Charge-transfer filtering

Linear discrete-time (sampled-data) filters can be implemented in monolithic form on an MOS chip using a variety of recently developed and newly emerging techniques without requiring analog-to-digital conversion. An analog signal sample can be represented by an isolated quantity of charge and such packets of charge can be stored, transferred, and manipulated in other ways to perform signal processing operations. Best known of these techniques is the use of a charge-coupled device (CCD) to operate as an analog shift register. A simple modification of the CCD shift register allows the realization of transversal filters. Other techniques can implement recursive filter operations offering a great flexibility for filter design. The possibilities and limitations of charge-transfer filtering are reviewed and examined.