A Fully Differential Digital Input Class D with EMI Spreading Method for Mobile Application

Remy Cellier(1,3), Emmanuel Allier(1), Carlo Crippa(2), Rossella Bassoli(2), Gael Pillonnet(3), Angelo Nagari(1), Nacer Abouchi(3)
(1) ST Ericsson, Grenoble, France. (2) ST Ericsson, Agrate, Italy. (3) Institut des Nanotechnologie de Lyon (INL) CPE Lyon, Lyon, France.

Class D audio amplifiers are widely used in embedded systems to achieve high efficiency. Digital class D accepts bit stream as input signal to drive loudspeakers. Major drawbacks of such systems are the nonlinearity due to the switched behavior and EMI radiations issued from the output low pass filter. This paper presents a digital class D amplifier with a local analog feedback loop to improve performances of the power stage and digital method to spread output spectrum in order to reduce EMI radiation. The amplifier, including digital modulator and analog power stage, was integrated in a single chip in 0.13 m CMOS technology. The silicon results confirm the validity of the theoretical analysis.

Conference sponsors: