CDS circuit with 0 to 18 dB, 9-bit VGA functionality

For processing charge coupled device (CCD) signals, a correlated double sampling (CDS) circuit must be used to eliminate noise. Usually, the amplitude of the CCD signals is uncertain, either too small or too large, hence a variable-gain amplifier (VGA) is also needed to amplify the CCD signals. Traditionally, the CDS and the VGA are separated, each of which consumes much energy and large area. If only the CDS and the VGA would be combined together, much energy and area could be saved. Hence, a CDS with VGA functionality is proposed to achieve this goal. Besides, the VGA functionality provides a gain range of 0-18 dB, programmable with a 9 bit resolution, which is far better than the traditional ones. Also, the VGA gain curve follows a linear-in-dB characteristic, hence the VGA functionality has rather good linearity. Finally, the VGA gain curve demonstrates the good performance of the VGA functionality.