High speed sampling of signals in active pixel sensors using buffer circuitry
First Claim
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.
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Accused Products
Abstract
Techniques are disclosed for enhancing the speed at which pixel levels are read out and sampled for processing. A method of processing pixel levels includes clamping a pixel readout line to a voltage level less than a voltage corresponding to a signal sensed by an n-MOS pixel. Subsequently, the pixel readout line is coupled to an output of an n-MOS source-follower and the pixel signal is read out onto the pixel readout line through the n-MOS source-follower. The pixel signal that was read out is passed through a p-MOS source-follower to a processing circuit. Before passing the pixel signal through the p-MOS source-follower to the processing circuit, a capacitive storage node in the processing circuit is clamped to a voltage greater than a signal at an input to the p-MOS source-follower. Subsequently, an output of the p-MOS source-follower is coupled to the processing circuit, and a signal corresponding to the pixel signal is stored by the processing circuit. Similar techniques are provided for reading out and sampling p-MOS pixels.
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Citations
12 Claims
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1. An imager comprising:
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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. - View Dependent Claims (2, 3, 4, 5, 6)
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7. An imager comprising:
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a pixel readout line; an active pixel sensor including a p-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 an n-MOS source-follower and a second n-MOS transistor connected to a source of the n-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 greater than a voltage corresponding to a signal sensed by the sensor, and subsequently to cause the sensor signal to be read out through the p-MOS source-follower to the pixel readout line and to be passed to the processing circuit through the n-MOS source-follower. - View Dependent Claims (8, 9, 10, 11, 12)
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Specification