jimeece13 said:Hello all,
I am designing an active continuous time filter and i have chosen a Tow-Thomas biquad to realize my circuit.My question is the following :
During the design of the opamp and the simulation procedure via cadence spectre,which is the proper load capacitance that i should concider for my opamp circuit?? 1pF or 2pF should be enough? Is there a way to evaluate the proper load capacitance value for my opamp via some kind of simulation of the ideal circuit,that is to measure the capacitance seen at the output of the first opamp for example in the TT biquad?
Apparently i need this info in order to make an initial estimation for the gm value of my differential pair at the input stage to obtain the required transition frequency since 2*pi*ft≈gm1/(Cout+Cload).
So,i need an estimation for the sum Cout+Cload.
Any helpful answer would be appreciated.Thanks in advance.
jimeece13 said:That's right,i intend to design my own opamp with some specifications i have derived from the filter structure.I have chosen a Tow-Thomas biquad for my circuit.
Exactly this capacitance concerns me : "the capacitance seen at the output of each of the three opamps".How can i determnine that??Do you have any idea?Maybe i will design an one stage opamp with gain boosting,so the output of the first stage will be the output of the overall opamp.I hope i am more clear to you now.
Megh said:@upvl,
Using "stb" is fine for Single ended structure. What if I have a fully differential opamp.
How would you suggest I should model the load seen by the opamp.
Thanks
Meghraj
sutapanaki said:There is another component from analogLib (I forgot the name) which can be used for differential case.
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