METHOD AND DEVICE FOR DIGITIZING AND PROCESSING ANALOG BAR CODE SIGNAL

PROBLEM TO BE SOLVED: To provide a bar code processing system which can perform flexible operation with use of variable filtering characteristic, variable threshold, etc., and also can perform the signal processing with no phase distortion. SOLUTION: The amplification, filtering, differentiation and A/D conversion are performed to output signals of a photodetector to acquire the digital 1st- order differential signals 104 and 106. These signals 104 and 106 undergo Gaussian filtering 110 and differentiation 112 for acquiring the 2nd-order differential signals. Then it is regarded that the negative and positive transitions are carried out when the 2nd-order differentiation has zero point crossing before and after the positive and negative peaks of 1st-order differential signals exceed the positive and negative thresholds 114 and 116 respectively.