op-amps and differential amplifiers

[masoodov]

Hi,

Can someone explain why the input stage of every op amp is a differential amplifier?

Thanks for your help.

 

[Audioguru]

A differential amp circuit has two inputs with opposite phase.
Then the one with the negative phase can be used as an input for negative feedback to control the amount of voltage gain and control the bandwidth.

Both inputs are exactly the same so their input offset voltage is low.

 

[jecyhale]

Hi,

Can someone explain why the input stage of every op amp is a differential amplifier?

Thanks for your help.

I think differential pair can cancel the DC offset. It is very important because the offset will be always exist.

 

[kwkam]

The reason of using differential pair in opamp input is, we want to compare the different between inputs

 

[layoutmaster]

The differential stage will determine the op-amp's CMRR (common mode rejection ratio) and knowing it you can get the common-mode gain for the amplifier.

In other words, with a correct design, it will allow you to minimize the offset at the output caused by a common mode offset voltage in the input.