Measurement Results for the Frequency-Tunable CMOS RF Power Amplifie - Linear CMOS RF Power Amplifiers for Wireless Applications - page 100

Chapter 7
Measurement Results for the
Frequency-Tunable CMOS RF Power Amplifie
Abstract The experimental characterization and measurement of the frequency-
tunable RF power amplifier is the subject of this chapter. The frequency-tunable
behavior could not be observed in the characterization of the integrated circuit at 3.7
and 5.2 GHz because of the low coupling factor of the integrated coupled inductors.
A hybrid implementation using an integrated stand-alone CMOS power amplifier
designed for test purposes, a discrete commercial RF transformer, and a discrete
bipolar transistor to control the current in the secondary winding of the transformer
was carried out. The circuit was designed for operation at 200 and 300 MHz. The
measurements have shown that at 200 MHz a relative improvement in efficiency
of a factor of 1.4 was achieved. Moreover, less distortion was generated with the
proposed tunable output matching network. The hybrid implementation allowed us
to demonstrate the feasibility of the frequency-tunable RF power amplifier based on
coupled inductors.
7.1 Introduction
This chapter begins, in Sect. 7.2 , with the characterization of a stand-alone PA equal
to the oned used as the core of the frequency-tunable amplifier. It continues then
with the description of the characterization procedure for the integrated coupled
inductors in Sect. 7.3 . As seen in the previous chapters, the coupling factor and
the value of the inductors are of major importance for the operation of the tun-
able PA. The measurement of the tunable PA is presented in Sect. 7.4 . The results
obtained were unsatisfactory. Hence, a hybrid implementation using the integrated
stand-alone CMOS PA, discrete coupled inductors, and a control circuit built with a
discrete bipolar transistor was carried out to validate the concept. This is the subject
of Sect. 7.5 .