Difference Amplifier

6 Key excerpts on "Difference Amplifier"

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  eBook - PDF

  Fundamentals of Electronics

  Book 1 Electronic Devices and Circuit Applications

  • Thomas F. Schubert, Ernest M. Kim(Authors)
  • 2022(Publication Date)
  • Springer

    (Publisher)

  A schematic of a Difference Amplifier is shown in Figure 1.16. 22 1. OPERATIONAL AMPLIFIERS AND APPLICATIONS NUL C v  v  CV  NULV  C NUL v o i   R C C NUL v b i   R B R A C NUL v a R D Figure 1.16: Difference Amplifier with input voltages v a and v b . By assuming an ideal OpAmp operating in the linear region, the current constraints can be used to yield the voltages at nodes 1 and 2 as a simple voltage division at the non-inverting input: v 1 D v 2 D v b R D R C C R D : (1.39) e node voltage method of analysis is used to determine the output voltage v o with respect to the input voltages v a and v b , 0 D v a v 1 R A C v o v 1 R B : (1.40) Solving for the output voltage v o yields, v o D R B R A .v 1 v a / C v 1 : (1.41) Substituting Equation (1.39) into (1.41) provides the output voltage as a function of the input voltages, v o D R D R C C R D R B R A C 1 v b R B R A v a : (1.42) e expression for the output voltage in Equation (1.42) can be simplified for the particular case where the resistor ratios are given by: R A R B D R C R D : (1.43) 1.3. BASIC APPLICATIONS OF THE OPAMP 23 By applying the ratio of Equation (1.43), the output voltage in Equation (1.42) is reduced to a scaled difference of the input voltages, v o D R B R A .v b v a / : (1.44) e Difference Amplifier is commonly used in circuits that require comparison of two signals to control a third (or output) signal. For instance, v a could be a voltage reading representing temper- ature from a thermistor (a resistor that changes values with temperature) circuit and v b a reference voltage representing a temperature setting. e output of the Difference Amplifier would then be the deviation of the measured temperature from the reference temperature setting. Example 1.5 e Difference Amplifier in Figure 1.17 has an input voltage v a D 3 V.

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  eBook - PDF

  Designer's Handbook Instrmtn/Contr Circuits

  • Joseph J. Carr(Author)
  • 2012(Publication Date)
  • Academic Press

    (Publisher)

  ADDITIONAL DIFFERENTIAL AMPLIFIERS T h e simple D C differential amplifier circuits shown in this chapter are useful for low-gain applications and for those applications where a low to moderate input impedance is permissible (e.g., 3 0 0 to 2 0 0 , 0 0 0 Ω). Where a higher gain is required, we must resort to a more complex circuit called the operational amplifier instrumentation amplifier, or IA. In the next chapter we will examine the classical three-device LA circuit, as well as several integrated circuit instrumentation amplifiers (IC IA) that offer the advantages of the IA in a single small IC package. Some of those devices are now among the most commonly used in many instrumentation applications,- they will be considered below. 326 14. DC Differential Operational Amplifier Circuits INSTRUMENTATION AMPLIFIERS T h e simple D C differential amplifier discussed earlier suffers from several important drawbacks. First, there is a limit to the input impedance ( Z i n is approximately equal to the sum of the two input resistors). Second, there is a practical limitation on the gain available from the simple single-device D C differential amplifier. If high gain is attempted, then either the input bias current tends to cause large output offset voltages, or the input impedance becomes too low. In this section we will demonstrate a solution to these problems in the form of the instrumentation amplifer (IA). All of these amplifiers are differ-ential amplifiers, but they offer superior performance over the simple D C differential amplifiers of the last section. The instrumentation amplifier can offer higher input impedance, higher gain, and better common mode rejection than the single-device D C differential ampli-T h e simplest form of instrumentation amplifier circuit is shown in Fig.

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  eBook - ePub

  Electronics

  • David Crecraft, David Gorham(Authors)
  • 2018(Publication Date)
  • CRC Press

    (Publisher)

  power supply. In the case of an electronic amplifier, the power supply is usually a d.c. voltage power supply (which gets its power from the a.c. supply mains) or a battery.

  The input signal causes the amplifier to control the flow of current from this voltage supply to the load. Thus more power may be delivered to the load than is taken from the input signal source. In practice, amplification usually means increasing the voltage amplitude of the signal into a given load. The opposite of amplification is called attenuation, and usually refers to a decrease in signal voltage.

  An electronic system which is designed primarily to give an output voltage proportional to the input signal voltage, without taking a significant amount of signal current, is called a voltage amplifier. Its voltage gain is specified, but its current gain is not, so it may give an increase in signal current if the load impedance is low enough.

  Voltage amplifier

  An example of this is the unity-gain buffer. It is designed so that its output voltage is almost equal to its input voltage, but the output current may be much larger than the input current. So the voltage gain can be specified as nearly 1, but the current gain cannot be specified.

  Current amplifier

  An amplifier designed primarily to give an output current proportional to the input signal current, without requiring a significant input signal voltage, is called a current amplifier.

  power amplification

  All these examples involve power amplification of course.

  Passive components

  In electronics a distinction is made between two types of component: those which can only absorb or transfer signal power, such as resistors and transformers, which are called passive components, and those, such as transistors, which can accept power from an extra power source and amplify signal power. These are called active components, or active devices.

  Active components or devices

  Throughout this chapter, there are occasional references to bipolar transistors and field-effect transistors (FET). You are not expected to know anything about transistors at this stage except that they are active devices. They are explained in Chapter 9

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  Available until 23 Dec |Learn more

  The Audio Dictionary

  Third Edition, Revised and Expanded

  • Glenn D. White, Gary J. Louie(Authors)
  • 2011(Publication Date)
  • University of Washington Press

    (Publisher)

  Before the advent of integrated circuits , differ-ential amplifiers were made by adding a transformer to the input and not connecting either side of the primary to ground; this is still done in the case of some microphone preamplifiers . Integrated circuit differential amplifiers without transformers are com-monly available. They allow balanced configurations to be easily built at lower cost than using a good transformer. Differential Amplifier Differential Amplifier 107 Diffraction The bending of a sound wave around an obstacle and the reflection of a sound wave from a discontinuity in its path are called dif-fraction. It is wavelength dependent. Where the wavelength is short (rel-atively high frequencies ) compared to the obstacle, reflection will occur as well as bending of the wave front. When the wavelength is long (lower frequencies) with respect to the obstacle, little reflection will occur and the bending will be more pronounced. The diffraction of light is analogous to that of sound, although it is sel-dom seen because of the extremely short wavelengths of light. Digital See digital audio ; Appendix 7. Digital Acoustics Processor, DAP A consumer audio device that attempts to simulate the acoustics of an auditorium or other room by adding suit-able digital time delays and synthetic reverberation to recorded signals. It is the latest in a long line of analog devices that began with the stereo-phoner designed by the Viennese orchestra conductor Hermann Scherchen in the 1950s and the xophonic made by Radio Craftsmen in the U.S. in the 1960s. The Xophonic had multiple outputs for feeding surround loud-speakers and came with preprogrammed delay settings to simulate certain existing concert halls. DAPs are often used to process the stereo audio sig-nals from prerecorded video tapes and video discs to enhance the illusion of ambience. Illusion is the proper word, since DAPs do not produce very accurate simulations of actual acoustical spaces.

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  eBook - PDF

  Essentials of Electrical and Computer Engineering

  • J. David Irwin, David V. Kerns, Jr.(Authors)
  • 2022(Publication Date)
  • Wiley

    (Publisher)

  However, as sophisticated as it appears, it is really nothing more than a high-quality linear voltage ampli- fier. The details of how this circuit is designed are beyond the scope of this book, but follows basic principles described here. A linear voltage amplifier is an electronic circuit that produces an output voltage signal that is an exact copy or replica of the input voltage signal, except the output is increased in amplitude (magnitude) by a factor, A v , called the voltage gain. This is illustrated in Figure 10.2 and by the following equation. Note that in Figure 10.2, A v = 2. v o = A v v i In practice, op amps have significantly higher gains, A v , than that illustrated, like 10,000 or 100,000 or more. 304 Differential Amplifiers 305 01 02 INVERTING INPUT NONINVERTING INPUT 03 04 05 R1 1k R2 1k R3 50k R4 5k R12 50k R11 50 OFFSET NULL OFFSET NULL 06 1 5 2 3 07 08 09 010 011 R5 39k R7 4.5k R8 7.5k R10 50 v – = V SS 4 6 v + = V DD R9 25 OUTPUT C1 30pF 022 012 013 014 7 015 015 017 020 Offset Null 1 2 3 4 8 7 6 5 Inverting (–) Noninverting (–) (Power)v + (V DD ) Offset Null Output v – (Power) (V SS ) Not Connected (NC) 741 Op. Amp. – + FIGURE 10.1 Analog devices op-amp schematic and pin diagram (Analog Devices, Inc. data sheet) 2 1 –1 –2 t 2 v 0 v i 1 0 –1 –2 t v i l i v 0 A v FIGURE 10.2 Illustration of linear amplifier DIFFERENTIAL AMPLIFIERS A differential amplifier has two inputs, generally labeled as v + and v − , the noninverting and the inverting inputs, respectively; and there is one output, v o . The output voltage is related to the dif- ference in voltage between the two inputs. Power is supplied to the device via the two dc voltage sources, V DD and V SS , which are typically balanced, e.g. plus and minus 1.5–15 V. The output volt- age of the amplifier is linear, i.e. not saturated, as long as it is within these limits. See Figure 10.3. The differential amplifier circuit can be represented by the circuit model shown in Figure 10.4.

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  eBook - PDF

  Innovative Instrument Design and Applications

  • Lazo M. Manojlovic(Author)
  • 2019(Publication Date)
  • Arcler Press

    (Publisher)

  Differential amplifier also suppress the common-mode input voltage, which is typically in the form of a DC level hum, or other type of interferences . The most generic form of a differential amplifier is presented in Figure Analog Signal Conditioning in Instrumentation 151 6.1, where the differential amplifier (DA) can be considered as the four-port device (V i , V’ i , V o , and V’ o ). However, most practical differential amplifiers have a single-ended output and thus they can be considered as the three-port circuits. Figure 6.1. Most generic form of a differential amplifier. At the beginning of analyze of a differential amplifier, it is convenient to define two input and output voltage signals, i.e., the differential-mode voltages and the common-mode voltages as: 2 2 2 2 o o oCM o o oDM i i iCM i i iDM V V V V V V V V V V V V ′ + = ′ − = ′ + = ′ − = . (6.1) The general input-output relationship of a differential amplifier can be expressed as following: , (6.2) where A DD , A DC , A CD , and A CC represents the corresponding gain factors. In the case of the single-ended outputs it is easy to show that the following is valid: . (6.3) For the single-ended output, V o the following can be written in terms of the actual inputs of a differential amplifier: Innovative Instrument Design and Applications 152 . (6.4) Typically, the single-ended output, V o of the differential amplifier is pre -sented in the form: , (6.5) where A DM and A CM are given by the corresponding terms in equation (6.3). For an ideal differential amplifier the following is valid: A CC = A DC = A CD = 0. So, in this case, we have fulfilled A C = 0 and A D = A DD . 6.1.1. Common-Mode Rejection Ratio The common-mode rejection ratio (CMRR) is an important parameter of any differential amplifier. The value of CMRR is typically expressed in decibels and it describes how well a real differential amplifier characteristics approach that of an ideal one.

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