There are two clock sources. A silicon voltage controlled oscillator (VCO) at roughly the correct frequency but with terrible accuracy and a reasonably accurate quartz crystal, normally in the 25-50 MHz range.
The output of the VCO is divided down so that it's nominal frequency is the same as the quartz crystal (e.g. 4GHz / 128 = 31.25MHz) and the two are compared. The output of that comparison is fed into the control input of the VCO to control the speed of its output.
The end result is that once things have stabilized (which can take a while) the VCO output will be an exact multiple of the quartz input.
This setup is called a Phase Lock Loop or PLL, this is only a very simplistic explanation of how they work, as with many things the complexity is in the details. Google PLL for far more detail and then ask again if you have specific questions.
manpreet![Tuteehub forum best answer]()
Best Answer
2 years ago
Let's say I have a computer running at 4 GHz.
I would say it means I need a way to measure increments of time of about 0.25 ns.
How does a computer do that? My question is both:
Technological: what is the "physical" technology of the raw sensor (is it quartz? What are its defining characteristics ?)
Practical: based on this raw sensor, what methods are put in place to actually be able to measure such a small increment of time somewhat correctly? E.g. if you tell me the clock uses a quartz whose frequency is about 32768 Hz, how do you use that to measure a 0.25ns increment? Do you amplify the quartz signal so massively that you can actually measure a 0.001% variation of amplitude in the resulting signal? in which case, what about noise in the amplification procedure?