A CMOS front-end for CCD cameras

Most modern camcorders use digital processing exclusively in the signal path for better performance even though image information from the CCD and the signal recorded on the internal VTR are both in analog form. Before the signal can be digitized, however, extensive clamping and low-noise gain must be applied. Consumer pressure for small camcorder size and low power have lead to the development of a system in which all the functions previously residing on a bipolar chip have been incorporated on the same CMOS die with the ADC, including a CDS block, an amplifier with variable gain from 0 to 34 dB, a black-level correction loop, an input clamp and a voltage reference. An emitter follower buffer is traditionally used between the CCD and the rest of the system for line driving, but this is the only portion of the analog signal chain external to the chip.