A switched-capacitor variable gain amplifier for CCD image sensor interface system

A new topology for a switched-capacitor variable gain amplifier (SC-VGA) is proposed and implemented in an analog-digital interface system for CCD image sensor. The SC-VGA exploits a positive feedback which leads to simpler circuit implementation, lower power consumption and reduced kT/C noise, compared to the conventional one. The gain, controlled by 8-bit digital signal varies from 0 dB to 24 dB with 0.094-dB step. The measured gain of the SC-VGA shows monotonicity over the whole range of the gain (DNL < 1). Fabricated in 0.25-um CMOS process with MIM capacitors, the VGA occupies 0.25 mm²and dissipates 5 mW at 8 MHz with a supply voltage of 2.8 V.