Self-calibrating anti-blooming circuit for CMOS image sensor having a spillover protection performance in response to a spillover condition

A method for preventing blooming in an image sensor array comprising the steps of:

• providing a plurality of imager cells, each including a reset transistor and a well;
• each imager cell being operable to selectively provide an output signal indicative of the amount of electrons stored in its well;
• providing a master pixel circuit having an output and having operational characteristics similar to those of one or more of the imager cells;
• providing a reference circuit having an output approximately representative of a maximum output of said imager cells;
• providing an amplifier having as a first input the output of said master pixel circuit, having as a second input the output of said reference circuit, and having an output coupled to an input of said master pixel circuit;
• and
• applying a voltage selectively to the reset transistors of at least some of said imager cells by using the amplifier output.

A method for preventing a spillover condition in a photosensitive imager containing a plurality of image cells comprising the steps of:

• producing, during an integration time, charge carriers at said imager cells in response to excitation radiation reaching respective imager cells;
• during said integration time, storing said charge carriers produced at said imager cell up to approximately a certain number and substantially removing from said imager cell any additional charge carriers produced in excess of that approximate number;
• and
• wherein the removal is accomplished by shunting said additional charge carriers through a reset transistor coupled to said imager cell, said reset transistor being selectively biased with a reset bias voltage determined in part by an output of a servo loop circuit that compares an output of a master pixel circuit having operating characteristics similar to said imager cells and a reference voltage approximately representative of the maximum linear output of said imager cells.