Rainbow-electronics MAX1198 Bedienungsanleitung PDF herunterladen (Seite 18)

MAX1198

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

, 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

) 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

Dual, 8-Bit, 100Msps, 3.3V, Low-Power ADC

with Internal Reference and Parallel Outputs

18 ______________________________________________________________________________________

1/4 MAX4252

MAX6066

1/4 MAX4252

1.47kΩ

21.5kΩ

47Ω

3.3V

REFOUT

REFP

REFIN

1µF

10µF

MAX1198

N = 1

REFN

29N.C.

N.C.

COM

REFOUT

NOTE: ONE FRONT-END REFERENCE CIRCUIT DESIGN MAY BE USED WITH UP TO 32 ADCs.

REFP

REFIN

MAX1198

N = 32

REFN

COM

2.0V AT 8mA

0.1µF

MAX4254 POWER-SUPPLY

BYPASSING. PLACE CAPACITOR

AS CLOSE AS POSSIBLE TO

THE OP AMP.

3.3V

1.47kΩ

47Ω

3.3V

1.5V

10µF

1.5V AT 0mA

1.47kΩ

47Ω

3.3V

10µF

0.1µF0.1µF0.1µF

0.1µF

2.2µF

10V

0.1µF0.1µF

1.0V AT -8mA

330µF

2.0V

1.0V

Figure 9. External Unbuffered Reference Drive with MAX4252 and MAX6066

1 2 ... 13 14 15 16 17 18 19 20 21 22

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