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.
A phase-shift self-oscillating stereo class-D amplifier for battery-powered applications
This paper presents a highly efficient stereo audio amplifier, based on a self-oscillating modulator. This modulation scheme has been analyzed and shows to have a higher bandwidth and error correction than standard Pulse Width Modulation (PWM). A practical implementation in CMOS 0.25um technology has been done to validate our theoretical and simulation results, based on a modified PWM amplifier. Our amplifier demonstrated a Total Harmonic Distortion plus Noise (THD+N) as low as 0.007%, current consumption is 3.88mA at 3.6V (stereo) and the efficiency reaches 88% into 8Ohms. The integrated circuit measures 1.6×1.6mm and is able to work at supply voltages from 2.3V to 5.5V.
Another contender in the arctangent race
Fast and accurate methods for computing the arctangent of a complex number x = I + jQ have been the subject of extensive study because estimating the angle /spl theta/ of a complex value has so many applications in the field of signal processing. Practitioners interested in high-speed arctangent computations typically use look-up tables where the values of I and Q specify an address in read-only memory (ROM) containing an approximation of angle /spl theta/. In this paper, another method to compute the arctangent approximation is proposed that uses neither the look-up table nor high order polynomials.