CMOS imager with wide dynamic range pixel

A sensor array comprising:

• a plurality of pixel cells, each pixel cell comprising:
• a radiation sensor;
• a reset switch coupled to the output of the radiation sensor;
• a sample and hold switch coupled to the reset switch;
• a clear switch coupled to the sample and hold switch;
• and
• a cell readout portion coupled to the clear switch, the readout portion comprising:
• a readout source-follower transistor coupled to the clear switch;
• a row select transistor coupled between the source-follower transistor and a supply voltage;
• and
• a column output line coupled to the source-follower transistor.

A method of operating a pixel cell in a sensor, the pixel cell having a radiation sensor coupled to a sample and hold switch, a clear switch coupled to the sample and hold switch, a row select switch coupled to the clear switch, a readout source-follower transistor coupled to the row select switch and having a gate coupled to the clear switch, and an output node coupled to the readout source-follower transistor, the method comprising:

• clearing the voltage on the output node;
• clearing the voltage on the gate of the readout source-follower transistor;
• increasing the voltage on the gate of the readout source-follower transistor in proportion to a photon-generated charge by the radiation sensor;
• and
• providing gain for increasing the voltage on the output node.

A method of operating a pixel cell in a sensor, the pixel cell having a radiation sensor coupled to a sample and hold switch, a clear switch coupled to the sample and hold switch, a row select switch coupled to the clear switch, a readout source-follower transistor coupled to the row select switch and having a gate coupled to the clear switch, and an output node coupled to the readout source-follower transistor, the method comprising:

• clearing the voltage on the output node;
• clearing the voltage on the gate of the readout source-follower transistor;
• increasing the voltage on the gate of the readout source-follower transistor in proportion to a photon-generated charge by the radiation sensor;
• increasing the voltage on the output node;
• and
• providing a gain greater than one to increase the voltage on the output node.