The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Simulators >> RF Simulators >> Dynamic Comparator Noise Analysis
https://designers-guide.org/forum/YaBB.pl?num=1268437202

Message started by Tainted_Cabbage on Mar 12^th, 2010, 3:40pm

Title: Dynamic Comparator Noise Analysis
Post by Tainted_Cabbage on Mar 12^th, 2010, 3:40pm

Hey Everyone --

I'm working on designing a dynamic latched comparator (for an ADC) and am trying to test the noise response (in spectre). My current simulation methodology is to run an AC simulation of a zero input comparator (that is on) and find the approximate bandwidth of the device. Then I switch to a transient analysis with noisefmax = AC bandwidth. I then find the BER of the output with an LSB/2 input and if I get above 99% accuracy I figure I'm ok.

My general question is whether this is accurate or not. While I haven't been on the forum for very long, I did see some posts questioning the accuracy of transient noise and suggesting using Pnoise to get the same information.

Even if Pnoise is more accurate, I'm still unsure of how to test the comparator. I would like to get the input referred integrated noise, but I'm not sure where to strobe the output (ie right before the comparator turns on or right after) and how the input referred calculation is made.

Thanks for the help and if someone could point me to a past post that I might have missed that would be great too!

Title: Re: Dynamic Comparator Noise Analysis
Post by sheldon on Mar 12^th, 2010, 9:44pm

Greetings,

I am not sure that this methodology will work. Please see,
"Noise Analysis of Regenerative Comparators for Reconfigurable
ADC Architectures", Pierluigi Nuzzo, Fernando De Bernardinis,
Pierangelo Terreni, and Geert Van der Plas, IEEE TRANSACTIONS
ON CIRCUITS AND SYSTEMS—I: REGULAR PAPERS, VOL. 55, NO. 6,
JULY 2008, page 1441-1454 for some discussion of the topic.

Transient noise is not inaccurate, however, the setup is not as push
button as traditional small signal noise analysis.

Best Regards,

Sheldon

Title: Re: Dynamic Comparator Noise Analysis
Post by Tainted_Cabbage on Mar 20^th, 2010, 5:24pm

Hi Sheldon --

Thanks for the post. I've been reading the paper recommended and will try to get Pnoise simulations for my comparator parameters.

On the transient noise front, why is it not as push button as you say? From the set-up it seems that most of the parameters are pretty simple, with "noisefmax" being the only possible question mark. Are there any references on doing "BER" type analysis using transient noise? Thanks a ton!

Title: Re: Dynamic Comparator Noise Analysis
Post by sheldon on Mar 23^rd, 2010, 5:56pm

Tainted_Cabbage,

There are two factors to consider. First is the circuit sampling, i.e.,
a sample and hold, or not, i.e., VCO, etc.? Then you need to consider
noisefmax. Depending on the badnwidth of the sampling front-end
noisefmax may need to set higher than you would think from just
looking at the blocks specifications, for example, a flip-around S/H
has a lot of bandwidth. I have not seen much discussion of BER
simulation with transient noise. It is a hard problem since you need
lots of samples at the same time the simulation cost, time, of the
simulation is high. Do have some ideas for how it could be done
but since I have not tried them do not know they would work:-(

Best Regards,

Sheldon