High frequency waveform engineering and its applications: Tutorial 54

It has been established that the terminal radio frequency (RF) current and voltage (IV) waveforms are the unifying theoretical link between transistor technologies, circuit design, and system performance, and therefore, greatly influence the radio frequency power amplifier's (RFPAs) performance [1]. Thus, it has become necessary to carry out detailed analysis of the time-varying RF voltage V(t) and current I(t) waveforms present on the device terminals for optimizing the output power and dc to RF power conversion efficiency of RFPAs. Alternatively, it can also be said that it has become a standard practice to identify the mode of operations of RFPAs by analyzing the V(t) and I(t) waveforms measured or simulated at the intrinsic terminals of the transistor. For example, Class A and Class F power amplifiers are represented by their respective current and voltage waveforms, as depicted in Fig. 1. It is apparent that in Class A, both the current and voltage waveforms are sinusoidal about the bias point, whereas in Class F, the current waveform is a half-wave rectified sinusoid, and the voltage waveform is a square wave [2], [3]. To experimentally support these established theoretical postulations with regard to current and voltage waveforms, there is a need for Waveform Engineering systems. In principle, waveform engineering is the ability to modify, in a quantified manner, the time-varying current and voltage waveforms present at the terminals of the transistor devices by changing the fundamental and harmonic impedances seen by the intrinsic transistor's access points. Effectively, the waveform engineering systems consist of two aspects, namely a waveform measurement component [1], [4], [5] and impedance tuning elements called the load-pull systems [6]-[8].