Patent attributes
Capacitance on a readout line is varied while receiving a signal, from a light sensing pixel or other sensing element through the line. Capacitance can be varied in accordance with a readout characteristic of the pixel, such as color sensed, conversion efficiency, or readout signal range. For example, a CMOS color image sensing array with pixels in an RGB Bayer pattern can include, for each column, a variable capacitance component with parallel switchable capacitors for signal sampling and readout sampling. The capacitors can all have equal values, or can be scaled in a binary format. The variable capacitance component can also include a constant capacitor. A controller can switch the capacitors to obtain capacitances that provide color equalization, and can use light level as well as pixel color for fine tuned color equalization. Sampled values from the capacitances can be provided in sequence to a readout amplifier at the beginning of a readout path to maintain signal-to-noise ratio. The readout amplifier's gain can depend on its input capacitance, which is determined by the switched capacitors to obtain color equalized output. In addition, the readout amplifier can block the effect of parasitic capacitance from column select switches. A second amplifier can perform further color equalization through variable gain. After an array is constructed, capacitor selection data can be obtained for each color and light level and used to program the controller.
