Passive CCD resonators [for high Q bandpass filters]

The passive CCD resonator is a recursive CCD building block which is well suited for the realization of high Q bandpass filters. Its realization is compatible with the standard double-poly NMOS technology. Advantages of the new approach are an extremely low sensitivity of the center frequency which is determined by an external clock frequency, a relative bandwidth which does not depend on the center frequency but is controlled by a capacitance ratio, and signal frequencies at least up to some hundred kHz. The analysis, design considerations, and performance results are presented. A loaded Q factor of 30, a maximum stopband attenuation of 26 dB, and a negligible insertion loss in the passband are typical for a single CCD resonator. The maximum overall center frequency deviation /spl Delta/f/f due to fabrication tolerances is proportional to the transfer inefficiency of the CCD and has the value of about 2/spl times/10/SUP -4/.