Waveform engineering: State-of-the-art and future trends (invited paper)

Abstract

The term waveform engineering denotes all those circuit design techniques that are based on shaping the transistor voltage and current waveforms. From a general perspective, these design techniques can be grouped in two main categories according to the adopted design tool: measurement- and model-based. In the last two decades, thanks to the proliferation of setups enabling calibrated waveform acquisition at microwave frequencies, waveform engineering has attracted continuously increasing interest in the microwave engineering community. In this article, a comprehensive analysis of the waveform-engineering based design techniques is reported, paying particular attention to the advantages and drawbacks associated to each approach

Efficiency enhancement by employing the transistor nonlinear capacitors effects in a 6W hybrid X-band Class-J power amplifier

“…Employing the efficiency enhancement methods, which can effectively reduce the transistor power dissipation and thus, increase the reliability and median lifetime of the device, is essential for high power applications. Several topologies have been proposed for realization of high efficiency PAs . Reduced conduction angle PAs such as Class‐C PA, can provide high efficiency but they do not have sufficient output power and suffer from nonlinearity problems.…”

“…In the inverse Class‐F PA, the drain voltage is formed as a half‐wave sinusoidal waveform whereas the drain current has a square waveform. Class‐F and inverse Class‐F PAs provide high efficiencies, but they usually suffer from limited bandwidths . In addition, the realization of matching networks at the third harmonic and higher harmonics is not practically possible at higher frequencies …”

“…Several topologies have been proposed for realization of high efficiency PAs. [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] Reduced conduction angle PAs 18 such as Class-C PA, can provide high efficiency but they do not have sufficient output power and suffer from nonlinearity problems.…”

“…The switching PAs such as Class-E and Class-D are well known for their ability to increase the efficiency; however, they cannot easily be realized at X-band frequencies. 19,20 In harmonic tuned PAs, [21][22][23][24][25][26][27][28][29][30][31] accurate shaping of the transistor drain voltage and drain current minimize the dissipated power in transistor. In Class-F PA designs, using a large number of harmonics, the drain voltage and drain current are shaped as a square and half-wave sinusoidal waveforms, respectively.…”

“…Class-F and inverse Class-F PAs provide high efficiencies, but they usually suffer from limited bandwidths. 22 In addition, the realization of matching networks at the third harmonic and higher harmonics is not practically possible at higher frequencies. 23 A Class-J PA was recently presented in Ref.…”