Class D amplifier

FIGURE 7.63 (a) The H-bridge full-wave Class D amplifier configuration. A diagonal pair of FETs is on, while the... 

Either the fuU-wave or half-wave Class D amplifier may be transformer coupled to T. It is only necessary to consider the turns ratio, but Pout and Pjn remain the same. 

Assume that a 25% duty cycle represents the halfway point between off and fidl on (50%) for each transistor set. Modulating up or down from 25% drives the amplifier to zero and 50% duty cycle for each set (100% total). The average of the output voltage across R will follow the pulse width represented drive signal. The output must be low-pass filtered to obtain the average, which is a reproduction of the signal to be amplified. (Use of the Class D amplifier in this way is sometimes referred to as Class S.)... 

Chips (ICs), 257 Chopper, 236, 243 Circuit breaker, 137 Class D amplifier, 236 Clip leads, 2, 10, 76... 

FIGURE 5.39 Transit time effects in a class C amplifier (a) control grid voltage, (b) electron position as a function of time (triode case), (c) electron position as a function of time (tetrode case), (d) plate current (triode case). Source Adapted from Terman, F.E. 1947. Radio Engineering, p. 405. McGrawHill, New York.)... 

The switch-mode Class D amphfier can be used as a baseband linear amphfier by applying a square gate signal, the pulse width (duty cycle) of which is proportional to the amphtude of the signal to be amplified. 

The transmitter amplifier chain consists of a linear, three-stage transistor amplifier from Amplifier Research (10 W), a class C single-stage field effect transistor (FET) amplifier (120 W) custom-built by H. Bonn GmbH, Munich, and a final tube amplifier with two tetrodes 4CX 350A that deliver more than 1.5 kW of pulse power. A special effort was made to match the input and output impedances of this tube amplifier to the characteristic impedance (50 ( ) of the cables connecting it with the probe and the driver, respectively. This impedance matching resulted in the virtually complete disappearance of antisymmetric phase transients (for a discussion of the effects of such phase transients on m.p. spectra, see Haeberlen, 1976, Appendix D). 

WAL 09] Wallikewitz B.H., Hertel D., Merrholz K., Cross-linkable polyspirobifluorenes a material class featuring good OLED performance and low amplified spontaneous emission thresholds , Chemistry of Materials, vol. 21, no. 21, pp. 2912-2919, 2009. 

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