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

 * [[Image:Opampfollowing.png]] $$ V_\mathrm{out} = V_\mathrm{in} \!\ $$


 * 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