# Semiconductors/Op-Amps

## Op-Amps Intro

Op-Amps stands for Operational Amplifier, a device usually manufactured as an Integrated Circuit (IC) . User don't need to know about the Itegrated Circuit inside in order to work with Op-Amps . All you need to know is that Op-Amps acts as an amplifier, it amplifies the difference of the 2 different voltages at input by a gain or amplification factor A

Output of an operational amplifier:

$V_{O} = A(V^{+}-V^{-})$

Ideally $A$ is assumed to be equal to infinity. However, in practical op-amps, it has a high value. Furthermore, the gain $A$ is a function of frequency.

Below is the most commonly used configuration of Op-Amps

## Negative Amplifier

200
$V_\mathrm{out} = - V_\mathrm{in} \frac{R_f}{R_\mathrm{in}}$

• The output voltage is a negative voltage equal to the input voltage amplified by a factor $\frac{R_f}{R_\mathrm{in}}$

## Positive Amplifier

$V_\mathrm{out} = V_\mathrm{in} \left( 1 + {R_2 \over R_1} \right)$
• The output voltage is a positive voltage equal to the input voltage amplified by a factor $\left( 1 + {R_2 \over R_1} \right)$

## Positive Buffer

$V_\mathrm{out} = V_\mathrm{in} \!\$
• From the circuit of Positive Amplifier, If R2 = 0 thì Vo = Vi

## Negative Buffer

200
• From the circuit of Negative Amplifier, If Rf/Ri = 1 then Vo = - Vi