A New Digital Phase Measurement System

Abstract : The Naval Research Laboratory (NRL) is developing a digital phase measurement system. The measurement system uses high speed Analog to Digital Converters (ADC) to make tens of millions of measurements per second, Digital Signal Processing (DSP) hardware for intermediate calculations, and a PC for the final phase calculations. Performance of the present configuration is limited by a 12-bit analog-to-digital converter. Averaging times can be as small as 0.0001 seconds. Multiple input frequencies to over 10 MHz can be measured simultaneously. Modular construction will allow for expansion to many channels. Absolute phase measurements are possible. Inputs to channels can be switched between frequencies and then returned to an original frequency without losing phase coherency of the measurements. This system to be used in the laboratory and may be used on the GPS satellites to monitor a hot backup clock. The basic system measures the coefficient of a Discrete Fourier Transform (DFT) at the assumed frequency of the input signal. This paper will describe the special purpose DSP hardware and software used to measure the signal and transform the measurements into conventional clock parameters.