# 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

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

• 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

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