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Sec. 5–1 Amplitude Modulation 317<br />

v 1 (t)=V 1 cos c t<br />

Oscillator<br />

(carrier frequency, f c )<br />

Intermediate-power<br />

amplifier (IPA)<br />

(class C amp)<br />

Power amplifier<br />

(PA)<br />

(class C amp)<br />

s(t)<br />

AM<br />

output<br />

DC supply<br />

voltage for PA<br />

v 3 (t)<br />

m(t)<br />

Audio<br />

input<br />

Pulse width<br />

modualtor<br />

(PWM)<br />

High-power<br />

electronic<br />

switch<br />

v 2 (t)<br />

Low-pass<br />

filter<br />

High voltage from<br />

DC power supply<br />

(a) Block Diagram<br />

m(t) = audio input<br />

t<br />

v 2 (t) = PWM<br />

t<br />

v 3 (t)<br />

t<br />

s(t) = AM output<br />

t<br />

(b) Waveforms<br />

Figure 5–2<br />

Generation of high-power AM by the use of PWM.

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