A question on phase locked loop Hspice simulation

May 17, 2006 3 Replies
F

Hi, Everyone,



I posted a question on Phase Locked Loop several weeks ago and thank you very much for everyone's reply.



Here I have another question related to hspice simulation on the phase locked loops -- I want to measure the lock time of the loop using hspice for 1000 times with different loop parameters. I tried to use derivative of the VCO input signal and I tried to use the phase difference between the reference signal and the VCO output.... basically, what I am using is the .measure command and find and when function.



However, all the things I tried do not work -- it does not really predict the lock time for me.



I read the hspice manual and I cannot find an existing function that can directly do it. Anybody here has some ideas, please?



Thanks a lot!



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T

Are you having difficulty finding when the loop is in lock, or are you having difficulty convincing HSPICE to measure it?

What sort of phase detector do you have?

What sort of loop filter do you have?

I'm not a big SPICE jockey, but the way I'd do this in SciLab or MatLab would be to take average VCO input at the very end of the run as the 'settled' value, then backtrack until the VCO input was outside of some bound around the settled value -- this would be easy in one of the above analysis packages, but I couldn't begin to tell you how hard it would be in SPICE.

Tim Wescott Wescott Design Services http://www.wescottdesign.com Posting from Google? See http://cfaj.freeshell.org/google/ "Applied Control Theory for Embedded Systems" came out in April. See details at http://www.wescottdesign.com/actfes/actfes.html
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J

This is a toughy. I'm not sure if you can force enough initial conditions to get Spice to walk into lock rather than jumping artificially to a lock solution.

Maybe force the VCO control voltage off-lock for a long period of time, then release and let it walk in.

...Jim Thompson

| James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
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E

I have several PLL articles using SPICE:

- Motorola AN1671 MC145170 PSpice modeling kit by Onis Cogburn

- Microwaves and RF November 1997 "SPICE Tools Provide Behavioral Modeling of PLLs" by Orlando Pena

- Choi and Connelly have a book devoted to PLLs and SPICE

Good luck, Dave

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