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Simulation Of Fully Differential OPAMP in MDAC Section Of Fully Diff. PIPELINED ADC

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Junior Member level 1
Aug 26, 2010
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Hello ......
I have a Problem related to Fully Differential Pipelined ADC Implementation. I have Problem in MDAC Section Only.

I have chosen SC MDAC topology to implement 1.5 bit MDAC.(Plz see attachment named "differential MDAC from Paper" attached)
I have big doubt while implementing MDAC differentially....

FOR SIMPLICITY I AM ONLY APPLYING DIFFERENTIAL SIGNALS DIRECTLY ...ASSUMING THEY ARE COMING FROM INPUT AND DAC AS WELL (as shown in the snapshot named "Our implementation... for simplicity i have shown only required part to be discussed)

In Sampling phase (Phi1=1), Cs and Cf capacitors will sample the inputs in both upper and lower branches
and in Amplification phase (Phi2=1), Opamp provide a gain of 2 at the output with the help of Cs and Cf.
While implementing MDAC single -ended, Opamp is biased with some bias potential at its positive terminal and
at negative terminal we implement gain of 2 and get the residue at the single ended output.
But in differential circuit, our both branches are sampling and amplifying differential inputs so how biasing is provided to opamp at amplification mode.

I also tried MDAC (given in paper publised (see the attached snapshot named D.Meganathan MDAC)) but again I face same problem of how to bias the Opamp in amplification mode. i am unable to find the way to apply the Vicm to the opamp during Differential mode of Amplification.
I have also attached Snapshots. :roll::x

Please guide/.help me so that I remain in right direction .

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