Charge-domain analog readout for an image sensor
AssigneePhotobit Corporation
InventorAlexander J. Krymski
Life of this patent
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Abstract
A CMOS imager includes an array of CMOS active pixel sensors and multiple column readout circuits each of which is associated with a respective column of sensors in the array and can perform correlated double sampling of values from a sensor in the respective column. Each column readout circuit also includes a crowbar switch which selectively can be enabled to force the stored values to an operational amplifier-based charge sensing circuit via a pair of buses. The operational amplifier-based charge sensing circuit, which includes a pair of switched integrators each of which is coupled to one of the buses, provides a differential output based on the values stored by a selected one of the column readout circuits.
Claims23
A charge-domain readout circuit comprising:
- a plurality of column readout circuits each of which can sample and store signal and reset values of an active pixel sensor, wherein each of the column readout circuits is associated with a respective column of sensors in an active pixel sensor array;
- a first bus for receiving the signal value stored by a selected one of the column readout circuits;
- a second bus for receiving a reset value stored by the selected one of the column readout circuits;
- and
- an operational amplifier-based charge sensing circuit, wherein the charge sensing circuit maintains a substantially constant voltage on the first and second buses and wherein the charge sensing circuit provides a differential output based on the values stored by the selected one of the column readout circuits.
A CMOS imager comprising:
- an array of CMOS active pixel sensors;
- a plurality of column readout circuits each of which can sample and store signal and reset values of an active pixel sensor, wherein each of the column readout circuits is associated with a respective column of sensors in the array;
- a first bus for receiving the signal value stored by a selected one of the column readout circuits;
- a second bus for receiving a reset value stored by the selected one of the column readout circuits;
- and
- an operational amplifier-based charge sensing circuit, wherein the charge sensing circuit maintains a substantially constant voltage on the first and second buses and wherein the charge sensing circuit provides a differential output based on the values stored by the selected one of the column readout circuits.
A CMOS imager comprising:
- an array of CMOS active pixel sensors;
- a plurality of column readout circuits each of which is associated with a respective column of sensors in the array and which can perform correlated double sampling of values from a sensor in the respective column;
- an operational amplifier-based charge sensing circuit including a pair of switched integrators for providing a differential output based on values stored by a selected one of the column readout circuits;
- a pair of buses each of which is coupled to a respective one of the switched integrators and each of which selectively can be coupled to an output of any one of the column readout circuits;
- wherein each column readout circuit further includes a crowbar switch which selectively can be enabled to force the values stored by the column readout circuit to one of the switched integrators via a corresponding one of the buses.
A method of reading out values from active pixel sensors in an array of sensors, the method comprising:
- selecting a row of sensors whose values are to be read out;
- storing correlated double sampled values for a plurality of sensors in the selected row, wherein the values for each sensor are stored by a respective readout circuit associated with a column in the array in which the sensor is located;
- sensing the stored values associated with the plurality of sensors in the selected row using an operational amplifier-based charge sensing circuit that is common to the readout circuits;
- and
- sequentially providing a differential output from the sensing circuit for each of the plurality of sensors in the selected row.
Dependencies are inferred from the claim text.