AD534

REV. B

–5–

FUNCTIONAL DESCRIPTION

Figure 2 is a functional block diagram of the AD534. Inputs are

converted to differential currents by three identical voltage-to-

current converters, each trimmed for zero offset. The product

of the X and Y currents is generated by a multiplier cell using

Gilbert’s translinear technique. An on-chip “Buried Zener”

provides a highly stable reference, which is laser trimmed to

provide an overall scale factor of 10 V. The difference between

XY/SF and Z is then applied to the high gain output amplifier.

This permits various closed loop configurations and dramati-

cally reduces nonlinearities due to the input amplifiers, a domi-

nant source of distortion in earlier designs. The effectiveness of

the new scheme can be judged from the fact that under typical

conditions as a multiplier the nonlinearity on the Y input, with

X at full scale (

±10 V), is ±0.005% of FS; even at its worst

point, which occurs when X =

±6.4 V, it is typically only

±0.05% of FS Nonlinearity for signals applied to the X input,

on the other hand, is determined almost entirely by the multi-

plier element and is parabolic in form. This error is a major

factor in determining the overall accuracy of the unit and hence

is closely related to the device grade.

V-1

V-1

V-1

SF

AD534

A

OUT

TRANSFER FUNCTION

SF

HIGH GAIN

OUTPUT

AMPLIFIER

+

–

+

–

+

–

STABLE

REFERENCE

AND BIAS

TRANSLINEAR

MULTIPLIER

ELEMENT

0.75 ATTEN

Figure 2. Functional Block Diagram

The generalized transfer function for the AD534 is given by:

SF

− (Z









where A = open loop gain of output amplifier, typically

70 dB at dc

X, Y, Z = input voltages (full scale =

±SF, peak =

±1.25 SF)

SF = scale factor, pretrimmed to 10.00 V but adjustable

by the user down to 3 V.

In most cases the open loop gain can be regarded as infinite,

and SF will be 10 V. The operation performed by the AD534,

can then be described in terms of equation:

The user may adjust SF for values between 10.00 V and 3 V by

connecting an external resistor in series with a potentiometer

tance for a given value of SF is given by the relationship:

SF

10

− SF

by

±25% using the potentiometer. Considerable reduction in

bias currents, noise and drift can be achieved by decreasing SF.

This has the overall effect of increasing signal gain without the

customary increase in noise. Note that the peak input signal is

always limited to 1.25 SF (i.e.,

±5 V for SF = 4 V) so the overall

transfer function will show a maximum gain of 1.25. The per-

formance with small input signals, however, is improved by

using a lower SF since the dynamic range of the inputs is now

fully utilized. Bandwidth is unaffected by the use of this option.

Supply voltages of

±15 V are generally assumed. However,

satisfactory operation is possible down to

±8 V (see Figure 16).

Since all inputs maintain a constant peak input capability of

±1.25 SF some feedback attenuation will be necessary to

achieve output voltage swings in excess of

±12 V when using

higher supply voltages.

OPERATION AS A MULTIPLIER

Figure 3 shows the basic connection for multiplication. Note

that the circuit will meet all specifications without trimming.

AD534

=

10V

OUTPUT ,

12V PK

X INPUT

10V FS

12V PK

Y INPUT

10V FS

12V PK

+15V

OUT

–15V

OPTIONAL SUMMING

INPUT, Z,

10V PK

SF

Figure 3. Basic Multiplier Connection

In some cases the user may wish to reduce ac feedthrough to a

minimum (as in a suppressed carrier modulator) by applying an

external trim voltage (

±30 mV range required) to the X or Y

input (see Figure 1). Figure 19 shows the typical ac feedthrough

with this adjustment mode. Note that the Y input is a factor of

10 lower than the X input and should be used in applications

where null suppression is critical.

sum an additional signal into the output. In this mode the out-

put amplifier behaves as a voltage follower with a 1 MHz small

signal bandwidth and a 20 V/

µs slew rate. This terminal should

always be referenced to the ground point of the driven system,

particularly if this is remote. Likewise, the differential inputs

should be referenced to their respective ground potentials to

realize the full accuracy of the AD534.