Photodetector quiescent current compensation method and apparatus
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United States of America Patent
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Jul 27, 1999
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N/A
app pub date -
Sep 5, 1997
filing date -
Sep 5, 1996
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Abstract
In a photodetector amplifier scheme, the invention compensates for variations in photodetector quiescent current by sampling the amplifier output and subtracting a controllable current from the input to the amplifier. When a chopper or other modulator is used on the optical signal, the samples are taken periodically during the chopping cycle. This sampled signal is processed by a combination of gain and low pass filtering. The result of this processing controls a current source which subtracts a significant fraction of the average quiescent current from the total detector current. In a typical application, the amplifier is of the resettable current integrator type. In this case, the invention makes it possible to use smaller integration capacitors resulting in larger signals than if the quiescent current were not reduced by the operation of the invention. The gain, frequency response, and range of compensated quiescent currents and can be altered by changing timing signals. Implementation is directed toward using components which take up little area when fabricated as an integrated circuit.
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