Signal Transduction with Differential Pulse Width Modulation

The Differential Pulse Width Modulation System presented here is a signal transduction scheme applicable to a wide range of data acquisition processes for either large systems such as industrial process control, aircraft flight testing, computerized medical information centers, etc. or individual users seeking low cost, compact measuring instruments. In this scheme, a variable capacitance or equivalent sensor, actuated by the physical quantities to be measured, is combined with an integrated circuit containing mainly logic elements, to generate a series of pulses with fixed height in voltage but varying width in time so that the difference/sum ratio of the width between two adjacent pulses is proportional to the input. Signals thus modulated can be converted readily into analog output by simple low-pass filtering and can also control a simple up-down counter to give digital output, bypassing the conventional analog-digital converter. For portable recording, this differential pulse width scheme facilitates the use of inexpensive tape recorders at no sacrifice in accuracy, since there is no need for precision speed control.