Hi,
If the question is: using one or two clock oscillators (of the same frequency) on one PCB but for multiple devices (microcontrollers, FPGA, ADCs, DACs...)
Then my answer is: Use ONE.
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Whats the alternative?
Using two equal XTAL oscillators each with 50MHz for example.
They will differ in frequency. This will cause interference. If this interference really causes problems depends on the application.
...
Example 1) If there is data communication from one processor to the other.. with independent oscillators you have an unknown relationship between data transfer egdes of both processors.
A clean solution is to double buffer (to avoid metastable states) the input signal and feed it via FIFO to the receiving processor.
With one single clock source, you get a known relationship of the transfer edges of both processors. It is easier to adjust read write edges of both processors.
Usually there is no need for double buffering and FIFO.
Example 2) (Maybe here not of relevance) One clock for microcontroller (or FPGA) and ADC control.
With one single clock source you don´t have the interferance problem. If the analog signal is influenced by the clock source, then most of it results in an offset in the converted digital data.
An offset is easy to compensate.
But interference results in unknown (alias) frequencies. It is about impossible to filter them. So they remain conversion as uncertainty or noise.
Imagine a 50.000 MHz clock and a 50.001 MHz clock. Expect interferance with a frequency of 1kHz. Both clocks will vary with temperature and time and so does the interference frequency.
Klaus