The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Simulators >> Circuit Simulators >> PLL: Frequency step response, Lock range simulation
https://designers-guide.org/forum/YaBB.pl?num=1490718832

Message started by deba on Mar 28^th, 2017, 9:33am

Title: PLL: Frequency step response, Lock range simulation
Post by deba on Mar 28^th, 2017, 9:33am

Hi,

1) How does one check the PLL closed loop transient response to a step change in the input frequency? Is there a source available which models frequency step?

2) How does one simulate/measure the lock range for PLL?

Thanks

Title: Re: PLL: Frequency step response, Lock range simulation
Post by Ken Kundert on Mar 28^th, 2017, 12:13pm

Easy to create such a source with Verilog-A.

-Ken

Title: Re: PLL: Frequency step response, Lock range simulation
Post by deba on Mar 31^st, 2017, 12:34am

Hi Ken,

Thanks for the suggestion. I managed to do it using dynamic parameter option in transient analysis.

Thanks

Title: Re: PLL: Frequency step response, Lock range simulation
Post by Hercules Poirot on Aug 8^th, 2017, 6:03am

Make a small signal model of the PLL.
The steps to do it are as follows:
1. Your PFD [well in this small signal 'phase' model its just going to be a phase detector] can be just a voltage controlled current source. [VCCS from analogLib].
2. The current source value will be Icp / (2*pi)
3. You can make the loop filter using R & C (from analogLib)
4. Your VCO will be VCCS followed by a 1F capacitor [to emulate an integrator] with a gain of your Kvco (make sure its in rads/s-V).
5. Your divider can be just a VCVS with a gain of 1.0/feedback_factor.

The output of the divider and the reference input goes to the VCCS of (1).

To simulate the effect of a frequency step, just give a ramp input with a slope of fstep*2*pi [the 2*pi factor is to account for Hz to radians/s-V conversion]

Title: Re: PLL: Frequency step response, Lock range simulation
Post by Hercules Poirot on Sep 8^th, 2017, 9:42am

See this image. I use this to run AC analysis using Spectre.