CHAPTER FIVE
Phase
Comp.
OSC
Divider
DAC
1PPS ref
1PPS
Phase Lock Loop Clock
For a very simple way to look at this process we can use the above diagram of a phase lock loop to
describe the function that is taking place. As you can see the 1pps that is derived from the oscillator
can be controlled by the DAC so that the phase relationship is that of the measured BIAS
information along with the 1pps reference. In this way all of the frequencies as well as the time
information provided by the clock is “disciplined” to the GPS reference information. Both the
integration (filtering) of the information in the computer as well as the oscillator stability form a very
stable system especially when the oscillator is a rubidium oscillator.
5-10 ET6xxx ExacTime GPS TC & FG (Rev C) Symmetricom Inc
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