PAPER SESSION 3: METHODS AND TOPOLOGIES
Multi-Carrier Modulation Audio Power Amplifier
with Programmable Logic
Theis Christiansen(1),
Toke Andersen(1), Arnold Knott(1), Gerhard Pfaffinger(2),
Michael A. E. Andersen(1).
(1) Technical University of Denmark, Kgs. Lyngby,
Denmark.
(2) Harman/Becker Automotive Systems GmbH,
Straubing, Germany
While switch-mode audio power amplifiers allow compact
implementations and high output power levels
due to their high power efficiency, they are very well
known for creating electromagnetic interference (EMI)
with other electronic equipment. To lower the EMI of
switch-mode (class D) audio power amplifiers while
keeping the performance measures to excellent levels
is therefore of high interest. In this paper a class D
audio amplifier utilizing Multi-Carrier Modulation
(MCM) will be analyzed, and a prototype Master-
Slave Multi-Carrier Modulated (MS MCM) amplifier
has been constructed and measured for performance
and out of band spectral amplitudes. The basic principle
in MCM is to use programmable logic to combine
two or more Pulse Width Modulated (PWM) audio signals
at different switching frequencies. In this way the
out of band spectrum will be lowered compared with
conventional class D amplifiers. Analytically expressions,
simulations, and measurements result in
reduced switching frequency amplitudes using MCM
techniques. It is also shown that the Total Harmonic
Distortion (THD) tends to be compromised compared
to conventional class D amplifiers due to intermodulation
products of the switching frequencies entering the
audio band. Still, the MS MCM topology with two carrier
signals shows a 6 dB reduction of the switching
frequency amplitudes as well as THD across the
audio band below 1 percent at 55 W output power
open loop.
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