Huiqiao He

A novel low-power high-efficiency 3-state filterless bang-bang class D amplifier

Of the reported modulation techniques for Class D amplifiers (CDAs), CDAs based on Bang-Bang control modulation are arguably the most advantageous in terms of power-efficiency for low-power power-critical applications. To date, only single-ended and 2-state Bang-Bang control CDAs have been reported, and are hence disadvantageous because they require a bulky and costly output lowpass filter. In this paper, we propose the first-ever 3-state Bang-Bang control filterless CDA applicable to regular-power and ultra-low-power applications. Compared to other filterless 3-state CDAs, the proposed filterless 3-state Bang-Bang control CDA features the simplest hardware and the highest power-efficiency, but with somewhat compromised fidelity. Nevertheless, the fidelity thereto is sufficient for typical ultra-low-power applications such as low-to-mid performance wearable devices.

An investigation into the effect of carrier generators on power supply noise in PWM Class D amplifiers

Class D amplifiers are ubiquitous as audio amplifiers due to their significantly higher power-efficiency compared to their linear counterparts (such as Class AB) due to the digital-like switching mode operation of the Class D output stage. However, one drawback of Class D amplifiers is the susceptibility to supply noise, qualified and quantified by Power Supply Rejection Ratio (PSRR) and Power Supply Induced Intermodulation Distortion (PS-IMD). In this paper, PSRR and PS-IMD of Single-ended, 2-state bridge-tied load (BTL) and 3-state BTL Class D amplifiers based on various carrier generators are investigated and compared. We show that the design of the carrier generator is critical and should be designed according to the structure of the Class D amplifier - we show in this paper that the same Carrier Generator may result in a high >70dB PSRR in a 3-state BTL Class D amplifier but an unacceptable 1dB PSRR in a 2-state BTL Class D amplifier. The investigation and comparison provide Class D amplifier designers useful insight on design and optimization of PSRR and PS-IMD.

An investigation of THD of a BTL Class D amplifier

Class D amplifiers are routinely employed as audio amplifiers due to their high power efficiency. Total Harmonic Distortion (THD) is one of the most important parameters to qualify and quantify their performance. In this paper, THD of a commonly used Bridge-Tied-Load (BTL) Class D amplifier is investigated, including the derivation of the analytical expression for the THD of the BTL Class D amplifier. We show that in some cases, the THD of the BTL Class D amplifier is independent of the integrator gain of the amplifier — this is unlike other Class D amplifiers and linear amplifiers whose THD is largely determined by their integrator gain. Instead, the THD of the BTL Class D amplifier is largely determined by the feedback amplifier. Further, unlike the single-ended Class D amplifier whose THD increases as the modulation index increases, the THD of the BTL Class D amplifier is maximum at the modulation index = 0.5. The analysis herein provide good insight to the design of BTL Class D amplifiers, including how various parameters may be varied/optimized to meet a given THD specification.