par projekta 2010/0283/2DP/2.1.1.1.0/10/APIA/VIAA/084 “Daudzfunkcionāla
signālu laika analizatora eksperimentāla izstrāde" tekošajiem rezultātiem
Augstas stabilitātes GPS pieskaņojamās atbalsta
frekvences ģeneratora moduļa izstrāde un izpēte
Projekta zinātniskais vadītājs
Dr.hab.sc.comp. Jurijs Artjuhs
Referents Armands Mezeriņš
Elektronikas un
Datorzinātņu
Institūts
Informatīvais seminārs, Rīga, 2012. gada 29.maijs
Institute of
Electronics and
Computer Science
1
Input
Signal Conditioner
(detector of zero crossings,
controllable prescaler)
Subject and objectives of research
Frequency
Standard
PC
EVENT TIMER
A033-ET
Analyser
software
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
Informatīvais seminārs, Rīga, 2012. gada 29.maijs
2
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
Informatīvais seminārs, Rīga, 2012. gada 29.maijs
3
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, 2012. gada 29.maijs
4
Commercially available GPS Disciplined Oscillators
Trimble Mini-T GPS Disciplined Clock board
www.trimble.com
Trimble Thunderbolt E GPS Disciplined Clock
ULN-2550 GPSDO
FTS375 Disciplined Reference
www.jackson-labs.com
Fury GPS Disciplined Frequency Standard
www.conwin.com
FTS500 XenithTBR
GPS-12R Portable GPS Rubidium Frequency Standard
www.spectracomcorp.com
Informatīvais seminārs, Rīga, 2012. gada 29.maijs
5
Frequency stability of some commercial GPS Disciplined Oscillators
Allan Deviation
1.00E-09
0.01
0.1
1
10
100
1000
10000
Trimble Thunderbolt E
1.00E-10
Trimble MINI T GPS Disciplined
Clock Board
Fury GPSDO frequency standard
ULN-2550
FireFly-IIA GPSDO DOCXO
1.00E-11
FTS375, FTS500
1.00E-12
• 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.
Informatīvais seminārs, Rīga, 2012. gada 29.maijs
5
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
Informatīvais seminārs, Rīga, 2012. gada 29.maijs
6
Experimental estimation of the module stability
FREQUENCY STABILITY
-9
10
Allan Deviation
GPS Disciplined State
Unlocked State (Holdover)
-10
10
-11
10
-2
10
-1
10
0
1
2
10
10
Averaging Time tau, seconds
3
10
10
Locked versus unlocked state of GPSDO module
FREQUENCY STABILITY
-9
10
Allan Deviation
-10
10
-11
10
Pendulum GPS-12R Rubidium Frequency Standard
GPS Disciplined Frequency Reference module
Trimble Thunderbolt GPS Disciplined Clock
-12
10
-2
10
-1
10
0
1
10
10
Averaging Time tau, seconds
2
10
GPSDO module versus Trimble Thunderbolt E GPS Clock
Informatīvais seminārs, Rīga, 2012. gada 29.maijs
7
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
Informatīvais seminārs, Rīga, 2012. gada 29.maijs
8
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.
Informatīvais seminārs, Rīga, 2012. gada 29.maijs
9