Augstas stabilitātes GPS pieskaņojamās atbalsta frekvences ģeneratora moduļa izstrāde un izpēte

1. Informatīvais seminārs, Rīga, 2012.gada 29.maijs par projekta2010/0283/2DP/2.1.1.1.0/10/APIA/VIAA/084 “Daudzfunkcionāla signālu laika analizatora eksperimentāla izstrāde" tekošajiem rezultātiem Augstas stabilitātesGPS pieskaņojamās atbalsta frekvencesģeneratora moduļa izstrāde un izpēte Projekta zinātniskais vadītājs Dr.hab.sc.comp. Jurijs Artjuhs Referents Armands Mezeriņš 1

2. , , Frequency Frequency ) ) Standard Standard PC PC Input Input detector of zero crossings detector of zero crossings EVENT TIMER EVENT TIMER Signal Conditioner Signal Conditioner controllable prescaler controllable prescaler A033 A033 - - ET ET Analyser Analyser software software ( ( Informatīvais seminārs, Rīga, 2012.gada 29.maijs Subject and objectives of research Time Analyser The performance of Frequency Standard directly defines accuracy of the Time Analyser • Research Objectives: • Comparative analysis of available high-stability clock oscillators • Design and investigation of Frequency Standard module 2

3. Informatīvais seminārs, Rīga, 2012.gada 29.maijs 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) • 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 3

4. Informatīvais seminārs, Rīga, 2012.gada 29.maijs 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. 4

5. Informatīvais seminārs, Rīga, 2012.gada 29.maijs Commercially available GPS Disciplined Oscillators Trimble Mini-T GPS Disciplined Clock board ULN-2550 GPSDO FTS375 Disciplined Reference www.trimble.com www.jackson-labs.com www.conwin.com Trimble Thunderbolt E GPS Disciplined Clock Fury GPS Disciplined Frequency Standard FTS500 XenithTBR GPS-12R Portable GPS Rubidium Frequency Standard www.spectracomcorp.com 5

6. Informatīvais seminārs, Rīga, 2012.gada 29.maijs Frequency stability of some commercial GPS Disciplined Oscillators • 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 × 10-13 or less after one day of averaging • indicates a device of very high quality. 5

7. Informatīvais seminārs, Rīga, 2012.gada 29.maijs GPS Disciplined Oscillator Module Design • The module consists of : • FTS375-010.0M 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 6

8. Informatīvais seminārs, Rīga, 2012.gada 29.maijs Experimental estimation of the module stability Locked versus unlocked state of GPSDO module GPSDO module versus Trimble Thunderbolt E GPS Clock 7

9. Informatīvais seminārs, Rīga, 2012.gada 29.maijs GPS receiver data using NS3Kview software NMEA Command Monitor Window - all NMEA data sentences received from the GPS receiver 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 8

10. Informatīvais seminārs, Rīga, 2012.gada 29.maijs Summary • GPSDO is self calibrating reference with an excellent long-term stability. • Application of GPS DisciplinedOscillatorModule as time-base in analyzer provides possibility for accurate and stable long-term measurements (frequency stability is in the range from 4·10-11 at 300s to 10-13 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. 9