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noise simulation concept (Read 7133 times)
nathanee
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noise simulation concept
Jul 03rd, 2008, 6:53am  
Hi, there,

Please help to clarify the following concept about noise and simulation method.

1. Thermal, flicker, and KT/C noise CAN NOT be simulated by using spectre/hspice transient method.
2. Thermal, flicker, and KT/C noise CAN be simulated by using spectre/hspice ac method.
3. Thermal, flicker, and KT/C noise CAN be simulated by using spectreRF.

Thanks in advance.

BR,
-nathan
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pancho_hideboo
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Re: noise simulation concept
Reply #1 - Jul 3rd, 2008, 6:26pm  
I can't find any design issue in your post.
Your question is not design issue but simple feature of specific vendor's EDA tool.  
Please post to "The Designer's Guide Community Forum ≫ Simulators ≫ RF Simulators".

nathanee wrote on Jul 3rd, 2008, 6:53am:
Please help to clarify the following concept about noise and simulation method.

What do you mean by "concept" ?

nathanee wrote on Jul 3rd, 2008, 6:53am:
1. Thermal, flicker, and KT/C noise CAN NOT be simulated by using spectre/hspice transient method.

Apart from accuracy, you can evaluate these noise using transient noise analysis in Spectre.
I don't think HSPICE supports transient noise analysis. So you can't evaluate these noise using HSPICE's transient analysis.

nathanee wrote on Jul 3rd, 2008, 6:53am:
2. Thermal, flicker, and KT/C noise CAN be simulated by using spectre/hspice ac method.

For time invariant circuit, you can evaluate thermal and flicker noise using AC noise analysis in both Spectre and HSPICE.
But you can't evaluate KT/C noise directly using Spectre's AC analysis.
On the other hand you can evaluate KT/C noise using HSPICE's combination analysis of ".AC", ".Noise", and ".SAMPLE" analysis, although it is not accurate evaluation.

nathanee wrote on Jul 3rd, 2008, 6:53am:
3. Thermal, flicker, and KT/C noise CAN be simulated by using spectreRF.

Yes, for periodically time varied circuit, you can evaluate these noise using Shooting Newton Method in both SpectreRF and HSPICE RF.
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daisy
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Re: noise simulation concept
Reply #2 - Jul 18th, 2008, 3:35am  
Hi!
In my opinion,when thermal noise 4KTR passes through a rc circuit,the output noise equals KT/C,so we call it KTC noise.I'm not sure whether it is correct or there is another kind of noise called KTC noise like thermal noise and flicker noise?
And I also have another question.What does the frequency mean in flicker noise?If I want to compute the output noise of  the circuit, should I integrate the psd of the filcker noise in the bandwidth or from 0 to infinity?I found it is hard to get the result if I integrate in the bandwidth.

Thank you for your explanation!
daisy

pancho_hideboo wrote on Jul 3rd, 2008, 6:26pm:
I can't find any design issue in your post.
Your question is not design issue but simple feature of specific vendor's EDA tool.  
Please post to "The Designer's Guide Community Forum ≫ Simulators ≫ RF Simulators".

nathanee wrote on Jul 3rd, 2008, 6:53am:
Please help to clarify the following concept about noise and simulation method.

What do you mean by "concept" ?

nathanee wrote on Jul 3rd, 2008, 6:53am:
1. Thermal, flicker, and KT/C noise CAN NOT be simulated by using spectre/hspice transient method.

Apart from accuracy, you can evaluate these noise using transient noise analysis in Spectre.
I don't think HSPICE supports transient noise analysis. So you can't evaluate these noise using HSPICE's transient analysis.

nathanee wrote on Jul 3rd, 2008, 6:53am:
2. Thermal, flicker, and KT/C noise CAN be simulated by using spectre/hspice ac method.

For time invariant circuit, you can evaluate thermal and flicker noise using AC noise analysis in both Spectre and HSPICE.
But you can't evaluate KT/C noise directly using Spectre's AC analysis.
On the other hand you can evaluate KT/C noise using HSPICE's combination analysis of ".AC", ".Noise", and ".SAMPLE" analysis, although it is not accurate evaluation.

nathanee wrote on Jul 3rd, 2008, 6:53am:
3. Thermal, flicker, and KT/C noise CAN be simulated by using spectreRF.

Yes, for periodically time varied circuit, you can evaluate these noise using Shooting Newton Method in both SpectreRF and HSPICE RF.
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pancho_hideboo
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Re: noise simulation concept
Reply #3 - Jul 18th, 2008, 5:48pm  
daisy wrote on Jul 18th, 2008, 3:35am:
In my opinion,when thermal noise 4KTR passes through a rc circuit,the output noise equals KT/C,so we call it KTC noise.

This is no more than thermal noise from resistor in time invariant circuit.
But generally term of "kT/C noise" is used for sampled, switched or chopped noise, e.g. noises seen in switched capacitor filter circuit.

daisy wrote on Jul 18th, 2008, 3:35am:
And I also have another question.What does the frequency mean in flicker noise?If I want to compute the output noise of  the circuit, should I integrate the psd of the filcker noise in the bandwidth or from 0 to infinity?I found it is hard to get the result if I integrate in the bandwidth.

I can't understand your question. What do you want to know ?
Maybe you don't understand flicker noise correctly.
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daisy
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Re: noise simulation concept
Reply #4 - Jul 18th, 2008, 6:31pm  
Hi!
Thank you for your answer!
1.Yes,I mean in a switched capacitor circuit,the switched mos works in the linearity region,so its thermal noise equals 4KTR,where R equals 1/gds,and it results a noise value KT/C in a capacitor which is parallelly connected to the mosfet.Is it right?
2.What I want to know is as follows:in flicker noise formula K/CoxWLf,what does the frequency mean?Does it mean any frequency within the circuit bandwidth?If it is,if I want to get the total flicker noise at the output node,should I integrate the PSD formula in the range of the bandwidth?

Thank you for your explanation!
daisy
pancho_hideboo wrote on Jul 18th, 2008, 5:48pm:
daisy wrote on Jul 18th, 2008, 3:35am:
In my opinion,when thermal noise 4KTR passes through a rc circuit,the output noise equals KT/C,so we call it KTC noise.

This is no more than thermal noise from resistor.
But generally term of "kT/C noise" is used for switched or chopped noise, e.g. in switched capacitor filter circuit.

daisy wrote on Jul 18th, 2008, 3:35am:
And I also have another question.What does the frequency mean in flicker noise?If I want to compute the output noise of  the circuit, should I integrate the psd of the filcker noise in the bandwidth or from 0 to infinity?I found it is hard to get the result if I integrate in the bandwidth.

I can't understand your question. What do you want to know ?
Maybe you don't understand flicker noise correctly.
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pancho_hideboo
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Re: noise simulation concept
Reply #5 - Jul 18th, 2008, 6:52pm  
daisy wrote on Jul 18th, 2008, 6:31pm:
1.Yes,I mean in a switched capacitor circuit,the switched mos works in the linearity region,so its thermal noise equals 4KTR,where R equals 1/gds,and it results a noise value KT/C in a capacitor which is parallelly connected to the mosfet.Is it right?

I don't know what test circuit you assume.
Do you assume a time invariant condition and no noise other than gds ?
If so,  right.

daisy wrote on Jul 18th, 2008, 6:31pm:
2.What I want to know is as follows:in flicker noise formula K/CoxWLf,what does the frequency mean?

It means operation frequency, that is analysis frequency.

daisy wrote on Jul 18th, 2008, 6:31pm:
Does it mean any frequency within the circuit bandwidth?If it is,if I want to get the total flicker noise at the output node,should I integrate the PSD formula in the range of the bandwidth?

Do you understand noise holding in periodically time varied circuit ?

You should integrate noise over bandwidth you have interest.
See
http://www.designers-guide.org/Forum/YaBB.pl?num=1211952319
http://www.designers-guide.org/Forum/YaBB.pl?num=1207830622
http://www.designers-guide.org/Forum/YaBB.pl?num=1059089369
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« Last Edit: Jul 18th, 2008, 8:04pm by pancho_hideboo »  
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