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How to design Gain Boosting AMP used in OTA

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wael_wael

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gain boosting

How to design Gain Boosting AMP used in OTA
I am looking for ur help to design CS AMP which used in Gain Boosting AMP or I have to design it before I start design hole OTA or just I combined them together and start simulation directly

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solidstate

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First build the OTA; see what kind of performance you get there, so that you know what kind of specs need to be fulfilled by the boosting amplifiers. Otherwise you'll get lost in simulation...

What kind of OTA are you going to make?
 

    wael_wael

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wael_wael

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thank u, fully differential OTA(Folded cascode), but still tha same question,how to simulate the the gain boosting part inside the circuit or just i design it and combined it after that, the second choice i fell is not correct bcs of the bias voltage not same
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solidstate

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In a folded cascode, you have pmos and nmos cascodes; instead of biasing them with a regular voltage source, you simply use ideal amplifiers as gain boosters. Once you know the gate and source voltages of the cascodes, you design the gain boosting amplifiers with those output and input common mode levels, respectively, and with the gain that you found from the ideal amplifier simulation..
 

    wael_wael

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wael_wael

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thank u so much, in fact i don't know how to find out the ideal op amp, do u mean i use one from the simulator or there is way to make it
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solidstate

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Are you using Cadence? Then you probably have a library of ideal components (check out ahdlLib, diffamp)..

But in this case, for a first test, a voltage controlled voltage source is enough to make an ideal amp; Connect it like this:

Vin+ = Vdrain,ref
Vin- = Vdrain,cascode
Vout+ = Vgate,cascode
Vout- = gnd

Can't make it easier than this ;) A negative voltage gain will regulate vgate to make (Vdrain,ref - Vdrain,cascode) close to zero..

Also check this out: https://www.edaboard.com/ftopic177508.html

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    wael_wael

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wael_wael

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thank u so much, in fact i am using T-SPICE and i found ideal OP AMP, any way i have more question that is i can use normal voltage source to bias the circuit, i knew that it is need a current to work, but i don't know ho to find ideal voltage source
regds
 

wael_wael

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could someone answer my question pls.
 

linan0827

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solidstate said:
In a folded cascode, you have pmos and nmos cascodes; instead of biasing them with a regular voltage source, you simply use ideal amplifiers as gain boosters. Once you know the gate and source voltages of the cascodes, you design the gain boosting amplifiers with those output and input common mode levels, respectively, and with the gain that you found from the ideal amplifier simulation..
Hi, I have a question about how to design the gain boosting amplifiers with certain output and input common mode levels?

I want to implement a folded cascode circuit as the gain amp, but I dont know which parameter should I adjust to make the common mode output corectly bias the cascode transistor in main amp.

Please help me with this issue, thank you in advance.
 

jeffsky520

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only if output swing of your gain-boosting amplifier is large enough, it works well when you put it in the loop of main amplifier.
 

megzhuy

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I think the voltage change is not very large in the outputs of booster , maybe it's not neccessary to use SC CMFB.
 

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