Design of the Frequency-Tunable CMOS RF Power Amplifie - Linear CMOS RF Power Amplifiers for Wireless Applications - page 76

Chapter 6
Design of the Frequency-Tunable CMOS RF
Power Amplifie
Abstract This chapter presents the design of an integrated frequency-tunable RF
power amplifier for operation in the 3.7 and 5.2 GHz frequency bands. A novel
tunable impedance matching network based on coupled inductors is employed at
the output of the amplifier. The design of the complete system is described, which
includes the integrated planar coupled inductors, the circuit that controls the current
flowing through the inductors, and the RF power amplifier. Simulation results for
the complete system integrated in a CMOS technology are presented.
6.1 Introduction
It was shown in the previous chapters that the output impedance matching network
is of fundamental importance for the performance of the PA and that the variation in
frequency alters the properties of this network, thereby changing the performance of
the PA. Hence, a careful analysis of the output impedance matching is carried out in
the Sect. 6.2 while the input matching network is subject of Sect. 6.3 . The design of
the RF PA, the coupled inductors, and the control circuit required to implement the
tunable matching network based on coupled inductors are the subject of Sect. 6.4 .
6.2 Output Impedance Matching
The function of the output matching network is to transform the antenna impedance
into the desired impedance seen by the output stage of the PA. The illustration of
a basic CMOS power amplifier circuit presented in Fig. 3.11 on p. 26 is repeated
in Fig. 6.1 for clarity. This desired impedance can be the complex conjugate of the
output impedance of the PA. This is the case of the conjugate match . On the other
hand, the desired impedance can be the optimum resistance ( R opt ). This is the case
of the powermatch [ 6 ], which leads to an optimum performance at maximum output
power. This performance is a trade-off between efficiency and linearity.