Physics
Inverting Amplifier
An inverting amplifier is a type of operational amplifier (op-amp) circuit that produces an output that is the opposite (inverted) polarity of the input signal. It uses negative feedback to stabilize and control the amplification process. The input signal is applied to the inverting input terminal of the op-amp, and the output is taken from the output terminal.
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eBook - PDF- Jiri Dostal(Author)
- 2013(Publication Date)
- Newnes(Publisher)
Parti The Operational Amplifier This page intentionally left blank 1. Basic Concepts 1.1 The Operational Amplifier The operational amplifier is a versatile amplifying device, originally intended for use in analog computers to perform linear mathematical operations. Forty years of development of the operational amplifier's internal circuit design reflects, to a significant extent, the development of electronic components from vacuum tubes to monolithic integrated circuits. An increasing refinement of the operational amplifier's properties has shifted the emphasis of its ap-plications from laboratories to industry. Due to its high performance, ver-satility, and low price, the operational amplifier now dominates the field of analog electronic systems. We generally define the operational amplifier as a direct-coupled amplifier with a high gain and a low level of inherent noise, capable of stable operation in a closed-feedback loop. The exact meaning of these characteristics will be given in Chapters 2 and 11. It should be mentioned here that the term direct-coupled does not imply an upper limitation of the amplifier's frequency re-sponse but, on the contrary, an extension of the operating range to zero frequency, or infinitely long periods. The direction of signal flow from input to output in an operational amplifier is given by the triangular shape of its symbol in Figure 1-la. Three of the four illustrated terminals represent the three signal terminals of an actual operational amplifier. These are the inverting input, noninverting input, and output. The fourth signal terminal, the ground, may be either actual (Figure 1—lb) or only virtual (power supply common in Figure 1-lc). In either case, it represents symbolically a group of at least two terminals intended for the supply of energy.
eBook - PDFCircuits, Signals, and Systems for Bioengineers
A MATLAB-Based Introduction
- John Semmlow(Author)
- 2005(Publication Date)
- Academic Press(Publisher)
This amplifier is termed a nonInverting Amplifier . (Somewhat of a double negative.) 10.2 THE OPERATIONAL AMPLIFIER The operational amplifier , or op amp for short, is a basic building block for a wide variety of analog circuits. One of its first uses was to perform mathematical oper-ations, such as addition and integration in analog computers, hence the name oper-ational amplifier. Although the functions provided by analog computers are now performed by digital computers, the op amp remains a valuable, perhaps the most valuable, tool in analog circuit design. In its idealized form, the op amp has the same properties as the ideal amplifier described above except for one curious departure: it has infinite gain. Thus, an ideal op amp has infinite input impedance (i.e., an ideal load), zero output impedance (i.e., an ideal source), and a gain, A v , of infinity. (The symbols A v or A VOL are com-monly used to represent the gain of an operational amplifier.) Obviously, an ampli-fier with a gain of infinity is of limited value, so an op amp is rarely used alone but usually used in conjunction with other elements that reduce its gain to a finite level. Negative feedback can be used to limit the gain. Consider the feedback system in Figure 10.5. The gain of the system can be found from the basic feedback equation first introduced in Chapter 1 (Eq. 1.7) and again in the last chapter (Eq. 9.3). Inserting A V and b into the feedback equation, the overall system gain, G , becomes: [Eq. 10.4] Letting the feedforward gain, A V (the gain of the operational amplifier) go to infinity: [Eq. 10.5] G A A A A A V V A V V V V = + = = Æ• Æ• lim lim 1 1 b b b G A A V V = + 1 b 374 CHAPTER 10 BASIC ANALOG ELECTRONICS: OPERATIONAL AMPLIFIERS Figure 10.4 A differential amplifier configured as an inverting ( left ) and noninverting ( right ) amplifier. If the overall gain is expressed in decibels (dB), then: [Eq. 10.6] If b < 1, then the gain G will be > 1 and if b = 1, G = 1.
eBook - PDF- Behzad Razavi(Author)
- 2021(Publication Date)
- Wiley(Publisher)
In this chapter, we study the operational amplifier as a black box, developing op-amp-based circuits that perform interesting and useful functions. The outline is shown below. 1 Vacuum tubes were amplifying devices consisting of a filament that released electrons, a plate that collected them, and another that controlled the flow—somewhat similar to MOSFETs. 355 356 Chapter 8 Operational Amplifier as a Black Box General Concepts • Op Amp Properties Linear Op Amp Circuits • NonInverting Amplifier • Inverting Amplifier • Integrator and Differentiator • Voltage Adder Nonlinear Op Amp Circuits • Precision Rectifier • Logarithmic Amplifier • Square Root Circuit Op Amp Nonidealities • DC Offsets • Input Bias Currents • Speed Limitations • Finite Input and Output Impedances 8.1 GENERAL CONSIDERATIONS The operational amplifier can be abstracted as a black box having two inputs and one output. 2 Shown in Fig. 8.1(a), the op amp symbol distinguishes between the two inputs by the plus and minus sign; V in1 and V in2 are called the “noninverting” and “inverting” inputs, respectively. We view the op amp as a circuit that amplifies the difference between the two inputs, arriving at the equivalent circuit depicted in Fig. 8.1(b). The voltage gain is denoted by A 0 : V out = A 0 (V in1 − V in2 ). (8.1) We call A 0 the “open-loop” gain. V V in1 in2 out V in1 in2 A 0 V V in1 V ( V in2 – out V (a) (b) ) Figure 8.1 (a) Op amp symbol, (b) equivalent circuit. It is instructive to plot V out as a function of one input while the other remains at zero. With V in2 = 0, we have V out = A 0 V in1 , obtaining the behavior shown in Fig. 8.2(a). The positive slope (gain) is consistent with the label “noninverting” given to V in1 . On the other hand, if V in1 = 0, V out = −A 0 V in2 [Fig. 8.2(b)], revealing a negative slope and hence an “inverting” behavior.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- The English Press(Publisher)
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 one megohm; etc. A basic circuit is designed, often with the help of circuit modeling (on a computer). Spe-cific 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 Non-Inverting Amplifier 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 V out because of the negative feedback through the R 1 R 2 network. R 1 and R 2 form a voltage divider, and as V – is a high-impedance input, it does not load it appreciably. Consequently: ________________________ WORLD TECHNOLOGIES ________________________ where Substituting this into the gain equation, we obtain: Solving for V out : If A OL is very large, this simplifies to . Inverting Amplifier 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.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
Consequently: where Substituting this into the gain equation, we obtain: Solving for V out : If A OL is very large, this simplifies to . ____________________ WORLD TECHNOLOGIES ____________________ Inverting Amplifier 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 V out and V in due to the voltage divider formed by R f and R in . Again, the op-amp input does not apply an appreciable load, so: Substituting this into the gain equation and solving for V out : If A OL is very large, this simplifies to . A resistor is often inserted between the non-inverting input and ground (so both inputs see similar resistances), reducing the input offset voltage due to different voltage drops due to bias current, and may reduce distortion in some op-amps. A DC-blocking capacitor may be inserted in series with the input resistor when a frequency response down to DC is not needed and any DC voltage on the input is unwanted. That is, the capacitive component of the input impedance inserts a DC zero and a low-frequency pole that gives the circuit a bandpass or high-pass characteristic. ____________________ WORLD TECHNOLOGIES ____________________ Positive feedback configurations Another typical configuration of op-amps is with 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 Schmitt trigger. Positive voltage level detector A positive reference voltage V ref is applied to one of the op-amp's inputs. This means that the op-amp is set up as a comparator to detect a positive voltage. If the voltage to be sensed, E i , is applied to op amp's (+) input, the result is a noninverting positive-level detector.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
Consequently: where Substi tuting this into the gain equation, we obtain: Solving for V out : If A OL is very large, this simplifies to . ____________________ WORLD TECHNOLOGIES ____________________ Inverting Amplifier 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 V out and V in due to the voltage divider formed by R f and R in . Again, the op -amp input does no t apply an appreciable load, so: Substituting this into the gain equation and solving for V out : If A OL is very large, this simplifies to . A resistor is often inserted between the non-inverting input and ground (so both inputs see similar resistance s), reducing the input offset voltage due to different voltage drops due to bias current , and may reduce distortion in some op -amps. A DC-blocking capacitor may be inserted in series with the input resistor when a frequency response down to DC is not needed and any DC voltage on the input is ____________________ WORLD TECHNOLOGIES ____________________ unwanted. That is, the capacitive component of the input impedance inserts a DC zero and a low-frequency pole that gives the circuit a bandpass or high-pass characteristic. Positive feedback configurations Another typical configuration of op-amps is with 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 Schmitt trigger. Positive voltage level detector A positive reference voltage V ref is applied to one of the op-amp's inputs. This means that the op-amp is set up as a comparator to detect a positive voltage. If the voltage to be sensed, E i , is applied to op amp's (+) input, the result is a noninverting positi ve-level detector.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- University Publications(Publisher)
Consequently: where Substitu ting this into the gain equation, we obtain: Solving for V out : If A OL is very large, this simplifies to . ____________________ WORLD TECHNOLOGIES ____________________ Inverting Amplifier 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 V out and V in due to the voltage divider formed by R f and R in . Again, the op -amp input does not a pply an appreciable load, so: Substituting this into the gain equation and solving for V out : If A OL is very large, this simplifies to . A resistor is often inserted between the non-inverting input and ground (so both inputs see similar resistances), reducing the input offset voltage due to different voltage drops due to bias current , and may reduce distortion in some op -amps. A DC-blocking capacitor may be inserted in series with the input resistor when a frequency response down to DC is not needed and any DC voltage on the input is unwanted. That is, the capacitive component of the input impedance inserts a DC zero and a low-frequency pole that gives the circuit a bandpass or high-pass characteristic. ____________________ WORLD TECHNOLOGIES ____________________ Positive feedback configurations Another typical configuration of op-amps is with 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 Schmitt trigger. Positive voltage level detector A positive reference voltage V ref is applied to one of the op-amp's inputs. This means that the op-amp is set up as a comparator to detect a positive voltage. If the voltage to be sensed, E i , is applied to op amp's (+) input, the result is a noninverting positive -level detector.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Research World(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter 4 Operational Amplifier A Signetics 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 pro-duces an output voltage that is typically hundreds of thousands times larger than the voltage difference between its input terminals. ________________________ WORLD TECHNOLOGIES ________________________ 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 that 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. 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).
- Dale R. Patrick, Stephen W. Fardo(Authors)
- 2020(Publication Date)
- River Publishers(Publisher)
The entire assembly is built on a small silicon substrate and packaged as an integrated cir- cuit (IC). ICs of this type are capable of high-gain signal amplification from dc to several million hertz. An op-amp is a modular, multistage amplifying device. Figure 4-60. IC power amplifier. 172 Electricity and Electronics Fundamentals Figure 4- 61. LM 379 dual 6-W audio amplifier. Operational amplifiers have several important properties. They have open-loop gain capabilities in the range of 200,000 with an input impedance of approxi- mately 2 MΩ. The output impedance is rather low, with values in the range of 50 Ω or less. Their bandwidth, or ability to amplify different frequencies, is rather good. The gain does, however, have a tendency to drop, or roll off, as the frequency increases. The internal construction of an op-amp is quite complex and usually contains a large number of discrete components. A person working, with an op-amp does not ordinarily need to be concerned with its internal construction. It is helpful, however, to have some gen- eral understanding of what the internal circuitry accom- plishes. This permits the user to see how the device per- forms and indicates some of its limitations as a function- ing unit. The internal circuitry of an op-amp can be divided into three functional units. Figure 4-62 shows a simplified diagram of the internal functions of an op-amp. Notice that each function is enclosed in a triangle. Electronic schematics use the triangle to denote the amplification function. This diagram shows that the op-amp has three basic amplification functions. These functions are gener- ally called stages of amplification. A stage of amplifica- tion contains one or more active devices and all the as- sociated components needed to achieve amplification. Figure 4-62. Op-amp diagram. The first stage, or input, of an op-amp is usually a differential amplifier. This amplifier has two inputs, which are labeled V 1 and V 2 .
eBook - PDFElectronics
Made Simple
- George H. Olsen(Author)
- 2016(Publication Date)
- Made Simple(Publisher)
These amplifiers will incorporate discrete transistors and resistors (i.e. will use separate components) so that readers can appreciate the principles in-volved. In the next chapter, dealing with integrated circuits, we shall see how audio and other amplifiers can be constructed when most of the design work and construction is done for us. This means that instead of building amplifiers from the separate 'bricks', we build a system by buying and incorporating whole 'walls'. An amplifier is a circuit that incorporates one or more transistors and is designed to increase an alternating signal applied to the input terminals. It is called a voltage amplifier if the size or magnitude of the output voltage is considerably greater than the input voltage. The ratio of the output voltage to the input voltage is called the voltage gain of the amplifier. The main function of a voltage amplifier is to produce a given gain with the minimum of dis-tortion, i.e. the output voltage should have the same waveform as the input waveform, but should of course be much increased in magnitude. Power amplifiers are used to drive the output mechanism, e.g. a loudspeaker, a pair of earphones, a moving-coil meter or some other type of indicating device. The main function of a power amplifier is to deliver a good deal of undis-torted power into the output device or load circuit; such an amplifier may often develop a voltage gain too, but this voltage amplification is of secondary importance. When a number of amplifiers, each of which uses only one or two transistors, are connected in series (called a cascade) so that the output of one amplifier provides the input to the next amplifier, each of these amplifiers is called a stage. A complete amplifier consists of several stages; the earlier stages of an audio amplifier are designed as voltage amplifiers whilst the last stages form the power amplifier.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- College Publishing House(Publisher)
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 one 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. A prototype is then built and tested; changes to meet or improve the specification, alter functionality, or reduce the cost, may be made. ____________________ WORLD TECHNOLOGIES ____________________ Basic single stage amplifiers Non-Inverting Amplifier 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 V out because of the negative feedback through the R 1 R 2 network. R 1 and R 2 form a voltage divider, and as V – is a high-impedance input, it does not load it appreciably. Consequently: where Substituting this into the gain equation, we obtain: Solving for V out : If A OL is very large, this simplifies to ____________________ WORLD TECHNOLOGIES ____________________ . Inverting Amplifier 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.
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