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Noise simulation in Spectrezd

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Sep 3, 2009
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Hi all;

I need a method to measure the thermal/ flicker noise contribution in frequency domain

So i run the transient simulation and noise simulation in Spectre, both way

Once i got the data-stream from the transient simulation and convert frequency domain with FFT//

there didn't exist thermal/flicker noise contribution in transient simulation result right?

I already know the inband noise power with noise simulation, I really have to measure the noise
contribution in transient environment however.

Can anyone help me?

Welcome answers , questions, discussion


Can you tell for what circuit you are looking for the noise results in transient. Are you looking for a noise shaping transfer cureve as in Sigma delta modulators? If you have DC signal level ( if you use single ended power supply) it would probably affect you tran noise results at low freq. I think you should simulate tran for around 20 to 40 cycles (Higher is better) and then use psd from calculator and then take db10 you should get it.

Hope this helps.
correct me if I am wrong.


I am now concerning delta sigma loop for adc.

In tran simulation, i can evaluate the effect of distortion to total performance as you told.

However there isn't amp thermal / flicker noise contribution in transient sim.

Those noise is consist of distortion from switched cap circuit by RC time constant and so on , no amp or res thermal / flicker noise

So i did capture the noise psd from noise sim and compare the SNDR result from

the transient sim

How long are you running your simulations for?

Hi fuelight,
Normaly the tran sim should cover evrything. So what was the result? Which was greater?

I mean how many microseconds of simulation time!
If you want to see 1/f, you need to run quite a long time... By the way, are you running transient noise?? If not, you will not see any noise at all!

Hi Joannes,
I use IC 5.1.41 n in that there is no option under transient analysis for Tran noise. So am I missing something? In btwn I ran the tran sim for about 40 cycles and step size set to 1/1000 of period and would a dc voltage affect noise results at 0.1hz?


If you are not running transient noise, you won't be able to see any noise at all in your transient simulation!

I am sorry, I do not understand what you mean by:
zopeon said:
In btwn I ran the tran sim for about 40 cycles and step size set to 1/1000 of period and would a dc voltage affect noise results at 0.1hz?

Could you tell me how to 'run transient noise' for transient simulation.

I had run the transient simulation for 40 cycles of my input frequency ( 33.33 sec for input signal frequency of 1.2 Hz) I am using a single ended supply, so my output has dc voltage. So would this dc voltage affect the noise results at 0.1 Hz if I take psd of the transient wave?

you need mmsim 7.1 to be able to run transient noise (in the transient set-up window there will be a check button and you need to specify some noise parameters).

how many samples are you using for your fft?

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