HIGH RESOLUTION PHASEMETER FOR TEMPORAL HETERODYNE SIGNALS

OPTRA PROPOSES TO DEVELOP A VERY HIGH PRECISION PHASEMETER FOR USE WITH HETERODYNE INTERFEROMETRY. IT IS BASED ON TWO INNOVATIONS: A PROPOSED POLARFASH PHASE-TO-DIGITAL CONVERTER, AND A HIGH-SPEED 3-PHASE DEMODULATOR WHICH TAKES THE MEASUREMENT AND REFERENCE SIGNALS FROM THE HETERODYNE INTERFEROMETER AND GENERATES THE INPUT SIGNALS FROM THE POLARFLASH CONVERTER. THE PROPOSED PHASEMETER HAS SHOT/ELECTRONIC NOISE-LIMITED RESOLUTION ( 0.001-CYCLE RESOLUTION SHOULD BE ATTAINABLE WITH A 5 KHZ BANDWIDTH), NEGLIGIBLE UNWRAPPING ERRORS, A VIRTUALLY UNLIMITED DYNAMIC RANGE, AND WILL WORK WITH HETERODYNE FREQUENCIES FROM 100 KHZ TO 40 MHZ. THE DEMODULATOR GENERATES BASEBAND SIGNALS THAT ARE PROPORTIONAL TO PHI,(PHI+2PI/3), AND (PHI-2PI/3), WHERE PHI IS THE INSTANTANEOUS INTERFEROMETRIC PHASE. THESE SIGNALS GO TO THE POLARFISH CONVERTER, WHICH FUNCTIONS IN AN ANALOGOUS MANNER TO A FLASH A/D. ONE OF THE ATTRACTIVE FEATURES OF THIS APPROACH IS THE LIKELIHOOD THAT IT WILL LEAD TO THE DEVELOPMENT OF AN INEXPENSIVE ASIC HAVING THE CAPABILITY OF 8- OR 12-BIT PHASE RESOLUTION FOR FREQUENCIES FROM DC TO PERHAPS AS HIGH AS 100 MHZ. PHASE UNWRAPPING WILL BE DONE WITH EXISTING AND PROVEN ELECTRONICS THAT HAVE ALREADY BEEN DEVELOPED AT OPTRA. UNWRAPPED PHASE DATA WILL BE AVAILABLE IN THE FORMS OF A 32-BIT PARALLEL WORD, AND ANALOG VOLTAGE, OR A PAIR OF A-QUAD-B PULSE TRAINS. THE PROPOSED PHASE MEASUREMENT SYSTEM SHOULD IMPROVE INTERFEROMETRIC PHASE-MEASUREMENT PRECISION BY A FACTOR OF AT LEAST 10 TO 100, AND WILL BE INEXPENSIVE.