The First Optical Character Recognition Systems Confer-ence

An analog arithmetic circuit has a modulator circuit for coverting an analog direct current input signal into a variable duty cycle signal with the duty cycle being controlled by the amplitude of the analog input signal. The variable duty cycle signal is subsequently applied to a demodulator circuit. The demodulator circuit is driven by the variable duty cycle signal to produce a switching signal for energizing a second switching device arranged to control the application of a third analog signal to an output circuit. The switching of the second switching device is maintained in phase with the operation of the first switching device to produce an output analog signal having a predetermined relationship to the three input analog signals.