초록 ▼

A system and method for improving the accuracy of edge detection under high Inter-Symbol Interference, or ISI, conditions is disclosed. The amplified and filtered first derivative signal is offset by equal amounts in both directions to generate positive and negative offsets which serve as inputs to

A system and method for improving the accuracy of edge detection under high Inter-Symbol Interference, or ISI, conditions is disclosed. The amplified and filtered first derivative signal is offset by equal amounts in both directions to generate positive and negative offsets which serve as inputs to negative and positive peak detectors, respectively. The offset is determined by a fast adaptive peak detector provided by attenuating and AC-coupling the first derivative signal to the positive supply to drive a peak detector with a fairly short attack time, such that its output is nearly settled on the first peak of the first derivative signal, but having a decay time long enough to keep the threshold level approximately constant across the label. Peaks are qualified if the peak in question differs in amplitude from the previously qualified peak by the offset amount. Thus, peaks are qualified if their modulation depth exceeds a threshold, regardless of the absolute level of the peaks (such qualification strategy is referred to as modulation depth gating).

대표청구항 ▼

1. A symbol reader, comprising:means for reading a symbol and generating an input signal thereby, said symbol having light and dark features, said input signal having an amplitude corresponding to the intensity of reflected light received from said symbol; means for conditioning said input signal, a

1. A symbol reader, comprising:means for reading a symbol and generating an input signal thereby, said symbol having light and dark features, said input signal having an amplitude corresponding to the intensity of reflected light received from said symbol; means for conditioning said input signal, and generating a conditioned input signal thereby; means for generating a replica signal of said conditioned input signal offset from said conditioned input signal by an offset value; and means for qualifying a peak in said conditioned input signal as indicative of a transition between a light feature and dark feature in said symbol based upon a modulation depth between the peak and an adjacent peak of opposite polarity, wherein the modulation depth for qualifying said peak is based upon said offset value.