Radio Frequency Integrated Circuit Design - Webs

Figure 10.36 Class H amplifier.
Power Amplifiers
As with the class G amplifier, this technique has mainly been used for
lower frequencies. However, this technique can be modified so that the power
supply follows the envelope of the signal rather than the signal itself. Discussion
of such circuits for code division multiple access (CDMA) RF applications can
be found in [2].
10.10 Class S Amplifiers
The class S amplifier, shown in Figure 10.37, has as an input a pulse-width
modulated signal. This turns Q 1 and Q 2 on or off as switches with a switching
frequency much higher than the signal frequency. L o and C o form a lowpass
filter that turns the pulse-width modulated signal into an analog waveform. If
only positive outputs are needed, only Q 1 and D2 are required. For negative
signals, only D1 and Q 2 are necessary. Since the switching frequency must be
Figure 10.37 Class S amplifier.
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