## Ⅰ Introduction

Although there are many** types of operational amplifiers**, different **amplifier circuits** are suitable for interfacing with different types of sensors, but most complex amplifiers are built by combining operational amplifiers. In order to get good amplication effect, it is necessary to design the circuit of the amplifier. This paper will introduce 20 **opamp formulas** as a design reference.

Op Amp Formulas For Voltage Calculation

**Catalog**

## Ⅱ Operational Amplifier Formulas

In almost cases today, op amps are configured in different ways using a feedback network to “calculate” the input signal. There are 20 formulas used to calculate.

Figure 1. Voltage Follower

Note: Buffer High Impedance Signal and Low Impedance Load

Figure 2. In-phase Op Amp

Note: In-phase Signal Amplification

Figure 3. Reversed-phase Op Amp

Note: Amplify and Invert Input

Figure 4. Voltage Subtractor, Differential Amplifier

Note: Amplify the voltage difference and suppress the common - mode voltage

Figure 5. Voltage Adder

Note: Summation of Adding Voltage Values

Figure 6. Low-pass Filter, Integrator

Note: Limit Signal Bandwidth

Figure 7. High-pass Filter, Differentiator

Note: Eliminate DC, Amplify AC Signal

Figure 8. Differential Amplifier

Note: Drive Differential Signal to Analog-to-Digital Converter From A Differential or Single-ended Signal Source

Figure 9. Instrumentation Amplifier

Note: Amplify the Low Level Difference Signal and Suppress the Common Mode Signal

Figure 10. Single State Op Amp Noise

Note: RTO NOISE=NG×RTI NOISE

RTI=Converted to the Input

RTO=Converted to the Output

**Decibel Formula (equivalent impedance)**

**Johnson-Nyquist Noise Formula**

**Ohm's Law (DC circuit)**

Figure 11. Closed-loop Frequency Response (voltage feedback amplifier)

**Transformer (step-up or step-down ratio)**

**Impedance Formulas (in series)**

Note: RL in series

RC in series

LC in series

RLC in series

**Voltage and Impedance Formulas (parallel connection)**

## 3 comments

Add something, the op amp can be simply viewed as a high-gain direct-coupled voltage amplifying unit with one signal output port, a non-inverting input, and an inverting put, which belong to high-impedance inputs. So non-inverting amps, inverting amps, and differential amps can be made based on these amplifying units.

We should know the principle before calculations, the power supply mode of the op amp is divided into dual power supply and single power supply. For dual-supply op amps, the output can be varied across zero voltage and the output can be set to zero when the differential input voltage is zero. With a single-supply op amp, the output varies over a range of power and ground.

The output signal of the operational amplifier is proportional to the difference between the signal voltages of the two inputs. In the audio segment: output voltage = A0 (E1-E2), where A0 is the low-frequency open-loop gain , E1 is the input signal voltage of the non-inverting terminal, and E2 is the input signal voltage of the inverting terminal.