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+Vin=Vincm

-Vin=Vincm

+8Vpp

THS4131

-VCC

0.1 F

m

+VCC

220pF

Vocm

1

2

8

5

4

6

3

C0G

COMMOUT

ADS8422

+IN

-IN

3

7

6

time

8Vpp

Vincm

+VIN

-VIN

390 W

390 W

12 W

12 W

0.1 F

m

1 F

m

390 W

390 W

ADS8422

SLAS512B – JUNE 2006 – REVISED DECEMBER 2006

PRINCIPLES OF OPERATION (continued)

A.

Input common-mode voltage (Vincm) range is restricted by the amplifier. Refer to the amplifier data sheet for more

information. Output common mode of the THS4131 is set by the voltage at pin 2. The COMMOUT pin of the

ADS8422 is designed to source pin 2 of the THS4131. However to use this feature both the positive supply and

negative supply rails must equal (|-VCC| = |+VCC|), absolutely.

Figure 30. Single-Ended Input Driving Circuit for When Input is Unipolar or Bipolar

17

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