μa741 operational amplifier, one of the most successful op-amps.
An Operational amplifier (“op-amp”) is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output. An op-amp produces an output voltage that is typically hundreds of thousands times larger than the voltage difference between its input terminals. Operational amplifiers are important building blocks for a wide range of electronic circuits. They had their origins in analog computers where they were used in many linear, non-linear and frequency-dependent circuits. Their popularity in circuit design largely stems from the fact the characteristics of the final elements (such as their gain) are set by external components with little dependence on temperature changes and manufacturing variations in the op-amp itself.
Op-amps are among the most widely used electronic devices today, being used in a vast array of consumer, industrial, and scientific devices. Many standard IC op-amps cost only a few cents in moderate production volume; however some integrated or hybrid operational amplifiers with special performance specifications may cost over $100 US in small quantities. Op-amps may be packaged as components, or used as elements of more complex integrated circuits.
Introduction Operational amplifiers (“op-amp”) are high gain electronic voltage amplifiers, which are the significant building blocks for most electronic circuits. In addition to this, they are still the ... are the fundamental circuits of operational amplifiers: non-inverting and inverting amplifier circuits, to analyze the difference between ideal and real op-amps. For the following ...
The op-amp is one type of differential amplifier. Other types of differential amplifier include the fully differential amplifier (similar to the op-amp, but with two outputs), the instrumentation amplifier (usually built from three op-amps), the isolation amplifier (similar to the instrumentation amplifier, but with tolerance to common-mode voltages that would destroy an ordinary op-amp), and negative feedback amplifier (usually built from one or more op-amps and a resistive feedback network).
TYPES OF AMPLIFIERS
1. Differential amplifier.
2. Summing amplifier.
3. Inverting amplifier.
4. Non inverting amplifier.
1941: First (vacuum tube) op-amp
An op-amp, defined as a general-purpose, DC-coupled, high gain, inverting feedback amplifier, is first found in U.S. 2,401,779″Summing Amplifier” filed by Karl D. Swartz Jr. of Bell labs in 1941. This design used three vacuum tubes to achieve a gain of 90 dB and operated on voltage rails of ±350 V. It had a single inverting input rather than differential inverting and non-inverting inputs, as are common in today’s op-amps. Throughout World War II, Sartell’s design proved its value by being liberally used in the M9 artillery director designed at Bell Labs. This artillery director worked with the SCR584 radar system to achieve extraordinary hit rates (near 90%) that would not have been possible otherwise.
1947: First op-amp with an explicit non-inverting input
In 1947, the operational amplifier was first formally defined and named in a paper by Professor John R. Ragazzini of Columbia University. In this same paper a footnote mentioned an op-amp design by a student that would turn out to be quite significant. This op-amp, designed by Lobe Julie, was superior in a variety of ways. It had two major innovations. Its input stage used a long-tailed triode pair with loads matched to reduce drift in the output and, far more importantly, it was the first op-amp design to have two inputs (one inverting, the other non-inverting).
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The differential input made a whole range of new functionality possible, but it would not be used for a long time due to the rise of the chopper-stabilized amplifier.
1949: First chopper-stabilized op-amp
In 1949, Edwin A. Goldberg designed a chopper-stabilized op-amp. This set-up uses a normal op-amp with an additional AC amplifier that goes alongside the op-amp. The chopper gets an AC signal from DC by switching between the DC voltage and ground at a fast rate (60 Hz or 400 Hz).
This signal is then amplified, rectified, filtered and fed into the op-amp’s non-inverting input. This vastly improved the gain of the op-amp while significantly reducing the output drift and DC offset. Unfortunately, any design that used a chopper couldn’t use their non-inverting input for any other purpose. Nevertheless, the much improved characteristics of the chopper-stabilized op-amp made it the dominant way to use op-amps. Techniques that used the non-inverting input regularly would not be very popular until the 1960s when op-amp ICs started to show up in the field.
In 1953, vacuum tube op-amps became commercially available with the release of the model K2-W from George A. Phil brick Researches, Incorporated. The designation on the devices shown, GAP/R, is a contraction for the complete company name. Two nine-pin 12AX7 vacuum tubes were mounted in an octal package and had a model K2-P chopper add-on available that would effectively “use up” the non-inverting input. This op-amp was based on a descendant of Loebe Julie’s 1947 design and, along with its successors, would start the widespread use of op-amps in industry.
1961: First discrete IC op-amps
With the birth of the transistor in 1947, and the silicon transistor in 1954, the concept of ICs became a reality. The introduction of the planar process in 1959 made transistors and ICs stable enough to be commercially useful. By 1961, solid-state, discrete op-amps were being produced. These op-amps were effectively small circuit boards with packages such as edge-connectors. They usually had hand-selected resistors in order to improve things such as voltage offset and drift. The P45 (1961) had a gain of 94 dB and ran on ±15 V rails. It was intended to deal with signals in the range of ±10 V.
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1962: First op-amps in potted modules
By 1962, several companies were producing modular potted packages that could be plugged into boards. These packages were crucially important as they made the operational amplifier into a single black box which could be easily treated as a component in a larger circuit.
1963: First monolithic IC op-amp
In 1963, the first monolithic IC op-amp, the μA702 designed by Bob Wilder at Fairchild Semiconductor, was released. Monolithic ICs consist of a single chip as opposed to a chip and discrete parts (a discrete IC) or multiple chips bonded and connected on a circuit board (a hybrid IC).
Almost all modern op-amps are monolithic ICs; however, this first IC did not meet with much success. Issues such as an uneven supply voltage, low gain and a small dynamic range held off the dominance of monolithic op-amps until 1965 when the μA709 (also designed by Bob Widlar) was released.
1966: First varactor bridge op-amps
Since the 741, there have been many different directions taken in op-amp design. Varactor bridge op-amps started to be produced in the late 1960s. They were designed to have extremely small input current and are still amongst the best op-amps available in terms of common-mode rejection with the ability to correctly deal with hundreds of volts at their inputs.
1968: Release of the μA741
The popularity of monolithic op-amps was further improved upon the release of the LM101 in 1967, which solved a variety of issues, and the subsequent release of the μA741 in 1968. The μA741 was extremely similar to the LM101 except that Fairchild’s facilities allowed them to include a 30 pF compensation capacitor inside the chip instead of requiring external compensation. This simple difference has made the 741 the canonical op-amp and many modern amps base their pinot on the 741s.The μA741 is still in production, and has become ubiquitous in electronics—many manufacturers produce a version of this classic chip, recognizable by part numbers containing 741.
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1970: First high-speed, low-input current FET design
In the 1970s high speed, low-input current designs started to be made by using FETs. These would be largely replaced by op-amps made with MOSFETs in the 1980s. During the 1970s single sided supply op-amps also became available.
1972: Single sided supply op-amps being produced
A single sided supply op-amp is one where the input and output voltages can be as low as the negative power supply voltage instead of needing to be at least two volts above it. The result is that it can operate in many applications with the negative supply pin on the op-amp being connected to the signal ground, thus eliminating the need for a separate negative power supply.
The LM324 (released in 1972) was one such op-amp that came in a quad package (four separate op-amps in one package) and became an industry standard. In addition to packaging multiple op-amps in a single package, the 1970s also saw the birth of op-amps in hybrid packages. These op-amps were generally improved versions of existing monolithic op-amps. As the properties of monolithic op-amps improved, the more complex hybrid ICs were quickly relegated to systems that are required to have extremely long service lives or other specialty systems.
Recently supply voltages in analog circuits have decreased (as they have in digital logic) and low-voltage op amps have been introduced reflecting this. Supplies of ±5V and increasingly 5V are common. To maximize the signal range modern op-amps commonly have rail-to-rail outputs and sometimes rail-to-rail inputs (the input signals can range from the lowest supply voltage to the highest).
APPLICATION OF OPERATIONAL AMPLIFIER
Use in electronics system design
The use of op-amps as circuit blocks is much easier and clearer than specifying all their individual circuit elements (transistors, resistors, etc.), whether the amplifiers used are integrated or discrete. In the first approximation op-amps can be used as if they were ideal differential gain blocks; at a later stage limits can be placed on the acceptable range of parameters for each op-amp.
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Circuit design follows the same lines for all electronic circuits. A specification is drawn up governing what the circuit is required to do, with allowable limits. For example, the gain may be required to be 100 times, with a tolerance of 5% but drift of less than 1% in a specified temperature range; the input impedance not less than one me ohm; etc.
A basic circuit is designed, often with the help of circuit modeling (on a computer).
Specific commercially available op-amps and other components are then chosen that meet the design criteria within the specified tolerances at acceptable cost. If not all criteria can be met, the specification may need to be modified.
A prototype is then built and tested; changes to meet or improve the specification, alter functionality, or reduce the cost, may be made.
Basic single stage amplifiers
An op-amp connected in the non-inverting amplifier configuration
In a non-inverting amplifier, the output voltage changes in the same direction as the input voltage.
The gain equation for the op-amp is:
However, in this circuit V– is a function of Vout because of the negative feedback through the R1R2 network. R1 and R2 form a voltage divider, and as V– is a high-impedance input, it does not load it appreciably. Consequently:
Substituting this into the gain equation, we obtain:
Solving for Vout:
If AOL is very large, this simplifies to
An op-amp connected in the inverting amplifier configuration
In an inverting amplifier, the output voltage changes in an opposite direction to the input voltage.
As for the non-inverting amplifier, we start with the gain equation of the op-amp:
This time, V– is a function of both Vout and Vin due to the voltage divider formed by Rf and Rin. Again, the op-amp input does not apply an appreciable load, so:
Substituting this into the gain equation and solving for Vout:
If AOL is very large, this simplifies to
* audio- and video-frequency pre-amplifiers and buffers
* voltage comparators
* differential amplifiers
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* differentiators and integrators.
* precision rectifiers.
* precision peak detectors.
* voltage and current regulators.
* analog calculators.
* analog-to-digital converters.
* digital-to-analog converter.
* voltage clamps.
* oscillators and waveform generators.
Most single, dual and quad op-amps available have a standardized pin-out which permits one type to be substituted for another without wiring changes. A specific op-amp may be chosen for its open loop gain, bandwidth, noise performance, input impedance, power consumption, or a compromise between any of these factors
.USES OF OPERATIONAL AMPLIFIER
Operational amplifiers are widely used in signal processing circuits, control circuits, and instrumentation. Of all analog integrated circuits, the operational amplifier is the analog integrated circuit which has the most sales and is the most widely used in the widest variety of electronic circuits. If you are an electrical engineer, you will probably encounter more operational amplifiers than any other integrated circuit device. It’s an important component for electrical engineers who design circuits using them and to all other kinds of engineers who use measurement and control circuits that contain operational amplifiers. In strain gage circuitry to measure deformations in structures like bridges, airplane wings and I-beams in buildings. In temperature measurement circuitry for boilers and in high altitude aircraft in a cold environment. In control circuits for aircraft, people movers in airports, subways and in many different production operations.
1. ^ MAXIM Application Note 1108: Understanding Single-Ended, Pseudo-Differential and Fully-Differential ADC Inputs — Retrieved November 10, 2007
2. ^ //www.analog.com/static/imported-files/tutorials/MT-044.pdf Analog devices MT-044 TUTORIAL]
3. ^ Jung, Walter G. (2004). “Chapter 8: Op Amp History”. Op Amp Applications Handbook. Newnes. p. 777. ISBN 9780750678445. Retrieved 2008-11-15.
4. ^ Jung, Walter G. (2004). “Chapter 8: Op Amp History”. Op Amp Applications Handbook. Newnes. p. 779. ISBN 9780750678445. Retrieved 2008-11-15.
5. ^ //www.analog.com/library/analogDialogue/archives/39-05/Web_ChH_final.pdf
6. ^ A.P. Malvino, Electronic Principles (2nd Ed. 1979. ISBN 0-07-039867-4) p. 476.
7. ^ D.F. Stout Handbook of Operational Amplifier Circuit Design (McGraw-Hill, 1976, ISBN 007061797X ) pp. 1–11.
8. ^ The uA741 Operational Amplifier