Understanding the Op Amp Feedback Loop: A Comprehensive Guide

Operational amplifiers (op-amps) are fundamental components in electronic circuits, and their feedback loops play a crucial role in determining their performance. In this article, we will delve into the intricacies of the op amp feedback loop, exploring its various aspects and their impact on circuit design.

What is an Op Amp Feedback Loop?

An op amp feedback loop is a configuration where the output of an op-amp is fed back to its input, either in the inverting or non-inverting configuration. This feedback can be positive or negative, and it significantly influences the stability, gain, and bandwidth of the circuit.

Types of Feedback Loops

There are two main types of feedback loops in op-amp circuits: inverting and non-inverting. Let’s explore each type in detail.

Inverting Feedback Loop

In an inverting feedback loop, the output is connected to the inverting input of the op-amp. This configuration provides a negative feedback, which means that the output voltage is inversely proportional to the input voltage. The voltage gain of the circuit is determined by the ratio of the feedback resistor (Rf) to the input resistor (Rin). The formula for the voltage gain (Av) is given by:

This configuration offers several advantages, such as a high input impedance, low output impedance, and a wide bandwidth. However, it also has some limitations, such as a phase inversion and a reduced voltage gain compared to the non-inverting configuration.

Non-Inverting Feedback Loop

In a non-inverting feedback loop, the output is connected to the non-inverting input of the op-amp. This configuration provides a positive feedback, which means that the output voltage is directly proportional to the input voltage. The voltage gain of the circuit is determined by the ratio of the feedback resistor (Rf) to the input resistor (Rin). The formula for the voltage gain (Av) is given by:

This configuration offers several advantages, such as a non-inverted output, a higher voltage gain, and a wider bandwidth compared to the inverting configuration. However, it also has some limitations, such as a lower input impedance and a higher output impedance.

Stability and Bandwidth

The stability and bandwidth of an op-amp circuit are crucial factors that determine its performance. The feedback loop plays a significant role in determining these parameters.

Stability

Stability refers to the ability of a circuit to maintain its output voltage when subjected to disturbances. An unstable circuit may exhibit oscillations or instability, which can lead to poor performance. The stability of an op-amp circuit is influenced by the gain and phase margin of the circuit. The gain margin is the amount of additional gain required to cause instability, while the phase margin is the amount of additional phase shift required to cause instability. A stable circuit has a positive gain margin and a phase margin greater than 45 degrees.

Bandwidth

Bandwidth refers to the range of frequencies over which the circuit can operate effectively. The bandwidth of an op-amp circuit is influenced by the gain and the open-loop gain of the op-amp. A higher gain and a lower open-loop gain result in a wider bandwidth. The bandwidth of the circuit can be calculated using the following formula:

where GBW is the open-loop gain of the op-amp and Av is the voltage gain of the circuit.

Applications of Op Amp Feedback Loops

Op amp feedback loops find applications in various electronic circuits, such as amplifiers, filters, oscillators