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Simulators >> RF Simulators >> LC VCO simulation issue
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Message started by aamar on Nov 18^th, 2010, 8:39am

Title: LC VCO simulation issue
Post by aamar on Nov 18^th, 2010, 8:39am

Hallo,

The case which I want to ask about is so
Verifying a LC VCO with amplitude regulation loop, I found that the amplitude and frequency stabilize itself in short time in liberal and moderate spectre settings. When simulating the same setup using the conservative setting the loop doesn't stabilize after 10 times the period required for stabilization in liberal settings and it seems that it will not come to a result. So, my questions are:
1. Which should I believe the liberal and moderate simulations or the conservative?
2. Which parameters should I try to adjust in the simulation option which lead to a compromisation bet. speed and accuracy in case of oscillator simulation?

Thanks in advance

Best regards,

aamar

Title: Re: LC VCO simulation issue
Post by sheldon on Nov 18^th, 2010, 5:18pm

Amar,

In general, my feeling is that simulating a VCO is not a place to
consider cost-performance. They are difficult circuits to analyze
and are sensitive to numerical noise because the their gain, kvco,
tends to be high. In addition, VCO tend to be relatively small so the
penalty of simulating with high accuracy is not as high. Having said
that, I would try one of the following options when using Spectre:

1) moderate
2) conservative
3) conservative w/ method=traponly
4) moderate w/ relref=alllocal or pointlocal

In general, using the trapezoidal integration method is better for
oscillators, there is a detailed discussion of the topic in Ken Kundert
SPECTRE book. If you are seeing differences between moderate
and conservative, then options # 3 & 4 may help explain the
difference.

Best Regards,

Sheldon