# please help me with these topics (Differential amplifiers, CMRR etc)

Thread Starter

#### russel096

Joined Jan 2, 2012
10
this so not yet discussed to us and I'm having difficulties understanding stuffs from the internet... please help me answer these question(s).
I did my research, still can't figure out what to do exactly.

1. calculate the CMRR of a voltage follower whose common mode gain is 0.0045.

>>all i know is that CMRR is the ratio of Ad and Acm... but where's the Ad?? and how am i suppose to get it.. (so frustrated with this one..grr )

2. what will be the output of a differential amplifier whose input is 1.5 mV for both inverting and non-inverting inputs?

>>THIS I NEVER UNDERSTOOD .

3.when an input voltage of 1v is applied to an op-amp having Av=1,000,000 and bias supply voltage of 15V, what is the output voltage available?

SUPER THANK YOU IN ADVANCE (BTW, this is my first post here, yah! im new..please be kind)

#### jegues

Joined Sep 13, 2010
733
Solve Ad for a voltage follower, Ad = Vo/Vi.

As for the 2nd question, why do you think they call it a differential amplifier?

Certainly an op amp cannot output a voltage larger than the range of its supply, regardless of the value of Av.

Thread Starter

#### russel096

Joined Jan 2, 2012
10
thank you so much.. im just having difficulties understanding concepts that were not discussed to us that's all.. thank you so much, you're right with that.. thank you thank you thank you.