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#Post#: 112--------------------------------------------------
Re: 10 MHz Crystal Model
DIR By: Robert
Date: March 23, 2025, 3:32 pm
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I am getting old! - I do appologize.
Wrong: C2 = 1/(2*Pi*1e7*2.27e6) = 7.01 F = 7 fF
Correct: C2 = 1/(2*Pi*1e4*2.27e6) = 7.01e-12 F = 7 pF
1e4 = 10 kHz the frequency, where
2.27e6 = 2.27 MOhm, the practically purely capacitive reactance
of the crystal
#Post#: 113--------------------------------------------------
Re: 10 MHz Crystal Model
DIR By: MC12
Date: March 23, 2025, 7:38 pm
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--- Quote from: Robert link ---
>
> 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.
>
--- End Quote ---
Well, you did (see your screen shot in Post 5) – but it makes no
difference.
Yes I agree 50; 1.05k; 2.05k; 3.05k, BUT look at the green
traces in Post 5: there are four of them, when the 50R trace
should be hidden behind the red trace. That's what I have been
going on about... why are there four traces when there should be
three, plus one hidden??
#Post#: 114--------------------------------------------------
Re: 10 MHz Crystal Model
DIR By: Robert
Date: March 24, 2025, 8:55 am
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- The screenshot is in post 4, no attachment in post 5.
- In the equivalent circuit L1 = 38.4 mH is a tiny bit too
large, therefore
the (green) series resonance is ca. 3 kHz lower than with
crystal X1.
- After changing the value of L1 in fine steps, L1 = 38.379 mH
seems to be just right.
F(X1)/F(Equi) = sqrt(38.4/38.379) = 1.00027355, i.e. difference
is 2.7355 kHz.
See AC analysis screenshot attached.
#Post#: 115--------------------------------------------------
Re: 10 MHz Crystal Model
DIR By: MC12
Date: March 24, 2025, 6:30 pm
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--- Quote from: Robert link ---
>
> - The screenshot is in post 4, no attachment in post 5.
>
--- End Quote ---
"Reply #4" = post 5 (the original post in this thread being post
1).
As for the rest: it doesn't answer my question.
#Post#: 116--------------------------------------------------
Re: 10 MHz Crystal Model
DIR By: Robert
Date: March 24, 2025, 10:01 pm
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You wrote: "the green traces in Post 5: there are four of them,
when the 50R trace should be hidden behind the red trace".
The green trace for 50 Ohm cannot be hidden behind the red trace
because the 4 green traces (stepping) are ca. 3 kHz lower in
frequency.
The red trace is the frequency response of the crystal X1
(without stepping).
My last screenshot shows that for L1 = 38.379 mH the red and
green traces are practically identical.
#Post#: 117--------------------------------------------------
Re: 10 MHz Crystal Model
DIR By: MC12
Date: March 25, 2025, 3:18 am
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Please explain why the green traces in Post 5 are all severely
damped compared with the red trace. If the green traces
correspond with R4 = 50R, 1.05k, 2.05k, 3.05k, I would have
thought that the 50R trace would show the same minimal amount of
resonance damping as the red trace (and therefore be
more-or-less coincident with it).
I believe that was the original point of this thread? You seem
to be satisfied that everything is explained, so what have I
missed?
It's never been spelled out, but is in fact X1 a standard
crystal model while X2 is an equivalent circuit macro? If so,
what have you done to correct the damping?
For other readers: if read casually, this thread might come
across as argumentative. It's not meant to be, this is the two
of us trying to explain what we mean using the limited
communications channel of an Internet forum, and at the moment
there is still some misunderstanding...
#Post#: 118--------------------------------------------------
Re: 10 MHz Crystal Model
DIR By: Robert
Date: March 25, 2025, 8:56 am
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- "Please explain why the green traces in Post 5 are all
severely damped compared with the red trace."
As R5 increases, the Q (quality factor) of the entire RLC series
circuit is decreasing.
Just think of Q = 2*Pi*f*L/R = 1/(2*Pi*f*R), i.e.the higher R,
the lower the Q.
- "is in fact X1 a standard crystal model while X2 is an
equivalent circuit macro?"
X1 is the crystal KDS_100_S (10 MHz) from the analog library of
MicroCap 12.
There is no X2 in my schematic, but the equivalent circuit
determined by simulating
X1 at a frequency far below (in this case at 10 kHz) of the
crystal resonance.
In one of the schematics I added the calculus for determining
the component values
of the equivalent circuit.
As already demonstrated, when making L1 = 38.379 mH ( instead of
38.4 mH) the red and
green plots are practically coincident.
The purpose of my efforts was to arrive at an equivalent circuit
that I can use for a filter design software.
Thank you again for your involvement.
#Post#: 119--------------------------------------------------
Re: 10 MHz Crystal Model
DIR By: MC12
Date: March 26, 2025, 2:51 am
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--- Quote from: Robert link ---
>
> As R5 increases, the Q (quality factor) of the entire RLC
series circuit is decreasing.
> Just think of Q = 2*Pi*f*L/R = 1/(2*Pi*f*R), i.e.the higher R,
the lower the Q.
--- End Quote ---
Are you saying (while avoiding the issue!) you had the series
resistance in your equivalent circuit too big, and that's why
the green lines in the simulation you first published are all
significantly damped?
--- Quote from: Robert link ---
>
> There is no X2 in my schematic, but the equivalent circuit...
>
--- End Quote ---
Clearly there is, in the information you first provided, and you
did not state that it was an equivalent circuit, which has been
the cause of considerable confusion. Perhaps you attached the
wrong screen-shot by mistake. From your first several posts,
for all I knew R4 provided the damping, and therefore with
R4=50R the green curves should have looked like the red curve.
From Post 5:
[attachimg=1]
It pays to re-read your own posts once in a while!
#Post#: 120--------------------------------------------------
Re: 10 MHz Crystal Model
DIR By: Robert
Date: March 26, 2025, 9:59 am
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You asked: "Are you saying (while avoiding the issue!) you had
the series resistance in your equivalent circuit too big, and
that's why the green lines in the simulation you first published
are all significantly damped?"
Answer: No. The series resistance in the equivalent circuit is
given with 80 Ohms in MC12 (macro of the crystal KDS_100_S).
It's the terminating resistor that I stepped in the simulation.
The larger the terimating resistor, the lower the circuit Q.
My appologies if I caused any confusion.
#Post#: 121--------------------------------------------------
Re: 10 MHz Crystal Model
DIR By: MC12
Date: March 28, 2025, 2:48 am
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I don't seem to be able to get my point understood and answered.
I give up.
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