Chapter 6 - Chapter 6 Large Signal Amplifier 1 2 Types of...

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1 Chapter 6 Large Signal Amplifier
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3 Types of Amplifiers (I) Based on Operation Point Class-A Amplifier: In this mode, each transistor in the amplifier operates in its active region for the entire signal circle. Class-B Amplifier: In this mode of operation, each transistor is in its active region for approximately half of the signal cycle. Class-AB Amplifier: In this mode, an amplifier operates in class A for small signals and in class B in for large signals. Class-C Amplifier: In this mode, an amplifier operation, each transistor is in its active region for significantly less than half of the signal cycle. The active regions of a transistor are shown in Figure 1. The transfer characteristic of a transistor is shown in Figure 2.
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4 Types of Amplifiers (II) Based on Operation Point Figure 1 Operating regions of a transistor. Figure 2 The transfer characteristics of a transistor with turn-on voltage V 0 . I b V b
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5 I b t Types of Amplifiers (III) Based on Signal Level Small-signal analysis is a method of analysis of an active circuit in which it is assumed that the signals deviate from (or fluctuate to either side of) the steady bias levels by such a small amount that only a small part of the operation characteristic of the device is covered and thus the operation is always linear. Large-signal analysis is a method of analysis of an active circuit under high amplitude signals that traverse such a large part of the operating characteristic of a device that nonlinear portions of the characteristic are usually encountered causing nonlinear operation of the device. Figure 3 The signal scale in I C -V CE region.
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6 Some Definitions Related to Large Signal Amplifier Power Added Efficiency PAE : The ratio between the RF power added in the amplifier and the DC power consumption of the amplifier P DC a measurement of how much the dissipated power is converted into RF power: DC in out P P P PAE = (1) The 1-dB Compression Point P 1-dB : The point of the output power at which the power gain is 1-dB lower than its small-signal linear power gain. The 1-dB compression point can be show in the P out versus P in plot as depicted in Figure 4. Figure 4 The 1-dB compression point and the minimum detectable signal level
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7 Minimum Detectable Signal Level P mds : The point of the output power at which the power level is SNR min dB above the noise floor at the output port of the amplifier. ) ( 3 ) ( ) ( log 10 174 ) ( 10 min 0 dB dB F dB G B dBm dB SNR F BG kT P A A mds + + + + = + = (2) where, k=Boltzman’s constant (1.374×10 -23 J/K); T=The resistor’s physical temperature (in Kelvin); B=The two-port network’s bandwidth; G A =The power gain of the amplifier; F=The noise figure of the amplifier. SNR min = The minimum signal to noise ratio for detecting the signal. For analog signal, the value is assumed to be 3dB.
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This note was uploaded on 05/01/2011 for the course ELECTRICAL EE5602 taught by Professor Xuequan during the Spring '11 term at City University of Hong Kong.

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Chapter 6 - Chapter 6 Large Signal Amplifier 1 2 Types of...

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