在线座谈

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关于本次座谈

座谈简介

便携式电子产品不断推陈出新,市场瞬息万变,新产品不但要有高性能、低成本、体积小及具有独特个性等优点,而且还要比竞争产品更快推出市场。对于系统设计工程师来说,这是极大的挑战。他们都希望有一款简单易用而又有明显成效的音频电路设计,让他们可以缩短设计周期的同时,又可满足广大用户的需要。

在这个研讨会中,美国国家半导体将会探讨便携式电子产品的发展趋势,指出设计音频电路时面对的挑战,并会讨论如何利用离散式及高度集成的解决方案彻底解决这些设计上的问题,以及指出不同音频电路设计的优劣。最后,美国国家半导体会提出多个建议,让工程师可以改善音频性能,降低系统功耗,以及充分利用简单的软件落实设计。

精彩问答

主题:为便携式电子产品的音频系统挑选合适的电路设计
在线问答:
[主持人:ChinaECNet] 各位听众(网友),上午好!欢迎参加中电网在线座谈。今天,我们有幸邀请到美国国家半导体公司的专家就“为便携式电子产品的音频系统挑选合适的电路设计”举行在线座谈。在座谈中,您可就您关心的问题与美国国家半导体公司的专家在线进行直接、实时的对话交流。中电网衷心希望通过大家的共同努力,不仅能够增进各位听众(网友)对“为便携式电子产品的音频系统挑选合适的电路设计”的了解和掌握,而且能够为大家事业的发展带来裨益。  [2007-9-19 10:00:43]
[问:sduboy] 设计音频电路有哪些挑战?有无技术方面的瓶颈问题? 
[答:Henry Kwok] The Challenge is now a day a mobile phone/portable device become a multimedia playback system, digital still camera mobilephone   PDA. One system included many features together, which means a system that have multiple audio signal source. Require a system to handle.  [2007-9-19 10:22:34]
[问:zengdezhi0401] 音频系统的好坏的主要指标一般有什么衡量?谢谢! 
[答:Kenneth Lee] Generally,the jugde a audio system performance, we ususally looking at few parameters 1. The output power 2. The THD+N value   3. The PSRR 4. The X=talk    It depends on what kind of application will need difference requirements.  [2007-9-19 10:25:29]
[主持人:ChinaECNet] 我们已经进入问答阶段如果听众想重温演讲或内容可以点击下面“回顾演示”重看演讲。  [2007-9-19 10:25:31]
[问:filthdx] 差分输出线间加电容会减小共模干扰嘛吗?? 
[答:Jeff Wang] 不会。  [2007-9-19 10:25:34]
[问:baiyq] 1、请问便携设备的(耳机)音频输出级的电容值如何选择? 2、便携设备中可能用高频处理单元、射频通信单元等,这时音频电路设计中电磁兼容性主要注意哪些方面?有何技巧? 
[答:Henry Kwok] Due to the output cap & the speaker act as a HPF, the cap value should match to the -3dB point. The formula equal to 1/2pi RC. For the RF immunity, customer should avoid those interference close to these output signal path, if there still have interference, can try to add a LPF.   [2007-9-19 10:26:12]
[问:basicbear] 请问专家:国半公司推出的音效芯片与其他厂家的产品相比,最大的优势在哪里? 
[答:Jasper Lam] Our Audio Products adopted a lot of new technology help system design engineer to resolve the technical problems. It can help to reduce the cycle time for development and debug.  [2007-9-19 10:26:36]
[问:callancc] 什么时候考虑使用D类放大器?什么情况下用AB类比较好呢? 
[答:Bruce Sun] 当您把音质作为最重要的因素时,请选用AB类音频放大器。 当您把高效率,低功耗作为最重要的因素时,请选用D类音频放大器。   [2007-9-19 10:27:28]
[问:sunny7555] 在D类功放的设计上,对EMI的处理往往是工程师比较头痛的问题,请问在设计上都要注意哪些,它相对AB类功放特别要注意的地方有哪些?谢谢! 
[答:Henry Kwok] By using the new technology Spread Specturm that can help to improve. We have LM4675 for Mono, LM48410 for stereo, LM49370 for sub-system. More detail you can found in National Web Site. www.national.com  [2007-9-19 10:29:00]
[主持人:ChinaECNet] 我们已经进入问答阶段如果听众想重温演讲或内容可以点击下面“回顾演示”重看演讲。  [2007-9-19 10:29:38]
[问:zzhenhao] 便携式应用中,低音效果往往不佳,有什么方法可以改善? 
[答:Henry Kwok] The low freq. respond was depends on speaker & audio amp design. Customer should focus on acoustic box and better speaker for improve the low freq. respond. All audio amp form NS that can support 20Hz to 20KHz.  [2007-9-19 10:33:49]
[问:elmer] 方案中,子系统与分立式系统成本上有多大差别? 
[答:Kenneth Lee] The sub-system will more integrated than discreted types. It can reduce the complex of the circuitry, lesser external compoenents and more simple design.It can save the PCB space as well. So generally, it can reduce the cost in producrion point of view.  [2007-9-19 10:34:54]
[问:zzhenhao] 将来的便携式电子产品中会是D类功放一统天下吗? 
[答:Jasper Lam] Both Class AB and Class D devices will adopted for portable device per customer requirement, however, we expect higher adoption for Class D due to lower power consumption and louder sound.  [2007-9-19 10:35:02]
[问:zzhenhao] 便携式应用中,低音效果往往不佳,有什么方法可以改善? 
[答:Alice Hui] The low freq. respond was depends on speaker & audio amp design. Customer should focus on acoustic box and better speaker for improve the low freq. respond. All audio amp form NS that can support 20Hz to 20KHz.  [2007-9-19 10:38:01]
[问:Rockyw] 在为便携式电子产品音频系统挑选合适的电路设计时,需要注意哪些方面的问题? 
[答:Bruce Sun] 音频系统是容易受到干扰的系统,因此电路设计是很重要的。需要注意的地方主要有: (1)选择最合适您整个系统的音频器件 (2)去耦电容,隔直电容,滤波电容要选择好 (3)布局:音频器件,数字器件,射频部分要分开 (4) 布线:输入和输出尽量走差分线,包地,输出线要尽量短,粗。  [2007-9-19 10:38:03]
[问:chuntian23] 音频系统集成度越高,集成的各部分模块之间的干扰问题怎么解决呢,谢谢 
[答:Henry Kwok] For the Audio sub-system, all signal path we have minimized the interference internally. So that using system can help to improve SNR, PSRR kind of parameter.  [2007-9-19 10:38:05]
[问:DONG97512] 全数字音频子系统的输出是模拟还是数字?驱动扬声器前还需要处理吗? 
[答:Robert Shen] 我们有各种型号供您选择,如LM4935,它有数字,模拟的输入输出,可以直接输出1W到喇叭。  [2007-9-19 10:38:58]
[问:dule] 对于音频方面的电路设计,其实我最关注的还是对信号噪音的虑除方面,怎样去实现机械波噪声和电流噪声的虑除?还有麦克风矩阵式设计去虑除背景噪声的线路设计应该注意什么?谢谢 
[答:Kenneth Lee] It will depends on many of things. Eg. the PCB design and the compoenent performacne and the value selection. Generally, differenct value of capacitor can corresponding to differeny frequency noise reduction. The PCB trace also need to clearer and as short as possible.  For microphone array. the position of microphone is inmportant. It need to far away to the speaker and have some correlation between the microphone, but different system have different requirement.  [2007-9-19 10:40:20]
[问:paynewang] 请问一般有什么样的方法可以有效地抑制来自RF发射的TDD noise, thanks! 
[答:Henry Kwok] Using a higher PSRR performance part, those NS part have good PSRR performance, for mono general Boomer, LM4995 for SE, LM4941 for diff. input, For Class-D part, LM4673 & LM4675 for mono. Those audio sub-system LM49370 have the good PSRR as well.  [2007-9-19 10:42:51]
[问:DONG97512] NS的全数字音频子系统包括那些产品?在性能和价格上有什么特色? 
[答:Jeff Wang] 我们有很多数子的音频子系统,例如:LM49370,LM4935,LM4934... 据有丰富的输入输出接口,把手提式产品需要的所有于音频有关的功能集成在一起。具体可访问www.national.com.  [2007-9-19 10:42:56]
[问:chuntian23] 音频系统在嵌入式产品占的成本大概有多少,如手机,mp3等 
[答:Jasper Lam] Total system cost will depends on features and performance requirement.  [2007-9-19 10:44:15]
[问:lengyuezhu] 便携音频系统的一个关键设计是总谐波失真 (THD+N) ,用于度量放大器的线性,这方面NS能做到多少,有没有采用软件支持? 
[答:Robert Shen] 您说得很对。THD+N对于便携音频系统是一重要的参数。我公司的产品都有这个参数的说明。对于便携音频系统的设计选择,我们有很好的工具,请参见http://www3.national.com/appinfo/audio/ http://www3.national.com/appinfo/audio/audio_selguide.html  [2007-9-19 10:44:21]
[问:jx882003] 可否介绍几种新型的数字音频子系统芯片,比如型号、性能等? 
[答:Bruce Sun] 有很多这样的产品,列举3个型号。 LM49370: 内置扩展频谱D类扬声器放大器及蓝牙收发器专用PCM接口的音频子系统.具有18 位立体声数字/模拟转换器及 16 位单声道模拟/数字转换器。I2S 兼容的双向音频接口 LM4934:内置双通道的AB类放大器,立体声耳机驱动器,具有3D增强立体声的音效,18位数字/模拟转换器。 LM4937:内置单通道的AB类放大器,立体声耳机驱动器,18位数字/模拟转换器。 [2007-9-19 10:45:12]
[问:sduboy] 音频电路设计的好坏体现在哪些方面? 
[答:Robert Shen] 品质,体积,效率,成本。  [2007-9-19 10:46:00]
[问:lengyuezhu] 请问如何使用软件来实现音频系统的性能改善? 
[答:Henry Kwok] Software only can help on the simulation, such as frequency respond, but that need the SPEC model for help. The best thing is match to the speaker used.  [2007-9-19 10:46:10]
[问:DONG97512] 和模拟音频子系统相比, 全数字音频子系统在性能和音色上有什么优缺点? 
[答:Kenneth Lee] Functionally, digital sub-system is not need extra DAC and ADC, can support the most popular PCM and I2S audio signal. Digital sub-system also provide some simple tone controlling (internal filtering)to enhance the sound nature. The audio sound quality and performance is depends on the amplifier and also the codec resolution etc... both N.S. analog sub-system and digital sub-system can provide high quality of audio performance as well.  [2007-9-19 10:47:14]
[问:chuntian23] i2c是由谁控制的,单片机还是dsp 
[答:Jasper Lam] I2C interface can be controlled by application processors such as MCU or DSP.  [2007-9-19 10:47:31]
[问:chuntian23] 复用器起的作用主要是什么呢,谢谢 
[答:Robert Shen] 通常指的是一个通道复用多路信号。  [2007-9-19 10:47:48]
[问:zhengyingjun] MP3音频设计的特别注意事项? 
[答:Jeff Wang] 要选择高效率,体积小的音频芯片,注意芯片的布局,audio 芯片要远离开关器件。  [2007-9-19 10:48:23]
[问:wugonglzh] D类放大器对输入级的信号有什么要求? 
[答:Robert Shen] 同一般放大器,没有特殊要求。  [2007-9-19 10:49:17]
[问:apenguin] 对于Class D 放大器,在什么条件下可以采用 Filterless 的方式设计?相比于采用LC滤波器的电路,有什么不同? 
[答:Bruce Sun] 要根据您选用的D类放大器是否具有Filterless的功能,如果具备此功能,就可以用Filterless的设计,不过输出串联一个磁珠会更好。 与LC滤波器的不同在于,它利用喇叭感性负载的特性。不需要外加一个大电感,这样能够节省PCB的布板面积,也不会对信号有损耗。  [2007-9-19 10:49:58]
[问:chuntian23] 外部音源如何接入音频系统进行输出放大 
[答:Jeff Wang] 请参照Datasheet参考设计,一般要加隔直电容,输入电阻。  [2007-9-19 10:50:08]
[问:mp44] 音频系统对电源有没有特殊要求 
[答:Kenneth Lee] Generally, not special requirement. Of course a more stable and low noise power can delivery a better performance for the chips. a higher PSRR devices can maintain the performance even lower quality power supply.  [2007-9-19 10:51:32]
[问:xxtaotao] 音频设计中干扰如何避免? 
[答:Henry Kwok] To avoid interference, customer should take care the PCB layout, components placement, or using a RF suppression part. For the PCB layout, avoid the signal path close to noisily trace, if possible add an shielding ground. The same thing to components placement, don"t place the audio part close to RF. For the RF suppression part from NS, LM4941 for Mono, LM4928 for stereo, LM4946 for audio sub-system.  [2007-9-19 10:51:42]
[问:xiaoxiongminmin] NS的全数字音频子系统是否可满足超低音声道的要求?它的低频特性能低到多少赫芝? 
[答:Kenneth Lee] yes,. If no any external components influence. It can provide full audio range output.  [2007-9-19 10:52:51]
[问:chuntian23] 音频系统是如何方便升级的呢 
[答:Henry Kwok] Those Audio sub-system have the I2C/SPI ready, that easy for customer to upgrade their products by using this control bus.  [2007-9-19 10:53:30]
[问:apenguin] 对于便携式的音频产品,如何在保证音质要求的前提下,降低产品的功耗延长用户的使用时间? 
[答:Kenneth Lee] Using class D audio amplifier to increase the efficiency.  [2007-9-19 10:54:34]
[问:chuntian23] lm49370有无应用的实例 
[答:Jasper Lam] LM49370 can be used for portable application such and smartphone, GPS navigation devices, PMP...etc.  [2007-9-19 10:55:11]
[问:basicbear] 请问专家:能否详细介绍一下国半音频子系统在音效方面的技术参数,尤其是低音方面的 
[答:Henry Kwok] For sound effect, LM49370 that had FIR filter & National 3D for help.  [2007-9-19 10:55:29]
[问:rogerliu123] 用AB类功放设计,用LM4935是否合适?注意写什么? 
[答:Bruce Sun] LM4935是一个功能全面的Codec,它内置了D类的speaker放大器,AB类的耳放,还有ADC,DAC等等功能。 如果您只需要选一个简单AB类功放,LM4923LQ应该更合适。 如果您需要功能全面的带AB类功放的DAC,可以选用LM4937或LM4934  [2007-9-19 10:56:03]
[问:chuntian23] 扩展频谱是如何抑制电磁干扰的 
[答:Jeff Wang] 扩频技术采用在一定范围内随机变化的载频,降低了单点的能量。  [2007-9-19 10:56:33]
[问:feihong] 请专家介绍一下,NS的D类放大器的PSRR性能指标,特别是217Hz的PSRR指标.谢谢! 
[答:Henry Kwok] Those class-D part from NS already have the 217Hz PSRR perfromace listed on data sheet. Say LM4675 can achieve 82dB.  [2007-9-19 10:58:14]
[问:chuntian23] 音频系统如何与其他嵌入式系统连接,i2c吗 
[答:Jeff Wang] 音频子系统控制接口一般采用I2C OR SPI.  [2007-9-19 11:00:46]
[问:xinyangliu] 手提设备的音频方案很多.请问NS手提设备的音频解决方案与其竞争对手如ST,NXP等的方案相比,有什么优点和缺点? 
[答:Henry Kwok] Those portable design should focus on total system efficiency, SNR & PSRR. On this area, each vendors will have there own advantage.  [2007-9-19 11:01:38]
[问:apenguin] 对于耳机放大器的设计,NS 有什么好的IC 推荐?有什么特别的性能? 
[答:Kenneth Lee] N.S. have many H/P driver. Eg. OCL is no need output capacitor to reduce the PCB size..   eg. LM48820 is one of the new product with OCL and good performance. Pls refer to N.S. website to get more information.  [2007-9-19 11:01:38]
[问:xinyangliu] 设计音频电路时,产生噪音有几种?原因是由那几个方面造成的?如何避免这方面的问题? 
[答:Bruce Sun] 电源噪音:由电源引起。需要在音频器件的电源管脚附近加上滤波电容,越近越好,一般用0.1uF, 1uF,10uF电容。 射频干扰噪音:由射频电路造成。音频器件要远离射频放大器,天线等大的干扰源。输入和输出线要走差分平行线,尽量包地。另外,加上滤波电容和磁珠也是有效的解决方法。 [2007-9-19 11:02:47]
[问:yuefan1213] 音频系统可否与视频系统同线同时传输传输! 
[答:Henry Kwok] It"s depend on what format you are using.  [2007-9-19 11:03:05]
[问:wugonglzh] 请问专家,家庭音响系统中的5.1和7.1声道有些什么区别? 
[答:Kenneth Lee] In fact, 7.1 is two more channels to enhance the surround sound feeling. Those are the AV standard. You can also get more information from , Say THX..etc..  [2007-9-19 11:05:49]
[问:chuntian23] 音频系统的调整转换功能是如何实现的 
[答:Jeff Wang] 国半的音频子系统一般都集成混频器,即可以混频也可以切换,通过调整寄存器的值来实现.  [2007-9-19 11:06:57]
[问:xiaoxiongminmin] NS的D类放大器是否可用在手机中的5.1声道耳机? 
[答:Henry Kwok] Could you please clarify your application. For those headphone application, we consider this is very close to ear, a little bit higher in distortion, customer can feel very easly, suggest to using Class-AB.  [2007-9-19 11:07:46]
[问:sduboy] 请问便携式电子产品的发展经历了哪些阶段?其将来的发展趋势如何? 
[答:Henry Kwok] The Challenge is now a day a mobile phone/portable device become a multimedia playback system, digital still camera mobilephone   PDA. One system included many features together, which means a system that have multiple audio signal source. Require a system to handle.  [2007-9-19 11:08:58]
[问:sduboy] 音频电路设计有哪些软件开发工具? 
[答:Henry Kwok] National Webench tool is very easily to use. It"s not necessary for you to learn. You follow step-by step on website instruction then key in specification, parameters, IC selection then do simulation. That"s all. You just need a PC with Internet connection.   We support Japanese, Chinese (simple, and traditional), Korean languages.  [2007-9-19 11:09:47]
[问:tomasline] NS在POP声消除方面有何特长?效果如果? 
[答:Kenneth Lee] For audio amplifier , most of them can be used differentail input and output. it will reduce the case of charging and discharging of the capacitor. H/P drive is using OCL, it will also avoid the "pop" noise. Most of N.S. part are built in click and pop suppression internally, so the performance is good.  [2007-9-19 11:10:06]
[问:jx882003] 使用音频子系统设计电路时,对程序软件有什么要求吗? 
[答:Bruce Sun] 没有特殊的要求,标准的I2C驱动程序就可以了  [2007-9-19 11:11:20]
[问:tiger_liangbin] NS的音频放大器是否具有虚拟环绕处理功能?是那款产品? 
[答:Henry Kwok] Yes, some of NS part have the 3D effect, such as LM4888, LM48410, LM4857, LM4859, LM49370. Also some of 3D effect available for headphone only in audio sub-system, such as LM4946, LM4845 & LM4846.  [2007-9-19 11:12:25]
[问:tomasline] 手提设备对功耗有特殊的要求,NS的音频放大器在功耗或效率上有何明显的特点? 
[答:Kenneth Lee] N.S is developing more and more class D amplifier. or Class D sub-system. As Class D amplifier will increase the efficiency over 80%. so the the power dissipated is reduced much and very suitable to portable devices/products.  [2007-9-19 11:14:08]
[问:basicbear] 基于PWM方式的典型D类放大器需要外部滤波元件,会产生EMI/EMC兼容性问题,并且THD+N性能较差,因此与线性放大器相比,它的高效优势大为失色。请问专家:国半的音频子系统中D类放大器采用了哪些新技术,克服上述问题 
[答:Jeff Wang] 国半的CLASS D主要采用两种技术,固定PWM和展频.小于3瓦,一定输出线范围内,可做到不需专门的滤泼电路.THD+N于AB类相当.  [2007-9-19 11:14:08]
[问:tiger_liangbin] PCB布局是如何消除或降低音频电路的噪声?有什么好的建议? 
[答:Henry Kwok] To avoid interference, customer should take care the PCB layout, components placement, or using a RF suppression part. For the PCB layout, avoid the signal path close to noisily trace, if possible add an shielding ground. The same thing to components placement, don"t place the audio part close to RF. For the RF suppression part from NS, LM4941 for Mono, LM4928 for stereo, LM4946 for audio sub-system.  [2007-9-19 11:14:18]
[问:shabble2004] 扩展频谱技术如何实现? 
[答:Jeff Wang] It is a technique on the modulation method inside the chips. Using random switching frequency. For application point of view. Not complicated, just same circuitry and design but reducing EMI interference.   [2007-9-19 11:15:26]
[问:ljf76499671] NS在D类放大器中采用的是那种技术?是PWM吗?还是扩展频谱技术? 
[答:Jasper Lam] For latest Class D products, we are adopting both Spread Spectrum and PWM technology. e.g. LM4675, LM48410. You can download details from our web page.  [2007-9-19 11:16:45]
[问:feihong] 要建7.1声道系统,NS的那些产品能满足通道数量和性能的需要? 
[答:Kenneth Lee] N.S. high performance operational amplifier can be suitable to 7.1 ch system as the preamp stage, filtering stage or buffering stage. eg. LM4562/LME49710 etc. For high output power, N.S. have high power audio amplifier driver as well eg. LM4702 for such system.  [2007-9-19 11:18:38]
[主持人:ChinaECNet] 各位观众,现在用户提问很踊跃,专家正在逐一回答。请耐心等待您问题的答案,同一问题请不要多次提交。  [2007-9-19 11:20:46]
[问:Rockyw] 便携式电子产品的音频系统的电路设计跟以往的电路设计有什么不同? 
[答:Bruce Sun] 电路PCB的体积,效率是便携式电子产品中需要着重考虑的问题,这与以往的电路设计是不同的。  [2007-9-19 11:20:46]
[问:rogerliu123] 请问如果做AB类功放,并采用LM4923LQ,如何避免噪声的出现(包括电源系统的干扰,外围电路等),若震动的话不会对IC有影响吧?若SMT的话,失效率大概是多少? 
[答:Henry Kwok] Customer should take care the PCB layout, components placement. For the PCB layout, avoid the signal path close to noisily trace, if possible add an shielding ground. The same thing to components placement, don"t place the audio part close to RF. For the PSRR performace in LM4923 that can achieve 85dB typical, for those design is good enough, customer can direct connect the power to battery terminal. For the SMT handling, customer should follow the AN-1112 for uSMD, AN-1187 for LLP.  [2007-9-19 11:21:52]
[问:liana] 请问如何对D类放大器外部电感的进行选择? 
[答:Jasper Lam] By using filterless class D audio power amplifier, it can eliminate the external LC filter.  [2007-9-19 11:22:08]
[问:mp44] lm49370有没有中文资料 
[答:Alice Hui] Although we don"t have the Chinese version of the product details, you can still check out the product folder which has listed the block diagram and features: http://www.national.com/pf/LM/LM49370.html   The application notes of the LM49370 evaluation board is translated into Chinese and available for download from: http://www.national.com/CHS/an/AN/AN-1609.pdf  [2007-9-19 11:22:30]
[问:basicbear] 如何降低RF噪音对放大器的影响 
[答:Jeff Wang] 1)国半有芯片具有RF SUPPRESSION功能,例如LM4941,LM4946,LM4947......可以很好的帮助解决问题. 2)两个器件尽量远离. 3)加一些标准的抑制电路.  [2007-9-19 11:22:36]
[问:callancc] 耳机音频电路中如果电源部分出现欠压状况,是不是电路就要停止工作了? 
[答:Kenneth Lee] If the supply voltage is under the operation voltage range. it will stop operate. But it has a wide operation voltage range.  [2007-9-19 11:23:42]
[问:baiyq] 4、很多时候电源噪声是导致音频性能变差的原因,对此专家有何建议? 
[答:Jeff Wang] 1)采用高PSRR器件 2)音频器件电源采用较粗走线直接接电池  [2007-9-19 11:25:08]
[问:baiyq] 5、是否MIC都应按差分方式连接 ,从而消除噪声源在携带 MIC 信号的感应电气噪声? 
[答:Kenneth Lee] not a must. Some is differential and some is Single end. Of ocurse the differential one will better to reduce the noise.  [2007-9-19 11:26:05]
[问:mp44] 国半公司的音效芯片有没有评估板 
[答:Alice Hui] 是有的, 大部分更可在网上订购:http://www.national.com/store/#Audio 其他评估板可向我们的代理商查询: http://www.national.com./CHS/contacts/Details/China_map.html 或电邮 ap.support@nsc.com  [2007-9-19 11:27:00]
[问:baiyq] 6、贵公司是否提供集成功放(如2、3W)的集成音频放大器? 
[答:Jasper Lam] We had wide range of Audio power amplifier under 5W such as LM4941, LM4675, LM48510 for mono, LM4928, LM48410 for stereo.  [2007-9-19 11:28:33]
[问:chuntian23] 设计音频系统的瓶颈有哪些,谢谢 
[答:Henry Kwok] Supply voltage, those design were using one single Li-ion battery, those audio amp need higher supply voltage for output power, National have the Boomer series to focus on this, the PSRR performance is typical 55dB or above, this allow customer to connect the audio amp supply direct to battery terminal to achieve higher output power, also class-D used to improve system efficiency.  [2007-9-19 11:29:11]
[问:bestcdb] 这个产品是仅仅只用于便携式的音频系统吗?是不是还能移植到其他方面?比如车载音频系统等。 
[答:Kenneth Lee] Can be using in a wide range of application. apart from protable product. It can be use in automative like G.P.S system in car audio system.  [2007-9-19 11:29:39]
[问:xdzq132] D类放大器工作在PWM模式,如何降低它对其它器件的干扰? 
[答:Jasper Lam] We are using Spread Spectrum technology instead of fixed frequency to reduce the EMI from class D audio power amplifier. It can help to reduce interference for other devices on the same system.  [2007-9-19 11:31:41]
[问:elmer] NS在音频系统电源转换方面有什么好的降低功耗的技术? 
[答:Kenneth Lee] 1.Class D is the solution. 2.Reduce the IDDq of the IC. [2007-9-19 11:31:48]
[问:mp44] 音频系统对嵌入系统有没有要求?如速度,等 
[答:Bruce Sun] 没有特殊的要求,一般的音频系统的I2C的速度最大是400kHz  [2007-9-19 11:32:19]
[问:apenguin] Class D 放大器具有效率高的优点,但是相比与 AB 类的放大器,其音质还有许多差距.请问,NS 有什么技术可以使其在音质方面有所提升吗? 
[答:Henry Kwok] In the pass, class-D amp distortion is an issue, but with the technology improving, now a day class-D amp distortion can achieve up to 0.02% (LM4675).  [2007-9-19 11:32:23]
[问:ljf76499671] 音频功放对电源有什么特别的要求?开关电源会对其造成什么影响?如何选择? 
[答:Jeff Wang] 对电源的要求要看芯片性能.具体就是PSRR.注意开关频率远离音频频域.  [2007-9-19 11:34:32]
[问:zhengfei] 如何购买贵公司产品? 
[答:Alice Hui] 可向我们在中国的代理商购买。代理商联络资料可在以下网页找到: http://www.national.com./CHS/contacts/Details/China_map.html [2007-9-19 11:35:33]
[问:zengdezhi0401] 各种环境噪声对音频电路的影响,有哪些好的解决方案?谢谢 
[答:Robert Shen] PCB的设计至关重要。尽量采用高品质的产品,如我公司的LME49720产品设计。  [2007-9-19 11:35:48]
[问:marshel] 音频放大器的热设计如何考虑?输出功率和额定输出功率应留有多大富余量? 
[答:Bruce Sun] 要根据您的应用场合来考虑散热。 如果是大功率的系统,需要加大的散热片。 如果是便携式的系统,输出功率在5W以下的情况:良好的接地散热是比较好的方法。如果芯片封装底部有一个大的接地焊盘是最好的。 输出功率和额定输出功率之间留10%-20%就可以了  [2007-9-19 11:36:01]
[问:lengyuezhu] 随着集成度不断提高,电源电流的量级要求也日益增加,需要非常高效的DC-DC转换过程、使用效率更高的开关稳压器,但是与线性稳压器相比,开关稳压器会在电源线中产生更多纹波,这个矛盾又是怎么解决的,NS有什么比较好的芯片呢? 
[答:Jeff Wang] National have integrated DC-DC and speaker dirver chip LM48510 for handset, GPS application.  [2007-9-19 11:37:19]
[问:niuniuniu2020] 有规范指导资料吗? 
[答:Robert Shen] 很好的音频参考书:http://www.national.com/appinfo/audio/ebook.html  [2007-9-19 11:37:51]
[问:dabayi2003] 关于降低音频放大器对温度敏感性方面的问题,专家有什么好的建议? 
[答:Henry Kwok] Using class-D amp that can help to improve the effeiciency, higher effieiency means less heat generate by audio amp. We have LM4673, LM4675 , LM4674, LM48410 & LM49370.  [2007-9-19 11:38:21]
[问:lengyuezhu] 便携音频系统由于需要较小的体积,电路板的空间变得非常珍贵,针对像音频放大器这种器件,NS采用主要哪几种封装来减少占用的电路板空间? 
[答:Jeff Wang] LLP, MicroSMD, MicroSMD XT.  [2007-9-19 11:39:05]
[问:天问] 请问,对于3V电池供电的系统,采用那款音频芯片合适,音频输出除了采用BTL接法是否还有别的方法,另音频功放前段最好采用什么放大滤波电路合适。 
[答:Kenneth Lee] Most of N.S. audio amplifier can suitable to you with this supply voltage, pls refer to N.S. website to get information. Apart from BTL, SE is also popular. No specail filtering need unless you need the tone controlling as active LPF, HPF.etc.. N.S. operational amplifier is a good choose for the filtering design.  [2007-9-19 11:39:21]
[问:sunok1974] 一个带音频压缩的耳麦音频控制系统的最小功耗是多少? 
[答:Henry Kwok] Please clarify this is a headphone application or speaker application?  [2007-9-19 11:41:35]
[问:mang999] 电位器产生躁声,有替代办法吗? 
[答:Jeff Wang] Adopt digital control, I2C or SPI.  [2007-9-19 11:42:57]
[问:w.liu] 请专家简单介绍一下I2S接口,谢谢 
[答:Kenneth Lee] I2S is a audio standard format. It use 3 lines for the bi-directional transmition. 1.SDI, 2.WS, 3.CLK . Most of Base band chip or DSP, codec chip will have this interface. Higher quality audio signal will ususally use this interface as the transmittion.  [2007-9-19 11:43:53]
[问:chauvin] 现在很多半导体厂家都推出在便携式电子产品应用的音频产品。请问NS还有哪些优势? 
[答:Jasper Lam] Our performance (high output power, high PSRR, low THD+N, low EMI class D audio power amplifier), simple software control (simple output mode table) and optimized features (analog, digital inputs) on Audio subsystem can give advantages to engineer for portable products design.  [2007-9-19 11:44:05]
[问:天问] NS音频子系统的供电电压最低能到几V? 
[答:Robert Shen] 针对LM49370,有多种电压,范围也不同,1.8V到4.5V,2.5V到4.5V,和2.5V到5.5V。其他的产品型号请参见我们网上的资料。  [2007-9-19 11:44:19]
[问:elmer] NS的电源解决方案在节能将耗方面有什么优越性? 
[答:Jasper Lam] NS的电源产品线非常齐全。在节能方面主要是转换效率高的DC/DC产品,Powerwise技术。详见http://www.national.com/CHS/appinfo/power/  [2007-9-19 11:44:40]
[问:liana] 请问采用扩展频谱技术的产品在降低了EMI的同时,其他参数是否有影响? 
[答:Henry Kwok] No, the Spread Spectrum will not affect other parameter. LM4675 that can achieve 2.65W output power, 0.02% THD, 82dB PSRR.  [2007-9-19 11:45:03]
[问:basicbear] 无瞬态杂音是便携式音频设备的关键卖点,请详细介绍一下国半产品在这方面的情况 
[答:Jeff Wang] National chip integrated Advanced Click and Pop circuitry. and taking the lead in industry.  [2007-9-19 11:46:45]
[问:wugonglzh] 请问怎样减少音频信号在放大电路里的失真,应注意那几个方面.谢谢! 
[答:Kenneth Lee] Choose a lower THD+N audio amplifier. For the design, the signal trace should be as short as possible, give enough trace width for enough crrent, keep apart from noisy circuitry etc.  [2007-9-19 11:48:05]
[问:filthdx] 怎样选责输出端的接地电容 
[答:Jeff Wang] Not suggest add output cap to Gnd.  [2007-9-19 11:48:07]
[问:basicbear] 做D类放大器设计时散热方面有哪些注意事项 
[答:Bruce Sun] D类放大器功耗很小,不需要做特殊的散热。接地良好就可以了  [2007-9-19 11:48:13]
[问:guojun0718] 有DEMO版吗?如何获取? 
[答:Alice Hui] 评估板或DEMO版大部分可在网上订购:http://www.national.com/store/#Audio 其他评估板或DEMO版可向我们的代理商查询: http://www.national.com./CHS/contacts/Details/China_map.html 或电邮 ap.support@nsc.com  [2007-9-19 11:48:19]
[问:dabayi2003] 选择全数字音频放大器的标准,主要有那些? 
[答:Henry Kwok] To select a Class-D amplifier, customer should focus on efficiency, output power, distortion, PSRR & EMI performace. LM4675 that can achieve 2.65W output power, 0.02% THD, 82dB PSRR. Also Spread Spectrum used for improve EMI performance.  [2007-9-19 11:48:22]
[问:chuntian23] 如何能智能识别音频系统中哪项功能使用还是未使用呢 
[答:Kenneth Lee] From the controlling bus I2C/SPI to read the status or acknowledge from the Chips.  [2007-9-19 11:50:10]
[问:basicbear] 国半在产品中有无与Maxim的DirectDrive技术相类似或更好的技术 
[答:Henry Kwok] NS do have the Ground referenced headphone driver. Such as LM48820 , LM48821 & LM4920.  [2007-9-19 11:50:20]
[问:tshan] 我用过贵公司的LM386功放器件,他主要针对的Speek为8~16欧姆,如果采用设计40W以上的影响,而且声音与乐器分开,如何设计电路?? 
[答:Robert Shen] 建议用LME49720进行设计。  [2007-9-19 11:50:54]
[问:guojun0718] 不加散热器,D类功放能到多大的功率? 
[答:Kenneth Lee] it depends. different package and chip ahve different requirement. generally, n.S. class D chip can reach even over 2.5W without any external heat sink.  [2007-9-19 11:52:01]
[问:hzchem] LMP8100A采用引脚是多少,采用什么采用封装技术。 
[答:Robert Shen] 是14脚 SOIC NARROW封装。 [2007-9-19 11:53:06]
[问:zzhenhao] 针对便携式产品体积的制约,选用什么样的扬声器可以达到好的外放效果? 
[答:Jeff Wang] 选择扬声器与结构设计关系很大, 尽量选择发声效率高,频率范围宽的扬声器,注意音腔设计.  [2007-9-19 11:54:41]
[问:w.liu] 扩展频谱D类音频放大器的开关频率是可变的,那么开关频率的变化范围是多少?它根据什么来变化? 
[答:Kenneth Lee] Depends on the design inside the IC. Like N.S. LM4675 class D frequency range is around +/-30%  [2007-9-19 11:54:47]
[主持人:ChinaECNet] 所有问题均已提交给美国国家半导体公司的专家。座谈期间未回答的问题,美国国家半导体公司专家也会逐一回答,并在中电网上公布,请大家注意收看。  [2007-9-19 11:55:07]
[主持人:ChinaECNet] 由于时间关系,本次中电网“在线座谈”马上就要结束了。虽然各位听众(网友)已与美国国家半导体公司的专家讨论了许多问题,但是还有许多提问没有来得及进行交流。本次在线座谈结束后,中电网将请美国国家半导体公司的专家继续答复所有的来自各位听众(网友)的提问,然后整理上载到中电网网站上,以便大家查阅。  [2007-9-19 11:55:26]
[问:lengyuezhu] 如何改善音频系统的性能,降低音频系统的功耗? 
[答:Jeff Wang] 采用高效率的CLASS D.  [2007-9-19 11:55:47]
[主持人:ChinaECNet] 在此,中电网特别感谢给予本次中电网在线座谈巨大支持的美国国家半导体公司,特别感谢专门在线回答各位听众(网友)提问的美国国家半导体公司的各位专家们,特别感谢各位听众(网友)积极热情的参与。  [2007-9-19 11:56:16]
[问:jx882003] 一般的音频子系统使用的工作电源是多少,其功率是多少? 
[答:Kenneth Lee] Generally, Voltage from 2.5V to 5.5V. Generally, Output power is over 2W into 4 ohm.  [2007-9-19 11:56:22]
[问:zhangyb] NS的电源解决方案中,大功耗和低功耗时,系统噪音相同吗? 
[答:Jeff Wang] 具体要看哪种解决方案.  [2007-9-19 11:56:54]
[问:sduboy] 美国国家半导体在便携式电子产品方面有哪些完整的解决方案? 
[答:Jasper Lam] We had a lot of Audio subsystem solution for portable applications such as LM49370, LM4935 which had flexible digital and anlog inputs. You can download details from our web pages. http://audio.national.com  [2007-9-19 11:56:58]
[问:sduboy] 音频电路设计能否同时做到提升性能和降低功耗? 
[答:Jasper Lam] Yes, especially for our Audio subsystem.  [2007-9-19 11:57:18]
[问:zhangyb] 如何通过PCB的设计来降低噪声? 
[答:Henry Kwok] Avoid high switching noise trace close to signal path, using ground shielding, place the 1/2VCC bypass close to the audio amp, make sure the supply line from battery to audio amp is wide enough.  [2007-9-19 11:57:48]
[问:shabble2004] D类放大器有它的优点,但是它的缺点有哪些?如何避免或减小? 
[答:Bruce Sun] D类放大器对EMI会有一定的干扰。 解决的方法有: (1)选用带扩频技术的D类放大器,比如LM4675,LM48410 (2) D类放大器要远离射频器件。输出走线要尽量短, (3)输出端加一些滤高频的磁珠和电容 [2007-9-19 11:57:57]
[主持人:ChinaECNet] 祝大家事业有成、生活愉快!欢迎多提宝贵意见,欢迎关注中电网,下次再见。  [2007-9-19 11:58:49]
[问:baiyq] 3、耳机的阻抗如何针对音频输出级进行选择? 
[答:Jeff Wang] 要看音频输出级的驱动能力.  [2007-9-19 11:59:08]
[问:dong82511] 为什么lm25574现在不怎么好买?定货期非常长?总是走香港那边? 
[答:Alice Hui] 请问您订的是哪一个package?  请问您是否向我们的代理商订购?  [2007-9-19 11:59:28]
[问:zhangyb] 大音量时,系统噪音怎么样? 
[答:Jasper Lam] noise will increase as output increase based on SNR of system.  [2007-9-19 11:59:39]
[问:kongqi00] 现在一般手机带有耳机通话的功能,那是怎样实现的? 
[答:Jeff Wang] 有很多方法.可参照LM49370 DATASHEET. [2007-9-19 12:00:24]
[问:ljf76499671] 在汽车应用中,对EMC/ESD的要求很高,请问NS的器件能用在汽车上吗?指标怎么样? 
[答:Jasper Lam] new parts are under development for automotive applications.  [2007-9-19 12:00:26]
[问:chuntian23] 音频系统的输出功率可根据系统不同系统进行选择吗 
[答:Robert Shen] 可能不行,除非系统能改变负载或供电电压。  [2007-9-19 12:00:33]
[问:zhangyb] 加散热器,D类功放能到多大的功率? 
[答:Jasper Lam] depends on which parts that you interest.  [2007-9-19 12:01:10]
[问:niuniuniu2020] 如何寻求帮助? 
[答:Alice Hui] 如果是技术问题,可以到以下的网页填一下您的问题,我们会尽快给您答复。 http://www.national.com/CHS/support/  [2007-9-19 12:01:28]
[问:blueplanet] how to reduce the noise 
[答:Robert Shen] It is not simple to reply. PCB design, componentor selection, system choice,.. etc is important.  [2007-9-19 12:02:10]
[问:lengyuezhu] 如何利用离散式及高度集成的方案彻底解决便携式音频系统设计上出现的问题? 
[答:Henry Kwok] SNR, PSRR, components count , system efficiency & control interface. With the Audio sub-system (LM49370) used, SNR improved due to shortern signal path, PSRR can achive 60dB, components count reduced, system efficiency improve to 84%  [2007-9-19 12:03:02]
[问:xiayu1985] 请问运放电路中的单电源和双电源提供,对信号的输出有什么直接的影响?谢谢. 
[答:Bruce Sun] 单电源供电时,信号的输出都会有1/2VCC的直流偏置电压。接到喇叭,耳机负载之前都需要加隔直电容。 双电源供电的时候,输出信号没有直流偏置电压。  [2007-9-19 12:03:11]
[问:chuntian23] 49usmdxt有无应用手机上的案例 
[答:Kenneth Lee] LM4935, LM49370 mobile phone or GPS have solution already.  [2007-9-19 12:04:40]
[问:zhangyb] NS的电源解决方案在EMI方面有考虑吗? 
[答:Alice Hui] 有的。详细的资料可以在我们的电源管理网页找到: http://www.national.com/CHS/support/  [2007-9-19 12:05:56]
[问:lengyuezhu] 将来的便携,意味着体积要更小,性能要更好,但是这两个肯定是矛盾的,怎么能两者都很好的满足呢? 
[答:Henry Kwok] Due to size are reducing, Audio sub-system is the best solution, it can reduce the total components count and impoved all the paratmeter. Also that have the flexability for signal conditioning.  [2007-9-19 12:06:01]
[问:apenguin] 有些公司的Class D 放大器需要稳压电源为其后级供电以降低THD提高S/N.请问,NS 的Class D 可以使用简单的电容滤波电源吗? 
[答:Henry Kwok] All NS class-D part no exteral LDO needed, because of the PSRR performance can achieve 60dB or above, customer can connect the supply line to battery terminal directly. The supply filter cap is depends on design & loading, higher value can provide more power, small vale can filter output the high frequency noise.  [2007-9-19 12:08:46]
[问:zhengyingjun] 分立式解决方案有哪些优势? 
[答:Henry Kwok] Good for single input/output, for multiple input output, discrete solution is very complex, and the long signal path will more have the interefence caused. LM49370, LM4946, LM4947 & LM4949 is the audio system can help to improve SNR, PSRR, input/output switching & mixing.  [2007-9-19 12:12:55]
非在线问答:
[问:lzy89c55] 我选用的CPU是MSP430,请问选用哪颗带PFO的复位芯片比较好,430的复位电压是1.8V;还有电池电压3.6V的监测用哪颗芯片比较好
[答:NS专家]  
[问:shabble2004] NS的音频子系统芯片有哪些型号?价格如何?
[答:NS专家] please check details on our web page or distributors, http://audio.national.com/CHS  
[问:rogerliu123] NS 是否有GPS接收IC和DDS之类的IC推荐?是否有可以代替XC9536(通过编程,可实现不同信号的输出)的IC?
[答:NS专家] Not at the moment  
[问:cj123_yu] 音频功放?
[答:NS专家] Audio Power Amplifier  
[问:zhangyb] D类音频放大器降低音频系统的功耗能达到什么程度?
[答:NS专家] depends on output power and design, it can be 2x or 3x improvement on power saving compare with class AB. Typical Class-AB max. efficiency is around 50-60%, but class-D typcial efficiency can up to 80-90%.  
[问:bestcdb] 请问您这个电路设计的原理是什么??如何挑选最合适的电路设计?
[答:NS专家] LM49370 is design for multiple inputs and outputs Audio singalling, engineer should choose the right features, then performance  
[问:hzchem] 便携式电子产品音频放大器的选择主要有那些要求。
[答:NS专家] Operating voltage, ouput power, speaker impedance, gain setting, number of input source, number of outputs…etc  
[问:feihong] NS那款产品满足高清BD影音的播放?是否配备了HDMI接口?
[答:NS专家] We have HDMI/DVI equalizer, DS16EV5110, which can be used for long cable (>20m) application  
[问:cyberxx] 高度整合方案是指利用尽可能的集成的模块吗?
[答:NS专家] our audio sub-system is integrate of audio signal path with best performance and optimized power consumption  
[问:cyberxx] 面对电子产品高速的换代更新,贵公司对设计人员有好的建议吗
[答:NS专家] we are continuous to develop and produce new audio sub-system with latest technology to resolve technical problems  
[问:hushuyu] 声音的调解频率范围
[答:NS专家] normally from 20Hz to 20kHz  
[问:hushuyu] 设计是否复杂
[答:NS专家] system design complexity will depends on end product features and performance requirement  
[问:mp44] 国半公司的音效芯片有没有设计实例下载
[答:NS专家] we provide applications note for engineer to download from our web page, http://audio.national.com  
[问:xxtaotao] 设计模式会趋向什么方向?
[答:NS专家] integration & high efficiency is trend for high performance portable device  
[问:hnzhengshasha] 支持什么接口?
[答:NS专家] LM49370 can support I2S, PCM, mono differential input, stereo single-ended input & Microphone input  
[问:hnzhengshasha] 设计用什么系统?
[答:NS专家] software control can be develop and debug by PC software  
[问:hnxxzkx] 便携电子产品设计趋向于模块化集成化?
[答:NS专家] audio sub-system integration is trend for high performance portable applications design  
[问:hnxxzkx] 声频电路设计中贵公司提供哪些产品?
[答:NS专家] please visit our web page for details, http://audio.national.com  
[问:zhengfei] 贵公司产品价位贵吗
[答:NS专家] please contact our distributors for details.  
[问:lengyuezhu] 请问NS的音频处理系统是不是采用基于DSP和ARM的?走线方式是不是I2C的?
[答:NS专家] LM49370 did not have DSP or ARM inside, this is fully controlled by I2C interface  
[问:lengyuezhu] NS用的音频处理芯片有哪些?
[答:NS专家] most of audio sub-system, e.g. LM49370, LM4935, LM4934, LM4937, can provide audio signal processing.  
[问:Zhijie Guo] 何处可以下载到本次演讲的文档?
[答:NS专家] The seminar materials can be downloaded in www.national.com/onlineseminar after Oct 8, 07  
[问:kkkk9942] 请问电路设计复杂度是怎么控制的
[答:NS专家] depends on system complexity  
[问:liang.jiang@huayamicro.com] 请问你们是怎么考虑emi/emc问题的
[答:NS专家] EMI can be reduce by spread spectrum technology and EMC can be improved by RF supression technology  
[问:chuntian23] 什么时候用嵌入式操作系统比自己开发带来的成本小些
[答:NS专家] less performance  
[问:chuntian23] 音频系统与分立式最大的优点是什么
[答:NS专家] For high performance design, integration is less power consumption, noise , easily to control, save GPIO and higher reliability  
[问:chuntian23] 音频系统是用什么软件进行编程的,编程时还需要考虑那些特殊的要求吗
[答:NS专家] audio sub-system debug will be start in the function development stage, it will require clear understanding of the different operating modes and system parameters (e.g. system clock, sampling frequency, filter response and gain setting)  
[问:chuntian23] 编程是使用专业设备吗
[答:NS专家] we provide user friendly PC software for software development  
[问:hu0500820411] 可否把一些常用的电子器件的资料给传一些,还有近期的一些电子制作指导报,非常感谢!!
[答:NS专家] please send your request to AP.support@nsc.com  
[问:zhouhao15917] 你们这里有没有和单片机有关的信息或者产品吗?
[答:NS专家] please visit our web page for details, http://MICROCONTROLLER.NATIONAL.COM  
[问:basicbear] 请问专家:今天介绍的国半的产品中是否有符合Windows Vista标准的笔记本电脑音频子系统
[答:NS专家] Not at the moment for Audio products  
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