m.188betcom�ֻ��- 為可攜式電子產品的聲頻系統挑選合適的電路設計(繁体中文版)-National Semiconductor厂商_在线座谈

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主题：為可攜式電子產品的聲頻系統挑選合適的電路設計
在线问答：
[主持人：ChinaECNet]	各位聽眾（網友），上午好！歡迎參加中電網線上座談。今天，我們有幸邀請到美國國家半導體公司的專家就“為可攜式電子產品的聲頻系統挑選合適的電路設計”舉行線上座談。在座談中，您可就您關心的問題與美國國家半導體公司的專家線上進行直接、即時的對話交流。中電網衷心希望通過大家的共同努力，不僅能夠增進各位聽眾（網友）對“為可攜式電子產品的聲頻系統挑選合適的電路設計”的瞭解和掌握，而且能夠為大家事業的發展帶來裨益。	[2007-9-11 10:27:08]
[主持人：ChinaECNet]	我們已經進入問答階段如果聽眾想重溫演講或內容可以點擊下面“回顧演示”重看演講。	[2007-9-11 10:27:23]
[问：taneliu]	如何规划在PCB layout时规避干扰音频电路的因素?
[答：Wayne Chen]	音頻信號線必須和其他數位信號保持距離. 保持足夠線寬與線距. 注意電源與接地的佈局.	[2007-9-11 10:30:27]
[问：taneliu]	目前中国大陆在音频方面的质量标准已经开始正式规范,厂家在前期设计时经验不足,能否给出一些音频电路方面的选择建议和调试思路?
[答：Kenneth Lee]	As the quality requirement is higher , the circuit design need more consideration and prefer simplify. So it need to choose some higher performance Audio Amp, simplified circuit with less external components, reduce EMI technique..etc Nation semiconduction audio had that kind of products for fit your expectation.	[2007-9-11 10:31:59]
[问：taneliu]	目前提供的电路设计主要应用于哪些便携产品上?
[答：Thomas Chang]	PDA ,Mobile Phone ,PMP	[2007-9-11 10:32:13]
[问：sduboy]	音頻電路設計有哪些軟體發展工具？
[答：Wayne Chen]	電路頻率響應可以用 Spice 等模擬. 信號品質則必須注意線路布局品質. 沒有特殊工具. 在信號品質測試上, 則可以利用 Audio Precision 等測試儀器	[2007-9-11 10:32:51]
[问：taneliu]	今天介绍的方案,能否从网页上获得相关链接,请提供一下?
[答：Alice Hui]	Yes. Your can click on http://www.national.com/CHT/appinfo/audio/ to get more information about our audio solution	[2007-9-11 10:34:07]
[问：Athena_lj]	1.怎樣高度整合？DSP與AD/DA及功率放大器可否集成？ 2.模擬與數字部分怎樣隔離,降低互相干擾?
[答：Wayne Chen]	DSP 和 AD/DA 可以集成. 但模擬和數字的信號走線則必須保持距離. 可以用接地良好的守衛接地線隔離.	[2007-9-11 10:34:07]
[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：Alan Chang]	Discrete solution has flexibility to implement, but PCB space is large. National sub-system solution built-in functions and features what you need to fit small space requirement. The other advantage is easy design, only few external R and C outside IC. You find National audio solution on website http://www.national.com/appinfo/audio Or you can contact with local FAE for support.	[2007-9-11 10:34:13]
[问：lengyuezhu]	聲頻系統里面功放的设计应该还是很难的，即要满足线性又要有好的效率？这些NS又是怎么衡量和优化的？
[答：Kenneth Lee]	N.S. will consider on both performance and the efficiency.. For portable application, class D have higher efficieny, N.S. will provide a good audio quality class d with low THD+N, higher PSRR..etc	[2007-9-11 10:34:54]
[问：sduboy]	設計音頻電路有哪些挑戰？有無技術方面的瓶頸問題？
[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.	[2007-9-11 10:35:04]
[主持人：ChinaECNet]	各位觀眾，現在用戶提問很踴躍，專家正在逐一回答。請耐心等待您問題的答案，同一問題請不要多次提交。	[2007-9-11 10:35:34]
[问：dicksonfu]	請問有什麼開發工具配合呢?
[答：Wayne Chen]	NS 網站有提供 Webench 模擬工具. http://webench.national.com/appinfo/webench/audio/design_requirements.cgi 非常適於設計輔助	[2007-9-11 10:35:47]
[问：luoaluo]	便携式音频放大器件的选取最主要的依据是什么?
[答：Thomas Chang]	Power save ,so Class D is major concern . And Integrate circuit reduce PCB size .	[2007-9-11 10:36:10]
[问：callancc]	音频电路设计时,何时用D类,何时用A.B类呢?
[答：Wayne Chen]	講究轉換效率採用 D 類. 非常講究音質時採用 AB 類	[2007-9-11 10:36:42]
[问：comorg]	目前有没有实际的应用在手机中，比如说品牌
[答：Alice Hui]	Please click on http://www.national.com/CHT/appinfo/audio to get more information	[2007-9-11 10:37:04]
[问：夏日香气2007]	关于接收机的动态范围，到底该怎么评估
[答：Kenneth Lee]	for receiver. If this is a hi -Fi or Higher end. the higher the SNR is expected. The dynamic range is depends on the internal codec and the output voltage requirement.	[2007-9-11 10:37:15]
[问：luoaluo]	同样的工作条件和输出功率下,D类放大器比AB类放大器的功耗能节省多大?有百分比数吗?
[答：Thomas Chang]	Class AB under 60 % ,Class D around 80% ~85%	[2007-9-11 10:37:34]
[问：callancc]	EMI方面效果如何?
[答：Kenneth Lee]	We have many parts considered on the EMI, Like spread spectrum, E2S, RF suppression etc...	[2007-9-11 10:38:33]
[问：zl184103]	3.隔直输出电容在体积有限的情况下，一般采用何种电容合适？
[答：Wayne Chen]	注意工作溫度低於 0 度時, 不建議電解電容. 電容和頻率響應有關, 誤差要小. Postcap 很合適但是價格稍高.	[2007-9-11 10:39:09]
[问：lengyuezhu]	如何改善音频系统的性能，降低音频系统的功耗？
[答：Robert Shen]	It is hard to answer in simple, Class "D" audio amplifier is better to reduce the power comsumption.	[2007-9-11 10:39:18]
[问：sduboy]	音頻電路設計的好壞體現在哪些方面？
[答：Alan Chang]	For audio evaluation, following parameters are key points: 1. PSRR, CMRR: higher is better 2. THD+N: small percentage 3. frequency response: which band you need Those factors are basic for audio performance. National offers many IC with high PSRR, and low THD+N, such as LM4562, LM4920, LM49370..	[2007-9-11 10:39:22]
[问：chyren]	请教专家,NS的音放支持哪些3D音效？
[答：Wayne Chen]	利用 phase shift 技術可延伸立體音場	[2007-9-11 10:40:28]
[问：techman]	NS的音频放大器是全数字的吗?
[答：Thomas Chang]	Some audio amp. embedded Codec . as like LM49370	[2007-9-11 10:40:42]
[问：taneliu]	目前国半的产品在CDMA2000产品中的应用如何?能否简要介绍一下?
[答：Henry Kwok]	If there is not bluetooth or digital interface, most of audio system were fit, say LM49100 (Mono AB Spk amp, stereo H/P with O/P cap-less), LM4947 (Mono Class-D spk amp, stereo H/P), LM4949 (stereo Class-D apk amp, stereo H/P). If that have digital interface, we do have LM4935 & LM49370, these audio system that have the capability to handle analog input (1set of SE (AUX), 1set of diff IN/Out (CP in/out), 2x Mic in), spk output (class-D), earpiece, digital interface (I2S & PCM). More information you can found in National web site.	[2007-9-11 10:41:04]
[主持人：ChinaECNet]	我們已經進入問答階段如果聽眾想重溫演講或內容可以點擊下面“回顧演示”重看演講。	[2007-9-11 10:41:24]
[问：yuchuanhong]	最新微型电声器件有哪些,主要材料/材质是什么?
[答：Robert Shen]	We think that the latest mini speaker should be made by ceramic.	[2007-9-11 10:41:32]
[问：techman]	音频放大器的带宽是决定音质的重要因素.NS的音频放大器的带宽低端能达到多少?
[答：Kenneth Lee]	Usually from 20Hz to 20kHz can be handling. for different response , the ecternal LPF or HPF can be adjust by the external components.	[2007-9-11 10:41:42]
[问：zl184103]	4.在采用无滤波的D类功放输出时，应该注意哪些问题？
[答：Wayne Chen]	輸出走線要短以降低 EMI, 如果仍然有 EMI 問題可使用 LM4675 或是 LM48410 等內建 Spread Spectrum 技術的放大器.	[2007-9-11 10:41:46]
[问：taneliu]	在产品的技术支持方面,国半提供了怎样的服务?在协同调试方面的工作做的如何?
[答：Henry Kwok]	Technical support by FAE or regional office, application note in web, web support.	[2007-9-11 10:42:41]
[问：luoaluo]	单芯片解决方案中的音频输出功率有多高?能驱动哪种类型的扬声器?
[答：Alan Chang]	Now, National LM4702 is able to provide up to 300W output using external driver. LM4780 is single chip for 60W.	[2007-9-11 10:42:54]
[问：xl_cumt]	什么样的电路可以称为合适的电路？
[答：Robert Shen]	I think that the good balance circuit is perfect circuit. For audio, BTL output is better.	[2007-9-11 10:43:14]
[问：lengyuezhu]	采用什么供电5V 或者3.3V等等？
[答：Jasper Lam]	Audio subsystem can be powered by battery for portable applications.	[2007-9-11 10:44:22]
[问：comorg]	NS的音放是否支持重低音输出？
[答：Jasper Lam]	We had FIR filter for setting different frequency response on LM49370.	[2007-9-11 10:46:09]
[问：zl184103]	1.最后一级驱动放大，在系统没有负电源的时候才用1/2VCC虚地输出是否需要采用输出电容？采用与不采用各有什么优缺点？
[答：Henry Kwok]	yes, the output cap are needed. The trade off will be more click-pop, output C & spk act at a HPF, cap value need to match, some time the cap size will big. For this case, we have LM48820 & LM48821 to address, more information in National web site you can found.	[2007-9-11 10:46:14]
[问：luoaluo]	NS单芯片中数字信号流程是如何控制的?它们之间的隔离度如何?
[答：Alice Hui]	For controlling we have I2C or SPI controlling bus. For audio signal we have I2S and PCM bus with internal DAC or ADC or codec. Good channel separation on digital signal	[2007-9-11 10:46:33]
[问：callancc]	音频电路电源部分遇到欠压情况,如何保护和补偿?
[答：Robert Shen]	The protection will depend on the designer based on the condition to shutdown, and etc. The Cap is importance for this case.	[2007-9-11 10:46:36]
[问：xl_cumt]	对于功放电路如何设计？
[答：Alan Chang]	You can access National Webench for audio design http://webench.national.com/appinfo/webench/scripts/my_webench.cgi Then select solution. It offers design spec., part recommendation, then built-it. Ususally, DS has detalis for design equation, layout, and notice.	[2007-9-11 10:47:05]
[问：lengyuezhu]	这类声频放大器需要多大的电流，效率做在哪一类，比如B类，D类等等，最大输出多少w？3D效果怎么样？
[答：Thomas Chang]	1. Power dissipation is around 100mW , 2.Class D 3.3D is enhance stereo	[2007-9-11 10:47:05]
[问：luoaluo]	NS中的CODEC能和那几种编码格式兼容?
[答：Henry Kwok]	PCM – I2S Bridge Bidirectional PCM compatible audio interface Bidirectional I2S compatible audio interface Read/write I2C or SPI compatible control interface	[2007-9-11 10:47:24]
[问：jszjjxq]	我最关心的是功耗问题
[答：Wayne Chen]	利用 Class-D 降低功耗. NS 音頻子系統可以視需求關閉內部的閒置功能可以降低功耗到最低	[2007-9-11 10:48:42]
[问：comorg]	NS音频编解码器输出是数字还是模拟信号?是否带有滤波器?
[答：Thomas Chang]	1.We have Analog and Digital (I2S, PCM) 2.No filter	[2007-9-11 10:48:44]
[问：wychen]	In our system, there is already an stereo headphone output. Which audio amplifier is recommended to convert the stereo into mono speaker (8 ohm 1.0W)?
[答：Jasper Lam]	We had a lot of analog audio subsystem which integrate mono speaker amp and HP output, e.g. LM4946, LM4947, it will depends on how many inputs on system.	[2007-9-11 10:49:33]
[问：chyren]	请问怎么消除影响模数转换器(ADC)的噪声？
[答：Robert Shen]	Digitalize noise is not avoided. Other noises can be reduced by PCB design, pre-amplifier design and etc.	[2007-9-11 10:49:45]
[问：tiger_liangbin]	数位与类比是什么意思?
[答：Robert Shen]	It is different from digital and analog.	[2007-9-11 10:50:30]
[问：zl184103]	2.在我的设计中为了增加驱动能力，特别增加了一级buffer（比如buf634），但问题是buffer往往会带来100mv左右的直流偏置，这个比较好的处理办法吗？
[答：Kenneth Lee]	To ensure the input without any DC , or with some input capacitor. and choose some low offset op-amp as the buffer. N.S. provide a serise of Op-amp with low offset. Eg. LME49710, LM4562...	[2007-9-11 10:50:43]
[问：skyliuyun]	讲座中关注了体积小、功耗低等等需求，那么在不同声频子系统之间的噪声干扰排除方面，有什么看法或者建议？
[答：Henry Kwok]	Most of audio sub-system that have digital filter build in.	[2007-9-11 10:50:52]
[问：techman]	NS的音频放大器是全差分的吗?采用全差分输入的音频功放有什么特点和优势?
[答：Henry Kwok]	Not all audio part form National are differential, here is some of parts using SE, LM4941, LM4905, LM4906. Using diff input, that can improve the PSRR & CMRR performance, also that can help to have the noise improvement.	[2007-9-11 10:52:40]
[问：lingf]	便携应用中对功耗要求比较严，国半在这方面有什么优势？
[答：Thomas Chang]	NS released ClassD audo Amp. and integrate audio subsystem for reducing power disspation .	[2007-9-11 10:53:01]
[问：chyren]	NS所采用的D类放大器是否通过FCC和CISPR认证?
[答：Henry Kwok]	yes	[2007-9-11 10:53:04]
[问：JC Wu]	請問一下 I2S and AC97 interface的優缺點???
[答：Wayne Chen]	AC"97 是 1997 年間推出的介面. AC"97 可以傳遞命令與資料. I2S 只傳遞資料, 命令則經由 I2C. AC"97 功耗較大因為不能在閒置時停 Clock. 因此 NS 的音頻子系統採 I2S 因其較適用於手持式裝置.	[2007-9-11 10:53:12]
[问：skyliuyun]	比较建议的声频系统工作电流是多大？
[答：Wayne Chen]	視輸出的功率而定. 一般建議在手持式產品預留 1.0A 的電源輸出能力.	[2007-9-11 10:54:07]
[问：lengyuezhu]	NS采用分立元件搭建的时候，体积怎么能保证，分立元件的尺寸是集成体积微小化的最大瓶颈？
[答：Kenneth Lee]	N.S. will will have the optimize on the chip design with small chips packages.	[2007-9-11 10:54:17]
[问：techman]	能否介绍一下新片中所用的复接器的主要性能?
[答：Alan Chang]	The mixer is used to decide which channel connection for input and output, speaker, headphone. Since LM49370 supports many different input source such as L/R, PCM, mic-phone, I2S, and many output type, such as speaker, headphone,it needs a switcher to connect different input and output.	[2007-9-11 10:55:12]
[问：comorg]	立体声音频DAC如何实现多路复用功能？
[答：Robert Shen]	The output of DAC is a analog, we do not understand the question, is it multi-analog line combine?	[2007-9-11 10:55:49]
[问：xiaoyongjun]	您认为贵公司的音频放大器最值得注意的优点有哪些？
[答：Wayne Chen]	高效率, 小封裝, 輸出品質, 集成性以及技術支援能力.	[2007-9-11 10:56:04]
[问：rockren]	请问陶瓷扬声器功放方案的效率能达到多少?最大输出功率现在能做到多少?
[答：Kenneth Lee]	The efficiency is even higher than the Class D audio amp. The output is considering on the voltage.. for some portable devices. around 15Vpp can be drive the portable ceramic speaker to a more than 80dB SPL.	[2007-9-11 10:56:23]
[问：tiger_liangbin]	数位与类比的区别?
[答：Robert Shen]	It is different from "Digital and Analog"	[2007-9-11 10:56:25]
[问：tiger_liangbin]	频谱是怎样扩展的?
[答：Wayne Chen]	將中心頻率 (一般 Class-D 為 300kHz) 向兩端稍加擴展.	[2007-9-11 10:56:49]
[问：lengyuezhu]	我们知道集成是便携，小型化的有效办法，但是带来的就是EMC和隔离不好等问题，请问这方面有什么有效办法？NS是怎么做到的？
[答：Jasper Lam]	Our Audio subsystem had RF suppression circuitry to resolve the EMC problem on portable system design.	[2007-9-11 10:56:58]
[问：xl_cumt]	对于便携产品有什么特殊的设计要求？
[答：Kenneth Lee]	1. The package is small. 2. The circuit is simple 3. Good performance 4. Low interference (like EMI)	[2007-9-11 10:57:52]
[问：skyliuyun]	高效能、体积小、功耗低这只是目前便携式产品在普遍追求的方向，这样的话，所谓声频系统的个体特色在介绍的系统设计方法中如何体现？请举例说明，谢谢！
[答：Henry Kwok]	Audio system that have multiple input port ready, 1set of SE (AUX), 1set of diff IN/Out (CP in/out), 2x Mic in), spk output (class-D), earpiece, digital interface (I2S & PCM). For the application I2S form application processor, PCM to BT, FM radio signal, mono signal form baseband, spk output, earpiece. More information you can found in National web site.	[2007-9-11 10:58:03]
[问：zl184103]	Does NS have any High-End level amplifier that can driver 32 Ohm to 300 Ohm headphones?
[答：Jasper Lam]	Please provde operating voltage, output power and THD+N requirement, thanks.	[2007-9-11 10:58:27]
[问：xiaoyongjun]	该音频放大器静态和动态时的功耗多少？
[答：Thomas Chang]	静态 : about 3mw 动态 :about 100mW	[2007-9-11 11:00:12]
[问：tiger_liangbin]	有没有较为简单的系统
[答：Jasper Lam]	Does it require digital inputs? or just analog inputs? any output requirement, such as speaker, headphone...	[2007-9-11 11:00:24]
[问：zl184103]	What is the difference when use op amp such as Lm4562,lm49860 and use specifical AB amp to diver headphones? Also their considerations?Thank you!
[答：Kenneth Lee]	LM4562 and LME49860 main different is the supply volatge +/-17V and +/-22V. LM4562, LME49860 can be using as line out and even drive H/P for higher performance devices. Consideration is the output current ability.	[2007-9-11 11:00:26]
[问：comorg]	如此多的功能，那么电源是不是负担更大，如果待机时间太短，那用户会很烦恼的。
[答：Henry Kwok]	The power consumption always is a Challenge, so that NS developed a series of system that build in the Class-D amp for help, say LM4947, LM4949 & LM49370. With this audio sub-system ready, all you can using software to control the power management much more effective.	[2007-9-11 11:01:37]
[问：dicksonfu]	Class AB 與 Class D音質的分別有沒有具體的參數/指標?
[答：Wayne Chen]	可參照各型號的 Datasheet, 數年前 Class-D 的 THD+N 往往在 1% 以上, 但近年來已逐漸改善到 0.1% 以下. 好的 Class-AB 放大器可輕易到達 0.01% 以下甚至 0.0001%.	[2007-9-11 11:02:21]
[问：rockren]	请问针对7.2V两节锂电的电源系统,是否有适合的D类功放方案?
[答：Alan Chang]	For 7.2V input, I think the best way is a 5V buck first then using class D audio. 5V is usually need for system. Class D audio with 5Vcc rating is majority in market, so you can get price benefit. National has power solution, LM2734/8, LM3491x, LM2557x for 5V buck. For class D, we have also LM4674 (stereo), LM4673/5 (low EMI solution) for your reference.	[2007-9-11 11:02:59]
[问：tiger_liangbin]	供电电压多大?音频功率能做到多大?
[答：Kenneth Lee]	Supply volatge is depend on different part. The supply volatge will affect the dynamic range of the output volatge to increase or decrease the output power. The output resistance also a consideration for the power output.	[2007-9-11 11:04:20]
[问：sduboy]	音頻電路設計能否同時做到提升性能和降低功耗？
[答：Henry Kwok]	With using audio sub-system who have the class-D amplifier available, that can help to improve the performance & improve efficiency. Here is some part no for your reference. LM4947 (Mono Class-D spk amp, stereo H/P), LM4949 (stereo Class-D apk amp, stereo H/P). If that have digital interface, we do have LM4935 & LM49370.	[2007-9-11 11:04:41]
[问：tiger_liangbin]	扩频是为了减少对外EMI干扰,还是为了本身的EMC抗干扰性能?
[答：Jasper Lam]	Our class D amplifier adopted Spread Spectrum technology to reduce the EMI from internal clock generator.	[2007-9-11 11:05:07]
[主持人：ChinaECNet]	各位觀眾，現在用戶提問很踴躍，專家正在逐一回答。請耐心等待您問題的答案，同一問題請不要多次提交。	[2007-9-11 11:07:53]
[问：sduboy]	美國國家半導體在可擕式電子產品方面有哪些完整的解決方案？
[答：Robert Shen]	We have Power management solution, audio sub-system, LVDS solution, Serdes solution, Signal Path Solution, PLL solution, Clock solution, temperature sensor solution, and etc.	[2007-9-11 11:08:05]
[问：zwlll]	NS的D类音放的输出提供保护措施?
[答：Henry Kwok]	all class-D part have the thermal protection.	[2007-9-11 11:08:11]
[问：zwlll]	音放中的小信号输入,在匹配设计中应注意哪些问题？
[答：Wayne Chen]	當使用單晶片音頻放大器時不用太擔心匹配, 因為其輸入阻抗夠高, 以 LM467X 來說, 輸入阻抗均有 150k ohm.	[2007-9-11 11:08:29]
[问：Cecil Chan]	What is the sampling rate to be supported in the audio sub-system codec?
[答：Kenneth Lee]	General up to 48kHz sampling for codec.	[2007-9-11 11:09:15]
[问：zwlll]	Which technology NS used in class-D Amplifier?
[答：Robert Shen]	We have fixed PWM, and xpread spectrum technology used in class-D audio amplifier.	[2007-9-11 11:10:09]
[问：zl184103]	Does NS have any High-End level amplifier that can driver 32 Ohm to 300 (power supply: 5-15V(LionBat and USB power sourse with boost),output power:100mW and THD+N <=0.001%) great thanks
[答：Jasper Lam]	Yes. such as LM4562 (dual channels) & LME49710 (single channel) & LME49740 (quad channels). You can find more on our web page. http://audio.national.com	[2007-9-11 11:11:20]
[问：tiger_liangbin]	模拟输入,输出有喇叭和耳机
[答：Thomas Chang]	Yes ,NS LM49370 including Analog input and speaker ,headphone ouput .	[2007-9-11 11:11:57]
[问：Cecil Chan]	Can the I2S and PCM operation at the same time?
[答：Henry Kwok]	Sure, the LM49370 I2S & PCM bus can operate at the same time.	[2007-9-11 11:12:06]
[问：tiger_liangbin]	模拟电路,输出有喇叭和耳机
[答：Alice Hui]	Please refer to LM4946, LM4947, LM4949 or LM49270.	[2007-9-11 11:12:52]
[问：rockren]	请问类D功放有最小驱功率要求？
[答：Wayne Chen]	沒有. 驅動功率視負載阻抗, 電源電壓與輸入信號而定.	[2007-9-11 11:15:03]
[问：lyn663013]	请问音频功率最高能到多少
[答：Henry Kwok]	For portable design operate with a Li-ion battery, the supply voltage typical was 3.6 to 4.2V, the maximum output power in to a 8 ohm speaker is around 390mW to 800mW, it"s depend on the supply voltage, we have some applicaiton available in web for reference.	[2007-9-11 11:16:48]
[问：liguang169]	美国国家半导体推出的电路设计软件是否有DEMO或者学习版提供下载？有哪些语种可以选择？
[答：Alan Chang]	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.	[2007-9-11 11:16:59]
[问：lingf]	便携产品是否一般都采用D类放大器？性能上有多少损失？
[答：Wayne Chen]	由於 Class-D 放大器效能的進步, 愈來愈多手持式產品開始採用 Class-D. 最大的改進就是功耗明顯降低. 以手持式產品的小型喇叭效能限制, 終端使用者不會感受到性能的損失.	[2007-9-11 11:17:18]
[问：liguang169]	美国国家半导体推出的电路设计软件都支持哪些操作系统？是否需要英文操作系统支持？
[答：Henry Kwok]	We have WEBENCH available in web, no chinese version availabe at this moment.	[2007-9-11 11:19:33]
[问：xy0325]	在功率Class-D中，如何解决电磁兼容问题？
[答：Kenneth Lee]	It depends on the supply volatge range. N.S. class D can genreally operate from 2.5V.. so it is mateching with the battery application.	[2007-9-11 11:20:29]
[问：lyn663013]	请问音频电路设计可否降低功耗
[答：Henry Kwok]	with Class-D amplifier used, that can improve the efficiency, say LM4673, LM4675, and some of audio system have the class-D amp build in, LM4947 (Mono Class-D spk amp, stereo H/P), LM4949 (stereo Class-D apk amp, stereo H/P). If that have digital interface, we do have LM4935 & LM49370.	[2007-9-11 11:21:11]
[问：chenty]	输入电源的波动影响输出功率吗？
[答：Robert Shen]	Depend on the range changed, in general it is not to influence the output power.	[2007-9-11 11:22:48]
[问：chinwei]	Class-D功放末级输出需要外置滤波器吗？如须如何设计？
[答：Wayne Chen]	一般小功率的 Class-D (LM467X, LM49370...) 不需末級濾波器. 高功率輸出者 (LM468X ...) 則需要 LC 低通濾波. 其值與 PWM 頻率有關. 可參照各型號的Datasheet.	[2007-9-11 11:22:58]
[问：张志民]	请问电路设计软件是否需要英文操作系统支持
[答：Henry Kwok]	For the WEBENCH in web, only english available in this moment. No matter Chinese or English OS, all can access.	[2007-9-11 11:22:59]
[问：liguang169]	美国国家半导体针对可持式电子产品的声音系统推出的应用于在高，中，低端的IC具体有哪些？相应的典型设计电路是否可以提供？
[答：Henry Kwok]	A typical application available in data sheet, LM4935 & LM49370 data sheet all have application available.	[2007-9-11 11:24:22]
[问：chinwei]	關于音頻放大器的輸入,一般會有什麼樣的要求?如果我輸入的原信號功率大于輸出,會產生什麼要的後果?
[答：Thomas Chang]	1.Audio Input depends on Analog or digital . Digital input : SPIDF ,I2S ,PCM ,...etc . Analog Input :no couple noise . 2.Input signal great than output signal with audio amp. The audio result will be not stable .	[2007-9-11 11:24:42]
[问：jumpge]	请问输入信号如果变化很大，NS的D类放大器输出是怎样保持稳定？
[答：Wayne Chen]	不需擔心信號變化因為音頻信號變化只在 20Hz~20kz. NS 的 Class-D PWM 取樣率多為 300kHz 左右. 音頻範圍輸出可以保持穩定.	[2007-9-11 11:25:20]
[问：xy0325]	采用扩展频谱技术,能降低EMI,其技术复杂程度如何?
[答：Kenneth Lee]	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.	[2007-9-11 11:25:24]
[问：zl184103]	假如设计中要采用一般的供电电压做虚地，NS是否有比较好的方案（性能优先，功耗不重要）
[答：Alan Chang]	If you mean BTL, or virtual GND on headphone, National has many parts for that, such as LM4949, LM48510..	[2007-9-11 11:25:36]
[主持人：ChinaECNet]	各位觀眾，現在用戶提問很踴躍，專家正在逐一回答。請耐心等待您問題的答案，同一問題請不要多次提交。	[2007-9-11 11:26:40]
[问：rockren]	针对数字语音单芯片需求，是否存在可直接连接喇叭和麦克，内置AD/DA，音频放大与功放（1W输出），并配有AGC的集成化芯片，请推荐
[答：Wayne Chen]	LM4935 或是 LM49370 是 NS 推薦的單晶片子系統. LM49370 具有單獨的 I2S 與 PCM 接口.	[2007-9-11 11:27:32]
[问：tiger_liangbin]	有没有带扩频技术的D类功放
[答：Jasper Lam]	yes, such as LM4675 (mono), LM48410 (stereo + national 3D), LM49370 (audio subsystem) with Spread Spectrum technology	[2007-9-11 11:27:48]
[问：jumpge]	D类放大器的放大幅度如何控制?它对基准电压有和特别的要求?
[答：Kenneth Lee]	1. But external input resistor 2. But gain select pin. No special requirment on the 基准电压.	[2007-9-11 11:28:11]
[问：张志民]	请问一下电源电压的输入范围
[答：Henry Kwok]	The audio sub-system that have some of supply input terminal, typical Supply Voltage in for digital interface 2.5V to 4.5V, Baseband supply rating = 1.8V to 4.5V, Speaker amp supply rating = 2.5V to 5.5V	[2007-9-11 11:28:32]
[问：shyuan]	多通道的音频功放的通道隔离度有多少？如何解决串音问题？
[答：Wayne Chen]	一般單晶片的多通道子系統可達到 60dB-FS 以上, 保持 PCB 上各通道的線距是最好的方法.	[2007-9-11 11:29:50]
[问：jumpge]	什么是D类放大器?它有那些优缺点?
[答：Thomas Chang]	Class D ,Audio signal modulate with PWM or Sigma -Delta . 优点:power save , high efficient 缺点 :EMI not good,THD+N not good.	[2007-9-11 11:30:26]
[问：shyuan]	如何解决数字功放的输出阻抗大、阻尼系数小的问题，也就是说负载能力差的问题?
[答：Henry Kwok]	In theory, Class-D output impedance is lower than Class-AB. The driving capability of class-D is much higher than class-AB.	[2007-9-11 11:31:39]
[问：rockren]	现在Class-D能做到的最大输出功率达到多少瓦的级别？
[答：Kenneth Lee]	It depends on the supply voltage and the loading resistance. N.S. Class D are focus on protable application it can reach around 3W into 4 ohm. We also have some with output to 10W into 8ohm for mid -power application.	[2007-9-11 11:32:32]
[问：rockren]	若开关电源供电，请问D类功放对于开关电源的纹波抖动有何要求？
[答：Robert Shen]	Our audio amplifier has the PSRR data, it is for power supply ripple. Please take datasheet as reference.	[2007-9-11 11:33:15]
[问：rockren]	Class-D工作时对电源的干扰严重？能否与噪声要求高的电路（如LAN）共一组电源？如何消除这种干扰？谢谢？
[答：Wayne Chen]	不建議 audio 與 digital 共用電源. 建議 Audio 採用單獨的 ground plane. 如干擾嚴重則建議採用穩壓器.	[2007-9-11 11:34:15]
[问：liguang169]	能介绍一下美国国家半导体针对可持式电子产品的声音系统推出的IC在音色上偏暖还是偏冷？哪些可以制造耳机放大器？
[答：Kenneth Lee]	偏暖还是偏冷 is very subjective.. It also depends on the PCB and the external components. For H/P driver, N.S. have many parts like LM48820, LM4911, LM4982 etc etc.. with good performance, you can get more information and datasheet from N.S. website.	[2007-9-11 11:35:41]
[问：lyn663013]	您好我想知道如何解决电磁兼容的问题
[答：Robert Shen]	First, xpread spectrum technology is the best to solve the EMI issue, please select audio amplifier used xpread spectrum, like LM4675, LM48410,LM49370. Second, PCB layout and design is important.	[2007-9-11 11:36:27]
[问：liguang169]	美国国家半导体针对可持式电子产品的声音系统推出的IC有无数字放大IC？
[答：Alan Chang]	Natioanl sub-system can input I2S, PCM format sources then drive speaker, such as LM49370, LM4937, LM4931. I think they are suitable for your application.	[2007-9-11 11:37:14]
[问：xy0325]	贵公司的音频放大有USB接口?
[答：Jasper Lam]	Not available	[2007-9-11 11:37:45]
[问：张载涵]	请问电路设计软件都支持什么操作系统
[答：Kenneth Lee]	Generally, We can support Window OS	[2007-9-11 11:38:12]
[问：lyn663013]	您好我想知道电源电压的输入范围
[答：Henry Kwok]	The LM49370 audio sub-system that have some of supply input terminal, typical Supply Voltage in for digital interface 2.5V to 4.5V, Baseband supply rating = 1.8V to 4.5V, Speaker amp supply rating = 2.5V to 5.5V	[2007-9-11 11:38:36]
[问：shyuan]	影响D类放大器的效率有那些?它的高效率是否得益于全数字功能?
[答：Wayne Chen]	高效率在於其信號放大操作在歐姆區, 理論上其效率可達 100%, 但是實際上內部 H-Bridge 的 RDS(ON) 會使效率無法達到理論值. Class-D 的 PWM 頻率以及上升, 下降斜率會影響效率.	[2007-9-11 11:38:45]
[问：chinwei]	NS音频放大器有什么特点？
[答：Thomas Chang]	1.High efficient 2.Hihgh performance 3.Power save 4.Integrate audio subsystem 5. 3D enhance	[2007-9-11 11:40:12]
[问：chenty]	电源电压的输入范围是多少？
[答：Jasper Lam]	please specify which device?	[2007-9-11 11:40:39]
[问：xy0325]	如何知道功率放大器与信号源输入是否匹配？
[答：Wayne Chen]	可以示波器量測信號是否發生反射, 但是單晶片音頻功率放大器的輸入阻抗多半很高, 通常不會發生匹配問題.	[2007-9-11 11:41:06]
[问：wychen]	Is it nessery to add external ESD components at the audio amplifier output pins?
[答：Wayne Chen]	Absolutely, you can use additional ESD protection components if you have ESD problem. However, for Class-D design, please make sure the capacitance of your ESD protection circuit is low enough. pF level is perfect.	[2007-9-11 11:43:33]
[问：jumpge]	PCB的布线对传统的模拟功放的品质有很大的影响，请问D类放大器的PCB布线有什么不同的要求?
[答：Henry Kwok]	For the Class-D application, PCB layout, customer should take care to separate the supply line between others, also keep the output trace as short as possible, Supply bypass cap needed, more information available in data sheet.	[2007-9-11 11:43:36]
[问：张载涵]	类D功放的最小驱动功率是多少
[答：Alice Hui]	沒有. 驅動功率視負載阻抗, 電源電壓與輸入信號而定	[2007-9-11 11:43:36]
[问：chenty]	你们的D类放大器与其它同类的比效率高多少？
[答：Alice Hui]	沒有. 驅動功率視負載阻抗, 電源電壓與輸入信號而定	[2007-9-11 11:43:52]
[问：张志民]	请问如何控制电路设计复杂度
[答：Henry Kwok]	For discrete soultion that need many GPIO to control, very complex. Using National Audio sub-system (LM4935 & LM49370), only one I2C/SPI that can controll all input/output, internal switching & mixing, volume, sampling rate, sampling frequency. Easy to use.	[2007-9-11 11:46:20]
[问：rockren]	请问DAC输出的信号能不能直接驱动CLASS-D？有没有输出功率（音量）可以调节的CLASS-D
[答：Kenneth Lee]	Yes, As DAC output is an analog signal. It can direct input to N.S. class D parts. Yes, we have class D with volume control. eg LM4681, LM4682 or gain selecting eg. LM4674, LM48410 etc.	[2007-9-11 11:47:18]
[问：liguang169]	美国国家半导体推出的电路设计软件是否支持元件库的在线升级和自定义元件功能？
[答：Robert Shen]	We have not symbol LIB and update LIB. In general, EDA software should supply this LIB.	[2007-9-11 11:47:25]
[主持人：ChinaECNet]	由於時間關係，本次中電網“線上座談”馬上就要結束了。雖然各位聽眾（網友）已與美國國家半導體公司的專家討論了許多問題，但是還有許多提問沒有來得及進行交流。本次線上座談結束後，中電網將請美國國家半導體公司的專家繼續答復所有的來自各位聽眾（網友）的提問，然後整理上載到中電網網站上，以便大家查閱。	[2007-9-11 11:51:17]
[主持人：ChinaECNet]	在此，中電網特別感謝給予本次中電網線上座談巨大支持的美國國家半導體公司，特別感謝專門線上回答各位聽眾（網友）提問的美國國家半導體公司的各位專家們，特別感謝各位聽眾（網友）積極熱情的參與。	[2007-9-11 11:57:32]
[问：sduboy]	請問可擕式電子產品的發展經歷了哪些階段？其將來的發展趨勢如何？
[答：Jasper Lam]	From the being single signal source to now multiple signal souce in the portable device, the trend will be highly integration, SNR, system efficiency, THD & low noise.	[2007-9-11 11:58:23]
非在线问答：
[问：zhz-141]	可攜式電子產品的聲頻系統電路設計如何使用软件进行设计？
[答：NS专家]	For the audio signal path, using a Audio sub-system that can replace all the discrete solution, all the input & output port can handled by I2C & SPI control. The digital control interface can help customer to simplify the software design, much more easy to handle switching, mixing, sound effect & volume control....etc.
[问：zhz-141]	可攜式電子產品的聲頻系統如何运用兰牙？
[答：NS专家]	Now a day some of design require to have BT ready for data transfer or voice comm. For the voice comm. application, audio sub-system that have the capability to handle. PCM bus for BT, sampling rate can support up to 48KHz.

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