Cancellation of aliasing in CCD low-pass filters

The spurious frequencies caused by aliasing in a CCD low-pass filter can be canceled in the passband by designing a prefilter into the CCDs input stage. In this paper, the authors describe how single- and multiple-stage prefilters can be used, the rejection band and attenuation being set by the number of stages. They describe the design of second-order and third-order prefilters. In a basic design, the filtering effect is obtained only around the odd multiples of clock frequency; in a more complex design, the filtering effect is also obtained around twice the clock frequency. A second-order prefilter has been integrated into the input stage of a CCD low-pass filter. Experimental results are presented.