AD524

REV. E

–13–

16

6

WR

14

7

15

2

1

18

19

3

17

10

6

2

20

1

4

AD524

DAC A

DB0

256:1

1/2

AD712

20k

+INPUT

(–INPUT)

G = 10

–INPUT

(+INPUT)

G = 100

G = 1000

4.44k

404

40

PROTECTION

20k

20k

20k

20k

20k

DAC B

DB7

AD7528

5

DATA

INPUTS

CS

DAC A/DAC B

1/2

AD712

9

16

11

12

PROTECTION

3

13

Figure 43. Programmable Output Gain Using a DAC

Another method for developing the switching scheme is to use a

DAC. The AD7528 dual DAC, which acts essentially as a pair

of switched resistive attenuators having high analog linearity and

symmetrical bipolar transmission, is ideal in this application.

The multiplying DAC’s advantage is that it can handle inputs of

either polarity or zero without affecting the programmed gain.

The circuit shown uses an AD7528 to set the gain (DAC A) and

to perform a fine adjustment (DAC B).

AUTOZERO CIRCUITS

In many applications it is necessary to provide very accurate

data in high gain configurations. At room temperature the offset

effects can be nulled by the use of offset trimpots. Over the

operating temperature range, however, offset nulling becomes a

problem. The circuit of Figure 44 show a CMOS DAC operat-

ing in the bipolar mode and connected to the reference terminal

to provide software controllable offset adjustments.

WR

CS

+INPUT

G = 10

–INPUT

G = 100

G = 1000

AD7524

OUT2

39k

AD589

MSB

LSB

DATA

INPUTS

1/2

AD712

1/2

AD712

R3

20k

R4

10k

R6

5k

C1

GND

R5

20k

OUT1

AD524

Figure 44. Software Controllable Offset

In many applications complex software algorithms for autozero

applications are not available. For those applications Figure 45

provides a hardware solution.

8

AD524

15

16

14

13

GND

0.1 F LOW

LEAKAGE

10

CH

1k

910

A1

A2

A3

A4

200 s

ZERO PULSE

AD7510KD

AD711

11

12

Figure 45. Autozero Circuit