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switched capacitor integrator noise simulation results (Read 7544 times)
pancho_hideboo
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Re: switched capacitor integrator noise simulation results
Reply #30 - Dec 07th, 2009, 4:33am
 
Reread all my appends from first.
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alireza
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Re: switched capacitor integrator noise simulation results
Reply #31 - Dec 7th, 2009, 8:58am
 
Thanks for your reply. About the output noise spectrum obtained from pnoise (type=sources) sim. you had mentioned that the freq. range from 0 to fs is the main lobe of the spectrum, but in any case I should integrate it from 0 to inf:

pancho_hideboo wrote on Nov 25th, 2009, 2:18am:
Not correct. You have to integrate from 0 to infinity ideally. However from practical point of view,
an integration from 0 to fs at least might be enough useful.
This range is mainlobe of output noise spectrum.


However for the input noise spectrum this is not the case. (as it is shown in your recent PSD as well) My specific question is: how do I find the total integrated "input" referred noise?

If I integrate the spectrum from 0 to inf (or the simulation bandwidth: say 100MHz) the result will be proportional to this bandwidth, as the spectrum does not roll off at high frequencies. This does not sound correct. Am I right?

Thanks,

Regards,

Alireza

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pancho_hideboo
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Re: switched capacitor integrator noise simulation results
Reply #32 - Dec 7th, 2009, 9:02am
 
alireza wrote on Dec 7th, 2009, 8:58am:
you had mentioned that the freq. range from 0 to fs is the main lobe of the spectrum, but in any case I should integrate it from 0 to inf:
Right.

alireza wrote on Dec 7th, 2009, 8:58am:
My specific question is: how do I find the total integrated "input" referred noise?
It seems you don't understand "Input Referenced Noise".

alireza wrote on Dec 7th, 2009, 8:58am:
If I integrate the spectrum from 0 to inf (or the simulation bandwidth: say 100MHz) the result will be proportional to this bandwidth,
as the spectrum does not roll off at high frequencies.
This does not sound correct.
No, it is very natural result.
You are still misunderstanding.

Consider noise spectrum from resistor, here PSD is unbounded in frequency.

alireza wrote on Dec 7th, 2009, 8:58am:
However for the input noise spectrum this is not the case.
You should learn a concept of ENBW(Equivalent Noise BandWidth) of System.

Again EDA Tool Play is no more than Tool Play.
There is nothing superior to the actual measurement using actual instruments.


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alireza
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Re: switched capacitor integrator noise simulation results
Reply #33 - Dec 7th, 2009, 9:01pm
 
Thanks very much. I can see your point about the fact that the "input-referred noise" output of pnoise simulation produces infinite power, as in a resistor.

But on the other hand for the switched-capacitor integrator, what is usually referred to and derived in literature is the "total integrated noise power at the input", which is effectively the white PSD*ENBW, as you mentioned. (e.g. to find the input referred SNR.) But I am not entirely sure what the ENBW of this circuit is. Based on the expected input-referred noise power, it should be fs/2. Is that correct?

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Alireza
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pancho_hideboo
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Re: switched capacitor integrator noise simulation results
Reply #34 - Dec 8th, 2009, 1:31am
 
alireza wrote on Dec 7th, 2009, 9:01pm:
But I am not entirely sure what the ENBW of this circuit is.
Based on the expected input-referred noise power, it should be fs/2.
Is that correct?
Read basic text books on classical communication theory or RF theory for very beginner.

You can determine ENBW from Integral[|gain(freq)|2, 0<=freq<+infinity].
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Re: switched capacitor integrator noise simulation results
Reply #35 - Jan 7th, 2010, 6:50pm
 
Interesting, this pnoise noise bandwith has puzzled me for quite some time as well. It infuriated quite a bit a real homeless Smiley

appendix C4 from Joel R. Phillips and mentioned by jeffyan is clear;

"Note that the spectrum of the discrete (sampled) process
is periodic in frequency with period 1/T . All noise power is aliased into the Nyquist interval [-1/2T; 1/2T] (or, equivalently the interval [0; 1/T ]). Generally it is the noise spectrum which is available from the circuit
simulator. To obtain the autocorrelation function or time-varying noise power, an inverse Fourier integral must be calculated"

http://www.cadence.com/rl/Resources/white_papers/tdnoise.pdf

mathematically you integrate the random variable on [-inf: +inf]
physically you integrate the (periodic and sampled) noise on [0; 1/2T]

[1/2T; 1/T] or [-1/2T; 0] is not used because the physical system (SHA, ADC else) does not work with negative frequencies.
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pancho_hideboo
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Re: switched capacitor integrator noise simulation results
Reply #36 - Jan 8th, 2010, 4:23am
 
pirate wrote on Jan 7th, 2010, 6:50pm:
mathematically you integrate the random variable on [-inf: +inf]
Wrong.
Integral range is [-1/2T,+1/2T] mathematically.

pirate wrote on Jan 7th, 2010, 6:50pm:
[1/2T; 1/T] or [-1/2T; 0] is not used because the physical system (SHA, ADC else) does not work with negative frequencies.
Not correct.
Reason of integral range [0,+1/2T] is simple.
Evaluated PSD is single sided value not both sided value.

http://www.designers-guide.org/Forum/YaBB.pl?num=1059089369/1#1
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Re: switched capacitor integrator noise simulation results
Reply #37 - Jan 8th, 2010, 10:38am
 
Quote:
Wrong.
Integral range is [-1/2T,+1/2T] mathematically.

Sorry, by random variable I meant a non periodic one.

Quote:
Not correct.
Reason of integral range [0,+1/2T] is simple.
Evaluated PSD is single sided value not both sided value.

Yes, PSpectrumD is single sided because it is a physical concept so, herein my simplistic view of negative frequencies (there is no signal beyond or equal to 0Hz).

at least periodic noise simulation is geting more and more popular and better undertsood
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« Last Edit: Jan 8th, 2010, 12:49pm by pirate »  
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pancho_hideboo
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Re: switched capacitor integrator noise simulation results
Reply #38 - Jan 8th, 2010, 10:48am
 
pirate wrote on Jan 8th, 2010, 10:38am:
Sorry, by random variable I meant a non periodic one.
You refered tdnoise of Cadence Spectre.
So an integral range is [-1/2T,+1/2T] mathematically.
pirate wrote on Jan 7th, 2010, 6:50pm:


pirate wrote on Jan 8th, 2010, 10:38am:
Yes, PSpectrumD is single sided because it is a physical concept so.
No.
Single Sided PSD has no relation with Physical System generally.

For example, consider Poly-Phase filter whose spectrum must be expressed as both sided not single sided.
But this is physical system.

Expression as Single-Sided Spectrum is restricted to "Real Value System".
On the other hand, expression as Both-Sided Spectrum can be applied for both "Real Value System" and "Complex Value System".
Here negative frequencies are also physical as well as positive frequencies.

Quadrature Sampling, I/Q-ADC etc. are also "Complex Value System".
See http://www.designers-guide.org/Forum/YaBB.pl?num=1238705966/3#3

pirate wrote on Jan 8th, 2010, 10:38am:
a least periodic noise simulation is geting more and more popular and better undertsood
What on earth do you mean by "a least periodic" ?

I don't think noise analysis like "tdnoise of Cadence Spectre" is popular.
And I don't know actual instruments which can evaluate noise as same manner as "tdnoise of Cadence Spectre".
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Re: switched capacitor integrator noise simulation results
Reply #39 - Jan 8th, 2010, 1:20pm
 
Quote:
You refered tdnoise of Cadence Spectre.
So an integral range is [-1/2T,+1/2T] mathematically

sorry, I meant mathematical in the core sense, tdnoise of Cadence Spectre is physics if not circuits to me.
A non periodic probability density ranging [-inf; +inf] = 1 or 100%.
At the circuit level that gives me a hint on the noise bandwidth [0; +1/2T] for a cyclostationary process.

Interesting your polyphase filter example, I have no experience with them. I have only done periodic noise, aka pnoise, (bda, cadence) simulations on low pass circuits where the density belong to the Real domain so I never considered the negative side of the spectrum.
Thanks for clarifying the real and complex domain.

:wq
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pancho_hideboo
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Re: switched capacitor integrator noise simulation results
Reply #40 - Jan 9th, 2010, 2:16am
 
pirate wrote on Jan 8th, 2010, 10:38am:
a least periodic noise simulation is geting more and more popular and better undertsood
What on earth do you mean by "a least periodic" ?

pirate wrote on Jan 8th, 2010, 1:20pm:
At the circuit level that gives me a hint on the noise bandwidth [0; +1/2T] for a cyclostationary process.
You are misunderstanding.
Noise bandwidth of [0, +1/2T] has no relation to cyclostationary process.

Even in "Pnoise(type=sources)", noises are treated as cyclostationary.

pirate wrote on Jan 8th, 2010, 1:20pm:
tdnoise of Cadence Spectre is physics if not circuits to me.
tdnoise of Cadence Spectre is Mathematics not Physics.

I mean results of "Pnoise(type=timedomain)" are virtual world where an ideal impulse sampling is assumed which is not realized physically,
while results of "Pnoise(type=sources)" are real world.
Again I don't know actual instruments which can evaluate noise as same manner as "tdnoise of Cadence Spectre".

pirate wrote on Jan 8th, 2010, 1:20pm:
I have only done periodic noise, aka pnoise, (bda, cadence) simulations
Maybe you are misunderstanding.

Pnoise of BDA's Analog FastSPICE is a type of "Pnoise(type=sources)"
not "Pnoise(type=timedomain)".
Don't you confuse post processing theory of Transient Noise Analysis of BDA's Analog FastSPICE with Pnoise ?
http://www.designers-guide.org/Forum/YaBB.pl?num=1259714206/2#2

Again I don't think noise analysis like "tdnoise of Cadence Spectre" is popular.

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« Last Edit: Jan 10th, 2010, 1:18am by pancho_hideboo »  
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Andrew Beckett
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Re: switched capacitor integrator noise simulation results
Reply #41 - Jan 16th, 2010, 9:30am
 
pancho_hideboo wrote on Jan 9th, 2010, 2:16am:
Again I don't think noise analysis like "tdnoise of Cadence Spectre" is popular.


The main thing I see tdnoise used for these days is for investigation of how the noise varies throughout the period, particularly in switching circuits. Not so much for actual measurements, but to aid understanding of the cause of the noise. So it does get used - not sure how you class "popular" though  ;)

In the past it used to be used more for measuring the noise at a transition, and converting that into jitter (using the slew rate at the transition) - again for switching circuits. Now that you can do this directly with the jitter mode of pnoise (actually pmjitter) there's less need to use tdnoise itself (although pmjitter is still using tdnoise underneath).

I would say that the jitter mode is quite "popular" though...

Regards,

Andrew.
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pancho_hideboo
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Re: switched capacitor integrator noise simulation results
Reply #42 - Jan 16th, 2010, 10:33am
 
pancho_hideboo wrote on Jan 9th, 2010, 2:16am:
Again I don't think noise analysis like "tdnoise of Cadence Spectre" is popular.
I mean that periodic noise PSD which tdnoise gives is not popular,
although both "sources" and "timedomain" are no more than small signal analysis in frequency domain.

There are many many many people who have much confusion about interpretations of this periodic noise PSD in this forum.
This is an original topics of this thread, "Pnoise(type=timedomain)" v.s. "Pnoise(type=sources)".

BTW, see BDA's Analog FastSPICE RF
http://www.berkeley-da.com/news/news_pr/news01_pr_2009_12_08.html
http://www.berkeley-da.com/prod/datasheets/Berkeley_BDA_AFS_RF_WP.pdf

BDA claims like followings.
AFS RF provides full-spectrum periodic analysis (AFS RF pnoise) that performs device noise computations directly in the time domain and then translates the results to the frequency domain.
Using a unique computational approach, AFS RF provides the equivalent of an infinite number of harmonics or sidebands on every run.


AFS RF also provides the industry’s only full-spectrum oscillator device noise analysis(oscnoise).
Phase noise is a large-signal effect, while amplitude noise is a small-signal effect.
AFS RF uses a proprietary non-approximate stochastic nonlinear engine for transistor level phase noise analysis and full-spectrum pnoise analysis for amplitude analysis.


Cadence Shooting-PSS also doesn't require setting of maximum harmonics,
but setting of maximum sideband is required in Cadence Pnoise. This is true for tdnoise.
See http://www.designers-guide.org/Forum/YaBB.pl?num=1257901096/1#1

On the other hand, BDA's AFS RF doesn't require setting of maximum sideband even in pnoise analysis.
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« Last Edit: Jan 17th, 2010, 7:35am by pancho_hideboo »  
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alireza
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Re: switched capacitor integrator noise simulation results
Reply #43 - Feb 18th, 2010, 9:26pm
 
Hi,
alireza wrote on Nov 28th, 2009, 8:43am:
Based on the theory, the integrated input-referred noise of the SC integrator should be 2kT/C.

pancho_hideboo wrote on Nov 28th, 2009, 8:52am:
This ignores folding effects.
Again folding is a reality.
http://www.designers-guide.org/Forum/YaBB.pl?num=1258339986/19#19
Output noise spectrum is a result of contribution from all sidebands, that is, multiple foldings.
While VGain of PAC considers only zero sideband.

I totally see your point regarding the fact that pnoise (sources) simulation takes folding effects into account, which is quite natural and physical, but PAC only considers zero-side band. However, I cannot accept that 2kT/C which is a well-known estimate for the input-referred noise of a switched-capacitor integrator "ignores" noise folding! Otherwise, design methodology used for design of SC delta-sigma modulators (and other SC filters) would all be in question!
I am quite sure that 2kT/C estimate does take noise folding into account. (Noise folding is the basic principle of noise analysis for SC circuits.)

Regards,
Alireza
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Re: switched capacitor integrator noise simulation results
Reply #44 - Feb 19th, 2010, 1:57am
 
alireza wrote on Feb 18th, 2010, 9:26pm:
However, I cannot accept that 2kT/C which is a well-known estimate for the input-referred noise of a switched-capacitor integrator "ignores" noise folding!
Otherwise, design methodology used for design of SC delta-sigma modulators (and other SC filters) would all be in question!
I am quite sure that 2kT/C estimate does take noise folding into account. (Noise folding is the basic principle of noise analysis for SC circuits.)
I can't understand what you want to claim.
Did you evaluate ENBW ?
http://www.designers-guide.org/Forum/YaBB.pl?num=1258339986/34#34
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« Last Edit: Feb 19th, 2010, 4:12am by pancho_hideboo »  
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