TABLE OF CONTENTS In Chapters 5 and 6, we studied the transistor as a small-signal device. Y and S parameters were introduced as a means of facilitating amplifier design, and design equations were provided. When the transistor is used as a large-signal device, however, these equations are no longer valid. In fact, bothY and S parameters are called small-signal parameters, and should not be considered in the design of RF power amplifiers. After looking at basic power transistor characteristics in detail, we ll cover the leading semiconductor materials used in today s RF power ICs.
Instead of specifying the Y and S parameters for a power transistor, manufacturers will typically specify the large-signal input impedance and the large-signal output impedance for the device. These parameters are typically measured on the device when it is operating as a matched amplifier at the desired DC supply voltage and RF power output level. A matched amplifier, in this case, refers to a condition in which the input and output impedances are conjugately matched to the source and load, respectively.
Pertinent design information for RF power transistors is usually presented in the form of large-signal input and output impedances, as shown in Fig. 7-1. Fig. 7-1 is a data sheet for the Freescale (formerly Motorola) MRF233 RF power transistor. This particular data sheet was chosen for instructional purposes because it includes both series- and shunt-impedance information. This gives the circuit designer the opportunity of using...
