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input and output noise simulation with Spectre Noise analysis?

Last post Thu, Jul 11 2013 10:55 PM by Andrew Beckett. 6 replies.
 Started by isazulkc 19 Nov 2010 11:15 AM. Topic has 6 replies and 5095 views
• Fri, Nov 19 2010 11:15 AM

• isazulkc
• Joined on Thu, Nov 27 2008
• Quebec, Quebec
• Posts 39
• Points 670
input and output noise simulation with Spectre Noise analysis?
 Hi, I would like to know if the output noise (V-rms) obtained when I simulate the output noise of a circuit with Spectre simulator (Noise) include the noise of ALL the components referred to the output ? In fact I got some inconsistant result when comparing the input and output noise (V-rms) given by the simulator. I got 1.4 mV-rms at the output while I have 13 mV-rms as input refered noise. I know input referred noise give the input equivalent noise (anasimhelp) considering a noise-free circuit, but I am note sure for the output noise. Thanks for your help!! Best regards
• Post Points: 20
• Mon, Nov 22 2010 1:29 AM

Re: input and output noise simulation with Spectre Noise analysis?
 The noise analysis in spectre (and indeed other simulators) compute primarily the noise at the output of the circuit, from all noise sources in the circuit. The only reason for noise not being included is if the noise on that component has been specifically disabled (for example, the instance parameter isnoisy=no has been set). The way it works is to compute the magnitude of the noise at the noise source (i.e. at the device) based on the bias point (if that matters - for example, for shot noise), and also compute the transfer function from the noise source (i.e. at the device) to the output. The noise powers at the output are then summed, and the total output noise computed.The input referred noise (which is a secondary output) is computed by taking the total output noise, and dividing it by the gain from the output back to the input that you specified on the noise analysis.If your circuit has attenuation, then the input referred noise at the input will be larger than at the output.You can use the noise contribution table (Results->Print->Noise Contributions) or the results browser to look at the noise contributions (at the output of the circuit) from each noise source in the circuit. This is a useful debugging tool to find out where the noise is coming from (or not!).You could also compare the gain with (say) an xf analysis to see what the gain is in the circuit, so you can see if it is attenuating. If it's not meant to attenuate, maybe you specified the wrong nodes, or maybe the circuit is not biased properly (so check the operating  point; it's amazing how often people don't check that, and commonly do things like forget to connect the supplies up. We've all done it!) Regards,Andrew.
• Post Points: 20
• Thu, Jul 11 2013 3:28 PM

• potsticker
• Joined on Fri, Jun 21 2013
• Posts 9
• Points 135
Re: input and output noise simulation with Spectre Noise analysis?
 hi Andrew, i found this post to be very similar to the question i have on hand so I am replying to it.(please let me know if i should start a new thread)Question: in the noise simulation, is there anyway to retreive the original device noise itself.for example, the simulation noise summary can report M1 contribute 2.5e-22 to the output, but how can i found out what the M1 device noise is itself before it is multiplied by the transfer function ? thanksFrank
• Post Points: 20
• Thu, Jul 11 2013 3:46 PM

Re: input and output noise simulation with Spectre Noise analysis?
 Frank,The pnoise analysis has a feature called "noise separation" which does precisely this - gives you the noise contribution from each sideband, but also gives the noise at the device, plus the gain from the device to the output as separate quantities. Conventional "ac" noise analysis doesn't provide this unfortunately - you only get the  noise contribution at the output.Regards,Andrew.
• Post Points: 20
• Thu, Jul 11 2013 5:24 PM

• potsticker
• Joined on Fri, Jun 21 2013
• Posts 9
• Points 135
Re: input and output noise simulation with Spectre Noise analysis?
 thank you very much Andrew.I understand that this is not available from the GUI, but if you know of any function or script i can use to retreieve individual device noise from the ac. noise sim I would appreciate it. I assume the ac. noise sim does indeed calaculate indivdual noise first?thx Frank
• Post Points: 20
• Thu, Jul 11 2013 5:51 PM

• potsticker
• Joined on Fri, Jun 21 2013
• Posts 9
• Points 135
Re: input and output noise simulation with Spectre Noise analysis?
 hi Andrew, i did ended up running pss and pnoise on the circuit and was able to retrieve the individual device noise. thanks Andrewttyl Frank
• Post Points: 5
• Thu, Jul 11 2013 10:55 PM

Re: input and output noise simulation with Spectre Noise analysis?
 Hi Frank, potsticker:I understand that this is not available from the GUI, but if you know of any function or script i can use to retreieve individual device noise from the ac. noise sim I would appreciate it. I assume the ac. noise sim does indeed calaculate indivdual noise first? Whilst this is computed inside the simulator, there's no option to output the date. You'll need to contact customer support to request this enhancement (which seems quite sensible and consistent to have to me).Glad you managed to use pss/pnoise as an alternative. Regards,Andrew.
• Post Points: 5