Digital automatic gain control circuit for image system

A digital automatic gain control circuit for a complementary metal-oxide semiconductor (CMOS) image sensor having associated therewith an analog-to digital (A/D) converter for converting analog electrical signals from the CMOS image sensor to corresponding digital codes, said circuit comprising:

• determining means for determining minimum and maximum electrical signal values from the digital codes of the A/D converter for each frame of image;
• a filter coupled to said determining means for dampening instantaneous changes of the minimum and maximum values by filtering to provide filtered minimum and maximum values;
• and
• a digital-to-analog (D/A) converter coupled to said filter for generating minimum and maximum analog reference voltages corresponding to the respective minimum and maximum filtered values, said reference voltages being applied to the A/D converter to control associated amplitudes of the digital codes provided thereby.

A method for performing digital automatic gain control for a complementary metal-oxide semiconductor (CMOS) image sensor having associated therewith an analog-to digital (A/D) converter for converting analog electrical signals from the CMOS image sensor to corresponding digital codes, said method comprising:

• determining minimum and maximum electrical signal values from the digital codes of the A/D converter for each frame of image;
• dampening instantaneous changes of the minimum and maximum values to provide filtered minimum and maximum values;
• generating minimum and maximum analog reference voltages corresponding to the respective minimum and maximum filtered values;
• and
• applying said reference voltages to the A/D converter to control values of the digital codes provided thereby.