Capacitance mismatch: deciding a sandwich or mos cap size

[patato]

capacitance mismatch

I am trying to choose an optimum capacitor value for my pipeline ADC,
and is currently working on capacitance mismatch

how do u guys decide a sandwich or mos cap size to get cap mismatch lower than , say 0.1%?
is there a good way to estimate mismatch by hand-caculation?

 

[jerryzhao]

cap mismatch

I don't think the mos capacitance fit for sample cap. if u use MIM or Poly to poly cap. you can lookup the mismatch form that from foundry.
I think if ur ADC not high speed or high resolution, and you layout better, their ratio can match to 0.1%.

 

[patato]

Re: capacitance mismatch?

I don't think the mos capacitance fit for sample cap. if u use MIM or Poly to poly cap. you can lookup the mismatch form that from foundry.
I think if ur ADC not high speed or high resolution, and you layout better, their ratio can match to 0.1%.

Thanks Jerry.
Well I did find mismatch form of MIM,but only logic process is available to me..
so i guess i'll have to get along with MOS or sandwich cap(such as M3-M4-M5 or M1-M2-M3).

more question:
1.MOS don't fit sample cap? why?
I've read some paper from Paul.R.Gray's lab, and they said MOS cap has enough linearity for a 10 bit ADC.

2.When it comes to SANDWICH cap, the problem is: no mismatch data for it!
so i am trying to estimate SANDWICH cap' mismatch.
Like this : for a M1-M2 cap , top and bottom plate width=W , length= L
σ of (δW/W)=x
σ of (δL / L)=y

σ of (δC/C) ≈ ( x² + y²)½
is it reasonable?

 

[jerryzhao]

Re: capacitance mismatch?

If you only use the MOScap sample, maybe is enough linearity .but you know the moscap's C_V character, you must contral the gate voltage region. otherwise it voltage character not better.
I think the sandwich cap is better.but it like you say no mismatch data.
I find some company's pipeline ADC datasheet write it use sandwich cap in logic process. I never design the pipeline ADC use sandwich cap in logic process .
So I am sorry, can't help you.

 

[eng_wael ashraf]

capacitance mismatch?

please if u have any papers that useful for using capacitor and its characteristic curves?
please send them to this e-mail
eng_wam2020@yahoo.com