Patent ID: 8362842
Filing Date: 2013-01-29
Classification: H03F

Abstract:
1. A circuit for controlling op-amp offset in a photodetector application comprising: a photodetector configured to produce a current in response to detecting light; an op-amp having an output terminal, a positive trim terminal, a negative trim terminal, and first and second input terminals, wherein at least one of the first and second input terminals is coupled to the photodetector and wherein an output produced at the output terminal of the op-amp when operational is based on the current produced by the photodetector; a variable trimming circuit configured to receive a current I, wherein the variable trimming circuit includes a plurality of current branches each configured to provide a portion of the current I to an output node of the variable trimming circuit; a test node; and a selector having an input portion coupled to the output node and an output portion that can be coupled to both the test node and a transmission node, wherein the transmission node is configured to couple to one of the positive and negative trim terminals, and wherein the selector is configurable to direct current received from the output node to one of the test node and the transmission node.