AD834

REV. C

–8–

Figure 14. Frequency Doubler Connections

Figure 15. Output Spectrum for Configuration of Figure 14

WIDEBAND THREE SIGNAL MULTIPLIER/DIVIDER

Two AD834s and a wideband op amp can be connected to

make a versatile multiplier/divider having the transfer function

W

=

(X1– X 2)(Y1–Y 2)

(U1–U 2)

+ Z

with a denominator range of about 100:1. The denominator in-

put U = U1–U2 must be positive and in the range 100 mV to

10 V; X, Y and Z inputs may have either polarity. Figure 16

shows a general configuration which may be simplified to suit a

particular application. This circuit accepts full-scale input volt-

ages of 10 V, and delivers a full-scale output voltage of 10 V.

The optional offset trim at the output of the AD834 improves

the accuracy for small denominator values. It is adjusted by

nulling the output voltage when the X and Y inputs are zero and

U = +100 mV.

The AD840 is internally compensated to be stable without the

use of any additional HF compensation. As the input U is re-

duced, the bandwidth falls because the feedback around the op

amp is proportional to the input U.

This circuit may be modified in several ways. For example, if

the differential input feature is not needed, the unused input

Figure 16. Wideband Three Signal Multiplier/Divider

can be connected to ground through a single resistor, equal to

the parallel sum of the resistors in the attenuator section. The

full-scale input levels on X, Y and U can be adapted to any full-

scale voltage down to

±1 V by altering the attenuator ratios.

Note, however, that precautions must be taken if the attenuator

ratio from the output of A3 back to the second AD834 (A2) is

lowered. First, the HF compensation limit of the AD840 may be

exceeded if the negative feedback factor is too high. Second, if

the attenuated output at the AD834 exceeds its clipping level of

±1.3 V, feedback control will be lost and the output will sud-

denly jump to the supply rails. However, with these limitations

understood, it will be possible to adapt the circuit to smaller

full-scale inputs and/or outputs, and for use with lower supply

voltages.