초록 ▼

A bar code scanner employs a digitizer for the signal produced by a photodetector in response to light reflected from a bar code symbol. The digitizer uses a first derivative of the signal to detect peaks, and determines the amount of movement of the signal after each peak to see if a threshold amou

A bar code scanner employs a digitizer for the signal produced by a photodetector in response to light reflected from a bar code symbol. The digitizer uses a first derivative of the signal to detect peaks, and determines the amount of movement of the signal after each peak to see if a threshold amount of movement has occurred. A second derivative of the signal is used to detect inflection points, and when one occurs after the threshold amount of movement following a peak, a valid transition of the signal is signalled. These valid transitions are decoded to recover the bar code pattern. The threshold used is adjustable to optimize the digitizing for different types of bar code symbols and other conditions, or to provide a squelch function. Dynamic control of the threshold provides a varying response to the scanned bar code symbol. Zero-crossing detectors used with the first and second derivative circuits may also have variable thresholds.

대표청구항 ▼

A digitizer circuit for producing a digital output from an analog input, comprising: a) a first differentiator and first zero-crossing detector receiving said analog signal and producing a pulse output representing peaks of said analog signal; b) a sample-and-hold circuit receiving said analog signa

A digitizer circuit for producing a digital output from an analog input, comprising: a) a first differentiator and first zero-crossing detector receiving said analog signal and producing a pulse output representing peaks of said analog signal; b) a sample-and-hold circuit receiving said analog signal and said pulse output to produce a sample output corresponding to the magnitude of the last peak of said analog signal; c) a circuit for subtracting said sample output from said analog signal and comparing the result to a selected threshold to produce a representation of when said analog signal has changed by an amount of said threshold since the last peak of the analog signal; d) a second differentiator and second zero-crossing detector receiving said analog signal and producing a gating signal representing inflection points of said analog signal; and e) an output circuit generating an output signal having transitions when said representation is active and said gating signal is active.