Analysis of switching frequency variation in self-oscillating class-D audio amplifiers
In this letter, a mathematical model in self-oscillating class-D audio amplifiers is proposed to describe the switching frequency variation as a fuction of the modulation depth. It is alleged in a very simple form which can be applied to any general structure adopting phase-shifting in the feedback filter, time delay of the loop, and the hysteresis window at the comparator. The main focus is set on the analysis of the phase-shifting filter which shows the least dependency on the modulation depth, which is not yet revealed.
Efficient approximations for the arctangent function
This paper provides several efficient approximations for the arctangent function using Lagrange interpolation and minimax optimization techniques. These approximations are particularly useful when processing power, memory, and power consumption are important issues. In addition to comparing the errors and the computational workload of these approximations, we also extend them to all four quadrants.
Globally Modulated Self-Oscillating Amplifier with Improved Linearity
Self-oscillating amplifiers are commonly classified into two categories: hysteresis-controlled (HC) oscillation and phase-shift controlled (PSC) oscillation. Yet it has been amply shown that both categories are not fundamentally different [1]. They are only so classified based on the analytical method that works best to predict their behaviour. The classic 360o phase shift criterion used to determine the idle switching frequency of PSC amplifiers is known to be inexact and incapable of predicting the modulation dependent switching frequency. The piece-wise linear time-domain approach used to understand HC amplifiers (such as used, for example, in [2]) does predict the exact oscillation frequency in function of modulation index but becomes inexact as soon as the loop pole is not at DC or when loop order >1.