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Design Languages >> Verilog-AMS >> Question about Verilog-A white_noise funtion
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Message started by gaom9 on Apr 1^st, 2008, 9:57pm

Title: Question about Verilog-A white_noise funtion
Post by gaom9 on Apr 1^st, 2008, 9:57pm

Hi,
I want to use the resistor as a thermal noise source.
I use spectres to simulate the thermal noise of the resistor, and make a noise source V²=4KTR serial with the ideal resistor to act as the thermal noise as showed below.

RES is the noise source. And it is verilog-A code is:

// VerilogA for random, rnoise, veriloga

`include "constants.vams"
`include "disciplines.vams"

module rnoise(p, n);

inout p, n;
electrical p, n;
parameter real r = 50k;
analog begin
V(p, n) <+ white_noise(4 * `P_Q * $temperature * r, "thermal");
end

endmodule

But when I use the tran simulation, the noise can not come out, also I add a amp the it the make the bandwidth big, but it could not come out.

What is the matter, please?

Is the white_noise funtion only used in .AC simulation? So it can not work in .tran simulation?

Please help me.

Thank you.
Best regards!

Title: Re: Question about Verilog-A white_noise funtion
Post by Stefan on Apr 1^st, 2008, 11:58pm

Use the latest IUS/MMSIM/IC Release and switch on the "transient noise" parameter.

Regards,

Stefan

Title: Re: Question about Verilog-A white_noise funtion
Post by gaom9 on Apr 2^nd, 2008, 12:50am

Hi, Stefan. Thank you for your reply.
I think I can not get the latest release version of cadence tools. My cadence version is 5141 usr4. I don't know does it have the transient noise feature. And I will try it.

And does any other simulator have the same feature, such as the latest version hspice?

Thank you.
Best regards.

Title: Re: Question about Verilog-A white_noise funtion
Post by Stefan on Apr 2^nd, 2008, 1:21am

The IC Version is fine, but you'll need an additional MMSIM license.
I don't know which version will do it, but MMSIM62 is the current release.
Check sourcelink for "transient noise" option.

Title: Re: Question about Verilog-A white_noise funtion
Post by gaom9 on Apr 2^nd, 2008, 1:48am

Thank you very much!
I will try it.

Title: Re: Question about Verilog-A white_noise funtion
Post by gaom9 on Apr 3^rd, 2008, 6:37am

Hi, Stefan.
I have installed the MMSIM61, and got the feature of tran noise analyse. I have tried it, and get the white noise.
But there is a strange question about it.
When I use a 80K resistor as the thermal noise souce, the simulator will show the max value of the thermal noise to be 1V.
I think it is too large. For V2 = 4KTR*(delta f), it is quite small. But I try to amplify it with a ideal amplifier, the result do not come out as what I though. And I used a nonideal amplifier to amplify it, but I find the noise do not change with the GBW of the amplifier.
What is the meaning of the 1V? Dose it mean the real 1V or it is only a symble? Or is there some error with this analyse?

Thank you.
Best regards!

Title: Re: Question about Verilog-A white_noise funtion
Post by Geoffrey_Coram on Apr 3^rd, 2008, 10:19am

4kTR is the power spectral density, in some sense the variance of the Gaussian distribution of the voltage samples. Transient noise will generate a new sample from the Gaussian distribution for each timepoint -- and parameters to the analysis determine how many timepoints are needed to accurately represent noise at a particular bandwidth. Because it's a Gaussian, there's a non-zero probability of a voltage (sample) greater than 1V.

You should probably read the white paper on transient noise.

Title: Re: Question about Verilog-A white_noise funtion
Post by gaom9 on Apr 3^rd, 2008, 7:37pm

Hi, Geoffrey_Coram
Thank you for your reply. I have find white paper of the transient noise analysis. And I find some mistake with my set to the analysis.
But I have still a question about it.
The noisefmax of the analysis is a bit higher than the Bandwidth of the circuit. Here the Bandwidth maens the -3dB bandwidth of the circuit, is that right?

Thank you.
Best regards! ;D

Title: Re: Question about Verilog-A white_noise funtion
Post by Geoffrey_Coram on Apr 4^th, 2008, 6:55am

I'd set the noisefmax to be at least a decade above the 3dB bandwidth, because something just above that point could still have a significant effect on your output.

Of course, if you've got noise folding/mixing/frequency translation, then you have to account for all of that, also.

It's probably not a bad idea to increase the bandwidth by a factor of 2 or 10 and see if it makes a difference before accepting the results as golden.

Title: Re: Question about Verilog-A white_noise funtion
Post by gaom9 on Apr 4^th, 2008, 7:18am

Thank you.
I will try it. ;D ;D ;D

Best regards!