Abstract: The active pixel includes a photodiode, a reset transistor, and a pixel output transistor. The photodiode is substantially covered with a protective structure, thus protecting the entire surface of the photodiode from damage. This substantially eliminates potential leakage current sources, which result in dark current. The protective structure has a photodiode contact formed therein to electrically connect the photodiode to the pixel output transistor.

Abstract: A method of sub sampling signals from an image sensor having a pixel array. The pixel array has a plurality of columns, each column having a column readout circuit. The method comprises averaging the signals output by a plurality of adjacent column readout circuits and outputting the averaged signal to an output bus.

Abstract: The image sensor includes a first group and a second group of column readout circuits for reading out pixel signals from said pixels. The total number of column readout circuits in each group is substantially less than the number of columns in the image sensor pixel array. Further included is a multiplexer bus system having selection switches for selectively switching pixel signals from a block of pixels in a column as input into the first group of column readout circuits. The multiplexer bus system also selectively switches pixel signals from another block of pixels in a column as input into a second group of column readout circuits. However, when the first group of column readout circuits is reading and storing said pixel signals, the second group of column readout circuits is transferring out the processed signals. Thus, the first and second groups work alternately.

Abstract: The present invention is directed to an analog delay line for a color CMOS image sensor which is compatible with MOS fabrication technology. The invention allows for the simultaneous reading of pixel signals from two rows of pixels so that combinations of signals from pixels in different rows may be obtained. The delay line includes a set of storage capacitors on which the pixel signals are stored, and a means for writing the signals from the pixels onto the capacitors in sequence. The stored analog pixel signals may then be read out from the delay line at the appropriate time so that they may be combined with pixel signals from adjacent pixels in different rows. In one embodiment, two delay lines are used, so that pixel signals from a current row can be written into one delay line, while the pixel signals from a previous row are being read out from the other delay line. In another embodiment, a single delay line is used in combination with a single pixel delay circuit.

Abstract: A column readout circuit for a CMOS image sensor is disclosed. The circuit uses MOS capacitors to store a photo signal and a reset signal. Correlated double sampling is used to eliminate fixed pattern noise and 1/f noise. Additionally, the signals are coupled through the capacitors using AC coupling. In this manner, a readout circuit compatible with conventional CMOS logic processes can be manufactured.

Abstract: A method of reading out a pixel signal from a pixel is disclosed. The method comprises first capturing a first black reference signal from the pixel prior to the pixel starting an integration period. Next, after completion of the integration period, a pixel signal is captured. Next, a second black reference signal is captured following completion of the integration period. Finally, the first black reference signal, second black reference signal, and pixel signal is output.

Abstract: In the field of imaging, various components may contribute to a loss in resolution at higher spatial frequencies, both horizontally and vertically. Higher spatial frequencies may occur at the edge of an image, where there may be a large transition in the signal output between adjacent pixels. To compensate, an edge enhancement method that produces overshoots in the transitions of the video image signal is used. One of the problems with the edge enhancement method is that the noise in the input signal may not be adequately suppressed. To suppress the background noise in the video image signal while still performing the desired edge enhancement function, biasing circuitry may be used to suppress the smaller transitions in the input signal. In particular, the biasing circuitry may be placed in the signal path between the output of a first delay line and the noninverting inputs of two of the signal amplifiers.

Abstract: An analog median filter for rejecting isolated impulse noise while preserving signal step changes in image processing. The analog median filter includes a number of transconductance amplifiers with additional CMOS inverters coupled to the outputs of the amplifiers. The outputs of the inverters are coupled together in a feedback loop configuration with the amplifiers. The CMOS inverters act as a type of additional current source for the amplifiers, so as to sharpen the corners of the transfer curve at various current levels. The low gain of the inverters improve the stability of the output range. Because inverters are used, the feedback loop is coupled to the noninverting inputs of the amplifiers, while the input signals are coupled to the inverting inputs of the amplifiers.

Abstract: An image acquisition and processing system that can eliminate or reduce the effects of offset voltage and threshold voltage is disclosed. The system contains a plurality of operational amplifiers each is used in an integrator. Each of the operational amplifiers has an offset voltage. The output of the integrator is sampled twice by a dual sampling circuit, one when connected to a photo-sensor and the other when not connected to the photo-sensor. The difference between the two samplings cancels out the effect of the offset voltage. The system also contains a plurality of transistors used as source follower. Each of the transistors is connected to an output terminal of the dual sampling circuit. These transistors have different threshold voltages. The output of a transistor is sampled. A predetermined voltage is then applied to the transistor and the output is again sampled. The difference between these two samples cancels out the effect of the threshold voltage.