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Simulating AC performance of the amplifier with switched capacitor circuit

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Junus2012

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Hello

I am trying to use switched type CMFB of my fully differential amplifier instead of the continous time counter part,

as surely you know such kind of CMFB works with clock control signals,

My problem is that, I never had an experience on how to simulate this amplifier with this type of CMFB. Suppose I want to find the ac charastericiticss from ac simulation, but clocks will be ignored in this simulation.
This problem is not only related to the amplifier, for any circuit working with clock or digital part and I want to perform analog simulation, I have no idea about it

I am looking forward for your help
best regards
 

Why don't you try doing ac or stb from transient? Pick a point when you have only the averaging caps connected to the amplifier output, perhaps phase2 of your clocks and when the transient simulation reaches that point run stb.
 
My problem is that, I never had an experience on how to simulate this amplifier with this type of CMFB. Suppose I want to find the ac charastericiticss from ac simulation, but clocks will be ignored in this simulation.
This problem is not only related to the amplifier, for any circuit working with clock or digital part and I want to perform analog simulation, I have no idea about it
I am looking forward for your help
best regards

Switched-capacitor circuits are sampled data systems. They are a kind of "bridge" between analog and digital systems (time discrete but amplitude continuous).
Therefore, there are some methods to simulate the frequency response (as analysis) of such circuits. For this purpose, the S-C parts have to be replaced by suitable analog elements.
Two methods are described in the literature.
 
This problem is not only related to the amplifier,
for any circuit working with clock or digital part and I want to perform analog simulation
What simulator do you use ?

Generally, there are two methods,
AC Analysis over one clock period average
or
AC Analysis at specific point during clock period.
 
Last edited:
What simulator do you use ?

Generally, there are two methods,
AC Analysis over one clock period average
or
AC Analysis at specific point during clock period.

Dear Pancho

I am using spectra simulator from cadence

your solution is smilar to Suta, but I dont know how to configure the setup implement this idea

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Why don't you try doing ac or stb from transient? Pick a point when you have only the averaging caps connected to the amplifier output, perhaps phase2 of your clocks and when the transient simulation reaches that point run stb.

Dear Suta,

As I have mentioned to Pancho, I dont know the setup in Spectra simulation to implement this idea

- - - Updated - - -

Switched-capacitor circuits are sampled data systems. They are a kind of "bridge" between analog and digital systems (time discrete but amplitude continuous).
Therefore, there are some methods to simulate the frequency response (as analysis) of such circuits. For this purpose, the S-C parts have to be replaced by suitable analog elements.
Two methods are described in the literature.

Can you please refer me to these literature

- - - Updated - - -

Thank you all for your kind help
 

Open transient simulation menu. Click on Options > Output, scroll down to ACTMES settings. In actimes enter the desired time and in acnames enter stb. Then, in the analysis set up not only transient but also stb analyses.
 
Can you please refer me to these literature

Nelin B.D.: "Analysis of Switched-Capacitor Networks using general purpose circuit simulation programs.", IEEE Trans. Circuit and Systems, vol CAS-30, pp 43-48.

Remark: I remember another paper proposing another (perhaps simpler) method....give me some time to find it...
 
Linearization is one method as LvW mentioned. However, if you have SpectreRF license you might try to use periodic simulations (pss, pac, pstb or pnoise).

Some info you can find in Spectre doc:
<spectre_installation>/doc/spectreRFexplorerWorkshop/spectreRFexplorerWorkshop.pdf
<spectre_installation>/tools.lnx86/spectre/examples/SpectreRF_workshop
 
Linearization is one method as LvW mentioned.

But it is important to know that methods I was refering to preserve the characteristics of sampled data system (periodic response of the clock period with real zeros)
 
Linearization is one method as LvW mentioned. However, if you have SpectreRF license you might try to use periodic simulations (pss, pac, pstb or pnoise).

Some info you can find in Spectre doc:
<spectre_installation>/doc/spectreRFexplorerWorkshop/spectreRFexplorerWorkshop.pdf
<spectre_installation>/tools.lnx86/spectre/examples/SpectreRF_workshop

Dear Dominik,

Right now I dont have Spectre RF license,
So I would prefer to practice the method of running the ac over transisent, like the one Suta explained,

Pancho commented

AC Analysis over one clock period average
or
AC Analysis at specific point during clock period.

I understancd the second choice but the first one is not clear, what mean of clock period average
 

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