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

The two simulations (pss and hb ) give different (slightly) results.

Do the following setups make sense?

PSS input.scs

simulatorOptions options psfversion="1.4.0" reltol=1e-3 vabstol=1e-6 \

    iabstol=1e-12 temp=27 tnom=27 scalem=1.0 scale=1.0 gmin=1e-12 \

    gmindc=1e-15 rforce=1 maxnotes=5 maxwarns=5 digits=5 cols=80 \

    pivrel=1e-3 sensfile="../psf/sens.output" checklimitdest=both  \

    sqldb_violating_ratio=yes

pss  (  vout  gnda  )  pss  flexbalance=yes  fund=10M  harms=100

+    errpreset=moderate  oscic=lin  oscmethod=onetier  tstabmethod=trap

+    annotate=status

Calculator function : ymax(leafValue( hb_spec_Pout "Design_Point" 1 )) gives 86uW

Harmonic Balance : input.scs

simulatorOptions options psfversion="1.4.0" reltol=1e-3 vabstol=1e-6 \

    iabstol=1e-12 temp=27 tnom=27 scalem=1.0 scale=1.0 gmin=1e-12 \

    gmindc=1e-15 rforce=1 maxnotes=5 maxwarns=5 digits=5 cols=80 \

    pivrel=1e-3 sensfile="../psf/sens.output" checklimitdest=both  \

    sqldb_violating_ratio=yes

hb  (  vinv_xto_inv  vinv_xti_inv  )  hb  saveinit=yes  autoharms=yes

+   autotstab=yes  oversample=[1]  fundfreqs=[(10M)]  maxharms=[5]

+   errpreset=moderate  oscic=lin  oscmethod=onetier  annotate=status

Calculator function : ymax(pvi('pss "/vinv_xto_inv" 0 "/V_xosc/PLUS" 0)) gives 76.4uW

Dear david j james,

Since Andrew has already commented on your simulator settings, I will default to his expertise.

david j james said:

Calculator function : ymax(leafValue( hb_spec_Pout "Design_Point" 1 )) gives 86uW

I noticed in your Calculator functions you are measuring the maximum power - this is not the value that a data sheet for a quartz crystal unit will specify. The maximum power dissipation is usually specified as an rms value. This is also why the Excel workbook uses the rms value of the voltage across the quartz crystal unit.

david j james said:

Is measuring the Power into a Quartz crystal by simulating the power into a terminal (of an ideal voltage source) a valid method in pss or hb?

I am not sure I understand enough about the topology of your measurement. How is the ideal voltage source configured relative to your quartz crystal unit and what is the opposite terminal of your quartz cyrstal unit connected to? Is your oscillator a Pierce or Colpitts topology?

Shawn

Thanks. I was not aware that hb-in-pss and hb are the same thing using the same engine.

The tool generates a spectrum with a single tone at 10MHz. I use the ymax function simply to get the magnitude of this tone. The rms calculator function doesn't work on this waveform.

The crystal Datasheets we have looked at, all quote 'Drive Level ( maximum)'. No mention of rms.

The oscillator is a Pierce type : like below but Ro is not used.

We strongly recommend using the hb interface.  It has all the "latest and greatest" features.   Two articles that I suggest you download and read from https://support.cadence.com are:

Getting the Most Out of Spectre® X-RF 21.1: Maximizing Performance 

How to simulate a high Q (LC or crystal) oscillator followed by strongly nonlinear circuitry (e.g. hard switching buffers) 

If you are a university student, please contact your professor (or Cadence contact at your university) and ask him to download these for you.

best regards,

Tawna

Dear david j james,

david j james said:

The tool generates a spectrum with a single tone at 10MHz. I use the ymax function simply to get the magnitude of this tone.

I would suggest you run a simple testcase where you apply a sinusoidal volatge across a resistor to determine if the peak value of the power represents an rms or peak power. If the spectruma relies on the Cadence dft(), it does not natively produce the rms value as its maximum. I have documented this and reported it.

david j james said:

The crystal Datasheets we have looked at, all quote 'Drive Level ( maximum)'. No mention of rms.

The maximum power dissipation is measured using the rms current. Please see, for example, the following two vendors suggestions for measuring power - both specify using the rms current. From a physics perspective, the peak power is not the important parameter but rather the rrns "heating" power. The latter impacts quartz resonator drive level effects and reliability (aging drift for example).

q-tech.com/wp-content/uploads/QTAN108-Crystal-Current-Measurement.pdf

www.renesas.com/us/en/document/apn/830-quartz-crystal-drive-level

david j james said:

The oscillator is a Pierce type : like below but Ro is not used.

I am sorry, but unless I am overlooking your Pierce schematic design, it does not show me how you voltage source is set up to measure power.

Shawn

When simulating high Q oscillators, set errpreset=conservative always.   hb accuracy depends more on harmonics.  pss accuracy depends more on errpreset.    These questions are answered in articles on https://support.cadence.com .  Do you have access?  

Firstly, sorry for the slow response cased by meetings at work. Thanks for your valuable support.

1. The testcase with a sinusoidal voltage (1V peak) across a 100 Ohm resistor gives hb = 5mW. Pout = V^2/R = 1^2/100 = 10mW. I have to think about where the x2 comes from, but I agree with you hb is giving MAXIMUM, not rms values.

2. the Quartz suppliers we looked at ( eg NDK), quote maximum drive. This has been confirmed with their rep.

3. the schematic I am using is this : bondwires, external caps with esr. the port and cds block are for stability sims. the 0V vdc used to measure power is called 'V_xosc'. The driver ( not shown ) is a simple Inverter.

Dear david j james,

david j james said:

1. The testcase with a sinusoidal voltage (1V peak) across a 100 Ohm resistor gives hb = 5mW. Pout = V^2/R = 1^2/100 = 10mW. I have to think about where the x2 comes from, but I agree with you hb is giving MAXIMUM, not rms values.

Please check your calculation, as I think the power of a 1 V amplitude sinusoid (2 Vpp) across a 100 ohm resistor is:

david j james said:

2. the Quartz suppliers we looked at ( eg NDK), quote maximum drive. This has been confirmed with their rep.

I'm not going to disagree, but the issue at hand is that the maximum drive refers to the rms power and not the peak power. From NDK's site:

reference:

Thank you for the schematic! I now understand that you are measuring the current through only the quartz crystal unit.

Shawn

Ok, thanks for the good support. This seems to clear up my issues.

Dear david j james,

Great! I am very happy to read you feel more comfortable with your results and thank you for letting us know. You put a lot of effort into your understanding and must be commended for that! Good luck!

Shawn

Dear david j james,

Great! I am very happy to read you feel more comfortable with your results and thank you for letting us know. You put a lot of effort into your understanding and must be commended for that! Good luck!

Shawn