Conjugate Matching S para?
—Contrary to some early articles on Mosfet circuit design, Polyfet has found that small signal impedance parameters are not suitable for the design of a large signal device. It is not to say that if a suitable circuit design exists, the insertion of an S parameter file will generate simulation results similar to the small signal response of the amplifier, but the design of the circuit cannot be accomplished with small signal data. In power amplifier design the output match is not the conjugate of the output impedance of the device. The output match is primarily a load impedance that takes into account the supply voltage swing available, the desired power and device saturation current. Likewise, the input impedance is a direct function of the output load impedance so one must start at the load line and work back toward the input match. The published S parameter data is measured with a load of 50 ohms and typical power load lines are usually between 2 and 6 ohms. 9.
