OP-AMP: OP-AMP is a solid state device capable of sensing and amplifying dc and ac input signals. OP-AMP is an amplifier with two inputs (different inputs) and a single output. OP-AMP consists of 20 transistors, 11 resistors and one capacitor. It usually requires a positive and negative power supply (dual power supply). This allows the output voltage to swing positive and negative with respect to ground.
Non-inverting amplifier:
The basic OP-AMP non-inverting amplifier is shown in Figure. The input signal Vin is applied to the non-inverting input terminal. The resistor Rin is connected from the inverting input to ground. The feedback resistor Rf is connected between the output and the inverting input.
Resistors Rf and Rin form a resistive ratio network to produce the feedback voltage (VA) needed at the inverting input. Feedback voltage (VA) is developed across Rin. Since the potential at the inverting input tends to be the same as the non-inverting input (as pointed out with the description of virtual ground), Vin=VA.
Since VA=Vin, the gain of the amplifier can be expressed as
Av=VoutVA
Howeverm, VA is determined by the resistance ratio of Rin and Rf, thus,
VA=RinRf+RinVout
(or) VoutVA=Rf+RinRin
VoutVA=1+RfRin
∴Av=1+RfRin
Finally, the output voltage can be found by,
Vout=(1+RfRin)Vin
It is seen that the input and output voltages are in phase.