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Noise-Lockout Circuit for Bar Code Scanner

IP.com Disclosure Number: IPCOM000046487D
Original Publication Date: 1983-Jul-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 47K

Publishing Venue

IBM

Related People

Broockman, EC: AUTHOR [+2]

Abstract

This article describes an improved lockout circuit for eliminating noise voltage perturbations in an analog signal generated by a bar code scanner. The lockout circuit has a generally C-shaped characteristic. Greater noise-suppressing voltages are provided for strong "white" signals and for strong "black" signals. A lower noise-suppressing or lockout signal is generated for intermediate signals.

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Noise-Lockout Circuit for Bar Code Scanner

This article describes an improved lockout circuit for eliminating noise voltage perturbations in an analog signal generated by a bar code scanner. The lockout circuit has a generally C-shaped characteristic. Greater noise- suppressing voltages are provided for strong "white" signals and for strong "black" signals. A lower noise-suppressing or lockout signal is generated for intermediate signals.

Referring to Fig. 1, a bar code scanner typically includes a white follower circuit 10 which detects and holds the maximum voltage in the signal produced by a bar code scanner. A typical circuit also includes a black follower circuit 12 for sampling and holding a minimum voltage in the signal provided by the scanner. The maximum (white peak) voltage (VWF) and the minimum (black peak) voltage (VBF) are applied to a threshold circuit 14 which generates the threshold voltage applied to one input of a comparator amplifier 16. The input signal is applied directly to the second input of the comparator amplifier 16. If the input signal is greater than the established threshold, the output of comparator amplifier 16 has a "one" binary value. If the input is less than the threshold, the output of comparator amplifier 16 has a "zero" binary value.

Ideally, a scanner input signal is a clean, bilevel signal. In practice, the input signal contains a high frequency noise or jitter component which may be severe enough to cause the output of co...