A Study Of High Integration Density Filterfree CMOS Audio Class-D Amplifier

The rapid development of consumer electronics,has made low-power and high power efficiency become the design destinations of portable electronics.Therefore in the field of audio power amplifier,compared with linear power amplifier,with characteristics of low power consumption and high efficiency,class-D power amplifier can significantly improve the use-time of portable electronic audio products,resulting in being more prevalent among the designers and the users.However the class-D power amplifier doesn't behave well in terms of linearity,noise and efficiency.A lot of researches are still needed.Hence researching and designing a class-D audio power amplifier which owns good performance and satisfies the user's requirements,have an important research and application significance.This article adopts three techniques to reduce the THD of class-D power amplifier and improve efficiency.Firstly the filter-free modulation technique is used to optimize PWM modulation method and reduce the chip power consumption when the differential input signal is around zero,resulting in improving the efficiency and avoiding the use of additional filter as well as reducing the chip area and cost.Secondly,the negative feedback technology is utilized to shape the noise in audio frequency bandwidth,improving the total harmonic distortion?THD?of the system and power supply rejection ratio?PSRR?,which represent the audio quality.Thirdly,the Pop-Click noise suppression and ACF?Anti-Clipping Function?are introduced.The former can effectively inhibit Pop-Click noise during power-on and power-off time.In the meantime when the input signal is too large,leading to the output signal clipping,the latter is able to automatically adjust the system gain to control output signal reaching maximum but not clipping,greatly improving the sound quality.A high integration density,no-filter,CMOS class-D amplifier is proposed in this article,implemented in CSMC 0.5um CMOS technology.The signal channel includes bandgap reference and bias circuit,pre_amplifier and integrator,PWM comparator,the output driving circuit and power tube.The over-temperature protection,over-current protection and under-voltage protection circuits are also designed to protect the power amplifier.Along with the introduction of the circuit,the detailed analysis and simulations of all modules are followed.Finally,the whole simulations of the class-D power amplifier are provided.The class-D amplifier driving a 4ohm load resistor achieves the input refered noise of 65?V/??Hz?,the efficiency of 89%(P_OUT=1W),the largest distortion output power of 3.8W?THD+N=10%?and the THD of 0.08%(P_OUT=1W)with a 5V power supply voltage.At the same time,through the timing simulation,anti-clipping function?ACF?can automatically control the gain of system when the clipping occurs to eliminate this phenominon.The filter-free CMOS D audio power amplifier designed in this paper can be used for various consumer electronics products.