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6.
Q~~RTER-SQLARE
MULTIPLIER
a.
General Description
The quarter-square multiplier is used in conjunction with a dc amplifier to pro-
duce a four quadrant product proportional to XY from inputs of +X, -X, +Y, and
-Yo
In addition to multiplication, the TR-20 multiplier is capable of performing
the mathematical operations of division, squaring, and square root extraction.
The operation of the quarter-square multiplier is based on the identity:
which reduces multiplication to the operations of summation and squaring.
The
squaring operations are performed by diode function generators (DFG's) that con-
tain biased diode networks.
The diode function generators or squaring cards gen-
erate a segmented straight-line approximation to a square law curve.
The complete
multiplier assembly contains four squaring cards that are connected so as to permit
multiplication of input signals of either plus or minus polarities.
(Only two of
the squaring cards conduct at anyone time.)
The outputs of the squaring cards
are summed in an external amplifier.
Operators who are interested in the circuit details of the quarter-square multi-
plier are referred to the TR-20 Maintenance Manual.
b.
Multiplication
The general configuration of the quarter-square multiplier is shown in Figure lla.
The DFG's contain biased diode networks' that produce a current proportional to the
square of the sum of the input voltages to the DFG when the sum of the input volt-
ages has the proper polarity.
A positive DFG conducts only when the sum of its
inputs is positive.
The unit is patched as a multiplier in Figure llb.
The squaring cards (DFG's)
form the input network of the amplifier; a 3550 ohm resistor (R65) is the feed-
back element.
The input voltages are patched to the +X, -X, +Y, and -Y terminations.
The output voltage from the amplifier is -
~~.
The output is changed to
+
~~
by
reversing the +X and -X inputs or the +Y and -Y inputs.
All four input voltages
must be patched in.
The squaring cards have a variable input impedance, therefore
the input voltages should not be obtained from potentiometers.
The output ampli-
fier can be used to sum additional inputs; the gain for an additional 10K ohm in-
put resistor is 0.355 since the amplifier has a 3550 ohm feedback resistor.
A programming symbol for the multiplier is shown in Figure llc.
c.
Division
Division of a variable voltage A by a variable voltage B is accomplished by placing
26
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