[SI-LIST] Re: How to do crystal simulation
- From: Ray Anderson <ray.anderson@xxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Thu, 19 Jun 2008 06:57:21 -0700
Lurker-
A couple things for you to try:
1) Your motional capacitance in the crystal model is way too high. Try
about .0008pF for C1 (crystals have very small motional capacitance and
really high motional inductance.The high L/C ratio enable very high Q).
Your crystal models shunt capacitance of 8pF is a little high for a real
crystal (usually around 3pF or less) and the series resistance of 600
ohms is pretty high for most crystal.
2) Also put in a .nodeset v(a4)=3D1.7 statement.
Changing C1 and adding the .nodeset statement are about the minimum you
need to do to get it oscillating but the entire circuit model needs some
work. =
Your ideal opamp model using the E element will enable the simulation to
oscillate, but they sure are hard to find at most vendors when you want
to build a circuit :
BTW, what's this got to do with SI ???
-Ray
Raymond Anderson
Senior Signal Integrity Staff Engineer
Silicon Engineering Group
Signal Integrity and Package Development Department
Xilinx Inc.
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]
> On Behalf Of Lurker
> Sent: Thursday, June 19, 2008 1:36 AM
> To: 'Beal, Weston'; si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: How to do crystal simulation
> =
> Hi Beal,
> =
> I'm li. Please check the script. It doesn't work.
> =
> *Crystal sim
> =
> .option acct post list
> =
> .param cu=3D2
> E1 a1 0 a4 0 max=3D+3.3 min=3D0 cu
> =
> L1 a1 a2 0.08h
> C1 a2 a3 8pf
> R1 a3 a4 600
> c2 a1 a4 8pf
> c3 a1 0 22pf IC=3D0.5
> c4 a4 0 22pf IC=3D0.5
> R2 a1 a4 1m
> =
> =
> .temp 50
> .tran 10ps 100ns start=3D0ns
> =
> .print PAR('v(a1)')
> =
> .end
> =
> =
> Best Regards,
> =
> Lurker Li
> =
> Tel: 86-21-58966996-1021
> =
> =
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]
> On
> Behalf Of Beal, Weston
> Sent: Wednesday, June 18, 2008 10:45 PM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: How to do crystal simulation
> =
> =3D20
> Based on your description of you circuit, I would not expect it to =3D
> oscillate. An oscillator needs some amplification element and all of
you =3D
> circuit is passive elements. You should find a reference on basic =3D
> oscillator design.
> http://en.wikipedia.org/wiki/Pierce_oscillator
> =
> It sounds like you got your circuit from an IC design guide that =3D
> suggested a circuit for the input to a clock generator. The part you =3D
> missed is that the IC itself provides the amplifier that you are
missing =3D
> in your circuit.
> =
> Regards,
> Weston
> =
> =
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx] =3D
> On Behalf Of ? ?
> Sent: Wednesday, June 18, 2008 6:40 AM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: How to do crystal simulation
> =
> Hi David and Haixiao
> =3D20
> Thank you!=3D20
> I just got the crystal internal circuit. It's L. C. R in serial
and =3D
> parallel with a C.
> I will have a try in Hspice with a initialized capacitor or
inductor.=3D20
> The outside circuit is two capacitor( both of them is about 22ps) =3D
> connected crystal's output and input with a R(1Mohm) in parallel.
> I don't have ADS tool. So I can't use it. If necessory I will
release =3D
> the Hspice simulation script tomorrow night. Then you can see the =3D
> electrical circuit clearly.
> I'm not sure whether it can run or not.=3D20
> =3D20
> =3D20
> =3D20
> =
> "Pommerenke, David" <davidjp@xxxxxxx> =3DD0=3DB4=3DB5=3DC0=3DA3=3DBA
> Li,
> =
> Your attached file was not delivered, but normally I just set initial
=3D
> conditions on the capacitor or the inductor that is part of the XTAL =3D
> model.
> =
> =
> Dr. David Pommerenke
> Missouri University of Science and Technology (MST), former name: UMR
> 118 EECH, 301 W. 16th Street, Rolla, MO 65409-0040
> 573 341 4531, cell: 573 308 2019
> =
> =
> =3D20
> Did you add stimulus to start the spice simulation? For example, a
1ns =3D
> pulse.
> ADS has more choice on crystal simulation. Check the ADS help on =3D
> oscillators.
> =
> Regards,
> Haixiao
> =
> =
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx] =3D
> On Behalf Of ? ?
> Sent: Tuesday, June 17, 2008 8:35 AM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] How to do crystal simulation
> =
> Hi all,
> =
> I have a problem with crystal simulation. Please check the attached. I
=3D
> can't get the crystal start to "shake". The frequency I want to get is
=3D
> 25MHz. I didn't get the internal circuit for crystal. The Pspice model
=3D
> seems didn't work. What shall I do?
> =
> =
> =
> =
> =
> =
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