Non-inverting Amplifier

The simple circuit configuration of the non-inverting amplifier is shown on Picture 1. Since the two terminals must be at the same voltage. For the currents which flows through the resistors R1 and R2 we can write:

i1 = -Vi/R1

i2 = (-Vi -Vo)/R2

But, since no current flows into the inverting terminal, we can write that i1 = i2.

So, according to these relations, the voltage gain (amplification) of this non-inverting amplifier is:

Av = Vo/Vi = 1 + R2/R1

Picture 1: Non-inverting Amplifier with OP Amp


For our circuit configuration shown on Picture 1, the voltage amplification is Av = 1 + 5K/500 = 11. This amplification can also be measured from the wave forms of the input and output voltage signals shown on Picture 2. These plots are generated with transient simulation in LT Spice. The power supply voltages are V+ = 12 V DC and V- = -12 V DC. The input voltage has amplitude of +/- 100 mV at frequency of 500 Hz. The green color plot line is input voltage Vi wave form and the blue color plot line is the output voltage Vo wave form.

Picture 2: Input/Output voltage wave forms of the Non-inverting Amplifier with OP Amp


The input impedance of this circuit is infinite. From the other side, the output impedance is very low.