
9.7
9.5
-70
-67
-64
dB
-3
-10
-5
-5
-5
±1.0
±5
±2
±3
±2
3
10
5
5
5
%FSR
mV/V
%FSR
-1
-1.5
±0.3
10
1
1.5
Bits
LSB
LSB
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Spurious-Free Dynamic Range
Total Harmonic Distortion
(first five harmonics)
Signal-to-Noise and Distortion
Effective Number of Bits
Intermodulation Distortion
SFDR
dB
THD
SINAD
ENOB
IMD
dB
dB
Bits
dBc
2
_______________________________________________________________________________________
10-Bit, 20Msps ADC
ELECTRICAL CHARACTERISTICS (continued)
(V
AVDD
= V
CMLP
= +5V, V
DVDD
= +3.3V, V
CMLN
= V
AGND
= V
DGND
= 0V, internal reference, digital output load = 35pF, f
CLK
= 20MHz
(50% duty cycle), T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
ANALOG INPUT
(INP, INN, CML)
Input Resistance
Input Capacitance
Input Common-Mode Voltage
Range
Differential Input Range
Small-Signal Bandwidth
Large-Signal Bandwidth
Input Resistance
Input Capacitance
Differential Reference
Input Current
Input Capacitance
REFP Input Range
CML Input Range
REFN Input Range
REFERENCE OUTPUTS
(REFP, CML, REFN; external +2.5V reference)
Positive Reference Voltage
Common-Mode Reference
Voltage
Negative Reference Input
Voltage
Differential Reference
Differential Reference
Temperature Coefficient
REFERENCE OUTPUTS
(REFP, CML, REFN; internal +2.5V reference)
Positive Reference
Common-Mode Reference
Voltage
Negative Reference
Differential Reference
Differential Reference
Temperature Coefficient
V
REFP
V
CML
V
REFN
(Note 1)
(Note 1)
(Note 1)
V
REFP
- V
REFN
, T
A
= +25°C
1.8
3.25
2.25
1.25
2
±150
2.2
V
V
V
V
ppm/°C
V
REFP
V
CML
V
REFN
V
REFP
- V
REFN
, T
A
= +25°C
1.9
3.25
2.25
1.25
2.0
±50
2.1
V
V
V
V
ppm/°C
I
IN
C
IN
R
IN
C
IN
V
CMVR
DR
SSBW
LSBW
R
IN
C
IN
Either input to ground
Either input to ground
CML (Note 6)
V
INP
- V
INN
(Note 7)
(Note 7)
REFIN (Note 8)
REFIN
V
REFP
- V
REFN
REFP, CML, REFN
REFP, CML, REFN
-325
15
3.25
±10%
2.25
±10%
1.25
±10%
6.5
10
2.0
325
3.5
8
2.25
±10%
±2
400
150
kΩ
pF
V
V
MHz
MHz
kΩ
pF
V
µA
pF
V
V
V
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
MAX1425
REFERENCE
(V
REFIN
= 0; REFP, REFN, CML applied externally)
_______________________________________________________________________________________
3
10-Bit, 20Msps ADC
MAX1425
ELECTRICAL CHARACTERISTICS (continued)
(V
AVDD
= V
CMLP
= +5V, V
DVDD
= +3.3V, V
CMLN
= V
AGND
= V
DGND
= 0V, internal reference, digital output load = 35pF, f
CLK
= 20MHz
(50% duty cycle), T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
POWER SUPPLY
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
DIGITAL INPUTS
(CLK,
OE/PD)
V
DVDD
> 4.75V
Input Logic High
V
IH
V
DVDD
< 4.75V
V
DVDD
> 4.75V
Input Logic Low
V
IL
V
DVDD
< 4.75V
V
DVDD
= 5.25V
I
CLK
I
OE/PD
-10
-20
10
V
DVDD
- 0.5
-10
10
0.1
Figure 4
Figure 4
20
20
25
25
5.5
5
7
20
10
10
20
20
30
30
2.4
0.7
·
V
DVDD
0.8
0.3
·
V
DVDD
10
20
µA
µA
pF
V
V
PD
I
DVDD
V
AVDD
V
DVDD
I
AVDD
REFIN = AGND
OE/PD
= DV
DD
V
DVDD
= 3.3V
V
DVDD
= 5.0V
OE/PD
= DV
DD
4.75
2.7
5.00
3.3
31
26
0.6
5.3
8.5
90
172
5.25
5.5
38
35
1
9
14
150
220
V
V
mA
mA
mA
mA
µA
mW
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Input Current Leakage
Input Capacitance
DIGITAL OUTPUTS
(D0–D9)
Output Logic High
Output Logic Low
Three-State Leakage
Three-State Capacitance
TIMING CHARACTERISTICS
Conversion Rate
Clock Frequency
Clock High
Clock Low
Pipeline Delay (Latency)
Aperture Delay
Aperture Jitter
Data Output Delay
Bus Enable
Bus Disable
CONV
f
CLK
t
CH
t
CL
t
AD
t
AJ
t
OD
VOH
VOL
I
OH
= -200µA, V
DVDD
= 2.7V
I
OL
= 200µA, V
DVDD
= 2.7V
V
DVDD
= 5.25V,
OE/PD
= DV
DD
OE/PD
= DV
DD
V
DV
DD
V
V
µA
pF
MHz
MHz
ns
ns
cycles
ns
ps
ns
ns
ns
0.5
10
5
25
20
20
4
_______________________________________________________________________________________
10-Bit, 20Msps ADC
ELECTRICAL CHARACTERISTICS (continued)
Note 1:
Note 2:
Note 3:
Note 4:
Note 5:
Note 6:
Note 7:
Note 8:
Internal reference, REFIN bypassed to AGND with a 0.1µF capacitor.
External +2.5V reference applied to REFIN.
Internal reference disabled. V
REFIN
= 0, V
REFP
= 3.25V, V
CML
= 2.25V, and V
REFN
= 1.25V.
Measured as the ratio of the change in midscale offset voltage for a ±5% change in V
AVDD
using the internal reference.
IMD is measured with respect to either of the fundamental tones.
Specifies the common-mode range of the differential input signal supplied to the MAX1425.
Defined as the input frequency at which the fundamental component of the output spectrum is attenuated by 3dB.
V
REFIN
is internally biased to +2.5V through a 5kΩ resistor.
MAX1425
Typical Operating Characteristics
(V
AVDD
= V
CMLP
= +5V, V
DVDD
= +3.3V, V
CMLN
= V
AGND
= 0V, internal reference, digital output load = 35pF, f
CLK
= 20Msps (50%
duty cycle), for dynamic performance 0dB is full scale, T
A
= +25°C, unless otherwise noted.)
INTEGRAL NONLINEARITY vs. CODE
MAX1425-01
DIFFERENTIAL NONLINEARITY vs. CODE
f
INP
= 2MHz
0.4
0.2
DNL (LSB)
0
-0.2
-0.4
-0.6
MAX1425-02
ANALOG INPUT BANDWIDTH
(FULL POWER)
-1.0
-2.0
AMPLITUDE (dB)
-3.0
-4.0
-5.0
-6.0
-7.0
-8.0
0.01
0.1
1
10
100
1000 10,000
MAX1425-03
0.8
0.6
0.4
0.2
INL (LSB)
0
-0.2
-0.4
-0.6
-0.8
-1.0
-1.2
0
200
400
CODE
600
800
f
INP
= 2MHz
0.6
0
1000
0
200
400
CODE
600
800
1000
BANDWIDTH (MHz)
INTERMODULATION DISTORTION
vs. FREQUENCY
MAX1425-04
SIGNAL-TO-NOISE PLUS DISTORTION
vs. POWER (f
IN
= 2.003MHz)
MAX1425-05
SIGNAL-TO-NOISE RATIO PLUS DISTORTION
vs. POWER (f
IN
= 5.009MHz)
MAX1425-06
0
-20
MAGNITUDE (dB)
-40
-60
-80
-100
-120
-140
0
1
2
3
4
5
6
7
8
9
CLK
= 20MHz
ff
CLK
= 20MHz
f1 = 5.01MHz
f1 = 5.01MHz
f2 = 5.03MHz
f2 = 5.03MHz
60
60
40
SINAD (dB)
SNDR (dB)
20
40
20
0
10
-60
-45
-30
INPUT (dB)
-15
0
FREQUENCY (MHz)
0
-60
-45
-30
INPUT (dB)
-15
0
_______________________________________________________________________________________
5
PCB Design
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