Op-amp ICs (some single, some dual) in 8-pin dual in-line packages ("DIPs")

An operational amplifier, usually referred to as an op-amp for brevity, is a DC-coupled high-gain electronic voltage amplifier with differential inputs^[1] and, usually, a single output. In its typical usage, the output of the op-amp is controlled by negative feedback which largely determines the magnitude of its output voltage gain, input impedance at one of its input terminals and output impedance. Image File history File linksMetadata Download high resolution version (883x494, 101 KB) Several operational amplifier chips in DIP-8 packages. ... Image File history File linksMetadata Download high resolution version (883x494, 101 KB) Several operational amplifier chips in DIP-8 packages. ... Integrated circuit of Atmel Diopsis 740 System on Chip showing memory blocks, logic and input/output pads around the periphery Microchips with a transparent window, showing the integrated circuit inside. ... ICs in DIP14-Package Several PDIPs and CERDIPS. The large CERDIP in the foreground is an 8080 processor. ... Direct current (DC or continuous current) is the continuous flow of electricity through a conductor such as a wire from high to low potential. ... In electronics direct coupling is a way of interconnecting two circuits such that, in addition to transferring the signal (or information), the first stage also provides DC bias to the nextÇ‚. Thus, there is no need for a DC blocking capacitor to be used in order to interconnect the circuits... The term amplifier as used in this article can mean either a circuit (or stage) using a single active device or a complete system such as a packaged audio hi-fi amplifier. ... This article does not cite any references or sources. ... Magnetostatics Electrodynamics Electrical Network Tensors in Relativity This box:      Electrical impedance, or simply impedance, describes a measure of opposition to a sinusoidal alternating current (AC). ...

Op-amps are among the most widely used electronic devices today, being used in a vast array of consumer, industrial, and scientific devices. General-purpose integrated op-amps of standard specification sell for well under one U.S. dollar. Modern designs are electronically more rugged than earlier implementations and some can sustain direct short-circuits on their outputs without damage. Short Circuit was a 1986 comedy sci-fi film starring Ally Sheedy and Steve Guttenberg and directed by John Badham. ...

History

A 741 operational amplifier in a TO-5 metal can package

The operational amplifier was originally designed to perform mathematical operations by using voltage as an analogue of another quantity,^[2] hence the name, "operational amplifier." This is the basis of the analog computer, where op-amps were used to model the basic mathematical operations (addition, subtraction, integration, differentiation, and so on). However, an ideal operational amplifier is an extremely versatile circuit element, with a great many applications beyond mathematical operations. Practical op-amps, based on transistors, tubes, or other amplifying components and implemented as discrete or integrated circuits, are good approximations to ideal devices. Image File history File links Download high resolution version (450x730, 43 KB) Summary This picture shows a 741 operational amplifier, in the a TO-5/metal can package. ... Image File history File links Download high resolution version (450x730, 43 KB) Summary This picture shows a 741 operational amplifier, in the a TO-5/metal can package. ... A page from the Bombardiers Information File (BIF) that describes the components and controls of the Norden bombsight. ... In mathematics, an operator is a function that performs some sort of operation on a number, variable, or function. ... 3 + 2 = 5 with apples, a popular choice in textbooks[1] This article is about addition in mathematics. ... 5 - 2 = 3 (verbally, five minus two equals three) An example problem Subtraction is one of the four basic arithmetic operations; it is the inverse of addition. ... This article is about the concept of integrals in calculus. ... For a non-technical overview of the subject, see Calculus. ...

While op-amps were originally developed in the vacuum tube era they are now normally implemented as integrated circuits (ICs), though versions with discrete components are used when performance beyond that attainable with ICs is required. Structure of a vacuum tube diode Structure of a vacuum tube triode In electronics, a vacuum tube, electron tube, or (outside North America) thermionic valve or just valve, is a device used to amplify, switch or modify a signal by controlling the movement of electrons in an evacuated space. ... Integrated circuit of Atmel Diopsis 740 System on Chip showing memory blocks, logic and input/output pads around the periphery Microchips with a transparent window, showing the integrated circuit inside. ...

The first integrated op-amp to become widely available, in the late 1960s, was the bipolar Fairchild μA709, created by Bob Widlar in 1965; it was rapidly superseded by the 741, which has better performance, stability, and is easier to use. 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." Better designs have since been introduced, some based on the FET (late 1970s) and MOSFET (early 1980s). Many of these more modern devices can be substituted into an older 741-based circuit and work with no other changes, to give better performance. The 1960s decade refers to the years from 1960 to 1969. ... Robert J. Widlar (November, 1937 – February 27, 1991) was a pioneer in the design of integrated circuits. ... Large power N-channel field effect transistor The field-effect transistor (FET) is a type of transistor that relies on an electric field to control the shape and hence the conductivity of a channel in a semiconductor material. ... The 1970s decade refers to the years from 1970 to 1979, also called The Seventies. ... The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is by far the most common field-effect transistor in both digital and analog circuits. ... The 1980s refers to the years from 1980 to 1989. ...

Op-amps usually have parameters within tightly specified limits, with standardized packaging and power supply requirements. Op-amps have many uses within electronics; with only a handful of external components they can be made to perform a wide variety of analog signal processing tasks. Many standard IC op-amps cost only a few cents in moderate production volume, but integrated or discrete amplifiers with non-standard specifications may cost over $100 US in small quantities. A wall wart style variable DC power supply with its cover removed. ... Signal processing is the processing, amplification and interpretation of signals, and deals with the analysis and manipulation of signals. ...

Basic operation

The amplifier's differential inputs consist of an inverting input and a non-inverting input and ideally the op-amp amplifies only the difference in voltage between the two. This is called the "differential input voltage." In its most common use, the op-amp's output voltage is controlled by feeding a fraction of the output signal back to the inverting input. This is known as negative feedback. If that fraction is zero, i.e., there is no negative feedback, the amplifier is said to be running "open loop" and its output is the differential input voltage multiplied by the total gain of the amplifier, as shown by the following equation: This article does not cite any references or sources. ... This article, image, template or category should belong in one or more categories. ...

where V₊ is the voltage at the non-inverting terminal, V₋ is the voltage at the inverting terminal and G is the total open-loop gain of the amplifier.

Because the magnitude of the open-loop gain is typically very large and not well controlled by the manufacturing process, op-amps are not usually used without negative feedback. Unless the differential input voltage is extremely small, open-loop operation results in op-amp saturation (see below in Nonlinear imperfections). An example of how the output voltage is calculated when negative feedback exists is shown below in Basic non-inverting amplifier circuit.

Another typical configuration of op-amps is the positive feedback, which takes a fraction of the output signal back to the non-inverting input. An important application of it is the comparator with hysteresis.

The ideal op-amp

For any input voltages the ideal op-amp has infinite open-loop gain, infinite bandwidth, infinite input impedances resulting in zero input currents, zero offset voltage, infinite slew rate, zero output impedance and zero noise. Thus the inputs of an ideal op-amp under negative feedback can be modelled using a nullator and the output with a norator. The open-loop gain of an operational amplifier is the gain obtained when no feedback is used in the circuit. ... Bandwidth is the difference between the upper and lower cutoff frequencies of, for example, a filter, a communication channel, or a signal spectrum, and is typically measured in hertz. ... The input impedance or sometimes loading impedance of a circuit or electronic device is the impedance actually experienced by a signal which is connected to its input. ... In electronics, the slew rate is a nonlinear effect in amplifiers. ... This article does not cite any references or sources. ... This article is about noise as in sound. ... In electronics, a nullator is a theoretical linear, time-invariant one-port which has zero current and voltage across its terminals. ... In electronics, a norator is a theoretical linear, time-invariant one-port which can have an arbitrary current and voltage between its terminals. ...

Real op-amps can only approach this ideal, and the actual parameters are subject to drift over time and with changes in temperature, input conditions, etc. Modern integrated FET or MOSFET op-amps approximate more closely these ideals than bipolar ICs where large signals must be handled at room temperature over a limited bandwidth; input impedance, in particular, is much higher, although the bipolar op-amps usually exhibit superior (i.e., lower) input offset drift and noise characteristics. Large power N-channel field effect transistor The field-effect transistor (FET) is a transistor that relies on an electric field to control the shape and hence the conductivity of a channel in a semiconductor material. ... The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is by far the most common field-effect transistor in both digital and analog circuits. ...

Where the limitations of real devices can be ignored, an op-amp can be viewed as a black box with gain; circuit function and parameters are determined by feedback, usually negative. IC op-amps as implemented in practice are moderately complex integrated circuits; see the internal circuitry for the relatively simple 741 op-amp below, for example. Black box is technical jargon for a device or system or object when it is viewed primarily in terms of its input and output characteristics. ... For the superhero, see Feedback (Dark Horse Comics). ... Integrated circuit of Atmel Diopsis 740 System on Chip showing memory blocks, logic and input/output pads around the periphery Microchips with a transparent window, showing the integrated circuit inside. ... Op-amp ICs (some single, some dual) in 8-pin dual in-line packages (DIPs) An operational amplifier, usually referred to as an op-amp for brevity, is a DC-coupled high-gain electronic voltage amplifier with differential inputs[1] and, usually, a single output. ...

Equations and sample op-amp circuits are here: Operational amplifier applications This article illustrates some typical applications of solid-state integrated circuit operational amplifiers. ...

Limitations of real op-amps

DC imperfections

• Finite gain — the effect is most pronounced when the overall design attempts to achieve gain close to the inherent gain of the op-amp.
• Finite input resistance — this puts an upper bound on the resistances in the feedback circuit. Some op-amps have circuitry to protect inputs from excessive voltage: this makes input parameters slightly worse. Some op-amps are available in protected (thus slightly degraded) and unprotected versions.
• Nonzero output resistance — important for low resistance loads. Except for very small voltage output, power considerations usually come into play first. (Output impedance is inversely proportional to the idle current in the output stage — very low idle current results in very high output impedance.)
• Input bias current — a small amount of current (typically ~10 nA for bipolar op-amps, or picoamperes for CMOS designs) flows into the inputs. This current is mismatched slightly between the inverting and non-inverting inputs (there is an input offset current). This effect is usually important only for very low power circuits.
• Input offset voltage — the voltage required across the op-amp's input terminals to drive the output voltage to zero.^[3] In the perfect amplifier, there would be no input offset voltage. However, it exists in actual op-amps because of imperfections in the differential amplifier that constitutes the input stage of the vast majority of these devices. Input offset voltage creates two problems: First, due to the amplifier's high voltage gain, it virtually assures that the amplifier output will go into saturation if it is operated without negative feedback, even when the input terminals are wired together. Second, in a closed loop, negative feedback configuration the input offset voltage is amplified along with the signal and this may pose a problem if high precision DC amplification is required or if the input signal is very small.^[4]
• Common mode gain — A perfect operational amplifier amplifies only the voltage difference between its two inputs, completely rejecting all voltages that are common to both. However, the differential input stage of an operational amplifier is never perfect, leading to the amplification of these identical voltages to some degree. The standard measure of this defect is called the common-mode rejection ratio (denoted, CMRR). Minimization of common mode gain is usually important in non-inverting amplifiers (described below) that operate at high amplification.
• Temperature effects — all parameters change with temperature. Temperature drift of the input offset voltage is especially important.

In electronics, gain is usually taken as the mean ratio of the signal output of a system to the signal input of the system. ... The input impedance or load impedance of a circuit or electronic device is the impedance actually experienced by a signal which is connected to it. ... In electricity, current refers to electric current, which is the flow of electric charge. ... Bipolar is a term used to define things with two (usually opposing) poles. ... For other uses, see CMOS (disambiguation). ... International safety symbol Caution, risk of electric shock (ISO 3864), colloquially known as high voltage symbol. ... Common mode rejection ratio (CMRR) is a measure of the capability of an instrument, ie. ...

AC imperfections

• Finite bandwidth — all amplifiers have a finite bandwidth. This creates several problems for op amps. First, associated with the bandwidth limitation is a phase difference between the input signal and the amplifier output that can lead to oscillation in some feedback circuits. The internal frequency compensation used in some op amps to increase the phase margin intentionally reduces the bandwidth even further to maintain output stability when using a wide variety of feedback networks. Second, reduced bandwidth results in lower amounts of feedback at higher frequencies, producing higher distortion, noise, and output impedance and also reduced output phase linearity as the frequency increases.
• Input capacitance — most important for high frequency operation because it further reduces the open loop bandwidth of the amplifier.
• Common mode gain — See DC imperfections, above.

Bandwidth is the difference between the upper and lower cutoff frequencies of, for example, a filter, a communication channel, or a signal spectrum, and is typically measured in hertz. ... Electronic Oscillation is the continuous recurrence of the same electrical periodic waveform. ... In electrical engineering, frequency compensation is a design technique for amplifiers which use negative feedback or those, such as operational amplifiers, that are intended for use with negative feedback. ... In electronic amplifiers, phase margin is the difference, measured in degrees, between the phase angle of the amplifiers output signal and -360°. In feedback amplifiers, the phase margin is measured at the frequency at which the open loop voltage gain of the amplifier and the closed loop voltage gain... Capacitance is a measure of the amount of electric charge stored (or separated) for a given electric potential. ...

Nonlinear imperfections

• Saturation — output voltage is limited to a minimum and maximum value close to the power supply voltages.^[5] Saturation occurs when the output of the amplifier reaches this value and is usually due to:
  • In the case of an op-amp using a bipolar power supply, a voltage gain that produces an output that is more positive or more negative than that maximum or minimum; or
  • In the case of an op-amp using a single supply voltage, either a voltage gain that produces an output that is more positive than that maximum, or a signal so close to ground that the amplifier's gain is not sufficient to raise it above the lower threshold.^[6]
• Slewing — the amplifier's output voltage reaches its maximum rate of change. Measured as the slew rate, it is usually specified in volts per microsecond. When slewing occurs, further increases in the input signal have no effect on the rate of change of the output. Slewing is usually caused by internal capacitances in the amplifier, especially those used to implement its frequency compensation.
• Non-linear transfer function — The output voltage may not be accurately proportional to the difference between the input voltages. It is commonly called distortion when the input signal is a waveform. This effect will be very small in a practical circuit if substantial negative feedback is used.

In telecommunications, the term saturation has the following meanings: In a communications system, the condition at which a component of the system has reached its maximum traffic-handling capacity. ... A wall wart style variable DC power supply with its cover removed. ... In electronics, the slew rate is a nonlinear effect in amplifiers. ... In electrical engineering, frequency compensation is a design technique for amplifiers which use negative feedback or those, such as operational amplifiers, that are intended for use with negative feedback. ... For other uses, see Linear (disambiguation). ... A transfer function is a mathematical representation of the relation between the input and output of a linear time-invariant system. ...

Power considerations

• Limited output current — the output current must obviously be finite. In practice, most op-amps are designed to limit the output current so as not to exceed a specified level — around 25 mA for a type 741 IC op-amp — thus protecting the op-amp and associated circuitry from damage.
• Limited dissipated power — an opamp is a linear amplifier. It therefore dissipates some power as heat, proportional to the output current, and to the difference between the output voltage and the supply voltage. If the opamp dissipates too much power, then its temperature will increase above some safe limit. The opamp may enter thermal shutdown, or it may be destroyed.

The practice in electronic circuits of imposing an upper limit on the current that may be delivered to a load with the purpose of protecting the circuit generating the current from harmful effects due to a short-circuit or similar problem in the load. ... For delivered electrical power, see Electrical power industry. ... For other uses, see Heat (disambiguation) In physics, heat, symbolized by Q, is energy transferred from one body or system to another due to a difference in temperature. ...

Notation

The "usual" circuit symbol for an op-amp is:

Image File history File links Op-amp_symbol. ...

(more usually seen with the '+' and '-' terminals exchanged, and with the power supply connections seldom shown except in detailed, pinout-style wiring diagrams), where:

• V₊: non-inverting input
• V₋: inverting input
• V_out: output
• V_S+: positive power supply (sometimes also V_DD, V_CC, or V_{CC +} )
• V_S−: negative power supply (sometimes also V_SS, V_EE, or V_{CC −} )

The power supply pins (V_S+ and V_S−) can be labeled in different ways (See IC power supply pins). Despite different labeling, the function remains the same. Often these pins are left out of the diagram for clarity, and the power configuration is described or assumed from the circuit. The positions of the inverting and non-inverting inputs may be reversed in diagrams where appropriate; the power supply pins are not commonly reversed (but are sometimes). Almost all integrated circuits (ICs) have at least two pins which connect to the power rails of the circuit they are installed in. ...

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.

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 1 megohm; 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. An electronic circuit is an electrical circuit that also contains active electronic devices such as transistors or vacuum tubes. ...

A prototype is then built and tested; changes to meet or improve the specification, alter functionality, or reduce the cost, may be made.

DC behavior

Open-loop gain is defined as the amplification from input to output without any feedback applied. For most practical calculations, the open-loop gain is assumed to be infinite; in reality it is obviously not. Typical devices exhibit open-loop DC gain ranging from 100,000 to over 1 million; this is sufficiently large for circuit gain to be determined almost entirely by the amount of negative feedback used. Op-amps have performance limits that the designer must keep in mind and sometimes work around. In particular, instability is possible in a DC amplifier if AC aspects are neglected. Generally, amplification is a basic process sometimes seen in nature, and often used in processes which involve a signal which must be made stronger. ... For the superhero, see Feedback (Dark Horse Comics). ...

AC behavior

The op-amp gain calculated at DC does not apply at higher frequencies. To a first approximation, the gain of a typical op-amp is inversely proportional to frequency. This means that an op-amp is characterized by its gain-bandwidth product. For example, an op-amp with a gain bandwidth product of 1 MHz would have a gain of 5 at 200 kHz, and a gain of 1 at 1 MHz. This low-pass characteristic is introduced deliberately, because it tends to stabilize the circuit by introducing a dominant pole. This is known as frequency compensation. The gain bandwidth product (GBW) for an amplifier is the product of the open loop gain (constant for a given amplifier) and its 3 dB bandwidth. ... A low-pass filter passes low frequencies fairly well, but attenuates, or blocks, high frequencies. ... In electrical engineering, specifically signal processing and control theory, BIBO Stability is a form of stability for signals and systems. ... In electrical engineering, frequency compensation is a design technique for amplifiers which use negative feedback or those, such as operational amplifiers, that are intended for use with negative feedback. ...

Typical low cost, general purpose op-amps exhibit a gain bandwidth product of a few megahertz. Specialty and high speed op-amps can achieve gain bandwidth products of hundreds of megahertz. For very high-frequency circuits, a completely different form of op-amp called the current-feedback operational amplifier is often used. The gain bandwidth product (GBW) for an amplifier is the product of the open loop gain (constant for a given amplifier) and its 3 dB bandwidth. ... The gain bandwidth product (GBW) for an amplifier is the product of the open loop gain (constant for a given amplifier) and its 3 dB bandwidth. ... Representative schematic of a current-feedback op-amp or amplifier. ...

Basic Non-inverting amplifier circuit

The general op-amp has two inputs and one output. The output voltage is a multiple of the difference between the two inputs (some are made with floating, differential outputs): Balanced audio connections are extremely important in sound recording and production because they allow for the use of very long cables with reduced introduction of outside noise. ...

V_out = G(V₊ − V₋)

G is the open-loop gain of the op-amp. The inputs are assumed to have very high impedance; negligible current will flow into or out of the inputs. Op-amp outputs have very low source impedance. Although related to the more mathematical concepts of infinitesimal , the idea of something being negligible is particularly useful in practical disciplines like physics, chemistry, mechanical and electronic engineering, computer programming and in everyday decision-making. ... This article does not cite any references or sources. ...

If the output is connected to the inverting input, after being scaled by a voltage divider K = R₁ / (R₁ + R₂), then: In electronics, a voltage divider is a simple device designed to create a voltage (Vout) which is proportional to another voltage (Vin). ...

Image File history File links Opampnoninverting. ...

V₊ = V_in

V₋ = K V_out

V_out = G(V_in − K V_out)

Solving for V_out / V_in, we see that the result is a linear amplifier with gain:

V_out/V_in = G /(1 + G K)

If G is very large, V_out/V_in comes close to 1/K, which equals 1 + (R₂/R₁).

This negative feedback connection is the most typical use of an op-amp, but many different configurations are possible, making it one of the most versatile of all electronic building blocks.

When connected in a negative feedback configuration, the op-amp will try to make V_out whatever voltage is necessary to make the input voltages as nearly equal as possible. This, and the high input impedance, are sometimes called the two "golden rules" of op-amp design (for circuits that use negative feedback):

1. No current will flow into the inputs.
2. The input voltages will be nearly equal.

The exception is if the voltage required is greater than the op-amp's supply, in which case the output signal stops near the power supply rails, V_S+ or V_S−. All op amps have two power pins. ...

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.

Internal circuitry of 741 type op-amp

LM741 pin assignment (Dual in-line package).

Though designs vary between products and manufacturers, all op-amps have basically the same internal structure, which consists of three stages: Image File history File links 741_pin_assignment_01_Pengo. ... Image File history File links 741_pin_assignment_01_Pengo. ... ICs in DIP14-Package Several PDIPs and CERDIPS. The large CERDIP in the foreground is an 8080 processor. ...

1. Differential amplifier
   • Input stage — provides low noise amplification, high input impedance, usually a differential output
2. Voltage amplifier
   • Provides high voltage gain, a single-pole frequency roll-off, usually single-ended output
3. Output amplifier
   • Output stage — provides high current driving capability, low output impedance, current limiting and short circuit protection circuitry

A component level diagram of the common 741 op-amp. Dotted lines outline: current mirrors (red); differential amplifier (blue); class A gain stage (magenta); voltage level shifter (green); output stage (cyan).

Simple form of a differential amplifier A differential amplifier is a type of an electronic amplifier that multiplies the difference between two inputs by some constant factor (the differential gain). ... The input impedance or sometimes loading impedance of a circuit or electronic device is the impedance actually experienced by a signal which is connected to its input. ... This article does not cite any references or sources. ... Image File history File links This is a lossless scalable vector image. ... Image File history File links This is a lossless scalable vector image. ... A current mirror is a circuit designed to copy a current flowing through one active device by controlling the current in another active device of a circuit, keeping the output current constant regardless of loading. ... Simple form of a differential amplifier A differential amplifier is a type of an electronic amplifier that multiplies the difference between two inputs by some constant factor (the differential gain). ... The term amplifier as used in this article can mean either a circuit (or stage) using a single active device or a complete system such as a packaged audio hi-fi amplifier. ...

Current mirrors

The sections outlined in red are current mirrors. The primary current, from which other standing (bias) currents are generated, is determined by the chip's power supply and the 39 kΩ resistor acting (with the two transistor diode junctions) as a current source. The current generated is approximately (V_S+ − V_S− − 2V_be)/39 kΩ. The input stage DC conditions are controlled by the two current mirrors on the left. Q10 and Q11 form a Widlar current source where the 5 kΩ resistor sets the collector current of Q10 to a very small fraction of the primary current. The constant Q10 current supplies the base current for Q3 and Q4 but must also supply the Q9 collector current, which the Q8/Q9 current mirror will try to make as large as the Q3 and Q4 collector currents. Thus the Q3/Q4 base current (which is of the same order as the input currents) will be a small fraction of the already small Q10 current. Another way of looking at this is that if the input stage current tends to increase above the Q10 current, the Q8/Q9 current mirror will draw current away from the common base of Q3 and Q4, throttling the input stage, and vice versa. Thus the input stage DC conditions are stabilized by a high-gain negative feedback system. The feedback loop also isolates the rest of the circuit from common mode variations by making the base voltage of Q3/Q4 follow tightly 2V_be below that of the highest input voltage. For other uses, see Red (disambiguation). ... A current mirror is a circuit designed to copy a current flowing through one active device by controlling the current in another active device of a circuit, keeping the output current constant regardless of loading. ... Widlar current source. ...

The top-right current mirror Q12/Q13 provides a constant current load for the class A gain stage, via the collector of Q13, that is largely independent of the output voltage.

Differential input stage

The blue outlined section is a differential amplifier. Q1 and Q2 are input emitter followers and together with the common base pair Q3 and Q4 form the differential input stage. In addition, Q3 and Q4 also act as level shifters and provide voltage gain to drive the class A amplifier. They also help to increase the reverse V_be rating on the input transistors. Simple form of a differential amplifier A differential amplifier is a type of an electronic amplifier that multiplies the difference between two inputs by some constant factor (the differential gain). ... Common base amplifier In electronics, common base refers to a type of bipolar transistor circuit configuration in which a transistor is connected such that its base terminal is wired to the ground or common rail of the circuit (or can be considered so for AC signals). ...

The differential amplifier formed by Q1 - Q4 drives a current mirror active load formed by transistors Q5 - Q7. Q7 increases the accuracy of the current mirror by decreasing the amount of signal current required from Q3 to drive the bases of Q5 and Q6. This current mirror provides differential to single ended conversion as follows:

The signal current of Q3 is the input to the current mirror while the output of the mirror (the collector of Q6) is connected to the collector of Q4. Here, the signal currents of Q3 and Q4 are summed. For differential input signals, the signal currents of Q3 and Q4 are equal and opposite. Thus, the sum is twice the individual signal currents. This completes the differential to single ended conversion.

The open circuit signal voltage appearing at this point is given by the product of the summed signal currents and the paralleled collector resistances of Q4 and Q6. Since the collectors of Q4 and Q6 appear as high resistances to the signal current, the open circuit voltage gain of this stage is very high.

It should be noted that the base current at the inputs is not zero and the effective (differential) input impedance of a 741 is about 2 MΩ. The "offset null" pins may be used to place external resistors in parallel with the two 1 kΩ resistors (typically in the form of the two ends of a potentiometer) to adjust the balancing of the Q5/Q6 current mirror and thus indirectly control the output of the op-amp when zero signal is applied between the inputs.

Class A gain stage

The section outlined in magenta is the class A gain stage. It consists of two NPN transistors in a Darlington configuration and uses the output side of a current mirror as its collector load to achieve high gain. The 30 pF capacitor provides frequency selective negative feedback around the class A gain stage as a means of frequency compensation to stabilise the amplifier in feedback configurations. This technique is called Miller compensation and functions in a similar manner to an op-amp integrator circuit. It is also known as 'dominant pole compensation' because it introduces a dominant pole (one which masks the effects of other poles) into the open loop frequency response. This pole can be as low as 10 Hz in a 741 amplifier and it introduces a −3 dB loss into the open loop response at this frequency. This is done to achieve unconditional stability of the amplifier down to unity closed loop gain using non-reactive feedback networks and makes this type of internally compensated amplifier easier to use. Magenta is a color made up of equal parts of red and blue light. ... The term amplifier as used in this article can mean either a circuit (or stage) using a single active device or a complete system such as a packaged audio hi-fi amplifier. ... Circuit diagram of Darlington configuration In electronics, the Darlington transistor is a semiconductor device which combines two bipolar transistors in tandem (often called a Darlington pair) in a single device so that the current amplified by the first is amplified further by the second transistor. ... In electronics, gain is usually taken as the mean ratio of the signal output of a system to the signal input of the system. ... In electrical engineering, frequency compensation is a design technique for amplifiers which use negative feedback or those, such as operational amplifiers, that are intended for use with negative feedback. ... An integrator is a device to perform the mathematical operation known as integration, a fundamental operation in calculus. ... An open-loop controller does not use feedback to control states or outputs of a dynamic system. ... Look up stability in Wiktionary, the free dictionary. ... This article, image, template or category should belong in one or more categories. ...

Output bias circuitry

The green outlined section (based around Q16) is a voltage level shifter or V_be multiplier; a type of voltage source. In the circuit as shown, Q16 provides a constant voltage drop between its collector and emitter regardless of the current passing through the circuit. If the base current to the transistor is assumed to be zero, and the voltage between base and emitter (and across the 7.5 kΩ resistor) is 0.625 V (a typical value for a BJT in the active region), then the current flowing through the 4.5 kΩ resistor will be the same as that through the 7.5 kΩ, and will produce a voltage of 0.375 V across it. This keeps the voltage across the transistor, and the two resistors at 0.625 + 0.375 = 1 V. This serves to bias the two output transistors slightly into conduction reducing crossover distortion. In some discrete component amplifiers this function is achieved with (usually 2) silicon diodes. It has been suggested that this article or section be merged with Current source. ... Crossover distortion is a type of distortion which is caused by switching between devices driving a load. ...

Output stage

The output stage (outlined in cyan) is a Class AB push-pull emitter follower (Q14, Q20) amplifier with the bias set by the V_be multiplier voltage source Q16 and its base resistors. This stage is effectively driven by the collectors of Q13 and Q19. The output range of the amplifier is about 1 volt less than the supply voltage, owing in part to V_be of the output transistors Q14 and Q20. Cyan (from Greek κυανοs, meaning blue) may be used as the name of any of a number of a range of colors in the blue/green part of the spectrum. ... Class A amplifiers tend to have very low distortion when used with small signals, and are very inefficient Class B amplifiers tend to be efficient but suffer from high distortion when used with small signals. ...

The 25 Ω resistor in the output stage acts as a current sense to provide the output current limiting function which limits the current flow in the emitter follower Q14 to about 25 mA for the 741. Current limiting for the negative output is done by sensing the voltage across Q19's emitter resistor and using this to reduce the drive into Q15's base. Later versions of this amplifier schematic may show a slightly different method of output current limiting. The output resistance is not zero as it would be in an ideal op-amp but with negative feedback it approaches zero.

Note: while the 741 was historically used in audio and other sensitive equipment, such use is now rare because of the improved noise performance of more modern op-amps. Apart from generating noticeable hiss, 741s and other older op-amps may have poor common-mode rejection ratios and so will often introduce cable-borne mains hum and other common-mode interference, such as switch 'clicks', into sensitive equipment. Although noise is a random signal, it can have characteristic statistical properties. ... Common mode rejection ratio (CMRR) is a measure of the capability of an instrument, ie. ...

Notes

1. ^ http://www.maxim-ic.com/appnotes.cfm/an_pk/1108 Retrieved November 10, 2007
2. ^ W.G. Jung, IC Op-Amp Cookbook (3rd Ed.1986. ISBN 0-672-22453-4) p. xvii.
3. ^ D.F. Stout Handbook of Operational Amplifier Circuit Design (McGraw-Hill, 1976, ISBN 007061797X ) p. 1-11. This definition hews to the convention of measuring op-amp parameters with respect to the zero voltage point in the circuit, which is usually half the total voltage between the amplifier's positive and negative power rails.
4. ^ Many older designs of operational amplifiers have offset null inputs to allow the offset to be manually adjusted away. Modern precision op-amps can have internal circuits that automatically cancel this offset using choppers or other circuits that measure the offset voltage periodically and subtract it from the input voltage.
5. ^ That the output cannot reach the power supply voltages is usually the result of inherent limitations of the amplifier's output stage transistors. See "Output stage," below.
6. ^ The output of older op-amps can reach to within one or two volts of the supply rails. The output of newer so-called "rail to rail" op-amps can reach to within millivolts of the supply rails when providing low output currents.

A chopper circuit is used to refer to numerous types of electronic switching devices and circuits. ...

Common applications

Main article: Operational amplifier applications

This article illustrates some typical applications of solid-state integrated circuit operational amplifiers. ...

Other applications

• audio- and video-frequency pre-amplifiers and buffers
• voltage comparators
• differential amplifiers
• differentiators and integrators
• filters
• 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

An example of a typical high-end stereo preamplifier. ... For the British rock band of the same name, see Amplifier (band). ... A buffer amplifier (sometimes simply called a buffer) is one that provides impedance transformation from high to low between one circuit and another. ... In electronics, a comparator is a device which compares two voltages or currents and switches its output to indicate which is larger. ... Simple form of a differential amplifier A differential amplifier is a type of an electronic amplifier that multiplies the difference between two inputs by some constant factor (the differential gain). ... For a non-technical overview of the subject, see Calculus. ... An integrator is a device to perform the mathematical operation known as integration, a fundamental operation in calculus. ... In electronics and signal processing, a filter is a device or process that modifies a signal. ... AC, half-wave and full wave rectified signals A rectifier is an electrical device, comprising one or more semiconductive devices (such as diodes) or vacuum tubes arranged for converting alternating current to direct current. ... The super diode or precision rectifier is a configuration obtained with an operational amplifier in order to have a circuit behaving like an ideal diode or rectifier. ... This article or section should include material from AD converters In electronics, an analog-to-digital converter (abbreviated ADC, A/D, or A to D) is a device that converts continuous signals to discrete digital numbers. ... In electronics, a digital-to-analog converter (DAC or D-to-A) is a device for converting a digital (usually binary) code to an analogue signal (current, voltage or charges). ... Electrophysiology is the science and branch of physiology that pertains to the flow of ions in biological tissues and, in particular, to the electrical recording techniques that enable the measurement of this flow. ... Cross coupled LC oscillator with output on top An electronic oscillator is an electronic circuit that produces a repetitive electronic signal, often a sine wave or a square wave. ... It has been suggested that this article or section be merged with Function generator. ...

See also

Electronics Portal

• Operational amplifier applications
• Instrumentation amplifier
• Active filter
• Current-feedback operational amplifier
• Operational transconductance amplifier
• George A. Philbrick

Image File history File links Nuvola_apps_ksim. ... This article illustrates some typical applications of solid-state integrated circuit operational amplifiers. ... Typical instrumentation amplifier schematic An instrumentation amplifier is a type of differential amplifier that has been specifically designed to have characteristics suitable for use in measurement and test equipment. ... An example of high-pass active filter. ... Representative schematic of a current-feedback op-amp or amplifier. ... Schematic symbol for the OTA. Like the standard operational amplifier, it has both inverting (−) and noninverting (+) inputs; power supply lines (V+ and V−); and a single output. ... George A. Philbrick was responsible, through his company George A. Philbrick Researches, for the commercialization and wide adoption of operational amplifiers, a now-ubiquitous component of analog electronic systems, and the invention and commercialization of electronic analog computers based on the operational amplifier principle. ...

External links

Wikibooks' Electronics has more about this subject:

Op-Amps

• Introduction to op-amp circuit stages, second order filters, single op-amp bandpass filters, and a simple intercom
• Hyperphysics — descriptions of common applications
• Single supply op-amp circuit collection
• Op-amp circuit collection
• Another introduction
• Op-Amp Handbook
• Opamps for everyone Downloadable book. Can also be bought
• Op Amp Applications Downloadable book. Can also be bought
• Operational Amplifier Noise Prediction (All Op Amps) using spot noise
• Noise Analysis in Operational Amplifier Circuits
• Operational Amplifier Basics
• History of the Op-amp from vacuum tubes to about 2002. Lots of detail, with schematics. IC part is somewhat ADI-centric.

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