Spectre noise type definitions

Dear livingstone,

livingstone said:

Are there documented definitions for the noise types in Simulation -> Options -> Analog and how the model parameters are overridden/modified when turned on/off?

There are a couple of documents in the response to the recent Forum post at URL:

https://community.cadence.com/cadence_technology_forums/f/custom-ic-design/52441/what-are-the-noise-options-under-simulator-options/1385408#1385408

In addition, with respect to your comment regarding checking or unchecking the flicker option and your simulation result, the note regarding "Confusing results when using noiseon_type and noiseoff_type..." at URL:

support.cadence.com/.../ArticleAttachmentPortal

may be of interest.

livingstone said:

I am specifically interested in what "ign" is referring to - induced gate noise?

Yes. "ign" is an acronym for "induced gate noise". In spite of its name, my understanding is its origin is in the thermal noise within the channel.

I hope these help livingstone!

Shawn

Hi Shawn, 

Yes that was helpful, thank you.

I am not 100% clear on how the 'noiseon_type' and 'noiseoff_type' selections work in my case (despite reading the troubleshooting post you shared), but after playing with it some more I realized that 'noiseoff_type' isn't doing much of anything whereas 'noiseon_type' is.

The logic seems to be something like: if nothing is checked in 'noiseon_type' then everything is on whereas if one or more are checked then the remaining are disabled, and again 'noiseoff_type' doesn't seem to do anything. Previously I had checked 'thermal' in 'noiseon_type' and 'ign' in 'noiseoff_type' and wrongly concluded that 'ign' was behaving like 'flicker'.

Dear liivingstone,

Thank you for letting me it was somewhat useful!

I can understand your confusion! I've put together an example where I've tried to show the noise results with and without flicker noise included. There are a couple of radio button settings that will accomplish the latter,  and I've documented each. Give me a little time and I'll send the example later today if you still have the time and patience!

Shawn

Dear livingstone,

A bit late, but Ive put together an example of four noise simulations with various combinations of the noise on/off settings in the analog options noise GUI. There is a priority as is evident when you examine the netlist that results from the various noise GUI choices. As is also evident, the noiseoff_type settings do function when not "trumped" by the noiseon_type setting. See what you think. The short note is at URL:

www.dropbox.com/.../ac_noise_on_off_functionality_091622v1p0.pdf

Shawn

Hi ShawnLogan

To my understanding, using on/off option for the instances divides them into two categories (on category and off category). Noiseon_type determines the noise sources for the on category and noiseoff_type determines the noise sources for the off category. To cover more combinations and have a better understanding of these options, you can create some cases where one of the inverters is in the off category. 

Mohammad

Hi Shawn, 

Thank you for looking into it and confirming that the behavior is the same. As Mohammad commented below the categories may make more sense when specifying individual instances. Still, I have to say that I find the GUI options somewhat confusing.

Dear MohNaj and livingstone,

MohNaj said:

To my understanding, using on/off option for the instances divides them into two categories (on category and off category). Noiseon_type determines the noise sources for the on category and noiseoff_type determines the noise sources for the off category. To cover more combinations and have a better understanding of these options, you can create some cases where one of the inverters is in the off category. 

Yes. This is what both livingstone and I pointed out. I believe the confusion arises when, for example, the noise_on "all" radio button is checked AND one of the noise_off noise source radio buttons is selected. The question is which option is applied. As I tried to show in the examples in the note at URL:

www.dropbox.com/.../ac_noise_on_off_functionality_091622v1p0.pdf

the "noise_on" setting appears to "trump" the noise_off setting. As also shown in the note, the best way to check which noise source is on or off is to inspect the simulationOptions setting within the netlist created from a specific set of noise_on/noise_off radio button choices and realize the noise_on takes preference to noise_off.

livingstone said:

Still, I have to say that I find the GUI options somewhat confusing.

I agree with you as I mentioned in my initial response!

Thank you for following up!

Shawn