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is this an amplifier?

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winsonpku

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i guess this circuit is an amplifer,but it 's some different from conventional amp
this circuit is a part of a fold-cascode amp,if it's an amp,then it's a booster
it 's used to generate the biase voltage of the pmos cascode.in1 and in2 is the sources of the two pmos cascode transistor.out1 and out2 is connected to the gate of the two pmos cascode transistor.
but if it's an amp,why not the cmfb circuit.in my opinion,fully differential amp must have the cmfb circuit.
plese help me,any answer is welcome!
thanks
 

i think the input pair connected with b3 set the common mode voltage of in1 and in2.
and it is an amp, and as u say, it is used as the booster

btw,can u show me the whole sch of the circuit including the boost amp?
thx
 

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    winsonpku

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do u mean that b3 is used as CMFB?
can you tell me some papers and books about this circuit?
in fact,b3's voltage is near with in1 and in2.
the main amp is a telescopic folded casecode amp,and it's cmfb is a conventional sc cmfb.

arsenal said:
i think the input pair connected with b3 set the common mode voltage of in1 and in2.
and it is an amp, and as u say, it is used as the booster

btw,can u show me the whole sch of the circuit including the boost amp?
thx
Click to expand...
 

Hi
It is a nice symetrical differential amplifier.
For more help please refer to "Design of Analog CMOS Integrated Circuits"
By Behzad Razavi. It is really a perfect book in CMOS design.
 

It is indeed a gain boost differential amplifier with built-in common mode feedback. This CMFB is done through the help of b3. To see why this is the case, think about in1 and in2 as one common-mode terminal, b3 is the other input for common-mode voltage. If the common-mode of in1/in2 changes with regarding to b3, the out1 and out2 will move to the opposite direction and will force in1/in2 to move back to their nominal value through cascoded PMOS transistors in the main amplifier.

There are several ways to design a gain-boost differential amplifier, and this is just one of the possible implementations.
 

Dear willyboy19:
from your explanation,i found some puzzles.you said,the b3 is used to set the common mode voltage of in1 and in2,but in fact,the commod voltage of out1 and out2 is need to be set. so can you tell me the details?thanks
 

in my openion,
if this amp is for gain-boost in ur folded cascode amplifier, then its function is only to "enlarge " the resistance of cascode mos, so why CMFB in this amp ?
there should already exist a CMFB in the main differential amp.
 

yes,its function is used to enlarege the output resistance of the main amp
but we must know it's differential or sigle ended amp?
if it's a sigle ended,then it doesn't need CMFB
otherwise, it must have a CMFB.


Btrend said:
in my openion,
if this amp is for gain-boost in ur folded cascode amplifier, then its function is only to "enlarge " the resistance of cascode mos, so why CMFB in this amp ?
there should already exist a CMFB in the main differential amp.
Click to expand...
 

why it is a fully differentital amp ?
why not it is two single end amp drawed together?
in fully differential, if one input change (vi+ or vi-) , then both output (vout+, Vout-) will change too, but in ur "circuit2. GIF", if in1 change it only affect out1, and out2 is no changed (cuase there is no path existed from left part to right part), vice versa.
so why u said it is fully differential ?
can u explain it?
 

    W

    winsonpku

    Points: 2
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yes,i agree with u,it 's two single endedd amp drawed together
so it dosen't need CMFB.
thanks for your explanation.
Btrend said:
why it is a fully differentital amp ?
why not it is two single end amp drawed together?
in fully differential, if one input change (vi+ or vi-) , then both output (vout+, Vout-) will change too, but in ur "circuit2. GIF", if in1 change it only affect out1, and out2 is no changed (cuase there is no path existed from left part to right part), vice versa.
so why u said it is fully differential ?
can u explain it?
Click to expand...
 

The extra transistors look like they are added to redce the input capacitance of the input driver transistors.

An iput signal should be seeing approximately Cgs/2 instead of Cgs. Of course the input transistor is now source degenerated and gm of the circuit is now half that of the input transistor.

It looks like an attempt to linearize the gm of the circuit.

Anyone?
 

Yes, it is an ota with fully differential input and output.
 

Hello there ,
this is a cascode amplifier with flexibilty for different operating points.

p.s : Kindly use appropriate symbols for the trans. it misled me to think of something in terms of the biasings b2 b4 etc and think of a multiplier.
 

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