A 9 b charge-to-digital converter for integrated image sensors

An alternative technique for digitizing charge signals, charge-to-digital conversion, is free from many difficulties with conventional methods. Its advantages occur because A/D conversion is performed in the charge, rather than the voltage, domain. Digitization may be consolidated by digitizing charge signals on-chip. In this method, charge packets are transferred directly into a charge-to-digital converter (CDC), implemented using CCD elements. Signals continue as discrete-time charge quanta throughout conversion and no charge-to-voltage translation or resampling occurs. The CDC described here is based on a fully-differential, bit-serial, successive approximation architecture.