Patent ID: 6572018
Filing Date: 2003-06-03
Classification: G02B,G06K,G07G

Abstract:
A scan data signal processor for receiving and processing an analog scan data signal in response to the scanning of a bar code symbol by a laser scanning beam, said scan data signal processor comprising:a first derivative signal generation circuit for deriving a first derivative signal from said analog scan data signal, said first derivative signal generation circuit including a plurality of focal-zone controlled first derivative signal pass-band filters and amplifiers integrated therewith; wherein said first derivative signal generation circuit further includes a first scan-range controlled first derivative signal pass-band filter and amplifier arranged along the first channel (A) of the circuit corresponding to a first scan range of the system, and a second scan-range controlled first derivative signal pass-band filter and amplifier arranged along the second channel (B) of the circuit corresponding to a second scan range of the system; a second derivative signal generation circuit for deriving a second derivative signal from said analog scan data signal, said second derivative signal generation circuit including a plurality of focal-zone controlled second derivative signal pass-band filters and amplifiers integrated therewith; a first derivative signal threshold-level generation circuit for generating upper and lower first derivative signal threshold levels for use in determining when said first derivative signal has attained its peak positive and negative values during signal processing operations; a binary A/D signal conversion circuit including a second derivative zero-crossing detector for detecting zero-crossings in said second derivative signal, a pair of first derivative signal comparators for comparing said first derivative signal with said upper and lower first derivative signal threshold levels so as to detect positive and negative peak values in said first derivative signal, and in response thereto, producing gating signals at the time of occurrence of said detected positive and negative peak values, a digital output signal generating circuit for receiving detected second derivative zero-crossings provided thereto as input, and producing a digital output signal for subsequent signal processing, and a second derivative zero-crossing gating circuit, responsive to said gating signals, for gating to said digital output signal generating circuit, only detected second derivative zero-crossings occurring between alternating positive and negative peaks in said first derivative signal detected by said pair of first derivative signal comparators; and a bar code element detection circuit for activating and deactivating said second derivative signal zero-crossing detection circuit in response to detecting the absence and presence of bar code element data in said analog scan data signal.