Augstas stabilitātes GPS pieskaņojamās atbalsta frekvences ģeneratora moduļa izstrāde un izpēte Projekta zinātniskais vadītājs Dr.hab.sc.comp. Jurijs Artjuhs.

Augstas stabilitātes GPS pieskaņojamās atbalsta frekvences ģeneratora moduļa izstrāde un izpēte

Projekta zinātniskais vadītājs Dr.hab.sc.comp. Jurijs Artjuhs

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par projekta 2010/0283/2DP/2.1.1.1.0/10/APIA/VIAA/084 “Daudzfunkcionāla signālu laika analizatora eksperimentāla izstrāde" tekošajiem rezultātiem

Elektronikas unDatorzinātņuInstitūts

InstituteofElectronics andComputerScience

Elektronikas unDatorzinātņuInstitūts

InstituteofElectronics andComputerScience

Informatīvais seminārs, Rīga, 2012. gada 29.maijs

Referents Armands Mezeriņš

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Subject and objectives of research

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The performance of Frequency Standard directly definesaccuracy of the Time Analyser


Research Objectives:

• Comparative analysis of available high-stability clock oscillators • Design and investigation of Frequency Standard module

Time Analyser

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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

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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.


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Commercially available GPS Disciplined Oscillators


www.trimble.com www.jackson-labs.com www.conwin.com

Trimble Mini-T GPS Disciplined Clock board ULN-2550 GPSDO FTS375 Disciplined Reference

Trimble Thunderbolt E GPS Disciplined Clock Fury GPS Disciplined Frequency Standard FTS500 XenithTBR

GPS-12R Portable GPS Rubidium Frequency Standard

www.spectracomcorp.com

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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 averagingindicates a device of very high quality.

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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

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Experimental estimation of the module stability


10-2

10-1

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Averaging Time tau, seconds

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FREQUENCY STABILITY

GPS Disciplined State

Unlocked State (Holdover)

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Averaging Time tau, seconds

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Pendulum GPS-12R Rubidium Frequency Standard

GPS Disciplined Frequency Reference module

Trimble Thunderbolt GPS Disciplined Clock

Locked versus unlocked state of GPSDO module

GPSDO module versus Trimble Thunderbolt E GPS Clock

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GPS receiver data using NS3Kview software


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

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Summary


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 4·10-11 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.

Augstas stabilitātes GPS pieskaņojamās atbalsta frekvences ģeneratora moduļa izstrāde un izpēte Projekta zinātniskais vadītājs Dr.hab.sc.comp. Jurijs Artjuhs.

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