Controlling the range and resolution of offset correction applied to the output of a charge coupled device
AssigneeTexas Instruments Incorporated
InventorsSubhashish Mukherjee, Suhas R. Kulhalli
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Abstract
An offset correction circuit which enables a designer to control the correction range irrespective of the amplification sought to be achieved to the image component of the input signal. The offset correction further enables the designer to perform offset correction to a low resolution. Both range and resolution can potentially be attained using only two stages thereby minimizing power consumption and also minimizing introduction of any undesirable components.
Claims10
A processing circuit for processing the output of a charge coupled device (CCD), said processing circuit comprising a plurality of stages, a first stage contained in said plurality of stages comprising:
- a first digital to analog converter (DAC) generating a first voltage in response to receiving a first digital value;
- a correlation double sampler (CDS) receiving an input signal via a first sampling capacitor, wherein said input signal comprises said output of said CCD;
- a first feedback capacitor coupled in parallel to said CDS;
- and
- a first DAC capacitor coupled to said first DAC, said first DAC capacitor being charged by said first voltage, a second terminal of said first DAC capacitor being coupled to said first feedback capacitor,
- wherein the output of said CDS contains an amplified component of said input signal less an amplified component of said first voltage,
- wherein the ratio of capacitances of said first sampling capacitor and said first DAC capacitor is maintained a constant.
A device for capturing an image in a digital form, said device comprising:
- a charge coupled device (CCD) containing a plurality of pixels, wherein each of said plurality of pixels stores a charge proportionate to the intensity of incident light and the time of incidence of said light on the pixel, said plurality of pixels further containing a plurality of black pixels and a plurality of active pixels, wherein said plurality of black pixels are not exposed to said light and said plurality of active pixels are exposed to said light;
- a lens focusing light from said image on said plurality of active pixels;
- an analog front end (AFE) comprising a plurality of stages, a first stage contained in said plurality of stages comprising:
- a first digital to analog converter (DAC) generating a first voltage in response to receiving a first digital value;
- a correlation double sampler (CDS) receiving an input signal via a first sampling capacitor, wherein said input signal comprises said output of said CCD;
- a first feedback capacitor coupled in parallel to said CDS;
- and
- a first DAC capacitor coupled to said first DAC, said first DAC capacitor being charged by said first voltage, a second terminal of said first DAC capacitor being coupled to said first feedback capacitor,
- wherein the output of said CDS contains an amplified component of said input signal less an amplified component of said first voltage,
- wherein the ratio of capacitances of said first sampling capacitor and said first DAC capacitor is maintained a constant.
Dependencies are inferred from the claim text.