AD538
When the input VX is tied to the +10 V reference terminal, the
multiplier transfer function becomes:
ONE-QUADRANT MULTIPLICATION/DIVISION
Figure 13 shows how the AD538 may be easily configured
as a precision one-quadrant multiplier/divider. The transfer
function VO = VY (VZ/VX) 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.
VZ
10 V
VO = VY
As a multiplier, this circuit provides a typical bandwidth of 400 kHz
with values of VX, VY, or VZ 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.
V
V
Z
X
V
= V
Y
O
By using the 10 V reference as the VY 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:
I
1
2
3
4
5
6
18
17
16
15
14
13
12
11
A
D
Z
Z
LOG
V
25kΩ
V
Z
RATIO
INPUT
B
I
X
V
X
V
X
VZ
VX
+10V
+2V
INPUT
25kΩ
VO = 10 V
100Ω
100Ω
SIGNAL
GND
PWR
GND
INTERNAL
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.
VOLTAGE
+15V
REFERENCE
AD538
C
7
8
9
–15V
OUTPUT
IN4148
25kΩ
I
V
Y
O
ANTILOG
OUTPUT
V
V
Y
Y
10
I
LOG
INPUT
25kΩ
Figure 13. One-Quadrant Combination Multiplier/Divider
By simply connecting the input, VX (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, VX can be tied to the 2 V reference.
Rev. E | Page 11 of 16
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