I have a couple of reference designs with 2 different crystal oscillators integrated into it. These are cellular radio and can generate standard LTE QAM signals out of it. But I do not have access to high end equipment which can demodulate the signal for vector measurements. So I am looking for ways to test it using available spectrum analyzer (safe to assume it supports the test signal specs). Also safe to assume DUT control gives ability to transmit a known signal.

What tests can I do to compare the oscillator performance on the 2 reference designs using a spectrum analyzer? Phase Noise, Frequency accuracy, etc? And how to measure?

  • \$\begingroup\$ You can demodulate some signals with an SA using an appropriate scope probe. Xtal testing alone depends on in circuit specs or vector impedance test methods \$\endgroup\$ – Tony Stewart EE75 Aug 4 '18 at 1:43
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    \$\begingroup\$ Vary the channels transmitted, and examine the phasenoise rolloff. Some PLLs have weird charge-cancellation/interference behaviors that lead to hunting in the PLL. You may see some unwanted FM modulation of what should be a pure carrier. \$\endgroup\$ – analogsystemsrf Aug 4 '18 at 4:14
  • \$\begingroup\$ @TonyEErocketscientist demod is no question. More curious on spectral measurements to evaluate integrated xtal. \$\endgroup\$ – eecs Aug 4 '18 at 6:43
  • \$\begingroup\$ @analogsystemsrf this will be tested in an rf enlosure so no outside interference and solely DUT performance (indirect xtal performance) \$\endgroup\$ – eecs Aug 4 '18 at 6:46
  • \$\begingroup\$ Did you try to measure XO phase noise? \$\endgroup\$ – Tony Stewart EE75 Aug 4 '18 at 11:49

Assuming you have audio spectrum analysis capability, get hold of a decent RF mixer, mix two identical oscillators, and analyse the (low side) result. This is easiest if you can pull one of the oscillators 1kHz or so,(e.g. by tuning the loading capacitances).

The noise, jitter, etc you see will be the sum of two nominally identical uncorrelated sources, so subtract 3dB to get the level from each source.


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