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 a good amplification 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 most 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)

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)

Ⅲ Frequently Asked Questions about Operational Amplifier Circuit

1. How do you make an op amp circuit?

2. What is amplifier with example?

Amplifiers are usually designed to function well in a specific application, for example: radio and television transmitters and receivers, high-fidelity ("hi-fi") stereo equipment, microcomputers and other digital equipment, and guitar and other instrument amplifiers.

3. Why do op amps have two inputs?

Operational amplifiers have two power supply rails because they usually need to swing bipolar - output voltages that go either positive or negative in response to the normal range of input signals. ... Without the dual supplies the output signal would clip at the ground potential.

4. Which type of amplifier is best?

Class “A” amplifiers are considered the best class of amplifier design due mainly to their excellent linearity, high gain and low signal distortion levels when designed correctly.

5. Are op amps AC or DC?

The basic Op-amp construction is of a 3-terminal device, with 2-inputs and 1-output, (excluding power connections). An Operational Amplifier operates from either a dual positive ( +V ) and an corresponding negative ( -V ) supply, or they can operate from a single DC supply voltage.

6. Can op amp amplify both AC and DC?

Infinite – An ideal operational amplifier has an infinite frequency response and can amplify any frequency signal from DC to the highest AC frequencies so it is therefore assumed to have an infinite bandwidth.

7. Do op amps work with DC?

In principle, yes, you can amplify DC with an op-amp, subject to the constraints of the amplifier. Mainly, the amplified output voltage must be between the output limits of the op-amp. ... (A fraction of the final output of the power supply is fed back to the op-amp's negative input to regulate the overall circuit.)

8. How do you amplify DC current?

A transistor can be used to increase current. You'll have a low current path, from base to emitter in an NPN, and a higher current path from collector to emitter. The collector current will be a multiple of the base current if the circuit allows it.

9. What are the ideal characteristics of op amp?

Ideal op amps use no power, have infinite input impedance, unlimited gain-bandwidth and slew rate, no input bias current, and no input offset. They have unlimited voltage compliance.

10. What is slew rate of op amp?

Slew rate is defined as the maximum rate of change of an op amp's output voltage and is given units of volts per microsecond. Slew rate is measured by applying a large signal step, such as 1V, to the input of the op amp, and measuring the rate of change from 10% to 90% of the output signal's amplitude.

Ordering & Quality

Photo	Mfr. Part #	Company	Description	Package	PDF	Qty	Pricing (USD)
	TLV171IDBVT	Company:Texas Instruments	Remark:General Purpose Amplifier Circuit Rail-to-Rail SOT-23-5	Package:SC-74A, SOT-753	N/A	In Stock:On Order Inquiry	Price: 1+: $1.03000 10+: $0.91900 25+: $0.87240 100+: $0.67000 250+: $0.67004 500+: $0.59212 1000+: $0.46746 2000+: $0.44100	Inquiry
	MC33078P	Company:Texas Instruments	Remark:General Purpose Amplifier 2 Circuit 8-PDIP	Package:8-DIP (0.300"", 7.62mm)	DataSheet	In Stock:On Order Inquiry	Price: 50+: $2.60720 1+: $4.66000 10+: $4.18900 25+: $3.96000 100+: $3.25600 250+: $2.92160 500+: $2.81600 1000+: $2.34080 2500+: $2.25280 5000+: $2.18240	Inquiry
	5962-9460206QCA	Company:Texas Instruments	Remark:J-FET Amplifier 4 Circuit 14-CDIP	Package:14-CDIP (0.300"", 7.62mm)	DataSheet	In Stock:On Order Inquiry	Price: 8+: $31.65000	Inquiry
	LF356N-NOPB	Company:Texas Instruments	Remark:IC OPAMP JFET 1 CIRCUIT 8DIP	Package:8-DIP (0.300", 7.62mm)	DataSheet	In Stock:15791 Inquiry	Price: 1+: $0.84000 10+: $0.74900 25+: $0.71120 100+: $0.54610 250+: $0.48260 500+: $0.45720 1000+: $0.35560 2500+: $0.33782 5000+: $0.32512	Inquiry
	AD8067ARTZ-REEL7	Company:Analog Devices Inc.	Remark:IC OPAMP VFB 1 CIRCUIT SOT23-5	Package:SC-74A, SOT-753	DataSheet	In Stock:On Order Inquiry	Price: 3000+: $2.37800	Inquiry
	TLV2372QDRQ1	Company:Texas Instruments	Remark:General Purpose Amplifier 2 Circuit Rail-to-Rail 8-SOIC	Package:8-SOIC (0.154"", 3.90mm Width)	DataSheet	In Stock:On Order Inquiry	Price: 1+: $1.87000 10+: $1.68000 25+: $1.58520 100+: $1.26800 250+: $1.10952 500+: $1.07780 1000+: $0.85590 2500+: $0.82420 5000+: $0.79250 10000+: $0.77982 25000+: $0.76080	Inquiry
	MCP6142-I-SN	Company:Microchip Technology	Remark:IC OPAMP GP 2 CIRCUIT 8SOIC	Package:8-SOIC (0.154", 3.90mm Width)	DataSheet	In Stock:263 Inquiry	Price: 1+: $0.80000 25+: $0.66000 100+: $0.60000	Inquiry
	MC33274APG	Company:ON Semiconductor	Remark:General Purpose Amplifier 4 Circuit 14-PDIP	Package:14-DIP (0.300"", 7.62mm)	DataSheet	In Stock:On Order Inquiry	Price: Call	Inquiry