Physical Layer: How do how frequency sources work

high frequency

This is likely basic: but how do the source that rapidly generate 0-1s thru a channel "work" so fast? If it is a electric signal that is the source [as it is I believe even for fiber optic where a source converts electric signals to light pulses to be transmitted along the fiber]: how are these high frequency signals generated?

I am thinking that there must be some "moving part"/mechanical part that "vibrates" so fast: but can we really have mechanical parts vibrating that fast? Or is there a frequency amplification from the mechanical to electrical that happens?

Best Answer

What kind of frequencies are you talking about? You can use crystals up to something like 50 MHz after which they become tricky to use.

Higher frequencies are often generated by VCO (Voltage Controlled Oscillator) circuits, which can generate frequencies of several gigahertz, but are themselves not very accurate. They are made accurate by a technique called Phase Locked Looping (PLL), where a digital divider circuit is used to divide the high frequency by some integer factor, for example 64, 128 or 100. Then the divided frequency is compared to a frequency of a crystal and the control voltage of the VCO is adjusted accordingly to make it stay at the desired frequency.