Preliminary Technology Overview
Programmable Surface Acoustic Wave Correlator
Invocon has teamed with NASA and Sandia National Labs to develop an ultra low power Direct Sequence Spread Spectrum (DSSS) radio based on a programmable Surface Acoustic Wave (PSAW) correlator. The PSAW will perform the primary function of the digital signal processor, down converter, demodulator, and baseband processor in a conventional (DSSS) receiver, but with no power consumption. The correlator forms a passive matched filter for symbol detection and possibly symbol generation.
Fixed code SAW correlators have been used for decades in special radar and communication applications, but after down conversion, essentially these devices worked at IF not carrier frequencies. The above diagram shows a fixed sequence SAW correlator. A SAW correlator makes use of the slow velocity of propagation of SAW signals to form a matched filter. The input signal is launched on the input Inter-Digitated Transducer (IDT) on the left of the figure. The signal then propagates to the right and is summed by successive output transducers, which are spatially placed for a temporal delay of one chip period. The polarity of connection (phase) of the output transducers is matched to the desired symbol or chipping sequence. When a signal is applied to the correlator, which exactly matches the hardwired chipping sequence, an output correlation pulse occurs at the operating frequency. The use of fixed code correlators in communication applications is very restrictive as only one symbol can be generated and detected per correlator. The programmable SAW correlator, illustrated below, will allow for the use of any symbol.
PSAW is in current research and development.