Augstas stabilitātes GPS pieskaņojamās atbalsta frekvences ģeneratora moduļa izstrāde un izpēte Projekta zinātniskais vadītājs Dr.hab.sc.comp. Jurijs Artjuhs 1 par projekta 2010/0283/2DP/ /10/APIA/VIAA/084 “Daudzfunkcionāla signālu laika analizatora eksperimentāla izstrāde" tekošajiem rezultātiem Informatīvais seminārs, Rīga, gada 29.maijs Referents Armands Mezeriņš

2 Subject and objectives of research EVENT TIMER A033-ET Frequency Standard Analyser software PC Signal Conditioner ( detector of zero crossings, controllable prescaler ) Input EVENT TIMER A033-ET Frequency Standard Analyser software PC Signal Conditioner ( detector of zero crossings, controllable prescaler ) Input The performance of Frequency Standard directly defines accuracy of the Time Analyser Informatīvais seminārs, Rīga, gada 29.maijs Research Objectives: Comparative analysis of available high-stability clock oscillators Design and investigation of Frequency Standard module Time Analyser

3 State-of-the-art Commonly used built-in clock oscillators: Temperature Compensated Crystal Oscillators (Stability:  1 ppm - over operating temperature range) Oven Controlled Crystal Oscillators (Stability:  10 ppb) Rubidium Oscillators (Stability:  0.05 ppb) Informatīvais seminārs, Rīga, gada 29.maijs Main drawbacks: Noticeable long-term instability Aging Requires regular calibration against a traceable reference with a high long-term accuracy Currently GPS disciplining the clock oscillators allows considerable reducing these drawback

4 GPS Disciplined Oscillator Basics Space based navigation system (such as NAVSTAR GPS) provides 3D position, velocity, precise time (traceable to UTC) and high accuracy frequency worldwide. GPS disciplining technique uses the signals obtained from a GPS receiver as a time and frequency reference to synchronize, calibrate or control a frequency source. In a simple GPS Disciplined Oscillator the voltage controlled oscillator VCO (10 MHz) signal is divided to a lower frequency prior to phase comparison with 1PPS derived from GPS receiver. A microcontroller monitors the phase difference, and software changes the control voltage applied to the VCO to held phase difference within an appropriate range. Informatīvais seminārs, Rīga, gada 29.maijs

5 Commercially available GPS Disciplined Oscillators Informatīvais seminārs, Rīga, gada 29.maijs Trimble Mini-T GPS Disciplined Clock board ULN-2550 GPSDOFTS375 Disciplined Reference Trimble Thunderbolt E GPS Disciplined ClockFury GPS Disciplined Frequency StandardFTS500 XenithTBR GPS-12R Portable GPS Rubidium Frequency Standard

5 Frequency stability of some commercial GPS Disciplined Oscillators Informatīvais seminārs, Rīga, gada 29.maijs Allan Deviation σ(τ) is a stability metric which shows the RMS frequency change we can expect over a τ second interval. Frequency deviations measured at 10 MHz relative to an atomic frequency standard. A stability of 1 × or less after one day of averaging indicates a device of very high quality.

6 GPS Disciplined Oscillator Module Design Informatīvais seminārs, Rīga, gada 29.maijs The module consists of : FTS M hybrid circuit – 10MHz CMOS and 10MHz phase-lock loop circuit synchronized with GPS signal PIC18F24K20 microcontroller unit - provide initial setup and monitoring functions; MAX202 transceiver circuit for RS232 to TTL level conversion

7 Experimental estimation of the module stability Informatīvais seminārs, Rīga, gada 29.maijs Locked versus unlocked state of GPSDO module GPSDO module versus Trimble Thunderbolt E GPS Clock

8 GPS receiver data using NS3Kview software Informatīvais seminārs, Rīga, gada 29.maijs Navigation window – current time, clock drift, longitude, latitude and altitude or elevation Satellite Azimuth & Elevation Window – azimuth and elevation for each satellite that is in view NMEA Command Monitor Window - all NMEA data sentences received from the GPS receiver

9 Summary Informatīvais seminārs, Rīga, gada 29.maijs GPSDO is self calibrating reference with an excellent long-term stability. Application of GPS Disciplined Oscillator Module as time-base in analyzer provides possibility for accurate and stable long-term measurements (frequency stability is in the range from 4· at 300s to at 1 day). For short-term measurements GPS disciplining may be turned off (time intervals less than 300 seconds). Timing data from GPS receiver and synchronization with UTC may provide time tagging of measured events in real time scale.