Autocalibrating Circuitry for Processing SAW Convolver Outputs

摘要

The application of 100-MHz-bandwidth convolvers to packet communications requires critically timed high-speed support circuitry. To process the 200-MHz-bandwidth convolver outputs it is essential to align the sampling circuits, which define the output-processing time-window, to within approx. 5 ns for rapid synchronization and demodulation. Autocalibrating techniques are need 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 suppression of multipath-generated intersymbol interference the record of the multipath profile obtained 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 be described requires less than 60 s to calibrate all critically timed signal paths, enabling calibration to be performed at predetermined intervals more often than worst-case temperature fluctuation require. (Reprints)