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Sep 19 2019

20 Formulas for Operational Amplifier Circuit Design

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

Ⅰ Introduction

Ⅱ Operational Amplifier Formulas


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

 

Voltage Subtractor, Differential Amplifier Circuit

Figure 4. Voltage Subtractor, Differential Amplifier

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

 

Voltage Adder circuit

Figure 5. Voltage Adder

Note: Summation of Adding Voltage Values

 

As a Low-pass Filter, Integrator

Figure 6. Low-pass Filter, Integrator

Note: Limit Signal Bandwidth

 

High-pass Filter, Differentiator.png

Figure 7. High-pass Filter, Differentiator

Note: Eliminate DC, Amplify AC Signal

 

Differential Amplifier

Figure 8. Differential Amplifier

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

 

Instrumentation Amplifier

Figure 9. Instrumentation Amplifier

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

 

Single State Op Amp Noise

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

Johnson-Nyquist Noise Formula

 

 

Ohm's Law (DC circuit)

 

Closed-loop Frequency Response (voltage feedback amplifier)

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

 

resistance formulas.png

Resistance Formulas

 

Reactance Formulas

 

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)

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pinglun 3 comments

    • pingluntus
    • Willile on 2019/10/23 16:54:19

    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.

    • pingluntus
    • Eills on 2019/10/28 13:45:51

    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.

    • pingluntus
    • Comie on 2019/11/11 17:55:57

    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.

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