Patent ID: 7821557
Filing Date: 2010-10-26
Classification: H04N

Abstract:
1. An imager comprising: a pixel readout line; an active pixel sensor including an n-MOS source-follower through which signals sensed by the sensor can be read out to the pixel readout line, a first switch that can be enabled to read out signals from the sensor, and a reset switch; a buffer circuit coupled to the pixel readout line including a p-MOS source-follower and a second p-MOS transistor configured as a current sink connected to a source of the p-MOS source-follower; a processing circuit including sample and hold circuitry having an input coupled to an output of the buffer circuit such that signals being sampled and held by the processing circuit are first buffered by the buffer circuit; and a controller configured to provide control signals to cause the pixel readout line to be clamped to a voltage level less than a voltage corresponding to a signal sensed by the sensor, and subsequently to cause the sensor signal to be read out through the n-MOS source-follower to the pixel readout line and to be passed to the processing circuit through the p-MOS source-follower.