With the increasing energy shortage, the requirements for energy efficiency of electronic systems are gradually increasing, especially for battery-powered systems, which require more stringent power consumption. With the popularity of multimedia portable devices such as mobile phones and MP3/4, audio amplifiers have become the standard configuration for audio parts. No matter whether the system engineer or the end user is no longer satisfied with playing the personalized music loudly, then the audio amplifier is put forward higher requirements: it consumes less current to extend the battery life and provides the entire audio range. Perfect sound quality, good RF suppression, reduced current sound, and stable output power to ensure speaker is not damaged. This article refers to the address: http:// Figure 1 BL6311 single-ended input application schematic Figure 2 BL6311 differential input application schematic Features of BL6311 Figure 3 BL6311 has an inhibitory effect on the GSM signal coupled into the power supply. 3, very low distortion and noise > dead time of power drive tube, conduction time, turn-off time, rise and fall time, etc.; > non-ideal features on switching devices such as on-resistance, limited switching speed and body diode characteristics; > Parasitic spurious parameters cause excessive edge oscillations; > Output nonlinearity of the low pass filter. Figure 4 BL6311 THDN vs Frequency BL6311 solves the above problem well. Figure 4 shows the sweep frequency curve of THDN. It can be seen that BL6311 has low distortion in the whole audio range, which can meet the sound quality requirements of portable devices. 310V 40Ah High Voltage Lithium Battery
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In the future, the demand for high-efficiency Class D power amplifiers will gradually increase, and the application of Class D amplifiers in portable devices has a very broad prospect. According to market research firm Gartner, the compound annual growth rate of Class D amplifiers between 2006 and 2011 will reach 15.6%, from $334 million to $688 million. The main growth drivers come from portable devices and limited space. The consumer electronics market, the mobile phone market is an important growth point.
This article introduces a high-efficiency class D audio amplifier BL6311 developed by Shanghai Belling. It is applied to portable devices such as mobile phones and provides a perfect solution with few external components.
BL6311 application schematic
The requirements of audio equipment for portable power amplifiers are small size and simple peripheral circuits. The BL6311 can be configured as a single-ended input (Figure 1) and a differential input (Figure 2) according to system requirements. 
1, efficient energy saving
Class D amplifiers have a significant advantage over linear amplifiers (Class A, Class B, Class AB). For linear amplifiers, the linear operation of the biasing element and the output tube consumes a lot of power, while the output tube of the class D amplifier operates in the switching state. The power consumption mainly comes from the on-resistance, switching loss and quiescent current of the output tube. Up to 90% efficiency, no heat dissipation, extending battery life and life of portable devices.
2, RF noise suppression
Mobile phones, personal digital assistants (PDAs), and other portable communication devices often operate in harsh and noisy environments. For audio amplifiers that do not address RF interference, the RF carrier information is demodulated into the audio band so that it is on the speaker. Undesirable currents are produced at the output. The RF signal is coupled to the amplifier's power supply, input, and output. The good PSRR and CMRR of the amplifier reduce the PCB and structure requirements of the system, minimizing current noise and ensuring proper operation of the device. Generally, the output of 10mV can be felt by the human ear, and as shown in Fig. 3, when the 500mV GSM signal is superimposed on the power supply voltage (VDD), the output end (Vo) of the BL6311 is still well suppressed.
For audio amplifiers, although all test metrics are measured in sine waves, the final judges are beautiful and smooth music. The beautiful tone depends on less harmonic distortion and noise. The ideal Class D amplifier has no distortion, no noise in the audible band and 100% efficiency. However, the actual Class D amplifier is not perfect, there will be distortion and noise, which is caused by the distortion switch waveform generated by the Class D amplifier, for the following reasons:
> PWM modulators are nonlinear due to sampling frequency limitations and time jitter;
Due to its high efficiency, low distortion and strong RF noise suppression, the BL6311 is especially suitable for portable products such as mobile phones. Figure 5 is a block diagram of the application scheme of the BL6311 in the mobile phone.
Figure 5 BL6311 in the mobile phone application.