A CCD wave filter with low sensitivity

Starting with a double terminated Chebyshev LC ladder filter, a CCD wave filter has been implemented by using CCD resonators and charge amplifiers as basic building blocks. The bandpass filter which was realized on a test chip has a center frequency of 50 kHz, together with a relative Chebyshev bandwidth of 2.6 percent, 5 dB insertion loss, and more than 60 dB stopband attenuation. Compared to known SC filters, the advantages of the new approach are in extremely low sensitivity of the center frequency which is controlled by an external clock frequency, and a relative bandwidth which does not depend on the center frequency, but is controlled by capacitance ratios. Filter design, some aspects related to implementation, and experimental results are described.