Antialiasing inputs for charge-coupled devices

An input scheme for analog charge-coupled signal-processing devices has been developed that acts as a prefilter to suppress the aliasing frequencies produced by the sampled-data nature of the CCD. Each charge packet injected into the CCD is a sum of several weighted subsamples taken at a multiple of the CCD clock rate. Various approaches that differ in their rates of oversampling and in their time periods over which subsamples are combined have been compared with respect to their usefulness to produce a sharp cutoff prefilter. A particular implementation using only a factor of 2 oversampling but an averaging period that extends over two CCD clock periods results in a good prefilter characteristic and has been applied to a charge-coupled split-electrode transversal filter. Different implementations of the basic scheme and layout considerations are discussed.