Patent ID: 7280140
Filing Date: 2007-10-09
Classification: H04N

Abstract:
1. A method of operating an image sensor, the image sensor having an array of pixels arranged in rows and columns, each pixel having a source-follower transistor and a reset voltage line, the method comprising: reading on reset a first sample value from the reset voltage line equal to a reset voltage less a gate-source voltage of the source-follower transistor, and reading on release from reset a second sample value equal to the first sample value less the sum of a charge injection voltage, a reset coupling voltage, and a thermal noise voltage, the first and second sample values corresponding to a first set of pixel values and being read onto respective sample capacitors from the pixels row-by-row; differencing the first set of pixel values to create reset-related values which are equal to the sum of the charge injection voltage, the reset coupling voltage, and the thermal noise voltage, and storing the reset-related values in a frame buffer; reading after exposure a third sample value equal to the second sample value less an exposure induced voltage change, and reading during reset a fourth sample value equal to the first sample value, the third and fourth sample values corresponding to a second set of pixel values and being read onto respective sample capacitors from the pixels row-by-row, interleaved with the reading of the first set of pixel values, and differencing the second set of pixel values to create signal related values which are equal to the sum of the charge injection voltage, the reset coupling voltage, the thermal noise voltage, and the exposure induced voltage change; the reading of said first and second sets of pixel values for a given row being offset by a number of row periods selected to control exposure of the image sensor; and subtracting the respective reset-related value for each pixel from the respective signal-related value of each pixel to provide the exposure induced voltage change as an output signal for the pixel.