[Moved]: [Cadence Virtuoso ADE Calculator] Difference between Freq and Frequency Function?

[etmsni]

[Moved]:[Cadence Virtuoso ADE Calculator] Difference btw Freq and Frequency Function?

I'm trying to find the period of a waveform in Cadence Virtuoso ADE using the calculator function. I see in the user manual that there's two things(please see below picture): (1) Freq function (2) Frequency Function



What's the difference between those two? My guess is that "Freq" function is instantaneous frequency, and "Frequency Function" is like frequency over a period?

Thank you!

 

[pancho_hideboo]

Re: [Cadence Virtuoso ADE Calculator] Difference btw Freq and Frequency Function?

Surely read OCEAN manuals.
Or launch Skill API Finder from CIW of Cadence dfII.
Then search "freq".

frequency() returns averaged frequency as numerical value.
On the other hand, freq() returns waveform.

 

[etmsni]

Re: [Moved]:[Cadence Virtuoso ADE Calculator] Difference btw Freq and Frequency Funct

Thanks!!! I tried out the freq() function, and see that it returns a waveform on top of the original signal. What does this waveform mean or represent?

 

[pancho_hideboo]

Re: [Moved]:[Cadence Virtuoso ADE Calculator] Difference btw Freq and Frequency Funct

Launch Skill API Finder.
Then search "freq" and read results.

 

[etmsni]

Re: [Moved]:[Cadence Virtuoso ADE Calculator] Difference btw Freq and Frequency Funct

I launched Skill API Finder, searched "freq", and read the results(please see 1st picture). The results are the same as the image of the user manual I posted in my original post(please see picture in original post). What I'm trying to understand is the physical meaning of freq, not the definition, which has already been looked up.



For example, say there is a basic 5-ring ring oscillator made out of invertors. I did the "freq" and it returns a squiggly line as in the below picture.


A ring oscillator has a periodic signal output, so it should only have one frequency. In this case, what does that squiggly line mean? Thanks!

 

[pancho_hideboo]

Re: [Moved]:[Cadence Virtuoso ADE Calculator] Difference btw Freq and Frequency Funct

I launched Skill API Finder, searched "freq", and read the results(please see 1st picture).

Surely read.
It says that "as function of time".

What I'm trying to understand is the physical meaning of freq, not the definition, which has already been looked up.

Everyone can understand its physical meaning by definition very easily except for you.

Simply only you can not understand this very easy definition.

A ring oscillator has a periodic signal output, so it should only have one frequency. In this case, what does that squiggly line mean?

Simply they are pertubation.
Your transient analysis result can not reach steady state.

 

[etmsni]

Re: [Moved]:[Cadence Virtuoso ADE Calculator] Difference btw Freq and Frequency Funct

Can you please explain why it isn't in steady state? The original signal from the ring oscillator is a periodic signal, so it should be in steady state. If it wasn't in steady state, the ring oscillator couldn't oscillate.

 

[pancho_hideboo]

Re: [Moved]:[Cadence Virtuoso ADE Calculator] Difference btw Freq and Frequency Funct

If it wasn't in steady state, the ring oscillator couldn't oscillate.

Wrong.
Surely study oscillator.

 

[etmsni]

Re: [Moved]:[Cadence Virtuoso ADE Calculator] Difference btw Freq and Frequency Funct

I've tried looking at "Design of Analog CMOS Integrated Circuits" by Behzad Razavi and googling, but haven't figured it out. Is it possible to please explain the general idea? My background is chemistry, so it's hard to understand the principles sometimes. Thank you!

 

[pancho_hideboo]

Re: [Moved]:[Cadence Virtuoso ADE Calculator] Difference btw Freq and Frequency Funct

Can you understand steady state ?

time=0~1nsec
fmax=16.8780GHz
fmin=16.8725GHz

f0=(fmin+fmax)/2=16.87525GHz
delta_f=fmax-fmin=0.0055GHz

(delta_f/2)/f0*100=0.016%

Try to increase end time such as 100nsec.

And Frequency pertubation until steady state could be varied with maxstep in Cadence Spectre or delmax in Synopsys HSPICE.

Generally it is impossible to evaluate oscillation frequency at true steady state with transient analysis.
https://www.edaboard.com/showthread.php?t=356560#11

Autonomous-Shooting-Newton-PSS is preferable for your circuit rather than Autonomous-HB-PSS.

 

[etmsni]

Re: [Moved]:[Cadence Virtuoso ADE Calculator] Difference btw Freq and Frequency Funct

1. Looking at this thread (https://www.designers-guide.org/Forum/YaBB.pl?num=1234428781/1#1 ), I'm now confused about steady state. Is it that steady state means that the signal doesn't change with time (https://www.quora.com/What-is-meant-by-steady-state-Is-it-defined-for-ac-circuits-also-If-yes-how), so a ring oscillator in steady state doesn't mean it has to oscillate? Oscillation has nothing to do with steady state; it is just a result of satisfying the Barkhausen condition? In this case, I don't understand what the steady state is for a ring oscillator.

2. "(delta_f/2)/f0*100=0.016%" => What is the purpose of this calculation?

3. Is the reason why "it is impossible to evaluate oscillation frequency at true steady state with transient analysis" due to the inability to get phase noise in transient analysis(https://www.edaboard.com/showthread.php?t=356560#13)? I'm not sure what phase noise has to do with oscillation frequency, or am I probably misunderstanding something?

4. Thanks for pointing out "Autonomous-Shooting-Newton-PSS". I'm studying it now from these two threads (https://www.edaboard.com/threads/145529/) & (https://www.edaboard.com/threads/154139/#post819260).

5. I increased the time to 100ns, and still see the similar perturbation ().

Thank you for your patience and help!

 

[pancho_hideboo]

Re: [Moved]:[Cadence Virtuoso ADE Calculator] Difference btw Freq and Frequency Funct

In this case, I don't understand what the steady state is for a ring oscillator.

Until it can reach steady state, both amplitude and period will be varied.

Study "Autonomous-Shooting-Newton-PSS" of Cadence Spectre.
It checks amplitude and period as Shooting Trial Intervals.

2. "(delta_f/2)/f0*100=0.016%" => What is the purpose of this calculation?

I mean frequency pertubation during transient is very small.

I'm not sure what phase noise has to do with oscillation frequency,
or am I probably misunderstanding something?

Can you understand Transient-Noise Analysis ?
Transient-Noise Analysis is available in both Cadence Spectre and Synopsys HSPICE.

However I think you do conventional Transient Analysis without Noise.
So phase noise is not concerned for your case at all.

5. I increased the time to 100ns, and still see the similar perturbation

Tighten simulation accuracy.
If you use Cadence Spectre, set "errpreset=conservative".
If you use Synopsis HSPICE, set "RUNLVL=6" or use HPP(HSPICE Precision Parallel).

Or set small value as "maxstep" of Cadence Spectre or "delmax" of Synopsis HSPICE.
For example, (1.0/16G)/100.0.

 

[etmsni]

Re: [Moved]:[Cadence Virtuoso ADE Calculator] Difference btw Freq and Frequency Funct

Thank you so much for your guidance!!! I am so grateful for your help, especially when pointing me in the right directions. I will study the ""Autonomous-Shooting-Newton-PSS of Cadence Spectre" and "Transient-Noise Analysis." I don't understand "Transient-noise analysis" well, but I have checked out some books on that topic.