Category Archive for: POWER AMLIFIERS

MOSFET AND CLASS D POWER AMPLIFIERS

Mosfet Amplifiers  MOSFET devices of the VMOS design (Figure 7-47) are becoming a popular choice for power amplifiers, particularly those designed to switch large currents on and off’,Examples include line drivers for digital switching circuits, switching-mode voltage regulators (discussed in Chapter 17), and class-D amplifiers, which we will discus presently. One advantage of a MOSFET switch is the fact…

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Amplitude Modulation

We have mentioned that amplitude modulation is a means used to transmit  by varying the .amplitude of a high-frequency carrier. In a typical apphea signal is a low-frequency audio waveform and the amplitude of a high-frequency (radio-frequency, or rf) carrier is made to increase and decrease as the audio Q:~al increases and decreases. Figure 16-36 shows the waveforms…

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CLASS C AMPLIFIERS

A c1ass-C amplifier is one whose output conducts load current during less than one half cycle of an input sine wave. Figure 16-33 shows a typical class-C current waveform, and it is apparent that the total angle during which current flows is less than 180°. This angle is called the conduction  angle Of course, the output of a…

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TRANSFORMERLESS PUSH-PULL AMPLIFIERS

Complementary Push-Pull Amplifiers The principal disadvantage of the push-pull amplifier circuits we have discussed so far is the cost and bulk of their output transformers. High-power amplifiers in particular are encumbered by the need for very large transformers capable of conducting large currents without saturating. Figure 16-25(a) shows a popular design using complementary (PNP and N PN) output transistors…

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DISTORTION IN PUSH PULL AMPLIFIERS

Cancellation of even Harmonics Recall that push-pull operation effectively produces in a load a waveform proportional to the difference between two input signals. Under normal operation the signals are out of phase so their waveform is reproduced in the load. If the signals were in phase cancellation would occur. It is instructive to view a push-pull output as the…

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Harmonic Distortion and Feedback

Harmonic Distortion Recall that any periodic waveform sinusoidal or otherwise, can be represented as the sum of an infinite number of sine waves having different amplitudes Ire and phase relations. The mathematical technique called Fourier analysts is concerned with finding the exact amplitudes frequencies and phase angles of the sine wave components that reproduce a given waveform when…

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PUSH-PULL DRIVERS

We have seen that the push-pull amplifier described earlier must be driven by out of-phase input signals. Figure 16-17 shows how a transformer can be used to provide the required drive signals. Here, the secondary winding has a grounded center tap that effectively splits the secondary voltage into two out-of-phase signals, each having one-half the peak value of…

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PUSH PULL AMPLIFIER PRINCIPLES

A push-pull amplifier uses two output devices to drive a load, The name is derived from the fact that one device is primarily (or entirely) responsible for driving current through the load in one direction (pushing), while the other device drives current through the load in the opposite direction (pulling). The output devices arc typically two…

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Class B Amplifiers

Transistor operation is said to be class B when output current varies during only one half-cycle of a sine-wave input. In other words, the transistor is in its active region, responding to signal input, only during a positive half-cycle or only during a negative half-cycle of the input. This operation is illustrated in Figure16-12. It is clear that…

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Transformer Coupled Class A Amplifiers

In Chapter 11. we reviewed basic transformer theory and discussed transformer coupled amplifiers. Transformers are also used to couple power amplifiers to their loads and, in those applications. are called output transformers. As in other coupling applications. the advantages of a transformer are that it provides an opportunity to achieve impedance matching for maximum power transfer and that it…

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