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In recent years, the demand for efficient performance audio amplifier products, the rapid development of the Class D audio power amplifier. This paper studied the modulation of the current domestic and international mainstream class-D audio power amplifier system and technology, based on traditional PWM method to improve. Improved modulation due to the differential voltage across the load is zero in the majority of system idle time, greatly reducing the overall power consumption, at the same time without filtering the output of the current change is much reduced, and the Class D power amplifier design. No filter designed to streamline the external components, greatly reduced the volume of the system design, reduce costs, and requirements on the market in recent years increasingly thin and light portable products such as mobile phones, PDA applications. Class D audio amplifier circuit design, the first system architecture model analysis, detailed calculation and optimization of the various indicators. Analysis of class-D audio power amplifier system principle; clarify the main performance indicators of the system; determine the modulation section. Special noise applications for mobile phones, PDA, RF interference in the environment, research to improve the PSRR, SNR, THD performance circuit structure. Select a single feedback the PWM modulation structure, analysis of factors affect the system PSRR, THD, efficiency indicators to determine the system performance requirements for each module. Class D audio power amplifier circuit module design based on the system model parameters, respectively. PTAT current reference source structure to achieve due to the temperature rise caused by operational amplifier transconductance change compensation. Fully differential input op amps, fully differential integrator, to reduce the level of common-mode requirements, eliminating the need for the external BYPASS capacitor and the input coupling capacitor, which reduces noise and offset voltage input op amp circuit chopper amplifier structure. The core of the design of the PWM modulation quantify the comparator circuit, the output power transistor drive circuit, over-temperature protection circuit, etc.. Dead-time and non-ideal factors of the system, considering the dead time, the reverse recovery current and electromagnetic interference (EMI), the three trade-off relationship based on dead time optimization settings. In this paper, based on the improved PWM method to construct a practical class-D audio power amplifier chip. Internal triangular wave signal with 250KHz frequency internal reference current 10.24μA, input supply voltage range of 2.5 to 5.5V. Colleagues with the completion of all circuit module design, the use of simulation tools Cadence simulation of the whole circuit. Followed by the design of the circuit layout and tapeout CSMC0.5 micron double-crystal metal craft (DPTM). The test results show that the low frequency PSRR of 61dB, THD 0.56% (5V, 1W 1KHz) Output power P 0 2.1W (5V, THD = 10%, 1KHz), basic desired design requirements.
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