Microchip Technology GPS-2700, User Manual

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GPS-2700 USER’S GUIDE
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2020 Microchip Technology Inc. DS50003016A-page 13
Chapter 1. Introduction
1.1 OVERVIEW
The GPS-2700, featuring the Chip-Scale Atomic Clock (CSAC), is a game-changing,
disruptive technology culminating from decades of research sponsored by the U.S.
Government. It is a breakthrough technology that allows a Cesium Vapor Cell Atomic
Reference Oscillator to be packaged in a unit several orders of magnitudes smaller
than legacy products, with more than an order of magnitude in power reduction, and
fewer than 2 minutes warm-up to be fully operational, while out-performing many indus-
try-standard Atomic Oscillators.
The CSAC oscillator provides an impressive frequency accuracy, long-term stability,
and fast lock with low power consumption. Through hardware and firmware support,
the GPS-2700 improves the phase noise performance of the unit, and adds an isolated
distribution amplifier with four output channels at 10
MHz. The GPS-2700 provides
LCD, RS-232 and USB serial links for command and control, as well as an aviation bus
compatible power supply that operates from 8V up to 36V with reverse polarity and over
voltage protection, and can thus be directly connected to an aircraft’s 12V or 24V power
bus.
For long term Stratum-1 frequency accuracy and constant calibration the GPS-2700
includes an extremely high-performance GNSS receiver that can acquire and track up
to 72 (50 for uBlox 6 GPS receiver) GNSS signals down to a state of the art
–160dBm, a 32-bit processor that runs a Real Time OS, a low-noise 10
MHz distribu-
tion amplifier with four highly Isolated 10 MHz Sine Wave outputs, one 5 MHz CMOS
output, one 1PPS UTC synchronized CMOS output, RS-232 and USB control inter-
faces, and a generic LCD interface. The GPS-2700 also includes a high-performance
time interval counter that can measure the internally generated 1PPS signal from the
GNSS receiver or an externally supplied 1PPS reference signal with a resolution of 20
picoseconds. The CSAC oscillator is phase-locked to either of these two 1PPS signals
with better than 0.3
ns average phase accuracy typically. Software compensation mea-
sures residual aging, thermal, and g-sensitivity errors of the CSAC oscillator, and
applies electronic compensation to reduce these residual errors. This error compensa-
tion can improve performance especially in GPS-denied environments, and allows
monitoring of the CSAC health and detection of performance abnormalities in the sys-
tem.
Generic NMEA and SCPI (GPIB) commands on two serial interfaces allow very fast
integration into legacy applications, and by using the NMEA serial strings the unit can
behave like a standard GPS receiver albeit with better than 1 meter horizontal accuracy
typically, and full WAAS/EGNOS/MSAS SBAS support.
1.2 OPERATING PRINCIPLES
A Cesium Vapor Cell is excited from a VCEL Laser source. The VCSEL is modulated
at 4.6
GHz to produce a complementary pair of sidebands separated by the cesium
ground state hyperfine frequency of 9.2 GHz. As Cesium supply depletion is not a life-
time limiting factor in the CSAC, the GPS-2700 implementation allows operational life-
times that potentially exceed those of Cesium beam standards by far.