The Study And Design Of Class D Audio Power Amplifier

With the fast development of portable electronic device market, Portable electronics such as MP3player, DVD players, mobile phone and so on, face the challenge to extend battery run time. Compared with the traditional Class AB linear power amplifier, Class D amplifier has the merits of lower power dissipation, higher efficiency, smaller volume, smaller PCB area and lower cost, so Class D amplifier will replace traditional class AB amplifier absolutely in most of cases. It is therefore of great importance to study it.In this paper, a PWM-modulated Class D audio amplifier used in Portable electronics is implemented. First of all, I introduce the various kinds of power amplifiers, to analyze advantages and disadvantages of them, and then carried out a detailed analysis of he working principle, sampling method, system model, the negative feedback effect on the total harmonic distortion (THD) of Class D audio power amplifier, finally the entail structure of the Class D audio power amplifier had been presented. It has some feature:Using noise shaping of the negative feedback to improve the system of linearity and lower distortion of the system; the new filterless PWM modulation scheme and fully-bridge output had been used to save the filter only using inductive speaker to restore the audio signal, it can save the size and cost of application circuit. This Class D audio power amplifier is based on CSMC0.5μm CMOS technology of double-poly-double-metal (DPDM), the detail analysis and design of each module had been carried out. The circuit simulation and verification are finished by Cadence Spectre tool. The hole circuit including the bandgap reference, the fully differential operational amplifier, PWM comparators, triangle-wave oscillator, driver circuit, power output circuit, over-current protection circuit, over-temperature protection circuit, and under voltage lock out circuit, and so on. The simulation result show that the chip operates perfectly under supply voltage ranging from2.7V to5.5V The output power can reach2W when4Q load and efficiency is75%when8Ω,387mW output power on the condition of supply voltage5V. The quiescent current is1.914mA without load and shutdown current is less then0.5uA. The amplifier mainly used in portable products of low output power.