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Please check my basic opamp+classAB circuit

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jutek

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basic opamp+classAB

hello

could you tell me if the circuit is ok?

i'm trying to use it as a buffer, but transistors M10,M12 are not turned on in the right moment. PMOS charges Cout when it shouldn't and NMOS discharges also when it shouldn't

When i only change M10 and M12 gates so M10 is driven by B and M12 is driven by A it doesn't help at all.

regards
 

basic opamp+classAB

Hi,

I would say that this structure is not a good one (I have read more than 500 papers about opamp design). There is a very fast path from input to output (from transistors M3 and M7) and also a very slow path thru transistors M10 and M12. The fast path is like a single-stage opamp, and the slow path is like a two-stage opamp. So transistors M10 and M12 can never turn on as soon as transistors M3 and M7.

I suggest you using other structures.

OpAmp
 

Re: basic opamp+classAB

M9 is connected to M1 whoose Vgs is controlled by input voltage. From another side if you want to define M9 current by constant current source its Vgs have to be constant.
Problem is that can not have in the same variable and constant M9 vgs.
It is the same for M11.
 

Re: basic opamp+classAB

I don't like this circuit either: if you really want to control the quiescent current at class-AB output stage, this structure can not do it. The configuration also looks very awkward. Where do you get this circuit from anyway?
 

Re: basic opamp+classAB

so, can you recommend a good class ab with low quiescent current, suitable for vdd=1.3V


regards
 

Re: basic opamp+classAB

jutek said:
hello

could you tell me if the circuit is ok?

i'm trying to use it as a buffer, but transistors M10,M12 are not turned on in the right moment. PMOS charges Cout when it shouldn't and NMOS discharges also when it shouldn't

When i only change M10 and M12 gates so M10 is driven by B and M12 is driven by A it doesn't help at all.

regards
Click to expand...

In your first configuration: M3 and M10 don't work in the same direction ( one is close while other open), thesame is for M7 and M12.
In your second configuration: M3 and M12 cannot get proper dc bias. So they don't work.
 

Re: basic opamp+classAB

The circuit donot include the class ab current control circuit , you should add them between net A and B, you can select the structure of float current source or feedback circuit which sense the output current ,and then select the min current and then convert the current to voltage, compare the voltage with the reference voltage and adjust the gate voltage of output
 

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