Patent ID: 7891570
Filing Date: 2011-02-22
Classification: G06K

Abstract:
1. An arrangement for improving performance of a sensor operative for collecting light from a target to generate a data signal in a presence of ambient light, comprising: a sample and hold circuit for operating the photodiode during a sampling time period in which the sensor only collects the ambient light to generate an ambient electrical current signal, and during a holding time period in which the sensor collects both the ambient light and the light from the target to generate a composite electrical current signal comprised of the ambient signal and the data signal; and a subtracting circuit for subtracting the ambient signal from the composite signal to produce the data signal as an output, the subtracting circuit including a transimpedance amplifier that generates the data signal at the output as an electrical voltage signal, the transimpedance amplifier having a non-inverting input to which the composite signal is applied, and an inverting input to which the ambient signal is applied, wherein the sample and hold circuit includes a switch for switching between the sampling and holding time periods, and a pair of sample and hold transistors connected to the switch and the transimpedance amplifier, one sample and hold transistor being operative for conducting the composite signal to the non-inverting input, and the other sample and hold transistor being operative for conducting the ambient signal to the inverting input.