VIAVI CSAC GPSDO Chip Scale Atomic Clock GPS Disciplined Oscillator Frequency Standard

GPS disciplined oscillator module built around a Microsemi SA.45s Chip Scale Atomic Clock for man-pack, airborne and vehicle use.

Long-Term Oscillator Aging: Less than 0.3 ppb per month in holdover without GPS; Zero aging with GPS
Frequency Stability Over Temperature: Better than ±0.5E-09
1 PPS Accuracy: ±15 ns to UTC RMS (1-Sigma)
Frequency Accuracy: Better than ±2E-010

Datasheet

Overview

The VIAVI CSAC GPSDO is a GPS disciplined oscillator module that integrates the Microsemi SA.45s Chip Scale Atomic Clock (CSAC). It is designed for mobile applications such as man-pack, airborne and vehicle installations.

The CSAC technology packages a cesium vapor cell atomic reference oscillator in a unit several orders of magnitude smaller than legacy atomic oscillators, with more than an order of magnitude reduction in power consumption. The technology originates from research sponsored by the U.S. Government.

The module includes a time-interval counter that measures either the 1 PPS signal generated by its internal 50-channel GPS receiver or an externally supplied 1 PPS reference, with a resolution of 20 picoseconds. The CSAC oscillator is phase-locked to either of these 1 PPS signals with typically better than 0.3 ns average phase accuracy, and typically provides better than 5E-12 stability per day in holdover.

Control and software

The GPS receiver supports WAAS, EGNOS and MSAS and drives the CSAC frequency reference under control of a 32-bit processor. The unit is controlled over RS-232 and USB using standard SCPI commands, with settings stored in non-volatile memory. It is compatible with the GPSCon Windows graphing and SNTP server software, and the JLTerm software is also available for download.

Key Features

Full atomic lock achieved in 110 seconds max. (<60 s typical) after power on
Phase noise of <125 dBc at >100 Hz offsets using an integrated phase noise filter
Power consumption of <1.4 W (Sine outputs) and <1 W (CMOS option)
Less than 0.1 ppb per g per axis typical g-sensitivity
Better than 1 µs drift per day typical in holdover
WAAS/EGNOS/MSAS GPS receiver drives a Chip Scale Atomic Clock frequency reference under control of a 32-bit processor
Holdover mode with aging compensation
Controlled via RS-232 and USB using standard SCPI commands
Settings automatically stored in non-volatile memory
10 MHz, 5 MHz, and 1 PPS outputs
Time-interval counter with 20 ps resolution measuring internal GPS or external 1 PPS
GPSCon Windows graphing and SNTP server software compatible

Specifications

Frequency and Timing

Long-Term Oscillator Aging	Less than 0.3 ppb per month in holdover without GPS; Zero aging with GPS
Frequency Stability Over Temperature	Better than ±0.5E-09 CSAC only, no GPS Disciplining, 0°C to +70°C
1 PPS Accuracy	±15 ns to UTC RMS (1-Sigma) GPS Locked in Position Hold mode
Frequency Accuracy	Better than ±2E-010 After 3 minutes operation with GPS lock
Holdover Stability	<±2 µs over 24 Hour Period @+25°C After 96 hours warmup; after 20 minutes with GPS lock
Warm Up Time/Stabilization Time Without GPS	<3 min at +25°C to <5E-010 Accuracy Typical

ADEV (with GPS lock)

1 s	<1E-10
10 s	<2.5E-11
100 s	<2E-11
1K s	<1E-11
10K s	<2E-12

Phase Noise

10 Hz	-90 dBc/Hz
100 Hz	-125 dBc/Hz
1 kHz	-145 dBc/Hz
10 kHz	-152 dBc/Hz
100 kHz	-153 dBc/Hz

Outputs

1 PPS Output (CSAC Flywheel Generated)	5 V CMOS output, can be shifted in 1 ns steps relative to UTC
10 MHz Output, 5 MHz Output	Four Isolated 10 MHz Sine Wave +13 dBm ±3 dBm, one 5 MHz CMOS 5 V
Distribution Amplifier Port Isolation, 2 MHz	>98 dB
Distribution Amplifier Port Isolation, 10 MHz	>85 dB
TTL Alarm Output	GPS Unlock and Hardware Failure indicator

GPS Receiver

GPS Receiver	50 Channels, Mobile, SBAS: WAAS, EGNOS, MSAS supported
GPS Frequency, Antenna	L1 C/A 1574 MHz, Passive or Active Antenna 5 V, MMCX Connector
Sensitivity, Acquisition	-144 dBm
Sensitivity, Tracking	-160 dBm
GPS TTFF, Cold Start	<45 sec
GPS TTFF, Warm Start	1 sec
GPS TTFF, Hot Start	1 sec
GPS Receiver Motion Adaptive Filter Settings	Optimized depending on vehicle velocity (Auto-sensing, Auto-switching)

Interfaces

RS-232 Control (Including USB Port)	Full SCPI-99 Control Commands at 9.6 K, 19.2 K, 38.4 K, 57.6 K, 115.2 K
RS-232 NMEA Output Sentences	NMEA 0183 rev. 2.3, Sentences: GGA, RMC, ZDA, PASHR, and others
USB, LCD support	Optionally USB powered and controlled, supports 16x2 LCD Displays

Power

Supply Voltage (Vdd)	Aircraft and Vehicle Power Range: 8 V to 36 V DC, or 5 V via Mini-USB
Power Consumption	<1.4 W Sine outputs (per product page)
Power Consumption CMOS output option	<1 W With CMOS output option (12 V Vdd)

Environmental

Operating Temperature	-10°C to +70°C
Storage Temperature	-45°C to +85°C
g-sensitivity	<0.2 ppb per-g per-axis Product page states less than 0.1 ppb per g per axis typical; datasheet value shown
Magnetic Sensitivity	Less than 0.4 ppb per Gauss
MTBF	>100,000 Hours 0°C to +70°C

Performance Highlights

Atomic lock time after power on	110 seconds max. (<60 s typical)
Holdover drift	Better than 1 µs drift per day typical
Time-interval counter resolution	20 picoseconds
Average phase accuracy	better than 0.3 ns Typical, phase-locked to internal GPS or external 1 PPS
Holdover stability per day	better than 5E-12 Typical