TABLE OF CONTENTS It seems that a chapter devoted to the nonlinear effects in RFPAs would not be complete without showing some actual measurements. The difficulty is what to measure, given the multitude of modulations standards and regulatory specifications, both of which are in any case in a continuous evolution. When dealing with a real PA rather than the more in-vogue virtual variety, there will always be effects which are visible, do not comply with theoretical expectations, and demand further explanations. One can thus quickly lose sight of the original objectives. The goal in this section is to show a few typical measurements which illustrate some of the more theoretical concepts discussed in this chapter, but it is not possible to do this comprehensively. The sample amplifier is a two-stage 2 GHz LDMOS PA. At the 1 dB compression point the output power is 45 dBm (30 watts), and the efficiency of the output stage is 55%. These are typical numbers for an amplifier using LDMOS devices at this frequency.
Figure 9.40 shows a set of output spectra, measured using a single channel IS95 forward link signal, having a PAR of 6.5 dB (see Figure 9.32). The maximum drive condition has been set such that the highest peaks cause the amplifier to reach its 1 dB compression point, causing an ACP level of about ?35 dBc. The mean efficiency is about 17% at this level, which represents about a 7 dB power backoff from the...
