jlee wrote on Nov 22nd, 2010, 11:01pm:Hi guys,
As the title, there are following puzzles on crystal oscillator design.
1. I have got the following element parameters in the crystal equivalent model: Cs(motional cap), Cp(parellel cap) and Rs(ESR). Are they enough to calaculate the remaining parameter, say Ls with a given oscillation frequency?
2. I have tried to run simulation by PSS and tran, but the oscillator can normally work without any initial condition under PSS and it doesn't work under tran, or the waveform becomes wired. What's the difference between these two analysis?
3. Why the simulated oscillation frequencies are different by changing tstab in PSS analysis, although oscillation has become a steady state?
4. For example, a frequency of 11.1111MHz is obtained from PSS. If an accuracy of 11.111111MHz is preferred, how to set up in simulation?
Thanks for advance!
Regards
Jlee
For Question 1, If you know the Freq and the R/C, you can calc. L.
You need to read some basic app notes on crystal design and resonant frequency equations between LRC and Freq.
Vittoz has a classic paper.
For Q2, transients are golden for startup sims.
You may need to use Trap, as explained in Ken's Spectre book, and
you may need to De-"Q" the model (change L/C); that will give easier and artificially quicker startup sims.
I haven't used PSS enough to comment on Q3,
and for Q4, I'd set your expectations lower on Frequency accuracy sims. However I doubt that is a critical sim.
Freq. can be pulled externally by the Crystal and components.
Wave