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Control Techniques for Audio Envelope Tracking

One of the main applications for class-D audio amplifiers is portable or battery-operated devices such as Bluetooth speakers, smartphones, car stereos, etc. These devices often use a boost converter to increase the battery voltage to a suitable level to achieve the desired power output. The use of envelope tracking (ET) has been shown to significantly improve the efficiency of a class-D audio amplifier, particularly at lower power levels. However, modulating a boost converter to provide envelope tracking at a high bandwidth is complicated due to the right half-plane zero in its transfer function. This paper discusses the effect of envelope bandwidth on the overall system performance, and how it affects the control of the boost converter. It also discusses the different control methods for boost converters, and variations of this type of DC/DC converter.

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