运算放大器基本介绍（台湾地区）-National Semiconductor厂商_在线座谈

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主題:運算放大器基本介紹
線上問答:
[问：Scout]	在实验中经常发生集成运放使用过程中过热,或工作不稳定的情况.怎么才能避免,并且改善有集成运放的电路的工作稳定性呢?
[答：Ricky]	Over heat usually is releated to output impedance. Resistive load & capacitive load at the output effect the stability of the opamp. We have to reduce the loading current or cap load in order to stable the opamp.	[2004-2-27 10:49:14]
[问：郭大偉]	何謂 rail to rail amp
[答：KK]	In short, Rail to rail input means that Common Mode Input Voltage of the op amp can be as high as the positive supply rail and as low as the negative supply rail (or ground for single power supply application). Rail to rail output means that op amp can output a voltage swinging to very close to the + rail and - rail.	[2004-2-27 10:49:53]
[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。	[2004-2-27 10:50:05]
[主持人：ChinaECNet]	在此回答問題的專家是美國國家半導體公司的：KK, Ricky, Hanks	[2004-2-27 10:50:38]
[问：鸿浩]	1。运算放大器主要分为几种？各自之间的区别？2。运算放大器的基本工作原理？在使用运算放大器对其各参数计算中是否有简便的计算方法？3。面对众多的运算放大器如何才能准确快速选出最佳型号？
[答：Hank]	1. There are three different "input" modes of OP-Amps, which are differential input mode, inverting mode and non-inverting mode.2. The easiest way to calculate the gain of an OP-Amp is to use "virtual ground" theory.3. From the data sheet, you can find out the major parameters which you concern.	[2004-2-27 10:54:01]
[问：m_m1]	您好，我以前没有做过高频的东西。上次做高频放大（30M）才开始注意到高低频放大电路接法不一样，低频接反相输入端，而高频接正相输入端。但接正相输入端后运放片发热太大，这正常吗？
[答：Ricky]	Not sure your question exactly. It sounds like that the part is oscillating to cause too much heat. Please ask again.	[2004-2-27 10:54:15]
[问：tommyshiu]	power supply rejection ration 愈小愈好嗎
[答：KK]	For PSRR spec, the higher the better.	[2004-2-27 10:54:48]
[问：hello2]	请问运放接正负双电源供电和单电源供电，动态范围加宽了，对设计有何影响？该考虑什么？
[答：Hank]	To use Rail to Rail input and output OP Amp can increase the 动态范围.	[2004-2-27 10:57:46]
[问：peterwangyu]	怎样计算使用运放的LPF电路的噪声，可否详细一些？谢谢！
[答：Ricky]	Please visit our web page www.national.com to download the application notes AN-104 & AN-779.	[2004-2-27 10:59:50]
[问：sxwuyuan]	我需要做一个16路的可控增益放大器电路，使用电压或数字控制增益，控制范围至少为50dB，请问有没有合适的多路的跨导运算放大器或数控增益放大器？谢谢！
[答：KK]	We currently have three Variable Gain Amplifiers avialble. They are LMH6502, LMH6503 and LMH6504.	[2004-2-27 11:00:44]
[问：lizhaoyang]	运算放大器在PCB布线时应注意哪些事项？
[答：Hank]	Be careful the Vcc and GND planes, separate analog and digital Vcc and GND will help you a lot in PCB layout. Besides, the digital siginal should kept away from analog input or output signals to prevent interference.	[2004-2-27 11:02:15]
[问：frank_gao]	1.NS运算放大器在筆記型電腦中的主要用途及主要的NS运算放大器產品.2.NS的lead free 產品
[答：KK]	For NB application, op amp could be found in :1. Microphone preamp2. Some voltage detection (using comparator) circuit such as headphone/external speaker detection.3. Some buffer application at power.4. LCD panel brightness adjustmentetc....	[2004-2-27 11:03:55]
[问：eplee2001]	opa可以放大電流嘛?
[答：KK]	Yes, OP amp can be config as buffer amplifier - Current gain but No voltage gain.	[2004-2-27 11:08:59]
[问：danielcheng]	How to avoid oscillation on op amp
[答：KK]	Avoid directly driving very heavy cap load. All put a resistor between the cap load and the output pin.	[2004-2-27 11:10:09]
[问：zyt888]	从基本原理分析,运放只有"虚短"\"虚断"二种性能,但是在实际应用中,运放种类很多,我公司是生产测量仪器的,我们开发产品一般是先模仿同行的产品,然后分析其长\短处,加以改进提高,但是往往不清楚为什么要用这种或那种运放,请主持人能详细分析各种运放的特性及适用范围.
[答：Hank]	National Semiconductor or distributors can hold a seminar for your company to describle more details about different kind of OP Amps and their Specs.	[2004-2-27 11:10:39]
[问：zhz966]	请问有些微功耗放大器的标称静态电流是几十uA，这种放大器使用时有何注意事项？如果该运放的输出负载电阻很大（大于10M）其静态电流能否达到其标称值？
[答：Ricky]	静态电流 usually spec. at no load condition. If output impedance is bigger than 10Mohm, I believe it doesn"t make large different.	[2004-2-27 11:12:02]
[问：lotusyan]	Hi,How to get Webench?
[答：KK]	You can find it in the following web page :http://www.national.com/appinfo/amps/	[2004-2-27 11:14:17]
[问：Lewiswen]	according to amp,how to make auto gain control?
[答：Ricky]	Please review apps note OA-16. You can visit our web page www.nationa.com for info.	[2004-2-27 11:14:31]
[问：jason_wang]	设计电荷放大电路时，如何选择运算放大器型号？
[答：Hank]	The easiest way to choose an OP Amp is in www.national.com. Just input the basic requirements, the Amplifier WEBENCH Tool will choose and calculate it for you.	[2004-2-27 11:14:50]
[问：ecnanjing_EBY7E]	What are better for the input step of transister and JFET?
[答：Ricky]	It depends the input impedance of your circuit. JFET has even larger input impedance but noisy.	[2004-2-27 11:16:06]
[问：chinghsi]	如何降低input offset voltage
[答：Ricky]	This is the characterisitic of the opamp. Customer has to choose the correct spec. of the opamp to fulfill the needs. Better input offset voltage, higher the price.	[2004-2-27 11:17:48]
[问：lotusyan]	Does the Op-Amp of NS support rail to rail input?
[答：KK]	Yes, some of our op amps support rail to rail input. Pls check the CMVR (common mode voltage range) spec of the datasheet.	[2004-2-27 11:18:02]
[问：Betty Lee]	甚麼時候才需要採用CMOS輸入運算放大器？
[答：Hank]	Normally the CMOS OP Amps have larger input impedence and sometimes need only lower supply voltage, or R-R I/O functions. These are the conditions to choose an CMOS OP Amps.	[2004-2-27 11:18:37]
[问：slwoo]	Please recommend instrument amplifier for thermocouple. I need gain of 400 so that I can get approximately lmV/c from k-type thermocouple from O degree l to 200 degree c.
[答：Ricky]	Please take a look on our low offset voltage parts...LMV771 & LMV2011.	[2004-2-27 11:20:56]
[问：minghaoxu]	在使用中如何才能有效的降低电路中的噪声干扰？
[答：Hank]	Layout, VCC and GND are the most importance issues in reducing noise interference. To seperate digital Vcc, analog Vcc, ditital GND and analog GND is the key in layout stage.	[2004-2-27 11:23:17]
[问：mordon]	何謂電壓回授型，何謂電流回授型opamp
[答：KK]	Pls refer to our App notes AN597 (available in our web) for very detail explanation.	[2004-2-27 11:23:38]
[问：gexd]	您好！我们生产的产品是采用3V锂电池便携式的，设计中需要微功耗，工作频率较高（信号在20KC-30KC）的双运放，负载为CMOS电路。市面上很难找到，希望专家能够推荐介绍几种便宜的品种。谢谢！
[答：Ricky]	Please take a look on our LPV358. Thank you.	[2004-2-27 11:26:25]
[问：shaoming-8]	如何防止运算放大器遭受外界电磁干扰？在使用运算放大器时，如何提高他的输入电阻？
[答：Hank]	Sometimes you have to 1. use shielding 2. use lower resistance value of resistors.Choose an CMOS OP Amp can have larger input impedence.	[2004-2-27 11:27:04]
[问：benny.zhao]	SlewRate与带宽有什么关系？
[答：KK]	Slew rate is related to the large signal bandwidth. Large Signal BW = SR/2piVout	[2004-2-27 11:27:17]
[问：eric_chuang]	如將OP運用於電池電源之電路，常因c耗電問題造成電池壽命很短，如何才能減低OP之耗電量？？
[答：Ricky]	Please choose low power opamp...like LPV321, LMC6442, LMC6041, LMC7111, LMC7215	[2004-2-27 11:28:13]
[问：minghaoxu]	现在运放的增益-带宽积可以达到多少？
[答：KK]	The GPB can reach over 1GHz for some high speed op amp. But pls note that most of them doesn"t work at unity gain. Usually it is for high gain applications like 100MHz at a gain of 10.	[2004-2-27 11:31:12]
[问：ecnan jing_EBY7E]	How to reduces noise in Op-amp at high freq. application
[答：Ricky]	Make sure have a proper bypass at supply line of the opamp. Try the best to place these cap as close as to the V+ pin. And even have guard-ring at both pos & neg input pins of the PCB.	[2004-2-27 11:32:56]
[问：yale.liu]	在使用运算放大器时候，除了关心其放大系数，还要考虑哪些要素？
[答：KK]	Different appliation will have emphasis at different parameters. For instance, low power (portable) design should pay attention on the Input current consumption spec, pesicision application should care the input offset voltage.	[2004-2-27 11:33:31]
[问：zhou4148]	本次是运算放大器的知识，我想问的是运算放大器的各种工作状态，它的各种调节，怎样选择运算放大器。
[答：Ricky]	Please visit our web page. http://amplifiers.national.com.Thanks.	[2004-2-27 11:33:54]
[问：hzh4656]	目前有没有超过4路以上的运算放大器？
[答：KK]	As for National, we don"t have any op amp beyond four channels.	[2004-2-27 11:35:04]
[问：lotusyan]	Can the differential input of Op-Amp restrain the common interfere?
[答：Ricky]	Sounds like coupling cap & isolation can help.	[2004-2-27 11:35:31]
[问：mordon]	Opamp 的輸入端分別有BJT input 跟FET input，請簡述這兩種輸入方式的優缺點。
[答：Hank]	The supply current of BJT OP Amp is normally larger than CMOS OP Amp. It has better noise immunity and larger supply voltage range. However, the BJT OP Amp is difficult to have rail to rail I/O functions, and normally the supply voltage of an CMOS OP Amp can be lower than an BJT OP Amp.	[2004-2-27 11:37:07]
[问：jerrychen]	請問為何op的輸出會因為溫度／溼度有所改變嗎？？（假設外部的電阻為定值）
[答：Ricky]	Ideally, op sould have temperture compensation by using ideal current source for internal bias called " PTAT " - proportional to absolute temperture. Absolute temperture means 0K. However, nothing is perfect in our real life...as a result, op"s temp. comp also vary to cause changing at the output. Hopefully, I answer your question. Thanks.	[2004-2-27 11:40:30]
[问：xzshan]	请告诉我有关运放设计方面应注意的问题,我在开发检测器件
[答：Hank]	For equipment instruments applications, a precision OP Amp is normally used. The input offset voltage, CMRR, and background noise are the most important parameters.	[2004-2-27 11:41:16]
[问：lotusyan]	贵公司的Op-Amp什么型号的产品可以提供CMRR大于100？
[答：KK]	It is difficult to get >100dB CMRR by using one single op amp. We recommend that you should build a Differential -Input, Differential-output amp by using two op amps (or an instrumentatl amp by using three op amps). The CMRR can reach >100dB. Final CMRR = CMRR1xCMRR2/CMRR1-CMRR2.	[2004-2-27 11:42:12]
[问：shaosl]	请问：1、对于放大器的选择上有什么比较好的方法（兼顾带宽和速度）？ 2、在进行电路测试时，对于放大器的测试有什么比较好的方法？对于测试条件有什么具体要求？ 3、放大器的转换速率和Slew Rate有什么具体含义？对于选片有什么影响？
[答：Ricky]	For 1.) Please check our op selection guide.2.) Try buffer config, and vary the input from min to max to test output.3.) Slew rate is similar to response time of the opamp.	[2004-2-27 11:45:01]
[问：hello2]	用运放对音频信号D/A后的音频信号有源滤波的电路该怎样设计。
[答：Ricky]	Please visit our web page & find AN-779	[2004-2-27 11:47:06]
[问：haishengg]	请问如何提高运算放大器的可靠性?你能带来运算放大器的一些最新用法吗?
[答：Hank]	We have to not only consider the circuit itself but also the products" reliability - does the supplier has good process, good testing and even tradition.	[2004-2-27 11:47:16]
[问：eplee2001]	如何利用opa放大視頻訊號?
[答：Ricky]	You better choose our high speed opa...like LMH series family.	[2004-2-27 11:48:16]
[问：eric_chuang]	為何OP工作於高頻時，輸出端會有類似電感之情形，造成接電容性負載時產生震盪？？
[答：Ricky]	You may try to add isolation resistor at the output.	[2004-2-27 11:49:05]
[问：feiyufly001]	能不能介绍一下一般运放的输入输出的计算方法
[答：Hank]	Please refer to the materials on page 18 to page 20 of this seminar.	[2004-2-27 11:49:34]
[问：xlei]	采用运放，如LM324做积分器的时候，将运放负极接地，则1，如果输入的是负电压是不是不能正常工作？2，输出与输入负之间的电容正极应该接哪边？怎样才能正常工作
[答：Ricky]	Would you like to try our webench live simulation? Please visit our web page www.national.com	[2004-2-27 11:51:06]
[问：atras]	The amp can applicat on the CATV PRODUCT?
[答：Ricky]	Yes! Please look at out LMH series Opamps. They are high speed opamp & designed for high speed video application.	[2004-2-27 11:52:28]
[主持人：ChinaECNet]	現在聽眾提問較多，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。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。	[2004-2-27 11:52:43]
[问：Eagle_chen]	If we use LM358 as portable device charge IC , how to detect the current of load ? how about his performance ?
[答：Ricky]	Yes. It can be done by any general opamp.Usually we will use high side current sensing to detect the load.	[2004-2-27 11:54:07]
[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。	[2004-2-27 11:54:18]
[问：lotusyan]	我们需要一个输入信号很小，mA级，能抑制共模干扰的运放，不知道贵公司有没有合适的型号？
[答：Hank]	There are many many OP Amps can meet your requirements, we need more specific parameters to give you a suggestion. For example, the supply voltage, CMRR value, Vio, R/R etc..	[2004-2-27 11:54:40]
[主持人：ChinaECNet]	恭喜您，台塑訊科的ricky_yang！經過電腦抽獎您在本次座談中獲得一部MP3播放器。請網名為 ricky_yang 的用戶與中電網聯繫(8610-82888222-7009 或 lilin@chinaecnet.com)。	[2004-2-27 11:55:21]
[主持人：ChinaECNet]	中電網開辦的“工程師之家/線上座談”欄目，是中電網向中國電子元器件領域廣大廠商、科研人員和工程師們推薦、推廣新產品、新技術、新應用而推出的一項重要的技術教育、培訓和支持活動。在這項活動中，中電網會不斷邀請一些世界著名電子元器件供應商的高級技術或高級經營管理人員主講國際半導體科技最新進展、電子元器件最新產品及其應用、全球半導體市場等方面的內容，著力構建起國內外同行業間直接技術交流的橋樑。希望在各位聽眾（網友）的積極參與下，中電網“線上座談”能越辦越好，其影響範圍越來越廣！	[2004-2-27 11:55:56]
[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。	[2004-2-27 11:56:08]
[问：YONGJUN]	接铂电阻pt100 运算放大器的用法，型号，最佳方案。谢谢。
[答：Ricky]	You may want to use high precison opamp...like LMV771, LMC606x, LMC608x.	[2004-2-27 11:57:33]
[问：linuc]	如何实现运算放大器电路中噪声的最小化?
[答：Ricky]	Please choose low noise opamp...like LMV721, LMV751, LMV771/2/4	[2004-2-27 11:59:32]
[问：mordon]	電容性的負載有哪些，可否以實際電路舉例一下
[答：Hank]	電容性的負載 are those components with capacitance factor. A capacitor can be treated as a pure capacitance load. Even an MOSFET has a parasitic capacitance.	[2004-2-27 12:00:14]
[问：linuc]	如何实现运算放大器电路中噪声的最小化?
[答：Hank]	To use analog supply voltage and seperate digital and analog GND is the most important issue and then to consider an OP Amp with better noise immunity capability, such as better CMRR, PSRR, and background noise.	[2004-2-27 12:05:55]
[问：chenkevin23]	设计放大器的时候，频率补偿方面通常是如何考虑的
[答：Ricky]	die size of the opamp is the most important. cap is the larger device in the IC process. Also, output condition is one of consideration as well.	[2004-2-27 12:06:21]
[问：zzh0705]	怎样放大MV级的信号？
[答：Ricky]	You may choose our low noise & high precison parts...like LMV721, LMV751, LMV771...LMV2011	[2004-2-27 12:07:50]
[问：zjy357]	在分析运算放大器的频率响应和极点时会用到一种“波特（Bode）图”，请详细讲解一下波特图。
[答：Ricky]	Usually we use 0 axis as ref point. For phase margin, it better more than 45deg. For gain margin, it better than more than 10dB in order to have stable system.	[2004-2-27 12:10:47]

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