Operational Amplifiers
An operational amplifier is a high-gain electronic voltage amplifier with differential input and single-ended output. It features high gain, low distortion, and high input impedance, and is typically used in signal processing, control systems, and many other types of electronic applications.
The main function of an operational amplifier is to amplify the input signal. This signal can be voltage, current, or any other type of signal. The amplified signal is then used for various applications such as control systems, signal processing, or driving speakers. Operational amplifiers can also perform mathematical operations such as addition, subtraction, integration, and differentiation, hence the name "operational" amplifier. Because of their versatility, operational amplifiers are widely used in a variety of electronic devices, including computers, smartphones, audio and video equipment, and scientific instruments.
Inverting Operational Amplifiers
The inverting operational amplifier is a basic operational amplifier circuit configuration using negative feedback connection. In simple terms, the amplifier inverts and changes the input signal.
An inverting operational amplifier is a type of operational amplifier circuit that produces an output that is 180° out of phase with its input, meaning, if the input signal is positive ( ), the output signal will be negative (-). The inverting operational amplifier is designed with an operational amplifier with two resistors.
Inverting amplifiers are considered one of the simplest and most widely used operational amplifier configurations. The following figure represents the circuit of an inverting operational amplifier:
Figure 1: inverting operational amplifier circuit diagram
From the above diagram, it can be seen that the feedback is given to the operational amplifier, allowing the circuit to work in a closed loop. To make the circuit operate accurately, negative feedback is provided. Therefore, in order to have a closed-loop circuit, an input is provided at the inverting end of the operational amplifier, as well as a feedback signal from the output.
The gain for the inverting operational amplifier circuit is:
Figure 2: Gain equation
Non-Inverting Operational Amplifiers
An amplifier that generates an amplified signal at the output, the phase of which is similar to the applied input, is called a non-inverting amplifier or a same-phase operational amplifier. This simply means that for an input signal with a positive phase, the output will also be positive. The same goes for a negative phase input. The following figure shows the circuit of a non-inverting amplifier:
Figure 3: Non-Inverting Operational Amplifiers circuit diagram
In this case, in order to have an output with the same phase as the input, the input signal is applied at the non-inverting terminal of the amplifier. But negative feedback needs to be provided here as well, so the feedback signal is provided to the inverting terminal of the operational amplifier. The closed-loop gain of the non-inverting amplifier is as follows:
Figure 4: Closed-loop gain of a Non-Inverting Operational Amplifiers
Comparison between Inverting and Non-Inverting Op-Amps
Inverting vs Non-Inverting Op-Amps
- Input Connection:
- Inverting Op-Amp: The input signal is applied to the inverting (-) input terminal.
- Non-Inverting Op-Amp: The input signal is connected to the non-inverting ( ) input terminal.
- Phase of Output:
- Inverting Op-Amp: The output signal is 180 degrees out of phase with the input signal (i.e., it is inverted).
- Non-Inverting Op-Amp: The output signal is in the same phase as the input signal.
- Gain:
- Inverting Op-Amp: The gain is given by the negative ratio of the feedback resistor to the input resistor (-Rf/Ri).
- Non-Inverting Op-Amp: The gain is given by 1 plus the ratio of the feedback resistor to the input resistor (1 Rf/Ri).
- Input Impedance:
- Inverting Op-Amp: The input impedance is relatively low because the input is through the resistor.
- Non-Inverting Op-Amp: The input impedance is high because the input is directly connected to the op-amp.
- Common Applications:
- Inverting Op-Amp: Used in applications such as audio signal processing, mathematical operations, and active filters.
- Non-Inverting Op-Amp: Commonly used as buffers, in active filters, and in circuits where a high input impedance is needed.
Applications
Inverting op-amp
1, sensor signal amplification: inverting amplifier can amplify the weak signal output by the sensor, so that it can reach the level that can be processed, common applications are temperature sensors, photoelectric sensors, sound sensors, etc.
2, signal filtering: by selecting the appropriate feedback resistance and input resistance, the inverting amplifier can achieve the filtering function, which is used to filter out some frequency components in the input signal, such as low-pass filtering, high-pass filtering, band-pass filtering, etc.
3, audio amplification: the inverting amplifier can be used as the basic circuit of the audio amplifier to amplify the audio signal, so that it is output to the speaker or headset, usually used in sound systems, radios and other equipment.
4, instrument amplification: inverting amplifier can be used as the basic circuit of instrument amplifier, used to amplify the signal of various test and measurement instruments, such as oscilloscope, spectrum analyzer, power meter, etc.
5, automatic control: invert amplifier can be used to build a feedback control system, the output signal is compared with the expected value, the error signal is generated and amplified to adjust the output of the control system, so that it gradually approaches the expected value, common applications are temperature control, humidity control and so on.
6, data communication: inverting amplifiers can be used to amplify and process digital signals, making them suitable for transmission or processing, such as data interfaces, network communications, modems, etc.
Non-inverting op-amp
- Voltage Follower (Buffer): A non-inverting op-amp with a gain of 1 (no resistors connected) is called a voltage follower. It is used to buffer signals, providing high input impedance and low output impedance, which can prevent the loading effect in multi-stage circuits.
- Amplifiers: Non-inverting op-amps are often used in audio and other signal amplification circuits, where preserving the phase of the signal is important.
- Active Filters: Non-inverting op-amps are used in active filter designs like low-pass, high-pass, band-pass filters because they can provide gain and do not load down the input signal source.
- Summing Amplifier: A non-inverting summing amplifier can add multiple input signals and provide a single output which is the sum of the input signals.
- Integrators and Differentiators: Non-inverting op-amps can be used in circuits to perform mathematical operations like integration and differentiation on input signals.
- Oscillators: Non-inverting op-amps can be used in the design of various oscillator circuits.
- Analog to Digital Converters: Non-inverting op-amps are used in ADC circuits for their high gain and phase preservation properties.
- Power Amplifiers: Non-inverting op-amps are used in power amplifiers to drive speakers and other high-power loads.
How to tell if an op-amp is inverting or non-inverting
From the above comparison, it's easy to understand the differences between inverting amplifiers and non-inverting amplifiers. The main differences are as follows:
The key factor that distinguishes an inverting amplifier from a non-inverting amplifier is based on the phase relationship between the input and output. In the case of an inverting amplifier, the output is out of phase with the input. For a non-inverting amplifier, the input and output are both in the same phase.
In an inverting amplifier, the input signal is applied at the negative terminal of the operational amplifier. In contrast, for a non-inverting amplifier, the input is provided at the positive terminal.The gain provided by an inverting amplifier is the ratio of resistors. On the other hand, the gain of a non-inverting amplifier is the sum of 1 and the ratio of resistors.
In an inverting amplifier, the non-inverting end is grounded. While in a non-inverting amplifier, the inverting end of the operational amplifier is grounded.The gain achieved by an inverting amplifier is negative, hence it provides an inverted output. But for a non-inverting amplifier, the gain is positive, so the output achieved is essentially non-inverted.
