An Advanced Spread Spectrum Architecture Using Pseudorandom Modulation to Improve EMI in Class D Amplifier

Abstract

With the purpose of reducing the radiated power per unit bandwidth for monolithic Class D amplifiers, an advanced digital spread spectrum technique utilizing a linear feedback shift register to apply modulation on the system clock when radio equipment is independently designed is proposed in this paper. Peak power reduction of more than 12 dB is measured with a frequency deviation of 20% by control strategy called pseudorandom modulation. The amplifier meets the FCC class B standard for radiated emissions without any LC filtering. It can accomplish this without any degradation to the other audio performance. The active area of the spread spectrum clock generator is 191 × 251μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , which is about 2% of the die size and the designed maximal power from simulation is only 10.08 μW at 3.6 V.