Datasheet

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
function V
O
= V
Y
(V
Z
/V
X
) allows three independent input
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.
25kΩ
25kΩ
100Ω
25kΩ
25kΩ
ANTILOG
LOG
OUTPUT
100Ω
AD538
I
Y
A
D
I
X
V
X
C
IN4148
V
Y
811
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
I
Z
V
Z
V
Z
INPUT
V
O
I
+15V
–15V
B
+10V
+2V
00959-014
OUTPUT
V
Y
INPUT
V
X
INPUT
V
O
= V
Y
V
Z
V
X
Figure 13. One-Quadrant Combination Multiplier/Divider
By simply connecting the input, V
X
(Pin 15) to the 10 V
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
is desired, V
X
can be tied to the 2 V reference.
When the input V
X
is tied to the +10 V reference terminal, the
multiplier transfer function becomes:








=
V
V
VV
Z
Y
O
10
As a multiplier, this circuit provides a typical bandwidth of 400 kHz
with values of V
X
, V
Y
, or V
Z
varying over a 100:1 range (that is,
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.
By using the 10 V reference as the V
Y
input, the circuit of
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
VV 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.