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The Si5351A is prone to crosstalk between outputs, if the outputs are heavily loaded (e.g. 50-ohm loads). There's only a single supply pin into the chip. Other suffix versions of the Si5351 in larger packages have separate?buffers with their own supply pins and this is less of a problem.?

Therefore if you want to use multiple?Si5351A outputs on different frequencies, and you don't want that level of crosstalk, you need to buffer them with a relatively higher input impedance buffer.?

Additionally phase noise performance is degraded when the outputs are heavily loaded. One partial remedy to this is to use a DC blocking capacitor, which appears to restore the phase?noise performance.?

Note?also that the output spectra of the Si5351A will depend somewhat on the internal configuration. For best low jitter performance (i.e. good phase noise performance) the datasheet?recommends even integer MultiSynth divider stage configuration where possible, using fractional feedback division on the PLL stage. There is quite a lot of bad Si5351A code out there in libraries and such, that does things the WRONG way.?

My article on phase noise measurements of the Si5351A might be of interest see?

73 Hans G0UPL