about KT/C noise in circuit simulation

[lhlbluesky]

kt/c noise

KT/C noise exsits in sc circuits, that is, when sampling a signal, the random thermal noise (KT/C noise) is also sampled to the sampling capacitor, so in different clock cycles, the sampling value for the same input signal should be different also. is that right?

but when circuit simulation, the value is almost the same.why?

someone says that, for some library, thermal noise model of MOS transistors is not included, that is, KT/C noise doesn't exist in circuit simulation, is that right or not? why ?

and how to find whether thermal noise model of MOS transistors is contained in the library?

for an ADC,if the simulated ENOB=9.7 or worse(for 10 bit resolution), then is KT/C noise included or not?

pls help me, i'm terribly confused.
thans all for reply.

 

[lhlbluesky]

ktc noise

anyone can help me, pls?

 

[dineshbabumm]

kt/c noise simulation

Don't we choose the Capacitor value large enough so that the KT/C noise becomes less in comparison with quantization noise? We allow the quantization noise to dominate over KT/C noise while designing a circuit right?

 

[lhlbluesky]

kt c noise

any other ideas, pls?

 

[PaloAlto]

kt over c noise

If your circuit is SC, then you cannot do a (small signal) noise analysis based on OP. If you do a transient, thermal noise is not included, so you don't see it. You need to either do hand calculations or try with tnoise analisys.

Those are all my ideas, do not ask for more, please?

 

[lhlbluesky]

kt c noise calculation

so, any more ideas, pls?

Added after 2 seconds:

so, any more ideas, pls?

 

[kuohsi]

small signal noise ktc noise

KT/C noise exsits in sc circuits, that is, when sampling a signal, the random thermal noise (KT/C noise) is also sampled to the sampling capacitor, so in different clock cycles, the sampling value for the same input signal should be different also. is that right?

but when circuit simulation, the value is almost the same.why?

someone says that, for some library, thermal noise model of MOS transistors is not included, that is, KT/C noise doesn't exist in circuit simulation, is that right or not? why ?

and how to find whether thermal noise model of MOS transistors is contained in the library?

for an ADC,if the simulated ENOB=9.7 or worse(for 10 bit resolution), then is KT/C noise included or not?

pls help me, i'm terribly confused.
thans all for reply.

You can't find KT/C in H-spice simulation.
You can use SIMULINK to find how many integration capacitor (Cs) value let thermal noise less than quantizer noise!

 

[lhlbluesky]

kt/c noise

for an ADC, if thermal noise is not included in circuit simulation, then, i have got some digital output codes from spectre simulation (such as 1024 points),and i make FFT conversion and get the dynamic parameters, such as SNR\SNDR\THD\SFDR\ENOB,then, is this right?
i mean, are the dynamic parameters obtained from FFT analysis resonable if no thermal noise included in circuit simulation? pls help me again.

 

[PaloAlto]

kt/c noise versus resolution

are the dynamic parameters obtained from FFT analysis resonable if no thermal noise included in circuit simulation?

I'm afraid not. Thermal noise is not included in a transient analysis, so you have to make sure that your thermal noise is below the noise floor of your transient analysis (quantization noise + "dynamic noise"). To do that is not trivial at all. Thermal noise simulations for SC ADCs are rather complicated and need very careful understanding of it. Another choice is to use tnoise analysis. This is available from mmsim6.2 or higher.

But anyway, try to calculate your KT/C noise and how they are transferred through your system, so if it goes through a gain stage, apply that gain to the noise. At least you should see if you are close to your quantization noise floor.

 

[lwjbh]

sc circuits ktc noise

maybe you should make the PSS simulation to check the noise

 

[lhlbluesky]

how to calculate ktc noise

but how to do PSS simulation for sc circuit?

 

[kuohsi]

kt/c adc

but how to do PSS simulation for sc circuit?

PPS is the fuction of tool SPECTRE .

 

[lhlbluesky]

noise floor kt -174

but how to do PSS simulation step by step for a sc circuit? pls tell me more.

 

[culho]

simulation circuit for l297

do a transient simulation and after that an fft to measure the quantization noise
do a mathematical noise analysis and choose the capacitor values to comply with the noise specification.
then make a tnoise simulation and compare the results.