Design of the Dynamic Supply CMOS RF Power Amplifie - Linear CMOS RF Power Amplifiers for Wireless Applications - page 18

Fig. 3.1 Dynamic supply
and gain compression

Fig. 3.2 Dynamic supply RF PA block diagram including the envelope processing

To describe the design of the dynamic supply PA, this chapter is divided in five
sections. Two of them deal with isolated parts of the dynamic supply system. Sec-
tion 3.2 presents the high-efficiency CMOS modulator design including the com-
parator, synchronous switch, and LC filter. Section 3.3 focuses on the design of the
CMOS RF power amplifier. Section 3.4 presents the system as a whole with simu-
lation results. Among the blocks shown in Fig. 3.2 , only the modulator and the RF
PA were integrated. The coupler, the envelope detector, and the envelope processing
block are treated in Sect. 3.4 .

3.2 High-Efficienc , Fast Modulator

As previously said, the modulator provides a voltage signal that follows the instanta-
neous envelope value of the input RF signal. This signal serves as the power supply
for the RF power amplifier and, hence, must be able to provide any amount of cur-
rent that the PA demands. In order not to lose the efficiency enhancement provided
by this technique, the modulator must execute its function as efficiently as possible.
This can be achieved through the use of a switched-mode power supply.