differential amplifier

[Chethan]

In a differential amplifier, what is the setup to find out which one is the positive terminal input and which is negative terminal.???
I have seen that both for P channel input DA and N channel input DA, the left hand side input is the positive terminal.Is it correct?

 

[wjxcom]

I don't think so. the positive terminal have the same sign with the output. and the negtive terminal have a reverse sign with the output terminal.

 

[hr_rezaee]

hi
Gain of output referred to negative input is negative and Gain of output referred to positive input is positive.

 

[Davood Amerion]

You must evaluate output change respet to input.
If input go high (increased voltage) what happen to output?
If output voltage is increased too, then that input is positive input.
But if output voltage decreased that input is negetive input pin.

 

[tuza2000]

in the common source amp,the gate has the oppsite polarity to the drain.
regards

 

[fnlee]

I think wjxcom said is right.

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the positive terminal have the same sign with the output. and the negtive terminal have a reverse sign with the output terminal.

 

[chu]

hi,

wjxcom is right abt same side of single-ended-diff-amp's output is the +ve terminal. If u have the output connected to common source, then refering to output of that common source, the input terminal must be switch (Davood is right), this is what happen in 2-stage-op-amp.

rgds,
chu

 

[huojinsi]

The noninverter terminal and inverter terminal always relative to the output terminal. If the phase of the output terminal is the same as the input terminal, the input terminal is noninverter, or else the input terminal is inverter!

 

[suria3]

It is not a matter actually. In diffamp design, the polarity can be set at any side, basically when one side is given input, the output of it is the inverted one like a common source amplifier. Only thing when this amp is design for a opamp in feedback system, then you have to consider the polarity of the input compared to output regulation.