Omnivision Technologies, Inc.

Kimble Dong

Datong Chen

Xinping James He

Hongli Yang

In a MOS imaging array, dead pixels may occur in that if the cell of the pixel has a defect in its PN junction, it may generate current leakage paths, thus causing the cell site to appear as a white spot in the image signal. The number of dead pixels on a CMOS image sensor is dependent on the process quality used for forming the image sensor. The present invention corrects for dead pixels with circuitry that may be fabricated on a single integrated MOS chip. When the MOS imaging device is first turned on, the pixel signals from the cell array are read out and a dead pixel determination method is used to determine dead pixels. A digital referencing scheme is used such that when a dead pixel is located, its digital location is stored in a designated storage area. Then normal data image signal processing begins, with the location of each pixel that is being read out being monitored. When a pixel with a location that corresponds to the stored location for a dead pixel is read out, the signal processing circuitry compensates for the pixel signal rather than providing it as part of the normal image signal. One method by which the signal processing circuitry may compensate for the dead pixel signal is to repeat the signal from the pixel that was read out immediately prior to the dead pixel.

On-chip dead pixel correction in a CMOS imaging sensor

Auto black expansion circuitry with a simplified digital control system. According to the system, a count of the number of pixels that fall below desired black level and mid-level ranges are maintained. The pixel counts are obtained by comparators that receive the adjusted signals at one input and the desired comparator signal levels at the other input. At the end of a field, when the pixel counts are complete, adjustment to the auto black expansion may be made for the following field. Once the pixel count at the end of a given field indicates that the auto black expansion has achieved the desired level, the automatic gain control may be adjusted for the following field. The method uses single comparators and single counters to obtain the pixel counts. The digital controller outputs an 8-bit control signal to adjust the analog auto black expansion and automatic gain control circuits to precise levels.

Auto black expansion method and apparatus for an image sensor

A CMOS camera image sensor that may be combined with additional CMOS camera image sensors to form a multiple-camera security monitoring system. Each CMOS image sensor includes phase-locked loop circuitry. The phase-locked loop circuitry receives a reference input signal and in response thereto synchronizes the video output of the CMOS image sensor to the reference input signal. In one configuration, one of the CMOS image sensors provides the reference signal, while in another configuration, the reference input signal may come from an external circuit. Each CMOS image sensor also includes state selection circuitry. The state selection circuitry allows the video output from the CMOS image sensor to be displayed on,, or all of a display. Thus, the video signals from multiple CMOS image sensors may be displayed on a video monitor simultaneously.

Analog video monitoring system using a plurality of phase locked CMOS image sensors

The present invention is directed to a method and apparatus for reading out signals from a MOS image sensor. The invention allows for a relatively high fixed pattern noise canceling rate, even in low light environments. The invention includes a digital processing structure for processing the signals from a pixel array. The pixel array includes a reference row that is formed by being covered by a light shield or black layer to cover the pixels of the reference row from light. The signals from the reference row are converted to digital values and stored in fixed pattern noise storage circuitry. Then, as each of the remaining rows of the pixel array are read out, they are converted to digital values and the digital reference row signals are subtracted therefrom to produce data image signals that are relatively free of fixed pattern noise. Thus, the fixed pattern noise canceling rate is made to depend on the precision of an analog-to-digital converter, rather than the process variations of an analog subtraction circuit.

Method and apparatus for digital column fixed pattern noise canceling for a CMOS image sensor

In a MOS imaging array, it is important to control the exposure time of the array to incident light. For varying changes in ambient light, the exposure time of the array must be changed. The present invention describes a method for controlling the exposure time of the imaging array. Each of the intensities of the pixels in a frame are analyzed to provide an indication of the number of pixels having an intensity above and below predetermined thresholds, NW and NB, respectively. If NW is above a predetermined threshold, KW, then an adjustment in the exposure time may be made. If not, then no adjustment is made.

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Sunnyvale, CA, United States of America

Kimble Dong