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#Post#: 102--------------------------------------------------
Re: 10 MHz Crystal Model
DIR By: MC12
Date: March 20, 2025, 10:32 am
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Can't you extract those values from the SPICE model for the
crystal?
#Post#: 103--------------------------------------------------
Re: 10 MHz Crystal Model
DIR By: Robert
Date: March 20, 2025, 12:07 pm
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I wouldn't know how to do that.
What I found is in the attachment. - Incomplete data.
I will try to determin the equvivalent component values by doing
AC analysis at different suitable frequency ranges.
Will let you know if I find out something useful.
#Post#: 104--------------------------------------------------
Re: 10 MHz Crystal Model
DIR By: Robert
Date: March 20, 2025, 3:39 pm
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Sweeping the crystal at far below the resonant frequencies and
making use of the macro data I finally arrived at the equivalent
circuit parameters. Due to inaccuracies in the calculus, the
equivalent circuit resonances are about 3 kHz lower compared to
X1.
Please have a look at the two screenshots. - What do you think?
#Post#: 105--------------------------------------------------
Re: 10 MHz Crystal Model
DIR By: Robert
Date: March 20, 2025, 3:41 pm
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Sorry, missed oiut on the schematic.
#Post#: 106--------------------------------------------------
Re: 10 MHz Crystal Model
DIR By: MC12
Date: March 21, 2025, 2:53 am
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I would say that's damn good! You've done well there.
The next thing is to use your equivalent circuit in place of X1
and X2 in your original experiment, and see whether the
simulation run with stepped resistor value produces the same
weird results.
#Post#: 107--------------------------------------------------
Re: 10 MHz Crystal Model
DIR By: Robert
Date: March 21, 2025, 4:15 pm
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The bigger R3 the the less pronounced becfomes the series
resonant peaking.
Obvious, since the constant voltage source is masked with a
constant current source (sort of).
#Post#: 108--------------------------------------------------
Re: 10 MHz Crystal Model
DIR By: MC12
Date: March 22, 2025, 4:08 am
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Things are beginning to make a glimmer of sense.
Assuming the annotations on your simulation dB/f mean values of
R4, you've gone 50 to 500 step 150.
In the dB/f from Post 5, the simulation parameters quoted on the
schematic are "50 to 3.55k step 1k" which implies 50, 1.05k,
2.05k, 3.05k.
If we ignore the 50R step, the 1k, 2k, and 3k runs would be
consistent with the green plots. The 50R plot should be hidden
behind the red line.
What I don't understand is why there are four green lines in the
"a few k" region of the graph (Post 5).
It seems to me the simulation parameters must be not what I
would have expected, and those four lines are runs with R4 =
1.05k, 2.05k, 3.05k, and 4.05k. I'm willing to bet that if you
plugged those values into your new simulation you would get
plots which mimic Post 5 (albeit shifted in frequency). If
correct, the question is why your step formula produced those
simulation run values.
You could verify by using the same step formula in a simple
potential divider network. It might also be worth running
simulations on the original circuit with specific values of R4
to see whether setting R4 to 1k, 2k, 3k, 4k produces the same
lines.
#Post#: 109--------------------------------------------------
Re: 10 MHz Crystal Model
DIR By: Robert
Date: March 22, 2025, 10:14 am
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I chose the values 50, 200, 350 and 500 for the sake of
demonstrating that the higher the termination resistor, the
lesser the series resonant peaking. For much higher values (in
the oder of kOhms) the peaking is masked by the high resistance
in series with the crystal.
The response plots for X1 and the equivalent circuit
respectively are qualitatively identical with the ca. 3 kHz
shift on the frequency axis.
I think we can't blame MC12 for any issues regarding the crystal
simulation. - Do you agree? Thanks for dealing with my posts.
#Post#: 110--------------------------------------------------
Re: 10 MHz Crystal Model
DIR By: MC12
Date: March 22, 2025, 2:16 pm
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--- Quote from: Robert link ---
>
> I chose the values 50, 200, 350 and 500 for the sake of
demonstrating that the higher the termination resistor, the
lesser the series resonant peaking. For much higher values (in
the oder of kOhms) the peaking is masked by the high resistance
in series with the crystal.
> The response plots for X1 and the equivalent circuit
respectively are qualitatively identical with the ca. 3 kHz
shift on the frequency axis.
> I think we can't blame MC12 for any issues regarding the
crystal simulation. - Do you agree?
>
--- End Quote ---
Unless I misunderstood your original post, the "much higher
values" used in your original simulation are to blame for the
stated problem (apparent lack of resonances) – am I correct?
I'm not sure what other "issues" remain, except...
I still don't understand why "50 to 3.55k step 1k" produces four
traces at values >>50R.
--- Quote from: Robert link ---
>
> Thanks for dealing with my posts.
>
--- End Quote ---
We're all learning. All I did was help you find an answer for
yourself.
#Post#: 111--------------------------------------------------
Re: 10 MHz Crystal Model
DIR By: Robert
Date: March 23, 2025, 9:34 am
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I don't understand: "I still don't understand why "50 to 3.55k
step 1k" produces four traces at values >>50R."
Stepping: Start = 50; End = 3.05k; Step = 1k, i.e. 50; 1.05k;
2.05k; 3.05k. - My mistake if I said 3.55k.
Correction: The calculus for C2 in the schematic has a printing
error.
It should be: C2 = 1/(2*Pi*1e7*2.27e6) = 7.01 F = 7 fF
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