Crystal Oscillator Design
There are
many OCXOs which are retired from 3G/4G base stations, following is one of them
which is widely available on markets. The parameters of the OCXO are extracted
by using a vector network analyzer (an N2PK variant designed by me many years
ago), where the Q is about 1.2M, Lq=1.63H, Cq=15.539fF, C0=4.8559pF, Rq=84.5
Ohm, and phase noise is about -104dBc@1Hz on average (square wave, without
filtering).
According to [1], the schematic and PCB are
designed while the spurious resonance filter (C16, C17,
L3) has been modified to C16=110pF and C17=200pF. With a tuning voltage of
2-4V, the output level is about -7dBm. The result is very similar with that in
[1]. The spurious resonance is about 10.88MHz, which is similar with that in
[1] also.
And the phase noise plot of the new circuit. It is averaged over about 30minutes without an oven control circuit. In a short time, the phase noise at 10Hz is about 10dB improvement. An oven control circuit will be added, and new results will be presented in a later time.
[1] J. Everard, T. Burtichelov and K. Ng, "Ultralow Phase Noise 10-MHz Crystal Oscillators," in IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, vol. 66, no. 1, pp. 181-191, Jan. 2019, doi: 10.1109/TUFFC.2018.2881456.
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