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How to reduce the noise of switched capacitor filter

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OMEsystem

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switched capacitor bw

I designed a SC filter of which the noise is quite high. Any guideline can be used
to reduce the noise? Increase the OPamp bandwidth? Increase the Cap size?

Please give recommendation, thanks.
 

steer

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how to reduce hf noice

Do NOT increase the op-amp bandwidth. It should be kept just at the minimum necessary to ensure a complete settling.
Increase of the capacitor size does helps. Also, look closely at the filter architecture. Some architectures are less noisy than others.
 

ken_cn

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use a nonoverlapping clock to control the switches.
incease op's gain, capacitaor value.
 

mists

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may you give more information about this issue, thanks!
steer said:
Also, look closely at the filter architecture. Some architectures are less noisy than others.
 

OMEsystem

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By the way, do you use cadence to be the simulator? what's the max sideband
in your simulation? I increase the value from 15 to 140, the noise of simulation
result is higher as the sideband is more. It looks like no saturation, and I'm
wondering how large value of sideband I should set?
Can you tell me your experience?
 

steer

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OMEsystem said:
By the way, do you use cadence to be the simulator? what's the max sideband
in your simulation? I increase the value from 15 to 140, the noise of simulation
result is higher as the sideband is more. It looks like no saturation, and I'm
wondering how large value of sideband I should set?
Can you tell me your experience?

This means your circuit has a lot of HF noise flolded into the passband. This is why I told you limit your ampls bandwidth to the bare minumum (see my post above).
 

OMEsystem

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steer said:
OMEsystem said:
By the way, do you use cadence to be the simulator? what's the max sideband
in your simulation? I increase the value from 15 to 140, the noise of simulation
result is higher as the sideband is more. It looks like no saturation, and I'm
wondering how large value of sideband I should set?
Can you tell me your experience?

This means your circuit has a lot of HF noise flolded into the passband. This is why I told you limit your ampls bandwidth to the bare minumum (see my post above).

Thanks for your advise. I still have several questions as following.

1) Do you mean the KT/C noise folded into passband depends on the bandwidth
of OPamp? Or, the high frequency noise of opamp(due to large opamp
bandwidth) is folded into passband by switching process?

2) Because the feedback factor of my SC circuit is quite small, it forces me to make
OPamp bandwidth larger. Any suggestion about this?

3) I have two SC circuits in cascade, one SC circuit is with small opamp BW,
another one is with high BW. I make the small BW one preceding larger BW one
, the noise result is worse than the reverse position arragement.
I'm wondering why I got this, could you give me several comments on this?

Thanks,
 

hebu

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OMEsystem said:
I designed a SC filter of which the noise is quite high. Any guideline can be used
to reduce the noise? Increase the OPamp bandwidth? Increase the Cap size?

Please give recommendation, thanks.

Maybe you don't give enough sideband to count all the folded noise from KT/C.

Or, the Rswitch and C is too small so that the noise bandwidth is too large.
 

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