CDS-1402

7

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CALIBRATION PROCEDURE

Offset Adjust (Figure 5)

Offset and pedestal errors may be compensated for by

applying external voltages to pin 1 (OFFSET ADJUST V1) and/

or pin 9 (OFFSET ADJUST V2) using either voltage-output

DAC’s or potentiometers configured to appear as voltage

sources.

1. Connect pin 8 (S/H2 SUMMING NODE) either directly to pin

7 (S/H1 ROUT) or through a 100 Ohm potentiometer to pin

6 (S/H1 OUT).

2. Tie pins 3 (ANALOG INPUT 1) and 4 (ANALOG INPUT 2) to

pin 5 (ANALOG GROUND).

3. Adjust OFFSET ADJUST V1 (while S/H1 is in the hold

mode) until pin 6 (S/H1 OUT) equals 0V.

4. Adjust OFFSET ADJUST V2 (while S/H2 is in the hold

mode) until pin 22 (V OUT) equals 0V.

5. To negate the effect of output droop on the offset-adjust

process, each S/H must be continually switched between its

sample and hold modes and adjusted so its output equals

zero immediately after going into the hold mode.

The sensitivity of the voltage offset adjustments is 5mV per Volt.

Pins 1 and 9 should be left open (floating) when not being used

for offset adjustment.

Gain Matching Adjustment (Differential Gain)

between S/H1 and S/H2

The user can adjust the gain matching (differential gain)

between S/H1 and S/H2 by leaving pin 7 (S/H1 ROUT) floating

(open) and connecting a 100 Ohm potentiometer between pin

6 (S/H1 OUT) and pin 8 (S/H2 SUMMING NODE). Note, offset

adjustment should take place before gain matching adjustment.

Apply a full-scale input to both pin 3 (ANALOG INPUT 1) and

pin 4 (ANALOG INPUT 2). Adjust the 100 Ohm potentio-

meter (with both S/H's in the sample mode) until pin 22

(V OUT) is 0V.

If gain matching adjustment is not required, leave pin 6 (S/H1

OUT) floating (open) and tie pin 7 (S/H1 ROUT) to pin 8 (S/H2

SUMMING NODE).

OFFSET ADJUST V1

1

+5V

–5V

DO NOT CONNECT

2

ANALOG INPUT 1

3

ANALOG INPUT 2

4

ANALOG GROUND

5

S/H1 OUT

6

S/H1 ROUT

7

S/H2 SUMMING NODE

8

OFFSET ADJUST V2

9

+5V

–5V

DO NOT CONNECT

10

S/H1 COMMAND

11

S/H2 COMMAND

12

100

Ω

0.1µF

2.2µF

+5V

+

0.1µF

2.2µF

–5V

0.1µF

2.2µF

+5V

+

24

23

22

21

20

19

18

17

16

15

14

13

ANALOG GROUND

V OUT

ANALOG GROUND

A/D CLOCK 2

A/D CLOCK 2

A/D CLOCK 1

A/D CLOCK 1

+5V DIGITAL SUPPLY

DIGITAL GROUND

ANALOG GROUND

–5V ANALOG SUPPLY

+5V ANALOG SUPPLY

CDS-1402

Figure 5. CDS-1402 Typical Connection Diagram