# Calulating the gain

#### dmanzay

Joined Oct 25, 2011
5
Can someone tell me if this is right, If Rf = 10k ohms and Ri =100 ohms would the gain be a -10, if the signal is 1V and the input frequency is 100 Khz, would the output voltage be -1.10v. I'm trying to find out if I'm right.

Dmanzay

#### crutschow

Joined Mar 14, 2008
33,310
Are you talking about an inverting op amp connection? If so then the gain is -Rf/Ri, which is not -10.

The frequency has little effect on the output voltage until you reach the gain-bandwidth limit of the op amp. If below that frequency then the output would be equal to the input voltage times the gain.

• dmanzay

#### dmanzay

Joined Oct 25, 2011
5
Yes it's a inverting Op-amp, so would the gain be Gain = 1+(-Rf/RI), if so that would give me 1.10v am I right.

Dmanzay

#### crutschow

Joined Mar 14, 2008
33,310
Yes it's a inverting Op-amp, so would the gain be Gain = 1+(-Rf/RI), if so that would give me 1.10v am I right.
No. The gain for an inverter is as I previously stated. The factor of 1 is used for the gain of a non-inverting op amp (without the minus in front of Rf/RI).

You math is way off. How do you get a gain of 10 and an output of 1.10v by multiplying -Rf/RI * 1V?

#### RiJoRI

Joined Aug 15, 2007
536
Hint: Change 10k to 10000

--Rich