Active pixel image sensor with reduced readout delay
AssigneeAptina Imaging Corporation
InventorRobert Johansson
Life of this patent
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Abstract
Methods, devices, and systems for improving (i.e., reducing) the settling time of an output signal read from a photo sensor and improving the PSRR of the supply voltage are disclosed, wherein a detected charge in a pixel is converted to a voltage and drives a source follower transistor. A bias transistor is coupled in series with the source follower transistor and includes an output therebetween. The bias transistor is driven to source a reduced current when the voltage results from a readout of a reset value of the pixel and the bias transistor is driven to source an enhanced current when the voltage results from a readout of a sensed signal value.
Claims30
A method of reading out a signal to an output from a pixel in an active pixel sensor (APS), comprising:
- converting a detected charge in the pixel into a voltage;
- driving a source follower transistor in response to the voltage;
- driving a bias transistor to source a first current when the voltage results from a readout of a reset value of the pixel;
- and
- driving the bias transistor to source a second current when the voltage results from a readout of a sensed signal value, the bias transistor coupled in series with the source follower transistor and having the output therebetween, wherein the second current is larger than the first current.
A readout circuit for an active pixel sensor (APS) circuit, comprising:
- a bias transistor configured for coupling in a source follower configuration with an output transistor of a pixel and having an output therebetween, the output transistor responsive to a voltage generated by a photo sensor of the pixel;
- and
- a minimum current selector coupled to a gate of the bias transistor and configured to drive the bias transistor to source a first current when the voltage results from a readout of a reset value and further configured to drive the bias transistor to source a second current when the voltage results from a readout of a sensed signal value of one of the plurality of pixels, wherein the second current is larger than the first current.
An active pixel sensor (APS) circuit, comprising:
- a plurality of pixels in at least one column of an array, each of the plurality of pixels including a photo sensor, an output transistor and a row select transistor, the output transistor responsive to a voltage generated by the photo sensor;
- and
- a readout circuit connected to at least one column of the plurality of pixels, the readout circuit including:
- a bias transistor connected in a source follower arrangement with the output transistor and the row select transistor, the bias transistor coupled in series with the output transistor and having the output therebetween;
- and
- a minimum current selector coupled to drive the bias transistor, the minimum current selector configured to drive the bias transistor to source a first current when the voltage results from a readout of a reset value and further configured to drive the bias transistor to source a second current when the voltage results from a readout of a sensed signal value of one of the plurality of pixels, wherein the second current is larger than the first current.
An imaging device, comprising:
- an active pixel sensor (APS) circuit including a plurality of pixels arranged in a plurality of rows and a plurality of columns, the active pixel sensor (APS) circuit including a readout circuit connected to each of the plurality of columns of the plurality of pixels and further configured to generate an output signal representative of a signal stored in one of the plurality of pixels wherein the readout circuit is driven to source the output signal from a first current when a reset value is read from one of the plurality of pixels and the readout circuit is driven to source the output signal from a second current when a sensed signal value is read from one of the plurality of pixels and wherein the second current is larger than the first current;
- a row decoder operably coupled to the active pixel sensor (APS) circuit and configured for selecting each row of the plurality of rows;
- and
- a column decoder operably coupled to the active pixel sensor (APS) circuit and configured for receiving in parallel, at least one signal from each pixel of a selected row.
An electronic system, comprising:
- a processor-based device;
- and
- an imaging device coupled to the processor-based device, the imaging device configured to read out a signal to an output from a pixel in an active pixel sensor (APS) circuit, the imaging device including a source follower circuit comprised of a source follower transistor and a bias transistor wherein a detected charge in the pixel drives the source follower transistor and the bias transistor is either driven to source a first current when the voltage results from a readout of a reset value of the pixel or driven to source a second current when the voltage results from a readout of a sensed signal value, the bias transistor and the source follower transistor include the output therebetween, wherein the second current is larger than the first current.
Dependencies are inferred from the claim text.