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AD532
Rev. D | Page 11 of 16
AD532 PERFORMANCE CHARACTERISTICS
Multiplication accuracy is defined in terms of total error at 25°C
with the rated power supply. The value specified is in percent of
full scale and includes XIN and YIN nonlinearities, feedback and
scale factor error. To this must be added such application-
dependent error terms as power supply rejection, common-
mode rejection and temperature coefficients (although worst
case error over temperature is specified for the AD532S). Total
expected error is the rms sum of the individual components
because they are uncorrelated.
Accuracy in the divide mode is only a little more complex. To
achieve division, the multiplier cell must be connected in the
feedback of the output op amp as shown i
n Figure 17. In this
configuration, the multiplier cell varies the closed loop gain of
the op amp in an inverse relationship to the denominator voltage.
Therefore, as the denominator is reduced, output offset, band-
width, and other multiplier cell errors are adversely affected.
The divide error and drift are then εm × 10 V/X1 X2) where εm
represents multiplier full-scale error and drift, and (X1 X2) is
the absolute value of the denominator.
NONLINEARITY
Nonlinearity is easily measured in percent harmonic distortion.
as a function of input signal level and frequency respectively,
with one input held at plus or minus 10 V dc. In
Figure 7, the
sine wave amplitude is 20 V (p-p).
AC FEEDTHROUGH
AC feedthrough is a measure of the multiplier’s zero suppression.
With one input at zero, the multiplier output should be zero
regardless of the signal applied to the other input. Feedthrough
as a function of frequency for the AD532 is shown i
n Figure 8.It is measured for the condition VX = 0, VY = 20 V (p-p) and
VY = 0, VX = 20 V (p-p) over the given frequency range. It
consists primarily of the second harmonic and is measured in
millivolts peak-to-peak.
COMMON-MODE REJECTION
The AD532 features differential X and Y inputs to enhance its
flexibility as a computational multiplier/divider. Common-mode
rejection for both inputs as a function of frequency is shown in
Figure 9. It is measured with X1 = X2 = 20 V (p-p), (Y1 Y2) = 10 V dc and Y1 = Y2 = 20 V (p-p), (X1 X2) = 10 V dc.
DYNAMIC CHARACTERISTICS
The closed loop frequency response of the AD532 in the multiplier
mode typically exhibits a 3 dB bandwidth of 1 MHz and rolls
off at 6 dB/octave, thereafter. Response through all inputs is
essentially the same as shown in
Figure 10. In the divide mode,
the closed loop frequency response is a function of the absolute
Stable operation is maintained with capacitive loads to 1000 pF
in all modes, except the square root for which 50 pF is a safe
upper limit. Higher capacitive loads can be driven if a 100 Ω
resistor is connected in series with the output for isolation.
POWER SUPPLY CONSIDERATIONS
Although the AD532 is tested and specified with ±15 V dc supplies,
it may be operated at any supply voltage from ±10 V to ±18 V
for the J and K versions, and ±10 V to ±22 V for the S version.
The input and output signals must be reduced proportionately
to prevent saturation; however, with supply voltages below ±15 V,
as shown i
n Figure 12. Because power supply sensitivity is not
dependent on external null networks as in other conventionally
nulled multipliers, the power supply rejection ratios are improved
from 3 to 40 times in the AD532.
NOISE CHARACTERISTICS
All AD532s are screened on a sampling basis to assure that output
noise will have no appreciable effect on accuracy. Typical spot