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I'm trying to draw a schematic that I need for selecting a single clock among four possible clock sources. I'd like to select the source using a simple 4 way mechanical switch.

The sources are:

  1. 22.5792MHz oscillator
  2. 24.576MHz oscillator
  3. external clock input (via BCN connector)
  4. the clock produced by ADAT receiver IC (AL1402)

Only one of these sources can be active at the same time. The two oscillators are divided by two before hitting the clock selector, only one frequency divider is employed since the two oscillator share the same input, so I'd like to enable the oscillators (using the EN pin) only when actually used. The external clock input (44.1KHz to 48KHz) is going to a PLL chip that multiply incoming frequency by 256. Another thing to note is that the 4th source (ADAT clock) is higher in level (0V/5V) so I'd need to bring it down to 0V-3.3V

What is the best way to implement this switching? My main idea was to use tri-state buffers or a multiplexer, but I am wondering if that would degrade the clock performance and if there are simpler/better ways to do this.

The output clock is the Master clock for audio I2S transmission.

enter image description here

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  • \$\begingroup\$ Why are you worried that the signal would "degrade"? What are your specific requirements for signal fidelity through the switch? Why not just use a SP4T mechanical switch and be done with it? \$\endgroup\$ Sep 11, 2021 at 20:48

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Any mux that can handle 12MHz signals (VHC153 or similar) should be fine. But I'd put the mux before the CS2300-03 PLL to help clean up any jitter introduced by the mux.

Configure CS2300 to multiply by 1 or 256 depending on selected input.

enter image description here

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