How to apply info about noise in transient simulation ?

[surianova]

noise in transient

hi

Some question about noise, I get noise around 100nv/hz in AC analysis, but the problem is how can i apply this info in transient simulation? Thanks.

Suria

 

[terryssw]

Re: noise in transient

I don't think you can do it since the machanism of simulating noise and transient is different. You can only obtain the noise level by noise analysis, and keeping in mind that it is your noise floor.

 

[borodenkov]

noise in transient

What you can do is to insert a nosie source with the PSD obtained from Noise simualtion to a behavioral (transient) model of your circuit and to estimate its effect on system performance. This technique can be used for example for PLLs or delta-sigma modulators.

 

[surianova]

Re: noise in transient

What you can do is to insert a nosie source with the PSD obtained from Noise simualtion to a behavioral (transient) model of your circuit and to estimate its effect on system performance.

1.Any command for the noise sourse with the PSD?
2. how to do behavioral (transient) model ?

TX

 

[crazyamd]

Re: noise in transient

noise is measured by a PSD - often as the amount of noise in 1 Hz BW. To simulate in time domain, you need to simulate it for a fairly long period with very small steps so that the high freq noise is included. So ac or xf simulation is more useful.

 

[surianova]

Re: noise in transient

noise is measured by a PSD - often as the amount of noise in 1 Hz BW. To simulate in time domain, you need to simulate it for a fairly long period with very small steps so that the high freq noise is included. So ac or xf simulation is more useful.

why run with long period with very small steps, high freq noise is included?

 

[terryssw]

Re: noise in transient

high-frequency components change value in very small time period, so if you want to simulate noise up to high-frequency, your time-step must be very small. This is also one of the reason why noise analysis do not embedded into the transient analysis in simulators since to cover all noise power with enough bandwidth, very small time-step must be used and this would very costly (and impossible) for transient simulations.

 

[surianova]

Re: noise in transient

high-frequency components change value in very small time period, so if you want to simulate noise up to high-frequency, your time-step must be very small. This is also one of the reason why noise analysis do not embedded into the transient analysis in simulators since to cover all noise power with enough bandwidth, very small time-step must be used and this would very costly (and impossible) for transient simulations.

But the noise i get is a low frequecy noise or what we call as fliker noise and it is not high frequency noise. How i can emulate the result i get in AC analysis in transient?

 

[layes2]

Re: noise in transient

there is glitch in tran
just multipy the ac gain with the tran signal

 

[markty]

noise in transient

I think this can be done in behavior level simulation, matlab has such noise source. But in circuit level, i have no idea.

 

[borodenkov]

noise in transient

Well, the main question here should be not HOW, but WHY! Why do you need to include noise in transient?

If you want to see, how device noise affects the work of your complex system (e.g. sigma-delta modulator or PLL) - build a behavioral model of your system (e.g. Matlab, Verilog-A etc) and include noise sources there with PSD obtained from noise simulation of circuit blocks.

 

[legend]

Re: noise in transient

there is glitch in tran
just multipy the ac gain with the tran signal

Hi,Layes2, Just multipy the ac gain with the tran signal. Can you tell me why?