An inverting amplifier is a fundamental electronic circuit used to amplify an input signal while inverting its polarity. It's commonly used in various applications like signal amplification, audio processing, and instrumentation. The circuit is based on an operational amplifier (op-amp) and a few passive components like resistors.
Here's how the inverting amplifier circuit works:
Operational Amplifier (Op-Amp): An op-amp is a versatile integrated circuit that amplifies the difference between two input voltages. It has a high input impedance, low output impedance, and a very large gain. In an inverting amplifier configuration, the op-amp is connected in a way that the output voltage is proportional to the negative of the input voltage.
Feedback Loop: The heart of the inverting amplifier is the feedback loop that connects the output of the op-amp back to its inverting input. This is achieved by using a resistor network.
Input and Output: The input signal, usually referred to as "Vin," is applied to the inverting (-) input of the op-amp. The output signal, "Vout," is taken from the output terminal of the op-amp.
Resistor Configuration: The key components in the feedback loop are two resistors: one connected between the inverting input (-) and the output, and another resistor connected between the inverting input and the ground (or a reference voltage). The resistor connected to the output is usually called the "feedback resistor" (Rf), and the one connected to the ground is the "input resistor" (Rin).
Inverting Action: Due to the high gain nature of op-amps, a small difference between the voltages at the inverting (-) and non-inverting (+) inputs results in a significant output voltage. In the inverting amplifier configuration, as the voltage at the inverting input increases, the op-amp output drives in a direction to decrease this difference, effectively inverting the polarity of the input signal.
Voltage Gain: The voltage gain (Av) of the inverting amplifier is determined by the ratio of the feedback resistor (Rf) to the input resistor (Rin), and it is given by the formula: Av = -Rf / Rin. The negative sign signifies the inversion of the input signal's polarity.
Virtual Ground: An important concept in this circuit is the creation of a "virtual ground" at the inverting input. This happens due to the high input impedance of the op-amp, making the voltage at the inverting input very close to the voltage at the non-inverting input (which is often connected to a ground or a reference voltage).
In summary, the inverting amplifier circuit using an operational amplifier provides a convenient way to amplify and invert input signals. It is a widely used building block in electronics for various applications where signal processing and amplification are needed.