RE : calculating the output power of a Quartz oscillator

Why would you use PSS and then use the time-domain waveform? Wouldn't it make more sense to use the frequency-domain output - that's complex after all?

Also, for a crystal oscillator, you might also want to consider using harmonic balance (unless the output is very square).

Regards,

Andrew

More details : I am simulating the digital output of a Quartz oscillator, so it is very square. For pss When I calculate Pout using 'Shooting' method I get 75uW, but with pss/Harmonic Balance it is 86uW. When I use Harmonic Balance Tool, it gives 86uW.

Dear david j james,

david j james said:

so it is very square. For pss When I calculate Pout using 'Shooting' method I get 75uW, but with pss/Harmonic Balance it is 86uW. When I use Harmonic Balance Tool, it gives 86uW.

I am guessing the difference is likely due to the difference between the steady-state (i..e., long term) frequency estimated by the two convergence algorithms. Did you compare the estimated steady-state frequencies of the shooting and Harmonic Balance simulations?

The estimated frequencies may be different as the final frequency is determined by the large signal impedance of your sustaining amplifier (including the external load capacitances). The frequency is determined by the imaginary part of this large signal impedance where its real part is equal in magnitude but opposite in sign to the real impedance of the quartz crystal unit. Since your sustaining amplifier is generating a waveform with a lot of harmonics, I would suspect the shooting algorithm will converge faster (fewer iterations) than a harmonic balance based algorithm. I would need to review your output log to provide any thoughts as to which frequency estimate might be most accurate. The accuracy with which it  estimates the large signal impedance will determine how accurate the estimated long term (steady-state) frequency.

Shawn

PSS simulation gives a Fundamental frequency of 10.0275 MHz, Harmonic balance gives Frequency= 1.0028e+07. That's a 0.0001% difference!

PSS simulation gives a Fundamental frequency of 10.0275 MHz, Harmonic balance gives Frequency= 1.0028e+07. That's a 0.0001% difference!

Dear david j james,

david j james said:

PSS simulation gives a Fundamental frequency of 10.0275 MHz, Harmonic balance gives Frequency= 1.0028e+07. That's a 0.0001% difference!

The difference appears to be about 40 ppm - which is actually a "large" frequency difference in the field of bulkwave quartz oscillators.

In any case,I suspect there may be a simulation accuracy issue or a possible power calculation issue as the shooting simulation result is indicating the steady-state oscillation frequency is closer to series resonance than the result of the Harmonic Balance simulation. Therefore, the quartz crystal unit power dissipation of the shooting PSS simulation should be higher that for the Harmonic Balance PSS simulation. Your data suggests the opposite. If you can, might you share the exact method you are using the compute the quartz crystal unit power dissipation and your PSS simulation settings (the two input.scs file simulation lines will contain the information)?

Shawn