Stability Analysis of Digital Microwave Power Amplifiers

Abstract

Abstract-This work presents a stability analysis of microwave power amplifiers (PA) driven by binary pulse trains, as in the case of class-S PAs. First, using a simplified digital PA test-bench in class-D configuration, different qualitative behaviors are obtained when varying the pulse width, including subharmonic and incommensurable oscillations. The mechanisms affecting the stability properties are studied with a harmonicbalance based formulation, by means of pole-zero identification and bifurcation detection. A sufficiently high number of harmonic components must be considered, together with Krylov decomposition for an efficient computation of the inverse of the Jacobian matrix. It is demonstrated that, when varying the pulse width, distinct pairs of complex-conjugate poles may shift to the right-hand side of the complex plane and, therefore, lead to different kinds of unstable behavior. This phenomenon is related to the dependence of the critical poles on the average value of the input signal. Boundaries of the various types of unstable behavior are traced in the plane defined by the pulse repetition rate and pulse width, using bifurcation detection techniques. All the predicted phenomena have been confirmed experimentally. In a second step, the algorithms derived from the simple class-D circuit are transferred to study the stability of a more complex tri-band class-S amplifier. It has been analyzed versus the input bitrate, obtaining a fully stable behavior that has been validated experimentally.

Catalyzing satellite communication: A 20W Ku-Band RF front-end power amplifier design and deployment

“…Meanwhile, owing to challenges in current PA research, particularly around modular design, researchers have proposed various new ideas and approaches, such as the design concept of the combination of discrete and integrated modules. These approaches can enhance the balance of power amplification, matching, and stability considerations [32][33][34][35][36]. Research on low-noise techniques and modulation approaches for PAs has also garnered significant attention [37][38][39][40].…”

Common-Mode Stability Test and Design Guidelines for a Transformer-Based Push-Pull Power Amplifier

“…However, there still exist unstable points that only appear under a specific level of RF input [7], and a small-signal analysis cannot detect these oscillations. Though transient simulation is an efficient method to view the unwanted behaviors of a circuit in a large-signal regime, it requires considerable computing resources for complex designs [8]. To check its stability properly, designers should excite perturbations in the circuit, e.g., by introducing a step function in the supply as well as bias nodes.…”