AD534

–6–

REV. B

A much lower scaling voltage can be achieved without any re-

duction of input signal range using a feedback attenuator as

= XY, so that the circuit can exhibit a maximum gain of 10.

This connection results in a reduction of bandwidth to about

the output offset voltage is increased by a factor of 10 making

external adjustments necessary in some applications. Adjust-

ment is made by connecting a 4.7 M

Ω resistor between Z

the slider of a pot connected across the supplies to provide

±300 mV of trim range at the output.

AD534

X INPUT

10V FS

12V PK

Y INPUT

10V FS

12V PK

+15V

OUT

–15V

OPTIONAL

PEAKING

CAPACITOR

90k

10k

SF

OUTPUT ,

12V PK

(SCALE = 1V)

Figure 4. Connections for Scale-Factor of Unity

Feedback attenuation also retains the capability for adding a

signal to the output. Signals may be applied to the high imped-

common ground connection where they are amplified by +1.

Input signals may also be applied to the lower end of the 10 k

Ω

resistor, giving a gain of –9. Other values of feedback ratio, up

to X100, can be used to combine multiplication with gain.

Occasionally it may be desirable to convert the output to a cur-

rent, into a load of unspecified impedance or dc level. For ex-

ample, the function of multiplication is sometimes followed by

integration; if the output is in the form of a current, a simple

capacitor will provide the integration function. Figure 5 shows

how this can be achieved. This method can also be applied in

squaring, dividing and square rooting modes by appropriate

choice of terminals. This technique is used in the voltage-

controlled low-pass filter and the differential-input voltage-to-

frequency converter shown in the Applications section.

AD534

1

RS

10V

INTEGRATOR

CAPACITOR

(SEE TEXT)

X INPUT

10V FS

12V PK

Y INPUT

10V FS

12V PK

OUT

CURRENT-SENSING

SF

Figure 5. Conversion of Output to Current

OPERATION AS A SQUARER

Operation as a squarer is achieved in the same fashion as the

multiplier except that the X and Y inputs are used in parallel.

The differential inputs can be used to determine the output

of the inputs is reversed). Accuracy in the squaring mode is

typically a factor of 2 better than in the multiplying mode, the

largest errors occurring with small values of output for input

below 1 V.

If the application depends on accurate operation for inputs that

are always less than

±3 V, the use of a reduced value of SF is

recommended as described in the Functional Description sec-

tion (previous page). Alternatively, a feedback attenuator may

be used to raise the output level. This is put to use in the differ-

ence-of-squares application to compensate for the factor of 2

loss involved in generating the sum term (see Figure 8).

The difference-of-squares function is also used as the basis for a

novel rms-to-dc converter shown in Figure 15. The averaging

filter is a true integrator, and the loop seeks to zero its input.

this technique is very high; at medium frequencies, and for

signals near full scale, it is determined almost entirely by the

ratio of the resistors in the inverting amplifier. The multiplier

scaling voltage affects only open loop gain. The data shown is

typical of performance that can be achieved with an AD534K,

but even using an AD534J, this technique can readily provide

better than 1% accuracy over a wide frequency range, even for

crest-factors in excess of 10.