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crystal oscilator phase response

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naisare

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I am designing an osillator with inverter and crystal combination. I want to check what is the phase shift. I agree it should be 360 degree or 0 degree. But I want the plot for verification. How can I do this. What is the circuit setup.
Please help me.
thanks
 

What kind of simulator do you use?
What you mean circuit setup? Is that simulation circuit?
Just insert Vdc=0V with Vac=1mV between invertor input and feedback network which include feedback resistor, crystal model, and two capacitors and run AC analysis. Than plot V1/V2 phase response, where V1 and V2 are Vdc source terminals.
 

How about the loopgain? Can I just use .probe vdb(V1,V2) to plot the loop gain?
 

Fom said:
What kind of simulator do you use?
What you mean circuit setup? Is that simulation circuit?
Just insert Vdc=0V with Vac=1mV between invertor input and feedback network which include feedback resistor, crystal model, and two capacitors and run AC analysis. Than plot V1/V2 phase response, where V1 and V2 are Vdc source terminals.
Click to expand...
---
hi fom,
i did AC analysis like u mentioned above.
but V1/V2 gives out openloop gain plot.(how to measue loopgain BETA*AOL directly).
to find out the phase response,i added PHASE(V1)+PHASE(V2).is that right?
please write me in details if my interpretation is wrong.
thanks in advance.
--
kamal.
 

If you break feedback and insert Vdc=0 with Vac=1m at the invertor input it will be BETA*AOL because the loop will include both AOL of invertor and BETA of feedback.
About phase you can use VP(Vout,Vin). This is for Hspice. I don't know which simulator do you use, because you didn't answered.
 

hi fom.
thanks for fast reply.
i use hspice and analog artist(ADE).
i have 5meg RF and inv gain of ~100v/v.
around 32khz i have only 269deg phase.still circuit oscilates.
can u plz suggest me the way to get 360 deg.
i read one texas doc. RF should be selected such that crystal's parallel resonance resistance =input impedance of inverter.{AN-101-00039en.PDF}.
if i calculate as per texas doc file,i have to use around 350MEG feedback.really confused..
could you plz help me if you know answer.

BEST REGARDS,
KAMAL.
 

About 32 kHz between series and parallel resonances phase changes greatly. You definetely should have 0 or 360 degree.
I suppose the X-axis scale in your simulation not very precise so you cannot catch it. Run AC simulation with sweeping frequency range from 32 kHz to 33 kHz for beginning and for next step change the frequency to more narrow range to get correct simulation result.
 

hi fom,
thanks for your info regarding osc pad.
rgds,
kamal.
 

just another word: It's interestig to plot the phase response by means of a PLL. In this technique the quartz is used as a Phase shifter whose phase depend upon frequency. Sending into the quartz a smal sinewave at different frequency by varying the PLL programmed freq and analyzing the difference on the locked phase you con evaluate the phase response
 

kamalakkannan said:
hi fom.
thanks for fast reply.
i use hspice and analog artist(ADE).
i have 5meg RF and inv gain of ~100v/v.
around 32khz i have only 269deg phase.still circuit oscilates.
can u plz suggest me the way to get 360 deg.
i read one texas doc. RF should be selected such that crystal's parallel resonance resistance =input impedance of inverter.{AN-101-00039en.PDF}.
if i calculate as per texas doc file,i have to use around 350MEG feedback.really confused..
could you plz help me if you know answer.

BEST REGARDS,
KAMAL.
Click to expand...

just use ac simulation and plot much more points at the side of resonant frequency because the crystal has a very high Q value!
 

Dear all :
How do we simulate the transient ? We can sim AC repsonse . But we can't guarntee the duty cylcle .
Does any comment
 

Fom said:
What kind of simulator do you use?
What you mean circuit setup? Is that simulation circuit?
Just insert Vdc=0V with Vac=1mV between invertor input and feedback network which include feedback resistor, crystal model, and two capacitors and run AC analysis. Than plot V1/V2 phase response, where V1 and V2 are Vdc source terminals.
Click to expand...

does 'Vdc=0V' setting affect the ac analysis result?
i think here should set vdc=vdd/2 or some near that.
yes or no?
 

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