OpAmp Application Circuits
Key Takeaways

The opamp differential amplifier features low output resistance, high input resistance, and high open loop gain.

In an inverting amplifier configuration, the opamp circuit output gain is negative.

All simple mathematical operations such as addition, subtraction, comparison, etc. are possible with opamp application circuits.
In the computing field, operational amplifiers, or opamps, represent amplifiers with the capability to perform mathematical operations. It is possible to perform math operations using various opamp application circuits. Signals can be added, subtracted, amplitudescaled, compared, etc. In this article, we will dive into what an opamp is and look at a few of its application circuits.
An Overview of OpAmps
In analog electronics, opamps are frequently used components. They form one of the fundamental elements in analog electronic circuits. Opamp application circuits can be found in signal conditioning systems, filtering applications, and wherever a mathematical operation is to be performed on the signals in an analog way.
If there are two inputs to an opamp, say signal A and signal B, signal A is given to the noninverting input terminal of the opamp and signal B is given to the inverting terminal. The difference (signal Asignal B) can be amplified using an opamp circuit.
OpAmp ICs
Opamps are available as integrated circuit packages. Some examples are LMV 358, LMV 341, TSV 522, etc. As shown in the figure below, most opamps consist of 5 terminals:
 Positive side power supply terminal (V+)
 Negative side power supply terminal (V)
 Noninverting input terminal
 Inverting input terminal
 Output terminal
Stable OpAmp Circuits
Open loop operation of opamps is restricted, as it leads to instability. In an open loop configuration, it is difficult to control the input signals of the opamp. The closedloop operation of opamps is preferred. The closedloop operation can be performed in two configurations.
Configurations of ClosedLoop OpAmp Operations
OpAmp Application Circuits
As an example, let’s use a circuit that I built. An alternating voltage needed to be sensed and there was some control technique to be developed based on the sensed voltage. The control was implemented using an FPGA, so the sensed voltage needed to be given to the ADC of the controller. However, as FPGA only takes positive values, the mathematical operation of ‘summing’ needed to be performed on the signal to make it entirely positive. I used an opampbased summing amplifier, which added the voltages so all the negative values of sensed voltage turned positive. After passing through the opamp circuit, the sensed voltage reached the ADC of the FPGA.
Summing Amplifier
The circuit above shows a summing amplifier based on an inverting amplifier configuration, as the three inputs are connected to the inverting input terminal through three resistors. Let’s assume the resistors R_{in} are equal. The output voltage V_{ out} is proportional to the sum of the voltages V_{1} + V_{2} + V_{3}.
Opamp summing amplifier output equation
As the input resistors are equal, the sum of given inputs is obtained in the output with the gain . If it is required to obtain a weighted sum of the input signals, the appropriate resistor values can be connected to the corresponding input signals.
Similar to the above example and the corresponding circuit, there are numerous application circuits available in analog electronics. We will look at a few of them in the upcoming section.
OpAmp Integration Circuits
All simple mathematical operations such as addition, subtraction, comparison, etc. are possible with opamp application circuits. But, what if we need to integrate a signal? For integration, there is one circuit using an opamp.
By replacing the resistive feedback in the inverting amplifier with a capacitor, the integration amplifier circuit can be constructed, as illustrated in the circuit diagram above. The integration amplifier circuit using opamps gives an output that is proportional to the input voltage given with respect to time. In an integration circuit, the capacitor charges and discharges in response to the changes in the input voltage and produces the output.
OpAmp Application Areas
Opamps are versatile devices that can perform math operations not limited to summing and integration. Opamp application circuits are extensively found in systems requiring filtering, signal conditioning, analog computation, analog instrumentation, etc.
Cadence offers simulation, analysis, and modeling tools for building analog circuits, including operational amplifiers. With Cadence’s OrCAD, it is possible to choose models of components, including opamps, from the library and accurately design the system by assessing the model parameters.
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