how does this integrator work?

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matin-kh

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Hello!
I extract this integrator from a paper which is used in AGC circuits to produce control voltage of VGA. I can not understand how it can perform as an integrator because it is a symmetrical CMOS OTA which amplifies the differnce between Vpeak and Vref and if we consider the output capacitor as the capacitor of integrator an amplifier which work as an Op Amp is absent yet.
the integrator shouldn't be like fig.2? so I can't understand how the fig.1 could act as integrator and can control the gain of VGA?
and what is the duty of two R?
Could you please help me?




with best regards
Matin
 

A gm-C circuit (OTA + capacitor) is perfectly working as integrator, if it's feeding a high impedance load, e.g. a MOSFET buffer. You should be able to find plenty of literature examples.

The resistors provide "source degeneration", reducing the OTA'S gain and increasing it's linearity and input voltage range.
 
matin-kh said:
..the integrator shouldn't be like fig.2?
Click to expand...

Why? The 2nd circuit shows an opamp based integrator circuit. This principle cannot be simply transferred to OTA circuits.
 
FvM said:
A gm-C circuit (OTA + capacitor) is perfectly working as integrator.
Click to expand...

FvM could you please tell me some books or pdf files about gm-c circuits to read more about it?
thanks a lot

- - - Updated - - -

LvW said:
Why? The 2nd circuit shows an opamp based integrator circuit. This principle cannot be simply transferred to OTA circuits.
Click to expand...

because of the picture below i found another integrator circuit which i think M12 acts as an Op Amp and M12, rf, cf is a integrator and i thought the first integrator which i attached isn't like this. i don't know i think i am wrong!!

 

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