Parametric circuit analysis of strip-coupled varactor SAW convolvers

The strip-coupled varactor SAW convolver is analyzed on the basis of a conventional parametric circuit theory. Expressions of bilinear factors are established, presenting convolution efficiency in terms of MSC and SAW delay-line geometries, piezoelectric parameters, varactor characteristics, coupling to external loading, and working frequency. The theory indicates that the varactor is intermediate between "voltage driven" and "E-field driven" conditions, and the figure of merit M can be made an order of magnitude greater than that of the normal airgap convolver. Experiments with Au-n-Si Schottky varactor/MSC/YZ LiNb03 convolvers give M ~ 4x10^-2 Vm/W at an input frequency of 10 MHz and agree with theoretical predictions satisfactorily.