AD534
FUNCTIONAL DESCRIPTION
The user may adjust SF for values between 10.00 V and 3 V by
connecting an external resistor in series with a potentiometer
between SF and –VS. The approximate value of the total resis-
tance for a given value of SF is given by the relationship:
Figure 1 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 F.S.; even at its worst
point, which occurs when X = ±6.4 V, it is typically only
±0.05% of F.S. 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 fac-
tor in determining the overall accuracy of the unit and hence is
closely related to the device grade.
SF
10 − SF
RSF = 5.4K
Due to device tolerances, allowance should be made to vary RSF;
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 us-
ing 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, satis-
factory operation is possible down to ±8 V (see curve 1). 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 volt-
ages.
AD534
+V
STABLE
REFERENCE
AND BIAS
S
SF
–V
S
TRANSFER FUNCTION
OPERATION AS A MULTIPLIER
X
1
+
Figure 2 shows the basic connection for multiplication. Note
that the circuit will meet all specifications without trimming.
V-1
(X – X ) (Y – Y )
1
2
1
2
–
X
2
TRANSLINEAR
MULTIPLIER
ELEMENT
V
= A
–(Z – Z )
1 2
O
SF
Y
Y
+
V-1
–
1
+V
X
+15V
S
1
2
X INPUT
±10V FS
±12V PK
2
A
OUT
X
OUTPUT , ±12V PK
HIGH GAIN
OUTPUT
AMPLIFIER
Z
Z
+
1
OUT
(X – X ) (Y – Y )
V-1
0.75 ATTEN
1
2
1
2
=
+Z
2
–
2
10V
Z
1
SF
AD534
Figure 1. AD534 Functional Block Diagram
OPTIONAL SUMMING
INPUT, Z, ±10V PK
Z
2
The generalized transfer function for the AD534 is given by:
Y
1
Y INPUT
±10V FS
±12V PK
(X1 − X2)(Y1 −Y2)
VOUT = A
− (Z1 − Z2)
–V
–15V
Y
S
2
SF
Figure 2. Basic Multiplier Connection
where A = open loop gain of output amplifier, typically
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 in-
put (see Optional Trimming Configuration, page 3). Curve 4
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.
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 high impedance Z2 terminal of the AD534 may be used to
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 re-
alize the full accuracy of the AD534.
(X1 − X2)(Y1 −Y2) = 10 V (Z1 − Z2)
REV. A
–5–
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