Autocalibrating Circuitry for Processing SAW Convolver Outputs

Abstract

The application of 100-MBz-bandwidt5 convolvers to packet communications requires critically timed high-speed support circuitry. To process the 200-M:Xz-bandwidth convolver outputs it is essential to align the sampling circuits, w5ich define the output-processing time-window, to within =5 ns for rapid synchronization and demodulation. 4utocalibrating techniques are needed since delays within the convolvers, differing delays between convolvers, and delays within the support circuits are all temperature dependent. Two aspects are considered: ( 1 ) Measurement of signal time-of-arrival. Accurate synchronization of the receiver pseudonoise reference code to the transmitted code inherently allows precise notation of the arrival time.(2) RAKE demodulation at a high data rate. For supression of multipath-generated intersymbol interference the record of the multipath profile oStained from a long convolver must be aligned with the data output of a short convolver. These disparate length convolvers have substantially different variations in output delay over temperature requiring periodic calibration. The circuit to Se described reqdires less than 60 s to calibrate a l l critically timed signal paths, enabling calibration to be performed at predetermined intervals more often than worst-case temperature fluctuations require.

Wide-band packet radio technology

“…The asynchronous detection of an incoming signal uses both of these convolvers, staggered in time by one 22-ps convolver length [8], [35], [36]. To obtain the full processing gain over all arrival times of the signal, a reference that is twice as long as the convolver interaction region is used.…”