 Operational amplifier circuits are complex amplifiers compacted into integrated circuits which makes them very powerful. The two most important operational amplifier circuits are classified as either non-inverting or inverting. For both of these amplifier circuits, a feedback network of only two resistors, R1 and RF, a feedback resistor, are needed to control the gain. We'll first look at the non-inverting circuit. The non-inverting circuit employs the amplifier's positive input to produce an output signal that is exactly in phase with its input signal. By adjusting the resistor value at the feedback resistor, RF, you can easily calculate different amplification factors with the equation 1 plus RF divided by R1. So, for example, inputting 1 volt peak to peak with a feedback resistor value of 100 kilo ohms divided by an R1 value of 10 kilo ohms plus 1 will yield an in-phase output voltage signal with a gain of 11 volts at the RL resistor. Reducing the feedback resistor value, RF, to 47 kilo ohms will yield a gain of 5.7 volts. Increasing the value to 200 kilo ohms will yield a gain of 21 volts. Thus, increasing the RF value in a non-inverting amplifier circuit results in the amplification of the output voltage that is in phase with the original input signal. An inverted amplifier circuit also uses a feedback network of two resistors to control an output gain. However, the inverted circuit runs its signal through the negative input to produce an output signal that is inverted from the original input. The equation for calculating this process is negative RF divided by R1. Therefore, an input of 1 volt with a feedback resistor value, RF, of 10 kilo ohms divided by an R1 value of 1 kilo ohms will yield a 10 volt output signal that is exactly inverted from the original input wave. Reducing the feedback resistor value, RF, to 5 kilo ohms will result in an output of 5 volts peak to peak but likewise inverted. Thus, increasing the RF value in an inverting amplifier circuit results in the amplification of the output voltage that is inverted from the original input signal.