MAX1198 Datasheet, PDF (18/22 Pages) Maxim Integrated Products – Dual, 8-Bit, 100Msps, 3.3V, Low-Power ADC with Internal Reference and Parallel Outputs

Dual, 8-Bit, 100Msps, 3.3V, Low-Power ADC
with Internal Reference and Parallel Outputs
3.3V
0.1µF
1
MAX6066
2 ^21.5kΩ
3
1µF
3.3V
0.1µF
MAX4254 POWER-SUPPLY
BYPASSING. PLACE CAPACITOR
AS CLOSE AS POSSIBLE TO
THE OP AMP.
2.0V
3
2
21.5kΩ
1.5V
5
6
21.5kΩ
1.0V
10
21.5kΩ
9
21.5kΩ
3.3V
4
1/4 MAX4252
1
2.0V AT 8mA
47Ω
11
10µF
330µF
6V
6V
1.47kΩ
3.3V
4
1/4 MAX4252
7
1.5V AT 0mA
47Ω
11
10µF
6V
330µF
6V
1.47kΩ
3.3V
4
1/4 MAX4252
8
1.0V AT -8mA
47Ω
11
10µF
6V
330µF
6V
1.47kΩ
NOTE: ONE FRONT-END REFERENCE CIRCUIT DESIGN MAY BE USED WITH UP TO 32 ADCs.
N.C.
29 _REFOUT
31 _REFIN
32 _REFP
1 _REFN
N=1
MAX1198
2 _COM
0.1µF 0.1µF 0.1µF
0.1µF
2.2µF
10V
N.C.
29 _REFOUT
31 _REFIN
32
REFP
N = 32
1 _REFN
2 _COM
MAX1198
0.1µF 0.1µF 0.1µF
Figure 9. External Unbuffered Reference Drive with MAX4252 and MAX6066
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 3.3V, 8-bit ADC MAX1198 and the
MAX2451 quadrature demodulator to recover and
digitize the I and Q baseband signals. Before being
digitized by the MAX1198, the mixed down-signal com-
ponents 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) perfor-
mance and minimizing intersymbol interference.
Grounding, Bypassing,
and Board Layout
The MAX1198 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 V_DD, 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 (OV_DD) 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
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