Design Of An Filterless Class D Audio Amplifier Based On UPWM

With the development of semiconductor technology, all kinds ofportable terminal has become a trend of electronic equipment. Excellentaudio performance is one of the most important characteristics of theseportable terminals. Class D audio amplifier possesses the advantages withhigh efficiency, less heat, low power consumption, long battery life whichmeet the rigorous requirements of the current consumer audio-visualequipment, and also follow the future trend. With the solvement ofelectromagnetic interference and filterless, class D audio amplifier hasbeen gradually replacing the traditional ClassAB audio amplifier andtaking the market-mainstream position.An improved filterless class D audio amplifier in0.35mBCDtechnology is introduced in this paper. This new architeture base onuniform pulsewidth modulation thenology. It attenuates most of theintermodulation distortion by sampling and holding the output of loopfilter at a proper frequency combined with hysteresis comparator andfeedback control technology.This paper describe the basic classification and theory of audio poweramplifier, briefly analyze different methods in filterless structure,discussthe frequency domain characteristics of the pulse width modulation andrelevent optimization techniques in detail. Considering both the circuitcomplexity and performance, carry out a detailed analysis of eachsub-module circuit design and simulation. These sub-module includesreference circuit, fully differential operational amplifier circuit, oscillationcircuit, modulation circuit, power output stage circuit, over-currentprotection circuit and over-temperature protection circuit. After the completion of the sub-module, the system modeling and simulation isfinished. Finally, the floorplan of the layout is depicted.This design simulates in cadence-spectre emulator with HuaHongNEC BCD350process. The results suggest in the condition of powersupply5V, load8Ω: output power is1.7W; efficiency is89%; totalharmonic distortion is0.21%. The test results meet design specifications.