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Andy aka
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You can make a voltage controlled oscillator (VCO) to run at any frequency that there is readily available technology. You input a voltage and out comes a certain frequency. If you increase the voltage the output frequency rises. You drop the control voltage and the frequency drops.

If you then divide down that output frequency to a much lower frequency of (say) 10MHz using digital clock dividers then you can use simple logic gates to compare that divided down frequency with a rock-solid 10MHz xtal-based clock. There are various digital ways of doing this but the bottom line is, after filtering/processing that "comparison" signal, you can use a version of it to nudge (or align) the VCO with an exact desired multiple of your reference 10MHz clock.

In this way, you get a very stable, very high frequency that the MCU (or FPGA or logic chip) doesn't really know anything about but has assisted along the way to produce. It's called a phase locked loop or PLL.

Andy aka
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