The sound quality of digital amplifiers has been plagued by many people. The bass is good and the treble is harsh. In fact, we found this problem in the process of developing products. We return to the principle of digital power amplifier: The audio signal (20~20K) is modulated by a PWM, then the PWM signal is amplified by a switching power amplifier circuit, and finally the PWM signal is filtered out through the filter, so that A high-powered audio signal can directly push the speakers. This modulation process is the key to digital power amplifiers. Generally, the PWM frequency of several popular digital amplifier schemes is working in the range of 300K~500k, and some bass runs even at frequencies below 100K. The higher the operating frequency, the harder it is to select the switch tube. If the speed of the switch is slower, it is easy to generate heat. If you want to reduce the heat, you need to increase the dead zone and increase the dead zone, which will cause the distortion to become larger. This is a dilemma. Therefore, the use of extremely fast switching tubes is the first priority of digital power amplifiers. The sampling frequency of the digital power amplifier directly determines the sound quality. This is an important phenomenon we found in the process of developing digital power amplifiers. For a simple example, this principle should be well understood. Assume that the PWM switching frequency is 300K (300~450K is the most common frequency of digital power amplifiers on the market today) 1. If a low frequency signal of 20HZ is input, it is equal to dividing a low frequency signal period of 20HZ into 15000 sampling points. This sampling point is enough to perfectly express a positive Xuan wave waveform at the output, and the bass can be well received. which performed. 2. If you input a 1K IF signal, then it will generate 300K/1K, which is 300 samples per cycle. This is acceptable, but it has begun to deteriorate. 3. If you input a 20K IF signal, then only 300K/20K, that is, 15 sampling points in a cycle, can not fully express a sinusoidal wave. Personally, this is the main reason why the treble is worse and worse. Let's come again. Look at how high the frequency can express the audio signal. Below is a set of tables: PWM 20 250 500 1K 2K 5K 10K 15K 20K 100K 5000 400 200 100 50 20 10 7 5 300K 15000 1200 600 300 150 60 30 20 15 500K 25000 2000 1000 500 250 100 50 33 25 600K 30000 2400 1200 600 300 120 60 40 30 1000K 50000 4000 2000 1000 500 200 100 67 50 2000K 100000 8000 4000 2000 1000 400 200 133 100 From the above table, it can be seen that if the frequency of the PWM is 100K inputting a 20K audio signal, he can only distinguish 5 signals from one cycle of 20K, which is obviously not good, and the 100K can express the signal of 1K better. There are 100 sampling points), so the digital amplifier working at 100K can only be used as a subwoofer (20~250HZ). A 300K digital amplifier can only perfectly express a high sound of 5K (with 60 sample points). A 600K digital amplifier can better express 10K audio. When the working frequency reaches 1~2M, the distortion of the high-pitched sound can be truly reduced. The reduction is not equal to perfection:) The pursuit of higher frequency is the dream of every digital power amplifier designer, but it must be based on more advanced devices ( Higher operating frequency power tube). The lower the sampling frequency, the more severe the high-frequency waveform is, and why are some low-frequency (400K) digital power amplifier distortions so low? This is mainly caused by the measurement method of distortion. The ordinary distortion measurement is input 1K signal, and the harmonic generated by 1K signal after measurement (2K 3K, 4K, 5K, etc.), 2K 4K is relatively high, that is even distortion ( The common distortion of the tube), the higher 3K5K is the odd distortion (common distortion of the transistor circuit), that is to say, the actual nominal distortion only represents the distortion of 1KHZ, and can not represent the distortion of other signal frequencies. As a result, the nominal distortion is very low, but the actual hearing is uncomfortable. You can go back and look at which table above, the digital amplifier above 300K is quite perfect for 1KHZ expression. From this perspective, it also proves the feeling of everyone, why the digital power amplifier treble is always uncomfortable. The key issue is that the fundamental frequency is not high enough. International standards of POE Switch: Poe Port,Poe Switch,Poe Switch Ethernet,Poe Power Supply Shenzhen GL-COM Technology CO.,LTD. , https://www.szglcom.com
POE is also known as a local area network-based power supply system (POL, Power over LAN) or Active Ethernet (Active Ethernet), sometimes also referred to as Power over Ethernet for short. This is the use of existing standard Ethernet transmission cables to transmit data and data at the same time. The latest standard specification of electric power, and maintains compatibility with existing Ethernet systems and users. The IEEE 802.3af standard is a new standard based on the POE of the Ethernet power supply system. It adds related standards for direct power supply through the network cable on the basis of IEEE 802.3. It is an extension of the existing Ethernet standard and the first international standard for power distribution. standard.
IEEE began to develop the standard in 1999, and the earliest participating vendors were 3Com, Intel, PowerDsine, Nortel, Mitel and National Semiconductor. However, the shortcomings of this standard have been restricting the expansion of the market. Until June 2003, the IEEE approved the 802.3af standard, which clearly stipulates the power detection and control items in the remote system, and connects routers, switches, and hubs to IP phones, security systems, and wireless LANs through Ethernet cables. The method of power supply for points and other equipment is regulated. The development of IEEE 802.3af includes the efforts of many company experts, which also allows the standard to be tested in all aspects.
The IEEE 802.3at standard was formulated in 2005 and promulgated in 2009. The 802.3at standard output power can reach 30W, and the available power at the receiving end is 25.5W.
The IEEE 802.3 working group and various manufacturer alliances launched POH-POWER OVER HDBASET in the industry at the end of 2012.
Using the current 4-Pair four-pair technology plus, the bilateral power supply can reach 60-100W power, which can be achieved by using Category 5 or 6 cables. It is used in high-definition video promotion to supply power to 42" LED TVs. According to the new regulations in 2010, the power consumption of 42" LED TVs needs to be less than 70W.
The production of 4-Pair four pairs of wires in China is low, so the industry with a long-term perspective should have the technology to upgrade from POE+ to POH as soon as possible!
[Audio Network Information]