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Multiply/Divide Circuit

IP.com Disclosure Number: IPCOM000123897D
Original Publication Date: 1999-Jun-01
Included in the Prior Art Database: 2005-Apr-05
Document File: 1 page(s) / 30K

Publishing Venue

IBM

Related People

Johari, GC: AUTHOR [+2]

Abstract

Disclosed is a circuit which performs the mathematical function (XY)/Z=R where X, Y, and Z are voltage level inputs to the circuit and R is a voltage level output. When one of the inputs is held at a constant value, the circuit can also perform the functions of multiplying two analog signals (XY), multiplying a signal by itself (XX), or dividing one signal by another (X/Z). All input signals must be positive voltages. A typical circuit response time is 50 milliseconds.

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Multiply/Divide Circuit

   Disclosed is a circuit which performs the mathematical
function (XY)/Z=R where X, Y, and Z are voltage level inputs to the
circuit and R is a voltage level output.  When one of the inputs is
held at a constant value, the circuit can also perform the functions
of multiplying two analog signals (XY), multiplying a signal by
itself (XX), or dividing one signal by another (X/Z).  All input
signals must be positive voltages.  A typical circuit response time
is 50 milliseconds.

   The circuit uses two voltage comparators.  One comparator
is used to generate a triangular voltage waveform with an amplitude
proportional to one of the analog inputs.  The input which sets the
triangular voltage amplitude is labeled Vz in the Figure.

   The second comparator produces an output pulse when the
triangular waveform is lower in voltage than the input voltage
labeled Vx.  The amplitude to the pulse is set by the third input
voltage labeled Vy.

   A resistor and capacitor filter the pulses to produce an
output voltage labeled Vout in the figure.  The steady state value of
Vout is approximately equal to (Vx Vy)/Vz.

   When using LM339 comparators, the following are typical
ranges allowable for the input voltages:
         +5 volts <= Vz <= +30 volts
         0 volts <= Vx <= Vz
         0 volts <= Vy <= +30 volts

   The error of a typical circuit was found to be less than
2% when all input voltages were above 8 volts but degr...