(A) high-performance fast switching charge dump assisted class-K* audio amplifier and a PLL-based high-stability single-inductor multiple output DC-DC buck converter

Abstract

In this thesis, an audio amplifier and a single-inductor multiple output DC-DC buck converter are introduced. A fast switching charge dump amplifier and a PLL-based multiple output bang-bang control are applied to a Class D audio amplifier and a DC-DC buck converter, respectively. Firstly, a new $Class-K^{\ast}$ audio amplifier with high power efficiency and high fidelity is integrated in a $0.35- \mu m$ CMOS process. It proposes a new topology connected Class-D amplifier with Fast-Switching Charge-Dump (FSCD) amplifier in parallel. The integration of the amplifier requires neither analog buffer amplifier nor a complex compensation circuit needed in hybrid audio amplifier (Class K). The FSCD amplifier composed of comparators and switches works at a high switching frequency in order to absorb the distortion caused by Class-D amplifier switching. Thus, this assists the audio amplifier to have good linearity under switching operation. With the proposed topology, the audio amplifier has a flat frequency response with -3dB bandwidth of 60 KHz, and is capable of delivering up to 257 mW into $4.1-\Omega$ load with maximum efficiency of 81%. A typical total harmonic distortion plus noise (THD+N) is less than 0.1% at the power level over 25 mW within the audio frequency range ($20 Hz \sim 20 kHz$), and the minimum THD+N is 0.025% with the audio input frequency of 1 kHz at the output power of 114 mW. Secondly, a single-inductor multiple output DC-DC buck converter employing $\It{PLL}$-based Multiple-output Bang-bang (PMB) control is presented. The DC-DC converter can operate at a fixed high frequency by adjusting current-information in the $\It{PLL}$-loop. The distinctive feature of PMB control comparing with other conventional current mode PWM controls is that it is free from stability problem and shows fast and accurate regulation against arbitrary load-current change as well as input voltage change because the DC-DC converter is basically controlled on the basis o...