在线座谈

热门关键字: 电磁兼容 工业控制系统 固态继电器 串行外设接口 

关于本次座谈

座谈简介

这次研讨会主要从便携式系统应用,便携式DVD、LCD显示器应用,高端LCD显示器应用的方面介绍了使用者的经验以及美国国家半导体的一些参赛可选器件。方便各位参赛者的选用。

精彩问答

主题:美国国家半导体针对便携式及消费电子应用的高性能音频解决方案
在线问答:
[问:liu.flex] 音频电路设计时,noise的主要是由于那几个方面造成的?以及该如何避免这方面的问题.谢谢 
[答:KevinC] May facotrs can cause noise issues.input capacitor,bypass capacitor,correct components with right values, PCB layout like sigal trace,power trace,GND trace etc  [2004-7-23 10:39:20]
[问:jxrouland] 请问美半在LCD电视、高端LCD显示器上具体做了那些应用。那部分采用美半的方案,将提高了产品质量,又保持价格优势? 
[答:Henry] For the LCD appliaction , we did some of soultion kit to customers for a reference, (LM4832 + LM4755, LM4832 + LM4866, LM4832+LM4950, LM4832 + 2.1 channel amplifier). This kind of solution can help our customer to speed up their audio design cycle & improve the sound quality.  [2004-7-23 10:41:31]
[问:rogerzhou] How to solve S/N question ? 
[答:Kenneth] We should has a specified S/N for the IC on certain condition. Of course,for the systematic view., it will also depend on the PCB designing,you can concentrate on the supply trace and the in/out signal path etc.  [2004-7-23 10:41:33]
[问:rockhanxj] 如果用LM4809实现LM4889,该注意哪些事项? 谢谢 
[答:Henry] Actually the LM4889 & LM4890 is a pin-to-pin comparable part, only the LM4890 has better THD & PSRR.  [2004-7-23 10:44:56]
[问:Raindy] 1、音频的PCB布线是否要数字地和模拟地分开。 2、MIC的前级放大使用一级高放大倍数运放好还是使用多级低放大倍数运放好。 3、Speaker的输出使用PWM好还是使用D/A好。 
[答:Kenneth] 1.yes.. 2.Depends. different part will allow different gain range. For a better linearity part. One amp with high gain is better. 3.PWM , you should use a LP filter for output audio only.  [2004-7-23 10:47:08]
[问:zhanghq] 将贵司的音频产品应用到无线公话中须注意到哪些细节? 
[答:Henry] For the GSM application, the maily concern is the PSRR, especialy in 217Hz. The second concern is turn-on time & click pop performance. Surround components also is part of concern.  [2004-7-23 10:48:29]
[问:gavinpanko] How do you think about class D amplifier 
[答:KevinC] it do have some advantage like higher efficiency, need heatsink, but designer should be careful for handling the EMI,noise  [2004-7-23 10:49:56]
[问:rogerzsx] BTL and SE mean? 
[答:KevinC] BTL:桥接,SE:单端. You can find the detailed application in our product datasheet.  [2004-7-23 10:53:22]
[问:wangfp] when you design the audio amplifier, do you consider the input signal dynamic range? 
[答:Kenneth] Yes.. You should know the maximum voltage that the input stage can give out. because you have the match the amplifier gain in order to get a certain output power.  [2004-7-23 10:54:24]
[问:liuzhao1971] 请问音频解决方案是否包括软件解决方案? 有没有一种合适的互联网上高性能实时音频传输方案?  
[答:Henry] The audio solution not included the software. Depand on the CODEC quality.  [2004-7-23 10:54:55]
[问:MINGDENG] 如何从整体上降低音频放大器的噪音? 
[答:KevinC] generally the correct components with correct values, reasonable PCB layout  [2004-7-23 10:56:33]
[问:caiqs] 什么是过调制保护? 
[答:Kenneth] This is that when the input signal range is too higher than the IC can accept. The IC will have a protection.  [2004-7-23 10:58:55]
[问:tangxzhong1] 差分输入和单端输入的放大器,在性能上和使用上有何差别? 
[答:KevinC] the purpose of Differential input mode is to amp the differential input but reduce common input, so that it can improve the CMRR.  [2004-7-23 11:02:23]
[问:lijt] 高性能音频解决方案中的音频放大电路,其低端频率和高端频率各是多少?频带宽度是多少?音频功率放大的输出功率有多少个等级?各等级的额定输出功率是多少 
[答:Kenneth] Down to 20Hz. Up to 20k Hz. This is the audio range. you can hear the sound between this range. Some higher -end amplifier can even more wider range. Amplifier power output has not special level. Only have different class. Class A,B,AB,D is most common.  [2004-7-23 11:03:03]
[问:yaobin800528] 我很想知道本次大赛作品要求 
[答:Jessie] 此次大赛希望希望参赛者能设计出音质更加完美的产品. 具体评判标准如下: 1.技术水平-选用最合适的组件并结合最佳的设计及成品制作水平 2.创意-创新的设计理念 3.模拟技术 - 有效利用国半的音频组件 4.更优化的音响性能 -其设计能呈现高素质的音频输出  [2004-7-23 11:03:36]
[问:akuann] 请问如何解决无线音频传输中系统内部产生的噪声?请问这些噪声源一般是哪些?digital ground 和analog ground在PCB布线时是不是一定分开?这部分对噪声有什么影响?谢谢! 
[答:Henry] It is due to MPU operation & PA, switching noise from MPU operation, 217Hz form PA, this noise you can find in the power line. For the grounding, if you can separate the analog & digital ground in PCB that can avoid the high frequency noise issue. Mainly you can hear "Da Da Da" when the PA is operate.  [2004-7-23 11:04:36]
[问:jungo] 音频放大器中,电流反馈和电压反馈电路有什么区别,如何应用 
[答:KevinC] CFA VFA 闭环  BW  不随闭环增益相对变化  根据GBW关系变化      AC/DC性能指标  较好的AC性能  较好的DC性能 稳定时间  较快  较慢 主要噪声源  反向输入电流噪声  输入电压噪声     输入阻抗  非对称  对称 偏置电流  消除DC误差困难  匹配输入阻抗可消除DC误差       反馈通路  不能用Cf  可以用Cf   [2004-7-23 11:04:49]
[问:hunter] For the high power Class-D solution,Would you give some advice with National Semiconductors" products? 
[答:KevinC] currently LM4651 and LM4652,which can provide 170W output  [2004-7-23 11:05:48]
[问:mycz1] 请问,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:Kenneth] The heat is depending on the power dissipate of the IC. this can be calculate by some formula. pls reference to our N.S. amplifier datasheet. After that you can find the thermal resistance of the IC and the heat sink etc.. to calculate what size of heat sink is enough for that IC.  [2004-7-23 11:07:33]
[问:rogerzsx] such as LM4950,many customers wish have DC volume control, NSC have the products in the future? 
[答:KevinC] We will release the product with DC volume control this year  [2004-7-23 11:08:14]
[问:mycz1] 如何消除音频放大器中的回声和尖叫声? 
[答:Kenneth] This depends on many things. may e the power suppply noise, the PCB design, the signal noise itself. A suitable bypass capacitor can help on this issue.  [2004-7-23 11:10:39]
[问:joyluo] Boomer产品是否都是模拟电路?有没有全数字化放大器?在音质和音色上,全数字化放大器和Boomer相比,有何优缺点? 
[答:Henry] Boomer is series name of power amplifier is NS, the power range is 20mW to 3W, including mono & stero. For the Boomer series we have Class-D amplifier, the mainly advantage of the Class-D amp. is power saving. Efficiency = more than 80%.  [2004-7-23 11:12:06]
[问:joyluo] 选择音频放大器的标准,主要有那些? 
[答:Henry] Operating voltage range, output power, THD+N, PSRR.  [2004-7-23 11:13:18]
[问:jungo] 音频功放在供电上有什么要求,开关电源会对其造成什么影响 
[答:Kenneth] The power should be clear and stable enough. eg. use tranformer. the transformer should has a more stable output between loading and unloading. It can protech the IC from over or under voltage.   [2004-7-23 11:13:35]
[问:jungo] 我看到有些电路中有加入直流中点伺服电路的,用来降低输出零点漂移,这个电路对音质有何影响 
[答:Kenneth] No big effect to the signal. but more stable output.  [2004-7-23 11:17:59]
[问:sjdwsf] 便携式及消费电子中的音频部分主要干扰源有哪些?清除干扰源的主要方法有哪些? 谢谢! 
[答:Henry] High frequency noise, which is come from the MPU operation, slove this issue is separate the digital & analog part by using the PCB layout.  [2004-7-23 11:18:17]
[问:lmast523] 音频放大器输入为零时,主要噪声源是电源吗?还有其它噪声源吗? 
[答:KevinC] power supply is one main source as well as white noise,external noise etc  [2004-7-23 11:21:59]
[问:MINGDENG] 音频放大器的高音和低音频响,目前能达到什么样的水平? 
[答:Kenneth] Depends on different kind of amplifier. The audio range is from 20 to 20k Hz. For higher quality. The frequency range can be more wide with a very good THD.  [2004-7-23 11:22:33]
[问:wangfp] Besides the LM4667 which is the Class D topology, how about other products? I mean, are they in the switching mode? how about their efficiency?  
[答:Henry] Only some of parts are using Class-D technology (LM46xx series), LM48xx is class-AB design, efficiency in 60% max.  [2004-7-23 11:24:02]
[问:hcsb] 阻抗匹配在音频放大电路设计中是否非常重要?需要注意哪些事项?谢谢 
[答:Kenneth] Yes. different loading resistance can giveyou different output power, the current is also different., so you have to make sure the amplifier can support this current or not and the output loading can support this output power or not.  [2004-7-23 11:25:14]
[问:ludongxin] 电源的干扰对放大器的影响很大,你认为是否都应采用线性电压调整器?在PCB设计时如何处理电源线的干扰? 
[答:Henry] Yes, the power noise is the big issue, if you can use a good PSRR part that can help you to away this issue, no need to add one more additional regulator. For the PCB layout, star ground.  [2004-7-23 11:27:06]
[问:letian] Boomer的性能主要给出了总失真的性能,它的噪音性能如何? 
[答:KevinC] we have detailed info about THD, S/N in each product datasheet.  [2004-7-23 11:27:50]
[问:caiqs] 如何降低音频可听见的噪音? 
[答:Kenneth] Depends on the system design. PCB design. The grounding arrangement is a important issue. (signal ground, power ground, digital ground.0  [2004-7-23 11:28:02]
[问:shirly] 在设计无线便携音频产品的时候,在 PCB布线上有哪些设计要点呢? 
[答:Henry] separate analog & digital ground, star ground, don"t parallel the high current trace with the signal path.  [2004-7-23 11:28:28]
[问:tangxzhong1] 美国国家半导体的音频放大器的效率最高能达到多高?能否给出它和输出功率的关系? 
[答:KevinC] 86% for LM4667. we have detailed info about efficiency Vs Output power in our datasheet  [2004-7-23 11:29:55]
[问:ladawang] 程先生是否注意到了不久前TI推出的TPA6120A2、OPA4134 国半是否有产品与其相当,请做比较分析 
[答:KevinC] I think customer can access our website and download the datasheet, then you can have everything you want.  [2004-7-23 11:32:26]
[问:laky] D类功放在便携式产品中的适用程度如何 
[答:KevinC] It should have great potential since it has higher efficiency,no need heatsink etc advantage  [2004-7-23 11:34:27]
[问:wangfp] For the LM4667, you use the Class D mode. Does it integrate one inductor in the chip? If yes, how much of it? 
[答:Henry] No , the LM4667 is a filter-less design, The maximum output frequency can up to 6.25MHz (160nS). The short drive pulses can be obtained with minimal load inductance. The typical transducer load in an audio amplifier is quite reactive. For this reason the load can act as it"s own filter.  [2004-7-23 11:34:44]
[问:fishbones] 我比较关心无线数字系统.无线数字家庭影院和传统的有线式优势在哪,劣势和将来的技术发展. 
[答:Kenneth] Wireless can give a more flexible placement for the end user and this is also the home audio system trend. It is no need to place and install on the speaker wire. it bring convenient to user. The sound quality will be depends on any interference around and may not as stable as the wireline one.  [2004-7-23 11:35:57]
[问:lmast523] 电路板上的地线如何分布可以减少音频放大电路噪声? 
[答:KevinC] we have audio application notes in our website, you can get detailed info for GND layout to reduce noise  [2004-7-23 11:36:17]
[问:smallwei] 你认为,全数字放大器的PSRR应有多高才比较合适,不影响到声音的质量? 
[答:Kenneth] Generally, more than 60dB should be OK. unless the end customer has higher requirement.  [2004-7-23 11:38:05]
[问:wangfp] what"s LM4835"s ear phone sensing function? Can you explain it more detail?  
[答:Henry] The detail operation you can find in LM4835 data sheet page 14 & 15 (HP-in function).  [2004-7-23 11:38:14]
[问:caiqs] D类放大器在设计上有何特别的考虑? 
[答:Henry] Switching frequency, output low pass filter  [2004-7-23 11:40:14]
[问:lmast523] 音频放大器对PCB设计的线宽有什么要求? 
[答:Kenneth] no special requirement but depends on your design size. in fact, we are suggest that the grounding path should keep wider is better.  [2004-7-23 11:41:58]
[问:shirly] How can an input capacitor and by pass capacitor creat noise? 
[答:Henry] It"s due to charge & discharge (create a DC off set) when the power amp turn-on & off.  [2004-7-23 11:41:58]
[问:jx882003] 一般来说,在便携式电脑中,由于体积的问题导致音频方面总是存在这样那样的缺陷。那么,我们如何才能使便携式电脑中的播放的声音效果更好,音频技术更为完善呢? 
[答:KevinC] Suggest our Boomer product with 3D effect  [2004-7-23 11:44:31]
[问:rogerzsx] how to choose heatsink size and mode for audio amp.? in what mode, we test ic highest case temperture with heatsink  
[答:Kenneth] Heatsink size can be calculated by calculate the max. power dissipate from the IC. then use the relationship of the thermal resistance to get a suitable heatsink size. The formula can get from our application note.  [2004-7-23 11:45:09]
[问:chenck345] 请问专家:有没有温漂低,宽带(100MHz以上),线性放大器.主要用于脉冲放大的集成运放.什么型号?设计时主要注意什么问题? 
[答:KevinC] What we are talking is audio product, but for op-amp,yes, we have many high speed op-amp with lower drift. you can get info from our website  [2004-7-23 11:48:09]
[问:lmast523] 滤波器和旁路电容会导致音频信号的失真吗?如何选择? 
[答:Kenneth] Depend on the circuit design. Generally, it will degrade the level on certain frequency. So you should choose and design the one that siutable for your application.  [2004-7-23 11:48:56]
[问:terry] Have any Class D amplifer with a PWM input? 
[答:KevinC] not yet.  [2004-7-23 11:49:51]
[问:terry] Have any other input interface suitable for Digital data (except I2S) 
[答:KevinC] there are other many interface for audio like PCM, 4 slot network  [2004-7-23 11:51:05]
[问:qzwu] Is there Depop circuit in all the productors of NS 
[答:Henry] no, only suppression circuit.  [2004-7-23 11:51:29]
[问:ludongxin] 要得到高保真的音质,该采用多少层PCB,在性价比上较为合适? 
[答:Kenneth] In fact, no direct relationship. depend on the PCB design. But more layer can separate different signal/power. it can give a better performance.  [2004-7-23 11:51:43]
[问:coldxj] Audio对输入、输出、Bypass电容的选择依据是什么? 
[答:Henry] PSRR, turn-on/off time & click-pop performance  [2004-7-23 11:52:00]
非在线问答:
[问:] 1.想请问专家在消费类DVD播放器中,选择什么样的LCD比较经济(低端机方案)? 2.在高端市场LCD的采用有何优势,在器件选型方面有何方法和宝贵经验?
[答:] STN LCD for low end model. 2.Because space saving and better brightness and contrast.
[问:] 3.在当今消费类电子市场相对疲软的情况下,采用经济、高质量方案,往往成为一个企业、工厂,其产品出奇制胜的法宝,请问在这方面有何宝贵经验,以及是否有可行的方案,提供给客户?
[答:] More function more features and integrated product
[问:] Boomer? 系列音频放大器的效果怎样?
[答:] Higher efficiency and good sound quality
[问:] Boomer的音量控制如何进行?是否采用数控?为什么? 
[答:] Have DC volume control and digital volume control.
[问:] Boomer放大器的防尖峰电压的保护功能如何?外接电路如何设计来提高这一性能? 
[答:] By external diode at output stage
[问:] D类放大器的放大倍数由什么决定?
[答:] Feedback resistor to determine the gain
[问:] how to desigen a excellent 3D sounds system in cellphone?
[答:] Depends on the IC 3D effect quality and the speaker/cavity design.
[问:] LCD显示器集成的控制器内有字库,请问可以有命令直接使字库内的代码送到显示缓冲器,还是把代码先读到mcu,之后再送到显示缓冲器?
[答:] Please refer to the IC datasheet/manual 
[问:] lmv921适合作为一个音频电路前级的低噪声放大器吗?
[答:] yes
[问:] use LM4857 to design a 3D sound system in cellphone,whether the soft of cellphone need to add the time delay between right and left channel?
[答:] No, all the 3D effect can be manage by the LM4857
[问:] 'What is the function of LM4930PCM audio, vedio, and data input port? What"s it for? 
[答:] Audio input 16 bit PCM bi-directional, I2S input for full range audio. 
[问:] When NSC release APU? 
[答:] Only audio sub-system or Audio control chips but no APU.
[问:] you say class D amplifier need heatsink? should do not heaksink,ths!
[答:] Depends on the power. Usually need har sink for some higher power 
[问:] 便携式产品主要包括哪些方面,主要应用领域是什么呢? 
[答:] Any devices that can bring outside. Including portable DVD, MP3, discman, multimedia player, gaming box.
[问:] 便携式及消费电子应用的高性能音频解决方案的发展前景如何?
[答:] More integrate, more user experience, more features,
[问:] 差分音频放大器有良好的噪音特性,在使用上要特别注意什么问题?
[答:] Loading, heat dissipate. 
[问:] 当数字通讯中,对其会否有大的干扰,有相应的处理么?
[答:] Will have certain interference but will not so large. Better to have separate grounding  
[问:] 对于多层电路板,地层放在顶层好,还是放在地层好?如何分布可以减少emc及噪声及回音? 
[答:] No speacial, depends on the layout. Large signal and low signal or digital and analog signal trace should arrange separately. 
[问:] 放大器的级间如何匹配 
[答:] Depend on the amplifier Input & Output impedance
[问:] 放大器管脚和外围电路的兼容性如何? 
[答:] 取决于你的应用需求。 
[问:] 关于软交换是怎么回事?
[答:] ???? 
[问:] 解决方案主要基于什么呢 
[答:] Base on audio solutions 
[问:] 美国国家半导体的传统模拟音频器件一直都是业界第一流的,在数字音频和便携数字音频的发展潮流中,美国国家半导体准备扮演什么样的角色,有什么技术和市场方面的新举措? 
[答:] NS is focus on analog solution 
[问:] 美国国家半导体针对便携式及消费电子应用的高性能音频解决方案与其它竞争对手的解决方案相比,有哪些突出的优点。 
[答:] System intergation, high performance, high efficiency, high sound quality
[问:] 目前boomer在国内销量如何?市场份额占多少 
[答:] Good! 
[问:] 能不能具体介绍一下设计竞赛的组织和进展情况。对参赛选手提供怎样的支持? 
[答:] 此次比赛由美国国家半导体公司主办,由我们的代理商棋港电子有限公司赞助,同时也得到中电网,《无线电》杂志社等媒体协助。参赛者可以直接在网上查询我们的产品,并可发邮件至:audiochina.contest@nsc.com提问。进入决赛的参赛者可以免费获得国半的设计所需音频器件。 
[问:] 你好,我想了解一下差分放大器的注意事项
[答:] No need the input coupling capacitors, improved PSRR 
[问:] 你们 的 最新 产品 的 特点是 什么 ? 
[答:] System intergation, high performance, high efficiency, high sound quality 
[问:] 您好:请问这次大赛是否所有器件必须应用美国国家半导体的器件.参赛的音频解决方案包括那几部分;是否指是功率输出放大.因为列出器件都是功率输出级的.请给出框图example.谢谢 
[答:] 参赛作品的音频部分必须选用国半的器件,但其它部分可选用其它公司的产品。关于框图,请参阅我们网站内容http://www.national.com/diagrams/" 
[问:] 请问AUIDIO AMP输出级可以选择那些结构?PMW,or Delta-sigma amplifier?您能比较一下这两种技术的优缺点吗? how do you chose the switching frequency? 
[答:] Low power with output filter-less design will prefer using delta-sigma, High power with LPF would prefer using PWM. The switching frequency is depend on the application, High switching frequency will degrade the efficiency.  
[问:] 请问Boomer? 系列音频放大器目前已经在那些品牌的产品中应用,以便我们有一个感性的认识? 
[答:] Many, most of mobile who used external amplifier. 
[问:] 请问LM4832与LN4866这个款IC的价格是多少 
[答:] For the pricing, you can contact NS local office for assistance 
[问:] 请问带有DC音量控制的AUDIO工作原理? 
[答:] The DC should be generate by the MPU/CPU using GPIO port. The GPIO should be a PWM. 
[问:] 请问高性能音频对于数字电路来说有那些挑战? 
[答:] No, only analog
[问:] 请问贵公司的便携式DVD、LCD显示器应用,高端LCD显示器产品是不是已经全部采用IC芯片,还有用到分立器件的地方吗?若有,能介绍一下具体用到电路的哪一部分?谢谢。 
[答:] Most of them using single chip solution
[问:] 请问贵公司的一般性的高性能音频解决方案的费用是什么水平? 
[答:] 请访问我们公司的中文网站,http://www.national.com/CHS,其中有我们代理的联系方式,请直接联系我们的代理。 
[问:] 请问目前boomer系列音频放大器在中国内地市场供货情况如何,销售量如何  
[答:] No problem with delivery.
[问:] 请问是不是dip封装很快就要退出历史舞台?贴面组件占领整个市场?能否将高性能的音频芯片置入人体? 
[答:] No , the dip package is still there, because of the new design need much more compress, so that NS has develop the new package. 
[问:] 如何测试音频的效果? 
[答:] You can using a audio analyze 
[问:] 如何开始使用boomer产品开发? 
[答:] 问题的范围太广,取决于你需要哪方面的应用。 
[问:] 如何判断和检测3D立体声的增强效果?环绕声呢?能否介绍一些检测仪表的型号? 
[答:] For some digital 3D system (like surround sound , AC3) ,you can using Audio analyze to measure the output. 
[问:] 是否设计只需要提供音频子系统,是否提供控制部分的设计? 
[答:] 如果你在设计中,仅使用子系统,无须开发硬件,只需通过I2C来控制内部MUX, 开关和音量。 
[问:] 我设计中,电源板和含音频放大器的电路板是平行放置的,距离在2.54厘米。如何防止电源板对放大电路的噪声干扰呢?有何良策?? 
[答:] Using a ground plate for separate this two board. 
[问:] 我想了解一下大赛要求提供一个什么样的参赛作品,能具体解释一下吗? 
[答:] 参赛者需要提供显示其创意和技术水平的作品,有效利用美国国家半导体的音频组件并能呈现优化的音响性能的作品。 
[问:] 我想问的是,对于国家广电总局即将推出的avs标准,你们有什么对应的解决方案? 
[答:] I think that is a digital coding standard for China. 
[问:] 我在使用LM4781时,发现电路在音量大一点的时候输出波形容易出现自激,有方法改善吗? 
[答:] Increase the heat sink area , lower supply voltage & increase the speaker loading. 
[问:] 西安有没有代理? 
[答:] 目前,美国国家半导体在西安没有代理,如有需要,可与我们北京销售办事处联络,电话:010-68042453 
[问:] 希望能提供一些应用的电路,以及相应元器件的价格!! 
[答:] 请访问我们公司的中文网站,http://www.national.com/CHS,其中有我们代理的联系方式,请直接联系我们的代理。 
[问:] 现在的音频电路对于数字电路方面有那些难点?
[答:] More user friendly, easly to use
[问:] 现在在国内的供货情况如何? 
[答:] 你可以联系美国国家半导体的中国销售办事处。 
[问:] 一般来说,在便携式电脑中,由于体积的问题导致音频方面总是存在这样那样的缺陷。那么,我们如何才能使便携式电脑中播放的声音效果更好,音频技术更为完善呢? 
[答:] Using NS audio solution 
[问:] 音频电路设计上如何才能达到最高效率?
[答:] Using Class-D amplifier 
[问:] 音频放大器的输出滤波器如何进行选择和设计?依据是什么?如何计算不同电感的波纹电流? 
[答:] Please reference to passive low pass filter design. 
[问:] 有音频放大器的电路板上的EMC如何处理? 
[答:] Depend on layout & components placement.  
[问:] 在公共电话网和IP电话网中,如何解决回音抑制?有相应方案吗? 
[答:] Echo cancellation 
[问:] 这些高性能音频解决方案中所用到的硬件和软件,市面上哪处有售? 
[答:] Please contact disty for help 
[问:] 针对LCDTV有何新方案 
[答:] LM4832, LM4866, LM4950, LM4940, LM4849, LM4668. 
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美国国家半导体致力开发各种高能源效率的模拟及混合信号半导体产品。该公司的PowerWise®系列产品旨在降低系统功耗,延长电池寿命,以及减少散热需求。美国国家半导体总部位于美国加州圣塔克拉拉(Santa Clara),截至2008年5月25日为止的2008年财政年度的营业额达18.9亿美元。欲查询美国国家半导体的公司资料及产品信息,欢迎浏览该公司的网页,网址:www.national.com