Digital audio power amplifier based on DPPC2006
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Abstract: A digital audio power amplifier based on DPPC2006 is designed by direct digital amplification technology. The system uses high-speed VMOSFET to form a complementary structure of H-bridge. The control function is realized by AT89S51. The test results show that the maximum undistorted output rate of the system is greater than 6W. The average efficiency can reach 73.24%, and the cost performance is higher.Keywords : digital power amplifier; DPPC2006; PWM; AT89S51
introduction
As the digitalization of electronic products continues to evolve, the digitization of audio equipment, especially the key product power amplifiers, is on the agenda. At present, many power amplifier products on the market have played the banner of “digitalâ€, but many of them only carry out some digital processing on the products. In the strict sense, they can only be called digital power amplifiers. The real audio signals are still analog. Digital power amplifiers refer to In the processing of the signal, the digital audio signal is used, and the signal is amplified by the switch. The biggest feature of the digital power amplifier is high efficiency, greatly reducing the requirements for power supply and heat dissipation, and also having large output power, wide frequency response, and volume. Small, high signal to noise ratio and other advantages. The author designed a pure digital power amplifier that uses direct digital amplification technology, processed by a dedicated audio signal processing chip DPPC2006, and then amplified by a H-bridge complementary symmetrical circuit composed of high-speed VMOSFETs.
Circuit composition
The scheme consists of the front and the rear stages. The digital signal processed by the DPPC2006 is converted into a PWM wave output, and the latter stage is composed of a high-speed VMOSFET H-bridge complementary symmetric amplifier circuit and a low-pass filter. The analog-to-digital converter is also used. (ADC) CS5333 achieves compatibility with analog signals. The single-chip AT89S51 performs volume control, display, channel, mute and other control functions. The whole machine is shown in Figure 1.
Figure 1 Digital audio power based on DPPC2006
How the chip works
The digital power amplifier processing chip DPPC2006 is a Hi-Fi level all-digital 6-channel audio power amplifier encoding and processing chip with complete independent intellectual property rights in China. The chip has 6 channels of all digital (PCM) input and independent pulse width coding (PWM) output; each channel volume can be adjusted independently, 124 levels can be adjusted; 352.8kHz or 384kHz high-speed switching frequency; support 24bit multi-pulse pulse Differential encoding, noise shaping, balanced bridge and other technologies; 6-channel data input, sampling rate supports 32kHz ~ 768kHz; built-in S / PDIF receiver, sampling rate support 44.1kHz ~ 96kHz; built-in input data set selection circuit; power supply + 3V ~ +5.5V; package form is QFP100A.
Main Specifications
Frequency response ±0.5dB (20Hz ~ 20kHz); dynamic range 95dB; total harmonic distortion <0.02%. The chip can directly receive CD, DVD and other digital audio source output coaxial or optical digital audio signal, all digital signal amplification processing, A single IC can amplify 6 channels, separated by front and rear stages, and different MOSFETs can be used in the latter stage to achieve different output power. The digital power amplifier circuit composed of DPPC2006 is simple and fully functional, and its input can be selected separately for fiber and coaxial. Data, CD, VCD, DVD and other internal DATA, BCK and LRCK format data can also be selected, and can also support high sampling rate data input; no digital signal input, external audio A / D converter can also Input DPPC2006 is available for selection and the application is very flexible.
Analog signal compatibility
In order to be compatible with common analog signals, the digital input interface of DPPC2006 can receive the data output by the serial ADC. As long as the digital audio data input in the format shown in Figure 2 can work normally (the left and right alignment is selected by the DP pin configuration of DPPC2006). In this solution, CIRRUS's 26bit, 96kHz stereo audio dedicated analog-to-digital converter CS5333 is used.
Figure 2 Serial Audio Data Format
Post-stage PWM amplification
The complete post-stage PWM amplification consists of a MOS tube H-bridge complementary symmetrical amplifier circuit and a low-pass filter (LPF). The actual circuit is shown in Figure 3 (there is only one channel in the figure). R307, C303, L303, C307, C308 is the EMC component; L301, L302, C304 are the filter circuits; R308 and C305 are the speaker matching circuits.
1) H-bridge amplifier circuit. Here U6 is the input driver of FET. The circuit uses 74HC541 or Tianao DB802 chip. Select MOSFET with different current to get output power of 80W~300W.
Figure 3 Rear stage PWM amplifier circuit
2) Low-pass filter. A second-order LC filter is used, which requires the upper limit frequency of the filter to be ≥20 kHz, and the characteristics are substantially flat in the passband. After simulation by EWB simulation software, the better parameters of L and C are L301=L302=22μH and C304=0.47μF.
Function control
The control of DPPC2006 is realized by 51 series single-chip microcomputer AT89S51, which completes the operation of chip mode setting, channel selection, volume control and display. The MCU has an ISP (programmable in system) function, which can be developed online directly through the download line. It is very convenient to use. The process flow of the MCU control program is shown in Figure 4.
Figure 4 MCU control program flow chart
Waveform and test results
1) PWM waveform: The PWM output waveform is shown in Figure 5. In the figure, a) is the unmodulated PWM output waveform, b), c) is the modulated PWM output waveform. As can be seen from Figure 5, the input signal amplitude The change has been transformed into a change in the output pulse width.
2) Power efficiency. The power efficiency is shown in Table 1. As can be seen from Table 1, the average efficiency η = (76.8 + 66.0 + 76.9 + 68.8 + 7717)% / 5 = 73.24%. From the test data, compared with the traditional analog power amplifier, The efficiency of the digital power amplifier is greatly improved. The efficiency of the power amplifier and the maximum undistorted output power are also different from the theoretical calculation values. This is caused by the static loss of the H-bridge output circuit and the drive circuit, especially when the power is output. More obvious.
Figure 5 DPPC2006 chip PWM output waveform
Conclusion
The system uses the dedicated digital audio signal processing amplifier chip DPPC2006 adopting direct digital amplification technology (DDX) as the core, and can directly input S/PDIF coaxial or optical digital signals. After internal calculation, the PCM signal is converted into PWM signal and transmitted to high speed. The complementary symmetrical H-bridge circuit formed by the VMOSFET tube amplifies and outputs the amplified dual-channel audio signal. At the same time, the expansion interface is reserved, the input is compatible with ordinary analog signals, and the output can be easily extended to surround 6 channels. By using different MOSFETs, it is easy to get an output power of 80W to 300W. In theory, the average efficiency can reach more than 90%, and even the post-amplifier tube does not need a heat sink at all. Use MCU for flexible control, achieve mute, digital volume adjustment, display and other functions. Can be applied to DVD player built-in amplifier, car amplifier, high-end desktop audio, computer multimedia and various multi-channel AV amplifier design, cost-effective, very Broad application prospects.
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