Digitizer signal processing circuit for a bar code

Details Digitizer signal processing circuit for a bar code Digitizer signal processing circuit for a bar code

1990-12-10

1992-04-07

Trafton, David

Registers

Coded record sensors

Error checking

235462, G06K 500

Patent

active

051030802

ABSTRACT:
A signal processor digitizer circuit is disclosed for reading bar code symbols by detecting the times at which a scanning light spot moves from a space onto a bar code symbol or moved from a bar code signal onto a space. The novel signal processor digitizer circuit obtains all of its information for digitizing, false transition rejections, and margin cleaning from the first derivative of an analog signal produced by a photodetector detecting the scanning light spot. The original analog signal and a second derivative signal are not used which results in several advantages. Since the original analog signal is not needed, the signal differentiator circuit is placed at a very early stage in an amplifier string. Additional amplification stages can then be used to amplify the differentiated signal until it is large enough to be digitized. This results in two benefits. The differentiator circuit effectively filters out the effects of ambient light that could otherwise cause the last amplifier stage to saturate, thereby improving ambient light immunity. It also eliminates the transient response of other forms of high pass filtering or AC coupling that are ordinarily required to improve ambient light immunity or to eliminate the build-up of large offset voltages associated with DC coupled amplifiers.

REFERENCES:
patent: 3751636 (1973-08-01), Coles
patent: 3969612 (1976-07-01), McJohnson
patent: 4000397 (1976-12-01), Hebert et al.

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