How to simulate the negative resistance of a crystal osc

[gingerjxb]

the frequency is the quartz crystal frequency, and the current is the working current, i.e. the ac current flowing through the RLC branch
in fact, i let the circuit with quartz crystal model work, then measure the negative resistance in that condition

 

[hung_wai_ming@hotmail.com]

Hi gingerjxb,

What's the value of the ac current you set? What should be the factors determining this value?

 

[gingerjxb]

Hi gingerjxb,

What's the value of the ac current you set? What should be the factors determining this value?

the ac current is the current flowing through the inductor when the crystal oscillator works normally
the ac current influences the feedback resistance formed by MOS biased in linear region, so influences the negative resistance, i think

 

[hung_wai_ming@hotmail.com]

Hi ginerjxb,

i still don't understand. when we first design inverter amplifier, how can we know the amount of current flowing thru inductor? i can't understand which value i should set in this case. would you explain in more details how your design approach?

 

[gingerjxb]

i think the simulation value may be different from the design value, in fact, the simulation is only a verification
when selecting the working ac current, the simulated result should be more accuracy

 

[hung_wai_ming@hotmail.com]

Hi gingerjxb

Then what's your setting for your current source?
And how would u determine the negr from this ?

 

[gingerjxb]

in Isin, the amplitude is the working current amplitude, offset is 0, frequency is the crystal frequency

i measure the voltage through the current source and take dft, v is the amplitude at working frequency, and the negative resistance is v/I where I is the current amplitude divided by sqrt(2)