Asynchronous audio pulse coded modulator - converts audio signals into binary pulses with duration proportional to input signal

摘要

A high quality asynchronous pulse coded modulator applicable to audio frequency input signals is presented. The input signal is fed into one input of a linear amplifier based comparator. The output of this is fed to a Schmitt trigger circuit via a low pass filter. The Schmitt trigger exhibits a carefully controlled hysteresis so that it produces an output when the input exceeds a certain threshold, but reverts to null output only where the input is less than some smaller fixed threshold. The Schmitt trigger output is the required signal and is also fed to the second input terminal of the input comparator, via an integrator. The exact frequency attained depends on the characteristics of the filter and integrator.