Direct sequence spread spectrum differential phase shift keying SAW correlator on GaAs

This paper presents the design, fabrication, and experimental results for a differential phase shift keying (DPSK) single SAW-based correlator on GaAs for direct sequence spread spectrum applications. The DPSK modulation format allows for noncoherent data demodulation; the SAW device correlator acts as the despreader. Unlike the conventional technique of using two parallel correlators and a one data bit delay element, this new system uses two inline correlators. When implemented on SAW devices, this in-line structure has the advantage of an inherent one data bit delay, lower insertion loss, and less signal distortion than the parallel structure. The DPSK correlator is fabricated on a {100} cut GaAs substrate with SAW propagation in the <110> direction, Using this cut, which is widely used in electronics, Rayleigh waves are generated with a piezoelectric coupling coefficient of the same order as ST-cut quartz. The piezoelectric semiconductor GaAs is of great interest because it is the only substrate that can be used to integrate SAW devices directly with electronics on the same chip, resulting in smaller packaging, reduction of packaging parasitics, lower cost, and greater system integration. This paper presents experimental results for SAW in-line correlator structures on GaAs along with their despreading system performances. Experimental measurements in both the time and frequency domains were performed and were found to be in good agreement with theoretical predictions.