AD534T Просмотр технического описания (PDF) - Analog Devices
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AD534T Datasheet PDF : 12 Pages
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AD534
A much lower scaling voltage can be achieved without any re-
duction of input signal range using a feedback attenuator as
shown in Figure 4. In this example, the scale is such that VOUT
= XY, so that the circuit can exhibit a maximum gain of 10.
This connection results in a reduction of bandwidth to about
80 kHz without the peaking capacitor CF = 200 pF. In addition,
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 MΩ resistor between Z1 and
the slider of a pot connected across the supplies to provide
± 300 mV of trim range at the output.
X INPUT
؎10V FS
؎12V PK
Y INPUT
؎10V FS
؎12V PK
X1
+VS
+15V
X2
OUT
AD534
SF
Z1
Z2
Y1
Y2
–VS
90k⍀
10k⍀
–15V
OUTPUT , ؎12V PK
= (X1 – X2) (Y1 – Y2)
(SCALE = 1V)
OPTIONAL
PEAKING
CAPACITOR
CF = 200pF
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-
ance Z2 terminal where they are amplified by +10 or to the
common ground connection where they are amplified by +1.
Input signals may also be applied to the lower end of the 10 kΩ
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.
X INPUT
؎10V FS
؎12V PK
Y INPUT
؎10V FS
؎12V PK
X1
+VS
X2
OUT
SF
Z1
AD534
Z2
Y1
Y2
–VS
CURRENT-SENSING
RESISTOR, RS, 2k⍀ MIN
IOUT
=
(X1
–
X2) (Y1
10V
–
Y2)
1
RS
INTEGRATOR
CAPACITOR
(SEE TEXT)
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
polarity (positive for X1 = Yl and X2 = Y2, negative if either one
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.
For this to occur, (VIN)2 – (VOUT)2 = 0 (for signals whose period
is well below the averaging time-constant). Hence VOUT is
forced to equal the rms value of VIN. The absolute accuracy of
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.
–6–
REV. B
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