can anyone explain this circuit for me

[xusoso]

thanks advance

 

[Fom]

Next time use GIF file less than 100K instead of JPG file. Nobody want to loss his valuable points.
First time I thought it is a differential comparator. It should compare voltage difference A-B and C-D. But I was confused by R1C1 and R2C2 frequency compensation. If it is comparator it doesn't need any frequency compensation, because never works with feedback. Another thing: it seems to me it is something wrong with this circuit. Where did you get that? As to me if disconnect gate of M21 from drain of M22 and connect to gate of M11 it looks much better.

 

[radiohead]

To my humble opinion I would not say it is a comparator, but an amplifier. The differential stages convert input voltage A-B and C-D to currents. These are substracted, so we get A-B-C+D. Finally the last stage is a transimpedance amplifier. It converts current back to voltage, with a factor 1k namely. The large cap is there to prevent influence of resistor on biasing.

 

[Fom]

But it seems to me if gate of M21 is connected to drain of M22 transistor M29 never will be switched off. So I prefer connection like I mentioned above.

 

[ramone]

the way i see it FOM seems to be right... allthough it also looks to me as an Amplifier... the amplifying stages look clear and the same seems for the noise rejection... well i can't be sure but that's my opinion...

 

[sunking]

It looks an amplifer mostly. And more, it seems a high frequency amplifer using dump factor comp. (DFC) amplifier

 

[tennad]

I think this is a amplifer,AB input and CD input have difference property.

 

[sda]

@xusoso

If you have posted the circuit as a quiz here, OK
If not, at least give a breif explanation of where you got it from, or what its supposed to do, as everyone here, isn't in the game of guessing or imagining the designers intentions.

Cheers
sda

 

[terryssw]

It seems to be a differential difference amplifier, but are you sure this circuit works? It is strange that why differential pair A-B and C-D not symmetric, and also why the current mirror in A-side connected to nothing?

 

[hanjiemy]

yes, i agree with terryssw. Is there no output of AB part?

 

[xusoso]

what is DFC amplifier, can you explain more?
thanks

 

[ME]

Next time use GIF file less than 100K instead of JPG file. Nobody want to loss his valuable points.

Actually it is much better to use .PNG instead of .GIF or .JPG.
PNG is smaller than GIF and you don't have ay quality loss as you have with GIF.

 

[xusoso]

this circuit is a part of DAC chip. we extract it using eda software.

 

[layes]

cd input of a diff_out two stage amp
ab control curernt (perhaps)used as CMFB

 

[ue]

as it sems to me circuti has four part

a-b diff pair
c-d diff pair.

buffer stage 1
buffer stage 2 - provide output

operation :

*a-b* provide output and it is provided to *bias c-d* pair's load and thus
biasing, magnitude of output provided by c-d stage.

probably reason for having *buffer stage 1* is not much clear to me but i suppose it is for freq compensation and making pair of load in *c-d circuit* identical.

purpose of *bufferstage 2* is to boost the current signal received from
*c-d stage*

--
considering this is circuit part of dac - probaly

(a-b) is less significant bit
(c-b) is more significant bit

and a and c are providing reference ground for the bit b and d.

/ue

 

[xusoso]

dear all

there is a mistake in the circuit.
the gate of m21 should connect to the gate of m18,not to the drain of m22

so this is the cmfb circuit. the input A is connected to a ref voltage, and input B is a feedback of common mode of output.

sorry for my mistake, and thank all of you.