- Inverting Amplifier Definition: An inverting amplifier is defined as a type of operational amplifier that outputs a signal 180 degrees out of phase with the input.
- Circuit Setup: The input signal is applied to the inverting input through a resistor, while the non-inverting input is grounded.
- Voltage Gain: The gain of an inverting amplifier is the negative ratio of the feedback resistor to the input resistor, indicating phase reversal.
- Input Impedance: The input impedance of the inverting amplifier is equal to the value of the input resistor, Ri.
- Applications: Inverting amplifiers are versatile, used in everything from audio mixers to converting current signals into voltage outputs.
What is an Inverting Amplifier?
An inverting amplifier (also known as an inverting operational amplifier or an inverting op-amp) is a type of operational amplifier circuit which produces an output which is out of phase with respect to its input by 180o.
This means that if the input pulse is positive, then the output pulse will be negative and vice versa. The figure below shows an inverting operational amplifier built by using an op-amp and two resistors.
The input signal is applied to the inverting terminal through resistor Ri, while the non-inverting terminal is grounded. Feedback from the output to the inverting input via resistor Rf stabilizes and controls the output voltage.
Mathematically the voltage gain offered by the circuit is given as
Where, 
However, we know that an ideal op amp has infinite input impedance due to which the currents flowing into its input terminals are zero i.e. I1 = I2 = 0. Thus, Ii = If. Hence,
In an ideal op-amp, the voltage at the inverting and non-inverting inputs is always equal.
As we have grounded the non-inverting terminal, zero voltage appears at the non – inverting terminal. That means V2 = 0. Hence, V1 = 0, also. So, we can write
From, above two equations, we get,
The voltage gain of the inverting operational amplifier or inverting op amp is,
This indicates that the voltage gain of the inverting amplifier is decided by the ratio of the feedback resistor to the input resistor with the minus sign indicating the phase-reversal. Further, it is to be noted that the input impedance of the inverting amplifier is nothing but Ri.
Inverting amplifiers, known for their excellent linear characteristics, are ideal for DC applications, converting input currents to output voltage as Transresistance or Transimpedance Amplifiers, and serving in audio mixers as Summing Amplifiers.
