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I am trying to simulate a quartz crystal equivalent circuit. The series LCR part simulates as expected, but when I add a parallel capacitor the simulation fails. What am I doing wrong?
It would help if you listed your value of lumped elements. Better yet show your schematic. Without seeing what you have, I suspect your parallel cap value is much too large.
Keep in mind, the parallel capacitance is the equivalent C of the holder and electrodes, so a value of around 4.5pf would be typical. The series L and C is the resonant frequency so, Fo= 1/2pi(SQR LC) the resistance is mechanical equivalent.
Hello, thanks for response.
Have you checked the second image?
the parralel Cap on schematic is too big.
but there is a problem -
according to books Cpar and Cser should be close.
but try to simulate it and take a look on frequencies.
in real world in my field (which is ultrasonic welding) - these freqs are very close - f,e for 20Khz range it might be 19,800 and 20,000 or something like that.
in order to get these freqs close in simulation I had to increase Cpar.
there are formulas -
there are 2 resonant freqs -
one for serial resonance( L, R, C_ser)
for Fo_ser= 1/(6.28(SQR(L* C_ser)))
and second one - for parallel resonance ( L, R, C_ser, C_par)-
for Fo_par= 1/(6.28 ( SQR ( L* (C_ser * C_par) / (C_ser + C_par)))
it means that C_par and C_ser are connected in serial for that matter.
BTW that why , serial resonance freq is always higher then parallel one.
in order to get these freqs close to each other - the one of caps should be much bigger then other, and then C_ser and Cpar in serial would be close to C_ser .
run the numbers your self and see. or run simulations , play with parameters and see the results.
and another question - what way \ technick do you use to measure these parameters - I mean - C+ser and C_par.???
thanks in advance for your opinion
If I understood the question right, the poster was trying to model a quartz crystal, I assume the type used in a crystal oscillator. I am not sure how close a Piezo transducer is to a quartz crystal used in a oscillator, but I am sure the values for the transducer are larger as the resonant frequency is much lower.
I found a App note that describes the quartz crystal model fairly well. https://www.maximintegrated.com/en/app-notes/index.mvp/id/2127
Note, this is a snippet from the App note concerning the parallel capacitance.
CL1 and CL2 are the loading capacitors. During the test, CL1 = CL2 and the value varies from 5pf to 59pf with the inverter supply voltage Vcc = 3.1V and Vcc = 2.3V. The crystal in the test has a nominal frequency of 27MHz at load capacitance of 14pF. It should be noted that the actual loading capacitance to the crystal equals CL1 || CL2 plus the parasitic capacitance of board and the terminals of the inverters.
The pdf for the app note. http://pdfserv.maximintegrated.com/en/an/AN2127.pdf
Well, perhaps we are thinking Apples and oranges here, so I may just have misunderstood the original question.
hello, thanks for response.
I guess you are right, we talking apple and oranges here indeed.
But common denominator of crystalls and transdusers is - they both have the same model, but differt set of paramenters of coarse.
it seems to me the best solution - to read some good book aboutpiezzoelectric materials.
with hope it helps