AD538

Rev. E | Page 11 of 16

ONE-QUADRANT MULTIPLICATION/DIVISION

Figure 13 shows how the AD538 may be easily configured

as a precision one-quadrant multiplier/divider. The transfer

variables, a calculation not available with a conventional

multiplier. In addition, the 1000:1 (that is, 10 mV to 10 V)

input dynamic range of the AD538 greatly exceeds that of

analog multipliers computing one-quadrant multiplication

and division.

25k

Ω

25k

Ω

100

Ω

25k

Ω

25k

Ω

ANTILOG

LOG

OUTPUT

100

Ω

AD538

A

D

C

IN4148

8

1

1

17

16

15

14

13

12

11

10

2

3

4

5

6

7

8

9

LOG

RATIO

INTERNAL

VOLTAGE

REFERENCE

SIGNAL

GND

PWR

GND

INPUT

I

+15V

–15V

B

+10V

+2V

OUTPUT

INPUT

INPUT

Figure 13. One-Quadrant Combination Multiplier/Divider

reference (Pin 4), and tying the log-ratio output at B to the

antilog input at C, the AD538 can be configured as a one-

quadrant analog multiplier with 10 V scaling. If 2 V scaling

multiplier transfer function becomes:

















=

V

V

V

V

Z

Y

O

10

As a multiplier, this circuit provides a typical bandwidth of 400 kHz

100 mV to 10 V). The maximum error with a 100 mV to 10 V

range for the two input variables will typically be +0.5% of

reading. Using the optional Z offset trim scheme, as shown in

Figure 14, this error can be reduced to +0.25% of reading.

Figure 13 is configured as a one-quadrant divider with a fixed

scale factor. As with the one-quadrant multiplier, the inputs

accept only single (positive) polarity signals. The output of the

one-quadrant divider with a +10 V scale factor is:













=

X

Z

O

V

V

V

V

10

The typical bandwidth of this circuit is 370 kHz with 1 V to

10 V denominator input levels. At lower amplitudes, the band-

width gradually decreases to approximately 200 kHz at the

2 mV input level.