“放大器+類比/數位轉換器＂線上研討會(繁體中文版)-National Semiconductor厂商_在线座谈

精彩问答

主題：放大器+類比/數位轉換器線上研討會
在綫問答：
[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“放大器+類比/數位轉換器線上研討會”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。	[2008-2-26 10:24:36]
[问：xuxm]	运算放大器单电源供电和双电源供电的输出有什么区别？
[答：Thomas Chang]	Single power supply : 1.Dynamic range smaller 1/2 2.Bias voltage concern 3.Negative signal need to bias shift.	[2008-2-26 10:30:14]
[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。	[2008-2-26 10:30:23]
[问：xuxm]	如何更好地消除干扰
[答：Thomas Chang]	1.Better PCB Layout 2.Add band pass filter	[2008-2-26 10:32:04]
[问：zhangcanfeng]	请问如何根据放大器的摆率（v/us）计算通过的最大频率
[答：Michelle So]	SR = 2π f VP If you know Slew Rate (SR) and Peak Voltage (VP), then you can calculate frequency (f).	[2008-2-26 10:32:13]
[问：flanix]	我想知道选型的方案,比如放大倍数,噪声,温度.
[答：Michelle So]	To choose an amplifer, first find out the bandwidth of your application, then slew rate, noise concern... etc.	[2008-2-26 10:33:30]
[问：zh2006ly]	怎樣的搭配才可確保系統能充分發揮其效能?
[答：Robert Shen]	Differential OP with differential input ADC.	[2008-2-26 10:33:55]
[问：nksdj]	如何增加放大器的输入阻抗?
[答：Thomas Chang]	1.AC couple 2.From Non-inverting to Inverting	[2008-2-26 10:34:06]
[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。	[2008-2-26 10:35:23]
[问：haicheng315]	如果想详细了解该技术，在那里能得到相关资料？谢谢
[答：Thomas Chang]	1.National Web site	[2008-2-26 10:35:28]
[问：liuyong6420]	请问根据哪些参数选择放大器和ad?如何提高稳定性?
[答：David Shaw]	OP_Amp:1. Slew rate 2. Bandwidth 3. 0.1 dB gain flatness Bandwidth. ADC: 1. Resolution 2. Sampling rate 3. SNR 4. THD, Stability: 1. Reduce noise, 2. PCB layout doesn"t induce noise.	[2008-2-26 10:35:49]
[问：lemo19]	请问讲师的联系方式是？
[答：Alice Hui]	If you want to get any technical support, pls visit http://www.national.com/CHS/support/	[2008-2-26 10:36:16]
[问：lvgx]	根据传感器，如何选择放大器。请介绍经验，谢谢。
[答：Michelle So]	Depends on the sensor type. We recommend Precision amplifer for it"s accuracy. Please see National Web Site for Precision Amplifiers.	[2008-2-26 10:38:25]
[问：xuxm]	放大器与转换器的匹配问题
[答：Thomas Chang]	1.PLease reference the presentation file .	[2008-2-26 10:39:15]
[问：sunds99]	如何根据不同的ADC确定需要哪一种运放?
[答：Thomas Chang]	1.Speed 2,Accuracy	[2008-2-26 10:41:29]
[问：logic001]	有没有具体的设计方案可供参考
[答：Thomas Chang]	1.In Nation website 2.NAtional Datasheet of LMH6555 or ADC08D1000.	[2008-2-26 10:42:37]
[问：zhangcanfeng]	放大器一般都提供“输入电压噪声”和“输入电流噪声”这两个参数，请问：什么情况下这两个参数的某个起重要作用？另外参数值的大小对系统的影响有多大？麻烦举例表明，谢谢。
[答：Robert Shen]	If this input noise influence the output signal, it is important for system design. Take example, if the input noise is large enough so that influence the ADC output error, it will influence the ADC resolution.	[2008-2-26 10:42:40]
[问：liuyong6420]	检测微弱信号时波动很大如何解决?
[答：Robert Shen]	Depend on the reason to influence. In general to use filter.	[2008-2-26 10:44:42]
[问：tianjiu]	在使用AD转换器的时候,如何确定是否需要前端的运放?
[答：Michelle So]	Since ADC operates best with full scale input dynamic range, i.e. 5V input range for a particular ADC. If your input signal peak to peak voltage is not 5V, then it"s recommended to gain up your input signal to 5V to optimize performance.	[2008-2-26 10:44:46]
[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。	[2008-2-26 10:44:49]
[问：yy_tseng]	ADC的输出延时主要受什么因素的影响?
[答：Michelle So]	Clock signal, Jitter, noise... etc.	[2008-2-26 10:46:58]
[问：maszcy]	若运放部分的误差是a,A/D转换部分的误差是b，那么两个部分的总误差是多少？
[答：Michelle So]	It"s not a simple addition. We look at system error in lost in dB. For example, amplifier"s error adds nLSB error for the ADC. ADC then convert this error with additional INL/DNL error. Then the total SNR will have XdB lost.	[2008-2-26 10:49:45]
[问：JASON]	请问，是不是所有的模数转换器的输入都需要阻抗匹配？如何考虑阻抗匹配问题？
[答：David Shaw]	High speed ADC required, low speed ADC doesn"t required impedance match. For impedance, you need to match ADC"s input impedance. If it is differential 100 ohm, you need to add 50 ohm at each Vo+ & Vo-. If it is single end input of ADC, you don"t need to add any input resistance.	[2008-2-26 10:50:58]
[问：maszcy]	如何定义A/D转换器的分辨率？为何A/D转换器分辨率的大小不用输入电压表示，而用输出代码最小有效位，即LSB表示？
[答：Thomas Chang]	ENOB is (SIAND-1.76)/6.02 , SIAND = 20log*Root(10^-SNR/10+10^THD/10)	[2008-2-26 10:51:57]
[问：logic001]	ad在设计时，数字地和模拟地有没有特殊要求
[答：Robert Shen]	depend on the frequency of the signal. In general, to avoid disturb from digital.	[2008-2-26 10:53:44]
[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。	[2008-2-26 10:54:52]
[问：yerenxjh]	请问如何确保放大器处在最大负偏状态？
[答：David Shaw]	Please control your gain and input signal level, and be sure your negative waveform * gain will not over minus voltage.	[2008-2-26 10:54:56]
[问：ldz84]	请问专家,不同类型的ADC如SAR, Delta-Sigma等,对放大器的要求有些什么区别?
[答：Thomas Chang]	Delta Sigma : low spped high accuracy SAR :middle speed , middle accuracy	[2008-2-26 10:56:12]
[问：wangsf2000]	如果模数转换器的输入阻抗不匹配，会有那些影响？
[答：David Shaw]	It will cause your sampling signal cause error signal.	[2008-2-26 10:56:49]
[问：zhiyu03]	我们在选择滤波器的时候，如何与模数转换器和放大器的参数进行匹配？
[答：Michelle So]	depending on the output/input mode of the amplifier and ADC, Bandwidth requirement of the Amplifier, noise... etc. Example: LMP2011: GBW = 3 MHz At a Gain of 20 - BW = 150 kHz For 12 Bit accuracy Max Signal Frequency is 0.0156(150 kHz) = 2.34 kHz	[2008-2-26 10:57:02]
[问：sky.sun.zz]	LMH6555大概什么价位
[答：Alice Hui]	Please visit our website to get the details: http://www.national.com/pf/master.html	[2008-2-26 10:57:08]
[问：zhz-141]	滤波器的通带特性如平坦度对模数转换器和放大器有何影响？
[答：Michelle So]	If filter"s transition band is wide, then some unwanted signal might enter the amp+ADC system and creates error.	[2008-2-26 10:58:17]
[问：licki518]	在高速语音信号处理方面,选择什么样的AD?或者说要考虑哪些方面?
[答：David Shaw]	1. select high resolution ADC. 2. Sampling rate need > 200 KHz	[2008-2-26 10:59:04]
[问：yerenxjh]	请问ad在设计时，如何区分模拟地和数字地？最终如何是否要吧两者连在一起，如何连接呢？谢谢！
[答：Thomas Chang]	Analog is input ,output is Digital signal. You could not connect it together.	[2008-2-26 10:59:12]
[问：reporter]	请问专家，在高速系统的设计中，如何解决驱动ADC的延迟问题?
[答：Robert Shen]	All ADCs have the time delay, it will be considered in the system design.	[2008-2-26 10:59:15]
[问：zmgg8008]	请问专家，哪些因素会影响cdma pa spurious emission，pa电源供应的去藕电容对这个问题以及power有多少影响，谢谢！
[答：Thomas Chang]	Please reference our SUPA product in National Web site . http://www.national.com	[2008-2-26 11:01:06]
[问：zhangjsh]	模数转换器的输入阻抗匹配对频率有一定关系，请问专家，此时如何做，从低频还是高频考虑？
[答：Robert Shen]	Depend on the which frequency you focus, using your focus frequency to calculate.	[2008-2-26 11:01:35]
[问：xdj]	ADC驱动放大器的输出噪声对ADC有何影响？该怎么考虑？
[答：Thomas Chang]	ADC driver with OP . So ,OP output noise is very important parameter. If Noise bigger ,ADC capture wrong signal . Improve way : low noise AMP, you can look NAtional precision amp in national web site.	[2008-2-26 11:04:31]
[问：jqin]	选择用于ADC的基准,我们主要需要看那些参数?
[答：Robert Shen]	In general, it will be speed, resolution,enob, etc.	[2008-2-26 11:05:00]
[问：jida_song]	带LVDS接口的ADC对匹配电阻的要求是否要高一些？
[答：Thomas Chang]	Yes . The impedance need to match LVDS requirement.	[2008-2-26 11:06:18]
[问：rurality]	进行阻抗匹配时候，主要需要考虑哪些因素？
[答：Michelle So]	Matching of the incoming signal to the next block. Use Termination resistors to match impedance.	[2008-2-26 11:06:58]
[问：logic001]	放大器的带宽是不是一定要大于ADC
[答：David Shaw]	Yes, it will make sure the signal will not distort to enter ADC	[2008-2-26 11:07:24]
[问：ivor]	ADC的种类有SAR，过采样和双斜率等几种, 请问专家, 它们的驱动电路会有什么不同?
[答：Thomas Chang]	the sampling and conversion methodologies are different, The driver cicuit focus on filter and sample and hold timing.	[2008-2-26 11:07:40]
[问：maszcy]	若ADC距离后面的控制器较远(比如>30米),对ADC的输出阻抗有何要求？
[答：Robert Shen]	There is not requirement of output impedance, but it will need a method to transfer the signal to more than 30 meters, like cable driver, LVDS, etc.	[2008-2-26 11:08:40]
[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。	[2008-2-26 11:10:51]
[问：su_hh]	高速ADC输入端的信号调理电路设计要注意些什么？
[答：David Shaw]	1. input impedance need to match with ADC input 2. sampling rate need to be high enough 3. need to design Anti-Alias Filter to filter input noise	[2008-2-26 11:11:12]
[问：purpleboy]	对ADC输入信号的调理有些什么的要求?
[答：Michelle So]	1. add anti-alias filter. 2. consider the ADC"s capacitance load presended to the previous block. 3. Maximize input dynamic range for the ADC.	[2008-2-26 11:11:54]
[问：liuxtjim]	如何保证输入放大器的输出达到平衡？
[答：Thomas Chang]	1.make sure input swing and output swing 2.COncern BW. 3.COncern output load is cap. or resistance. 4.Concern phase margin	[2008-2-26 11:12:12]
[问：liguang169]	国家半导体推出的芯片中支持CTSD技术的模拟/数字转换器芯片有哪些？
[答：Robert Shen]	Please see detail in our web site: http://www.national.com/appinfo/adc/sigma_delta.html	[2008-2-26 11:12:27]
[问：wzmpl]	对高速24位的ADC,请专家推荐一款NS的放大器。谢谢！
[答：Michelle So]	Depends on your power supply requirement, ADC"s input type (single or differential), Bandwidth of your system... etc. Please see National"s selection flash table at www.national.com/cat/	[2008-2-26 11:14:04]
[问：w19347]	在实际应用中，如何将一个单端输入转换为差分输入？
[答：David Shaw]	Please refer to NS LMH6555 or LMH6550/6551 datasheet. You could download from NS Website	[2008-2-26 11:14:24]
[问：yerenxjh]	请问，在哪些网站可以找到比较多的放大器设计资料，要中文的哦，有，请举些例子，谢谢！
[答：Robert Shen]	We have the Chinese web site also, like following link: http://www.national.com/CHT/signalpath/	[2008-2-26 11:15:09]
[问：idiodynamics]	在PCB 布局时,对差分输入的ADC 电路有什么特别的要求?
[答：Thomas Chang]	Good question. 1.Two trace need to closer . 2.Short trace length 3.same Two trace lenth	[2008-2-26 11:15:20]
[问：rogerliu123]	在欠采样应用的时候应该怎样考虑模数转换器前端的滤波器设计？
[答：Thomas Chang]	Sample rate is lower ,so you should cnsider anti-aliase band is different .	[2008-2-26 11:16:36]
[问：shaobo_xu]	ADC 的转换精度除了与转换的位数有关, 还与什么因素有关?
[答：David Shaw]	ADC"s THD, SNR, SIAND Spec.	[2008-2-26 11:21:23]
[问：jiang.xie]	如何降低放大器输出通道的寄生负载？
[答：Michelle So]	Generally, the output impedance is very low. It is generated from the internal circuit of the amplifier and cannot be minimized externally. Please choose another amplifier if output impedance excessed requirement.	[2008-2-26 11:22:47]
[问：shenbz]	ADC输入端的抗混淆滤波器有什么要求? 那种类型的滤波器较好？
[答：Thomas Chang]	It is depends . How many poles do you need ? Freom present material page 7 , you can select what kind of filter do you need .	[2008-2-26 11:24:27]
[问：wdefu]	怎么提高ADC对高频抗干扰特性？
[答：Michelle So]	1. bandpass filter 2. Use EMI hardened amplifiers before ADC.	[2008-2-26 11:25:03]
[问：laijp]	基准源信号和电源对ADC的性能影响很大,请问如何选择呢?
[答：Robert Shen]	Each bit of ADC will be influenced by reference voltage. It will be selected independent, other factors, like temperature do not influence it. Power supply is simple compared wiht reference voltage, it should comply the specification.	[2008-2-26 11:26:29]
[问：gumulaoyi]	请问，AD转换中，影响精度最关键的因素有哪些？
[答：Thomas Chang]	Reference voltage . SNR	[2008-2-26 11:27:47]
[问：b03212316]	高速ADC在工作中会对电源线和地线上产生很大的噪声，请问如何解决？有什么好的建议吗？
[答：Robert Shen]	The layout of component and PCB trace will be important. In our ADC datasheet, there is the suggestion on layout.	[2008-2-26 11:29:13]
[问：gumulaoyi]	在普通工业环境中使用ADC，是否需要专门的抗干扰措施？
[答：Michelle So]	It is recommended to optimize performance.	[2008-2-26 11:29:47]
[问：yerenxjh]	请问，在哪里可以找到放大器设计的简体中文资料？谢谢
[答：Robert Shen]	Here is http://www.national.com/CHT/appinfo/amps/	[2008-2-26 11:30:32]
[问：lulu2890]	贵公司ADC的转换位数是多少？
[答：Thomas Chang]	Currently we have 14 bit ADC including high speed and low speed range	[2008-2-26 11:30:42]
[问：lvkush0903]	混叠频率是指的什么，对于AD转换结果有什么影响？谢谢
[答：Thomas Chang]	混叠频率 is Aliasing frequency You can review the material page 4 to 8 .	[2008-2-26 11:31:07]
[问：wongsky]	Can you explain more details about National"s leading CTSD?
[答：Robert Shen]	Please see the detail in our web site: http://www.national.com/appinfo/adc/sigma_delta.html	[2008-2-26 11:31:08]
[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。	[2008-2-26 11:31:50]
[问：xiaoyongjun]	请问NS公司在放大器和模数转换器间接口技术上有何独到之处?
[答：David Shaw]	NS some ADC device has built in Anti Alias Filter, so noise immunity is very good. NS OP_Amp slew rate is very high, noise is very low.	[2008-2-26 11:32:08]
[问：lulu2890]	NS有有32位的ADC吗？
[答：Robert Shen]	Not, we do not have 32 bits ADC.	[2008-2-26 11:32:38]
[问：gumulaoyi]	是否转换位数越高，精度就越大？
[答：Michelle So]	no. higher resolution does not equal better performance. Still need to look at the ADC"s INL, DNL, SNR, ENOB, THD specs. For example, a 12-bit ADC could have better performance than a 16-bit ADC depending on other ADC specs.	[2008-2-26 11:33:05]
[问：cjwelltech]	请问怎样使ADC的输入最优化？
[答：Michelle So]	1. maximize dynamic range of the input signal to Full Scale of the ADC. 2. filter out all unwanted frequency. 3. Input signal must be settled before ADC"s sampling clock.	[2008-2-26 11:35:08]
[问：lulu2890]	请专家告知您的email，已便于日后请教问题。
[答：Thomas Chang]	For all technical questions, please visit our Technical Support Group at http://www.national.com/CHS/support/	[2008-2-26 11:35:11]
[问：qjc1221]	请问当前驱动高性能模数转换器时遇到的最主要的挑战有哪些？如何克服？
[答：David Shaw]	1. Noise coupling 2. need to have low noise reference voltage. 2. Need to add Anti Aliasing filter to filter input noise. Need to add good decoupling Capacitor at reference pin and ground.	[2008-2-26 11:35:45]
[问：jameswangsynnex]	影响ADC转换精度的主要因素有哪些？如何避免或消除？
[答：Michelle So]	1. Clean clock signal 2. pay attention to the amp+adc interface 3. input signal"s accuracy 4. aliasing filter 5. choose an ADC based on it"s performance spec instead of just resolution alone.	[2008-2-26 11:37:00]
[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。	[2008-2-26 11:38:38]
[问：sxj0456]	在ADC中使用差分输入有什么好处？如何把单端输入转成差分输入？
[答：Michelle So]	Differential amp + ADC give better dynamic performance. You can use single ended to differenial amplifier to convert single for the differential ADC.	[2008-2-26 11:41:08]
[问：whp6359]	ADC在PCB布局时如何考虑EMC方面的要求？有什么好的方法来提高抗干扰的问题呢？
[答：David Shaw]	ADC input impedance need to match with output of OP_Amp. Add Anti Alias Filter to filter those unneed signal.	[2008-2-26 11:41:58]
[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。	[2008-2-26 11:42:10]
[问：sd2620]	针对ADC驱动放大器的噪音，贵公司有无专门的消除设备？
[答：Michelle So]	Suggest to choose a low noise amplifier with better noise specs. Noise can only be reduced at the sourse.	[2008-2-26 11:43:07]
[问：jiang.xie]	精度和转换速率如何平衡？
[答：Thomas Chang]	1.FIrst you can consider : " what is your application ? " 2.You know your system LSB ,and sample rate demand .	[2008-2-26 11:46:16]
[主持人：ChinaECNet]	所有問題均已提交給美國國家半導體公司的專家。座談期間未回答的問題，美國國家半導體公司專家也會逐一回答，並在中電網上公佈，請大家注意收看。	[2008-2-26 11:49:01]
[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。	[2008-2-26 11:49:52]
[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。	[2008-2-26 11:50:26]
[主持人：ChinaECNet]	祝大家事業有成、生活愉快！歡迎多提寶貴意見，歡迎關注中電網，下次再見。	[2008-2-26 11:50:35]

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