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panditabupesh

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spectre transient noise
Feb 27^th, 2008, 6:24pm

Hi
I have been trying transient noise simulation on a switched capacitor filter. Without noise enabled, I was getting an SNR of greater than 90 db, but with noise enabled the SNR dropped to 42 dB.
The output power spectral density shows a flicker noise kind of noise floor. I forced the flicker noise parameters in the models to zero, but despite that I am not seeing any improvement in the SNR and also the output PSD continues to shown an 1/f shape. I am simulating an audio circuit.

Any insights on what is going on would be helpful.

Thanks
Bupesh

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Stefan Senior Member Offline Posts: 124	Re: spectre transient noise Reply #1 - Feb 28^th, 2008, 2:40am Maybe you should check the generation of the clock for the switches ... You can use the simulator to check for the noise sources that distribute to the output. What does it say ?
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panditabupesh

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Re: spectre transient noise
Reply #2 - Feb 28^th, 2008, 5:57am

Hi
Today I tried with noisefmin greater than noisefmax (basically, to eliminate flicker noise contribution) and the SNR improved to 70 dB (about 30 dB improvement). With flicker noise parameters in the models zero, I can not understand how spectre is generating flicker noise. I generated a report, in Ocean, on the models and confirmed that the flicker noise parameters are zero.

The clocks are from an ideal non-overlapping clock generator. Also, how can I use the simulator to tell me about the contribution of each device to the output noise.

Thanks
Bupesh

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HdrChopper Community Fellow Offline Posts: 493	Re: spectre transient noise Reply #3 - Feb 28^th, 2008, 4:52pm Hi, A couple of quick questions: is the SC circuit an integrator?, what do you have at the input of the SC filter? Tosei
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Ken Kundert Global Moderator Offline Posts: 2384 Silicon Valley	Re: spectre transient noise Reply #4 - Feb 28^th, 2008, 9:42pm Have you considered using SpectreRF's PNoise analysis? -Ken
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panditabupesh Community Member Offline Posts: 36 Toronto	Re: spectre transient noise Reply #5 - Feb 29^th, 2008, 5:58am Hello Yes the circuit is an integrator, and the input is an ideal sine wave. Ken, with flicker noise parameters made zero (BSIM4 parameters with fnoimod=1, and all flicker noise parameters, noia noib noic including kf made zero), pnoise, unlike transient noise, shows flicker noise disappearing. Thanks Bupesh
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HdrChopper

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Re: spectre transient noise
Reply #6 - Feb 29^th, 2008, 7:12am

I'm not completely sure about this but, what if you have a white noise component at the input of your SC integrator? My point is that the white noise, once integrated, looks like flicker noise at the output of any integrator (I guess). What source of white noise do you have at the very input of your integrator? May be the input switches?. An easy test would be just to put ideal switches at the input just to see if your flicker like output noise gets reduced in the transient sim....

Tosei

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panditabupesh Community Member Offline Posts: 36 Toronto	Re: spectre transient noise Reply #7 - Feb 29^th, 2008, 7:59am Hello Tosei The idea that integrator is coloring the white noise is really possible, and I am planning to explore it further. But, then why should making noisefmin greater than noisefmax impact the output noise psd. Thanks Bupesh
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panditabupesh

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Re: spectre transient noise
Reply #8 - Feb 29^th, 2008, 8:49am

Hello
Perhaps, I am confused about one more thing:

For noisefmin = noisefmax condition, does spectre use the thermal noise parameters of the devices (or just the 4kTBR equation for the resistors)? The transient noise application note says that, "spectral noise density will be zero above noisefmax, constant below noisefmin, and will follow the device noise equation in between".

How does spectre decide the noise magnitude below noisefmin?

Thanks
Bupesh

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Ken Kundert Global Moderator Offline Posts: 2384 Silicon Valley	Re: spectre transient noise Reply #9 - Feb 29^th, 2008, 2:04pm Trying to perform flicker noise simulations with transient noise is expensive and error prone. So, given that SpectreRF is giving you the expected results, why are you bothering with transient noise? -Ken
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panditabupesh Community Member Offline Posts: 36 Toronto	Re: spectre transient noise Reply #10 - Feb 29^th, 2008, 2:54pm Ken, the idea was to find SNR and harmonic distortion etc., under real signal conditions. Thanks Bupesh
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safwatonline Junior Member Offline Posts: 20	Re: spectre transient noise Reply #11 - Mar 13^th, 2008, 7:28am Hi, i noticed that i don't have the transient noise in my cadence version, what is the version u r using?
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kDaniu New Member Offline Posts: 6	Re: spectre transient noise Reply #12 - Apr 3^rd, 2008, 6:22pm does anybody How to use the same spectre advantages "transient noise" in hspice (I mean auto generation (on the fly) the noise during transient simulation) ? right now to get the noise I just put the artificial noise using pwlf component, but that is not comfort in the case of long time simulations thanks Dan
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Geoffrey_Coram Senior Fellow Offline Posts: 1998 Massachusetts, USA	Re: spectre transient noise Reply #13 - Apr 4^th, 2008, 7:22am I've heard that Eldo has transient noise, but I'm not aware that HSpice does (yet?).
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kDaniu New Member Offline Posts: 6	Re: spectre transient noise Reply #14 - Apr 4^th, 2008, 4:22pm I know that such possibility is absent. but I'm asked about any another mechanizm to get it in scheme (at least on the imporant places).. maybe present some way to auto generation (on the fly) the noise during transient simulation f.e. by using Monte Carlo possibilities (right now this way do not help me) etc... thanks, Dan
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