Registers – Coded record sensors – Particular sensor structure
Patent
1997-01-24
1999-06-22
Hajec, Donald
Registers
Coded record sensors
Particular sensor structure
235454, 23546229, 23547202, G06K 710, G06K 712
Patent
active
059144785
ABSTRACT:
A bar code scanner and method of operation includes intelligent AGC to maintain a constant signal level while not delaying a decoder in identifying indicia when noise or specular reflection occurs during a scan period. A light detector receives light and generates an analog signal representative of the scanned indicia. The analog signal is provided to a pre-amplifier which provides a first output to a digital voltage controlled amplifier and a second output to an intelligent AGC circuit which controls the amplifier. The amplifier output is provided through filters to a decoder for detecting the indicia scanned by the light source. The intelligent AGC circuit includes a first path for determining the occurrence of a specular or glitch noise in the analog signal. A second path derives the overall signal strength using first derivative of the analog signal which is immune to low frequency noise and ambient light. By taking the mean and variance of the signal strength, a programmable processor is able to set the gain for the digital voltage control amplifier in the next scan. A short, predetermined time before a Start-Of-Scan signal, the processor calculates the signal strength. Since the signal strength does not change rapidly between scans, the gain of the next scan will be based on the signal scan. A fixed signal gain throughout the entire scan prevents gain modulation at frequencies lower than the time constant of the signal strength indicator, and is more tolerant to noise from ambient light and other low frequency noise sources.
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Cyr Daniel St.
Hajec Donald
Symbol Technologies Inc.
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