Transversal Filter Application of A High Speed Gallium Arsenide CCD

Substantial progress toward the incorporation of a 1 GHz continuous clock rate GaAs CCD in a monolithic transversal filter design has been achieved. This paper will discuss performance results for the GaAs CCD at frequencies from 1 MHz to 1000 MHz. This device performs with a CTE of at least 0.999 per transfer at 1 GHz continuous clocking, measured by the magnitude response of the modulation transfer function. A half-banding analog filter is described in detail. The CCDs in the filter are arranged in a pipe-organ structure and provide three important signal processing functions in the charge domain: weighted sampling, programmable delay, and accurate summing. The current design specifications provide for a clock rate from below 50 MHz to in excess of 900 MHz, corresponding to an input bandwidth of 0 to 450 MHz. The filter will select the upper or lower half band of the input. This design allows for convenient cascading of chips to provide narrower passbands and higher out-of-band attenuation. Since these are complex band-pass filters, there is an in-phase branch and a quadrature branch in the complete filter. The current developments have stemmed from work previously reported (1) and from the obvious need to incorporate GaAs CCDs with suitable high speed support circuits. Therefore, the device has been mono!ithically integrated with MESFET IC technology to enable its use in circuit applications where the 1 GHz GaAs CCD has performance advantages. This VHF/UHF filter is a good example of such applications.