BAR CODE DETECTING CIRCUITRY

摘要

A wide bandwidth slope detector (100) has a comparator (102) with first and second time constant circuits (104a, 104b) coupled to first and second inputs thereof (102a, 102b). Where one time constant is on the order of three times the other, the comparator will change state in response to the slopes of an input analog signal on line (104c) coupled to the time constant circuit. Feedback can be provided by a fixed resistor (109) or by a tracking circuit. A smoothing or clipping circuit can be used to pre-process the input analog signals to eliminate noise therefrom. A bar code reading system combines first and second clipping circuits to smooth the highs and lows of the input signal, coupled to a slope detector (100). The tracking circuit can be used to provide a symmetrical hysteresis characteristic.