Patent ID: 7128264
Filing Date: 2006-10-31
Classification: G06K

Abstract:
1. An arrangement for improving performance of an electro-optical reader for reading indicia across a range of ambient light, comprising: a) a sensor for collecting light from the indicia, with concomitant collection of ambient light, to generate a sensor signal proportional to collected light intensity; b) an amplifier having an amplifier input connected to the sensor, and operative for amplifying the sensor signal to generate at an amplifier output an output amplified signal proportional to the collected light intensity; c) a resistor connected across the amplifier input and the amplifier output, for imparting to the amplifier a high gain sufficient to drive the amplifier into saturation in ambient light of high intensity; d) an offset adjustment circuit connected across the amplifier input and the amplifier output, for preventing the saturation, without reducing the high gain, of the amplifier in high intensity ambient light, the adjustment circuit including a field effect transistor (FET) having a gate terminal connected to the amplifier output, a source terminal connected to the amplifier input, and a drain terminal connected to a voltage source, the FET serving as a variable resistor having a variable resistance controlled by, and inversely proportional to, the output amplified signal, the resistance being decreased at the amplifier input when the output amplified signal is increased in high intensity ambient light to drive the amplifier away from saturation; and e) a filter circuit connected to the drain terminal of the FET, for filtering out high frequency noise from the voltage source from reaching the amplifier input.