SAW-correlator module for spread-spectrum DPSK asynchronous demodulation

Details of the design and performance of a SAW (surface acoustic wave) correlator module for the demodulation of a direct sequence DPSK (differential phase shift keying) modulated spread-spectrum signal are presented. In contrast to convolver solutions, neither reference code nor synchronization is needed. This leads to a low system complexity and a high electromagnetic interference immunity. The module consists of two parallel SAW correlators on one chip. The preprocessed correlator outputs allow easy detection of the data bits. The cross-correlation time-sidelobes are minimized by additional taps and appropriate weighting. A bandpass-function with sharp cutoff is integrated in the correlators without degrading demodulation performance. The center frequency is 217 MHz, the chip-rate is 25.75 Mchip/s, and the data rate is 250 kb/s. Multipaths up to 4 mu s are suppressed.<
>