초록 ▼

An electronic edge detection system for use in a barcode scanning system utilizing second derivative signal processing wherein the temporal offset between the first and second derivative signals is eliminated so as to enable edge detection for signal levels down to the noise level of an input signal

An electronic edge detection system for use in a barcode scanning system utilizing second derivative signal processing wherein the temporal offset between the first and second derivative signals is eliminated so as to enable edge detection for signal levels down to the noise level of an input signal. In a preferred embodiment, an overall filter network receives an input signal and comprises two real poles as the last elements of two parallel output channels. The first output channel terminates with a low pass filter and produces the first derivative of the input signal. The second output channel terminates with a high pass filter and produces the second derivative of the input signal. Implementing the second differentiator as one real pole of the overall edge detection system filter polynomial and placing the poles of the two output filters at the same frequency eliminates the temporal offset. Substantially constant and equal group delay over the system passband for both first and second derivative signals is also provided.

대표청구항 ▼

[ What is claimed is:] [1.] In a barcode scanner system, a second derivative signal processor for detecting edges representing bar and space transitions in an input signal, said second derivative signal processor comprising an overall filter polynomial having even order which further comprises:a fir

[ What is claimed is:] [1.] In a barcode scanner system, a second derivative signal processor for detecting edges representing bar and space transitions in an input signal, said second derivative signal processor comprising an overall filter polynomial having even order which further comprises:a first filter receiving the input signal and providing a filtered signal;a first output channel terminating with a first filter having a complex pole pair with a first cutoff frequency and damping ratio, said first output channel receiving the filtered signal and producing the first derivative of the input signal; and,a second output channel parallel to said first output channel and terminating with a second filter having a complex pole pair with the first cutoff frequency and damping ratio; said second output channel receiving the filtered signal and producing the second derivative of the input signal,wherein the first filter is a low pass filter of second order and the second filter is a high pass filter of second order, and wherein the cutoff frequency and damping ratio of the low pass filter and the high pass filter are substantially equal.