Differentiating and integrating circuit for translating bar code signals into corresponding pulses

Abstract

A system for converting analog bar code signals from the photo detector of a bar code reader or scanner into pulses occurring in time in correspondence with the spacing of the edges of the bars of the code which has a differentiator circuit and a circuit for integrating in time the differentiated signal to produce a second signal lower in amplitude and delayed with respect to the differentiated signal. A comparator compares the differentiated signal and the integrated signal. The output of the comparator is a train of pulses having edges occurring when the differentiated signal and integrated signal are in a certain amplitude relationship (i.e., approximately equal to each other). The peaks of the differentiated bar code signal occur in coincidence with the scanning of the edges of the bar code. The integrated signal is delayed by a fixed time delay. Accordingly, the edges of the pulses are produced by the comparator when the differentiated signals become smaller and become greater than the integrated signal in relative amplitude thereby producing pulses with the same spacing as the edges of the bars of the code and offset slightly in time. Since the differentiated signal is processed to produce the pulses corresponding to the bar code, errors in timing of the pulse edges due to drifting in amplitude of the analog signal and false transitions are substantially obviated.

Dependencies are inferred from the claim text.