MAX1422 Datasheet, PDF (8/15 Pages) Maxim Integrated Products – 12-Bit, 20Msps, 3.3V, Low-Power ADC with Internal Reference

12-Bit, 20Msps, 3.3V, Low-Power ADC with
Internal Reference
Pin Description
PIN
1, 4, 5, 8, 9,
12, 13, 16,
19, 41, 48
2, 3, 10, 11,
14, 15, 20,
42, 47
6
7
17
18
21, 31, 32
22, 29, 30
23–28
33–38
39
40
43
44
45
46
NAME
AGND
AV_DD
INP
INN
CLK
CLK
DV_DD
DGND
D0–D5
D6–D11
OE
PD
REFIN
REFP
REFN
CML
FUNCTION
Analog Ground. Connect all return paths for analog signals to AGND.
Analog Supply Voltage. For optimum performance, bypass to the closest AGND with a parallel
combination of a 0.1µF, and a 1nF capacitor. Connect a single 10µF and 1µF capacitor combination
between AV_DD and AGND.
Positive Analog Signal Input
Negative Analog Signal Input
Clock Frequency Input. Clock frequency input ranges from 100kHz to 20MHz.
Complementary Clock Frequency Input. This input is used for differential clock input. If the ADC is
driven with a single-ended clock, bypass CLK with 0.1µF capacitor to AGND.
Digital Supply Voltage. For optimum performance, bypass to the closest DGND with a parallel
combination of a 0.1µF and a 1nF capacitor. Connect a single 10µF and 1µF capacitor combination
between DV_DD and DGND.
Digital Ground
Digital Data Outputs. Data bits D0 through D5, where D0 represents the LSB.
Digital Data Outputs. D6 through D11, where D11 represents the MSB.
Output Enable Input. A logic "1" on OE places the outputs D0–D11 into a high-impedance state. A
logic "0" allows for the data bits to be read from the outputs.
Shutdown Input. A logic "1" on PD places the ADC into shutdown mode.
External Reference Input. Bypass to AGND with a capacitor combination of 0.22µF in parallel with
1nF. REFIN can be biased externally to adjust reference levels and calibrate full-scale errors. To
disable the internal reference, connect REFIN to AGND.
Positive Reference I/O. Bypass to AGND with a capacitor combination of 0.22µF in parallel with 1nF.
With the internal reference disabled (REFIN = AGND), REFP should be biased toV_CML + V_DIFF/2.
Negative Reference I/O. Bypass to AGND with a capacitor combination of 0.22µF in parallel with
1nF. With the internal reference disabled (REFIN = AGND), REFN should be biased to
V_CML - V_DIFF/2.
Common-Mode Level Input. Bypass to AGND with a capacitor combination of 0.22µF in parallel with
1nF. With the internal reference disabled (REFIN = AGND).
Detailed Description
The MAX1422 uses a 12-stage, fully differential,
pipelined architecture (Figure 1), that allows for high-
speed conversion while minimizing power consump-
tion. Each sample moves through a pipeline stage
every half-clock cycle. Including the delay through the
output latch, the latency is seven clock cycles.
A 2-bit (2-comparator) flash ADC converts the held-
input voltage into a digital code. The following digital-
to-analog converter (DAC) converts the digitized result
back into an analog voltage, which is then subtracted
from the original held-input signal. The resulting error
signal is then multiplied by two and the product is
passed along to the next pipeline stage. This process
is repeated until the signal has been processed by all
12 stages. Each stage provides a 1-bit resolution.
Digital error correction compensates for ADC compara-
tor offsets in each pipeline stage and ensures no
missing codes.
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