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an urgent question about regulator

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Hafedh

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hi!
why is it better to use an OTA rather than AOP in a linear drop out regulator?????
is there any one who can help me???
 

I have worked on many LDOs; but firstly what is "AOP" ?

may be then I can help you out
 

hi
AOP is " Operational Amplifier"

I'm waiting for help....
 

An OTA is actually an opamp without an output stage, so it has high rout. So if you can bare a high rout in your application than use an OTA to save power and area
 

    H

    Hafedh

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Hi,

OTAs are faster, but limited in output swing, whereas an AOP (better call it OPA), has a second stage which serves as additional gain stage and larger output swing. Sometimes when you need to drive resistive loads with your amplifier, you need to make sure that the output resistance is lower than the resistance you will drive.
In this case you sometimes need to buffer your OPA with a low gain stage with low output resistance.
 

    H

    Hafedh

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Hafedh said:
hi!
why is it better to use an OTA rather than AOP in a linear drop out regulator?????
is there any one who can help me???
Click to expand...

Ｉ think it is because the regulator don't require very large gain. OTA should be enough.
And I think OTA is more easy to be stable than OPA.

But I agree that both are ok.
 

    H

    Hafedh

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I agree both are OK .

But it is definetly easier to compensate the loop with OTA then with OPA .(with usual OTA structures u have one pole less then the OPA)

You need to make your choice depending upon your specs.
 

I think you refer using OTA to the one with common
source output stage, if so, that's because of its
lower dropout voltage then.
 

First of all ,please refer operational amplifier as opamp .
typically OTA is used in regulators .
 

What's that OTA and OPA, can any one tell me to what they stand for?
 

OTA : operational transconductance amplifier. (the name implies function)
OPA: operational amplifier; usually OTA + buffer.

I think if the pass element capacitance is large a buffer may be a good thing to get faster response , but I need some one to confirm for this.
 

you are right "Quaternion". It is a good idea to use a buffer for getting a faster response.
 

In fact, OPA maybe more stable than OTA because the parasitic pole will be put on the high frequency
Drawback is this will add the quiescent current.

quaternion said:
OTA : operational transconductance amplifier. (the name implies function)
OPA: operational amplifier; usually OTA + buffer.

I think if the pass element capacitance is large a buffer may be a good thing to get faster response , but I need some one to confirm for this.
Click to expand...
 

I think OPA itself can be thought of as an OTA+buffer.

and thats what we said in previous post!!
 

OTA is tetter for stability control
 

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