Application of high-efficiency class D audio power amplifier in portable equipment With the increasing tension of energy sources, the requirements for energy efficiency of electronic systems are gradually increasing, especially for battery-powered systems, which have more stringent requirements on power consumption. With the popularity of mobile phones, MP3 / 4 and other multimedia portable devices, audio power amplifiers have become the standard configuration of the audio part. Both system engineers and end users are no longer satisfied with playing personalized music loudly, and then put forward higher requirements for audio power amplifiers: consume less current to extend battery life, provide in the entire audio range Perfect sound quality, good radio frequency suppression capability reduces current sound, and stable output power to ensure that the speaker is not damaged. In the future, the market's demand for high-efficiency class D power amplifiers will gradually increase, and the application of class D amplifiers in portable devices has very broad prospects. According to a report by market research firm Gartner: Class D amplifiers will grow at a compound annual growth rate of 15.6% from 2006 to 2011, from US $ 334 million to US $ 688 million. The main growth drivers are portable devices and space constraints Of consumer electronics, the mobile phone market is an important growth point. This article introduces a high-efficiency Class D audio power amplifier BL6311 developed by Shanghai Belling. This product is applied to portable devices such as mobile phones and requires only a few external components to provide a perfect solution. BL6311 application schematic The requirements of portable devices for audio power amplifiers are small size and simple peripheral circuits. BL6311 can be configured into single-ended input (Figure 1) and differential input (Figure 2) according to system requirements. Features of BL6311 1. High efficiency and energy saving Compared with linear amplifiers (Class A, Class B, Class AB), Class D amplifiers have great advantages in power efficiency. For linear amplifiers, the linear operation of the bias element and the output tube will consume a lot of power, and the output tube of the class D amplifier works in the switching state. The power consumption mainly comes from the on-resistance of the output tube, the switching loss, and the quiescent current. The efficiency can reach 90%, without heat dissipation, thereby extending the battery life and life of portable devices. 2. RF noise suppression Mobile phones, personal digital assistants (PDAs) and other portable communication devices often work in harsh environments with considerable noise. For audio amplifiers that do not solve RF interference, the RF carrier information will be demodulated to the audio frequency band. Unexpected current sounds will be generated at the output. The RF signal will be coupled to the power supply, input and output of the amplifier. The good PSRR and CMRR of the amplifier can reduce the requirements on the system PCB and structure, minimize the current sound, and ensure the normal operation of the device. Generally, the output of 10mV can be felt by the human ear, and as shown in Figure 3, when the GSM signal of 500mV is superimposed on the power supply voltage (VDD), the output terminal (Vo) of the BL6311 is still well suppressed. 3. Very low distortion and noise For audio amplifiers, although all the test indicators are measured by sine waves, the final judge is still beautiful and smooth music. The beautiful timbre depends on less harmonic distortion and noise. The ideal Class D amplifier has no distortion, no noise in the audible band and the efficiency meets 100%. However, the actual Class D amplifier is not perfect, and there will be distortion and noise. This is due to the distorted switching waveform generated by the Class D amplifier. The reasons are as follows: > PWM modulator's non-linearity of PWM signal due to sampling frequency limitation and time jitter; > Dead time, turn-on time, turn-off time, rise and fall time of power drive tube; > Non-ideal characteristics on switching devices, such as on-resistance, limited switching speed and body diode characteristics; > Parasitic stray parameters cause excessive edge oscillations; > Non-linearity of the output low-pass filter. BL6311 solves the above problems well. Figure 4 shows the frequency sweep curve of THDN. It can be seen that BL6311 has a low distortion in the entire audio range, which can meet the sound quality requirements of portable devices. Because BL6311 has high efficiency, low distortion and strong RF noise suppression ability, it is especially suitable for applications such as mobile phones and other portable products. Figure 5 is a block diagram of BL6311 application in mobile phones. Contributed by Shanghai Belling Co., Ltd.
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Figure 1 BL6311 single-ended input application schematic
Figure 2 BL6311 differential input application schematic
Figure 3 BL6311 has a suppression effect on the GSM signal coupled into the power supply.
Figure 4 BL6311 THDN vs Frequency
Figure 5 BL6311 application in mobile phones. 