Signal Processing Using Surface Acoustic Wave Devices and Its Application to Spread Spectrum Communication Systems.

Three Surface Acoustic Wave (SAW) devices, the separated-medium convolver, the memory correlator and the chirp filter are analyzed for signal processing applications. Emphasis is placed on convolution/correlation and Fourier transformation processes. The chirp filter theory is more general and applied equally well to chirp filters fabricated by alternate techniques. In the SAW convolver there is a piezoelectric delay line. Two surface waves are introduced onto the delay line surface by interdigital transducers at its opposing ends. The two waves overlap beneath a semiconductor spaced above the surface and their fields interact with its charge carriers. A non-linear potential is produced and averaged over the semiconductor. From its back contact is obtained the time-compressed convolution of the two signals. The memory correlator is similar to the convolver except that the semiconductor possesses a charge-storage mechanism. Also additional transducers are required for recovery of stored information. (Author)