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| 主题:运算放大器基本介绍 | ||
| 在线问答: | ||
| [问：yjems] | 多枚运放封装在一起的芯片与只包含一枚运放的芯片相比，性能上有差异吗？使用的时候需要注意什么？谢谢！ | |
| [答：KK] | In general, there should not be any significant difference on the op amp performance. However, something we need to take care such as cross talk between pins. | [2004-2-27 15:56:42] |
| [问：liwid] | 对于有开关电容的运放怎样分析其 幅频和相频特性？ | |
| [答：Ricky] | Sounds like this is not NS opamp. Otherwise, please ask more specific. | [2004-2-27 16:13:28] |
| [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。 | [2004-2-27 16:13:45] |
| [问：yjems] | 高输入阻抗、低偏置电流的运放在使用时需要注意什么？调零电路是否必须？ | |
| [答：Ricky] | null-offset (调零电路) is not necessary for nowaday opamp as long as the max offset voltage is acceptable. Basically, the tolerance of the resistor should be kept as min level for high input impedance & low bias current opamp. | [2004-2-27 16:17:23] |
| [问：张振坤] | 我用国半的运放做成正弦波振荡器,但稳定性能不太好.它和那些因素有关?如何提高它? | |
| [答：KK] | Pls be more specific on the type of osciilator circuit you are using. Different factors will affect the stablilty of the oscillators in different circuits. | [2004-2-27 16:21:12] |
| [问：baods] | 请问国半的运放哪个品种用在音频领域最好？ | |
| [答：KK] | For Audio application, low noise op amp is suggested. LMV721, LMV821 are some suitable op amps. | [2004-2-27 16:22:50] |
| [问：kwqiang] | 国半的放大器设计工具如何描述运算放大器的参数?库中的运放有多少?是否都是国半的产品?如何调用? | |
| [答：Ricky] | First of all, you should ask yourself if you have some part number in mind for your design. You can search this part number & start simulation from there with selected part into your design. Otherwise, you can pick the system with all the parameters. Then, our design tool will help you to choose the right opamp as well. Of course, all the suggested parts are NS opamp. | [2004-2-27 16:24:37] |
| [问：lineare] | 双电源运放和单电源运放有多啥差别？对双电源运放我能用单电源吗，会照成什么问题吗？谢谢！ | |
| [答：KK] | In theory, no matter single or dual supply, the op amp actually care the voltage range it operates. In reality, usually the single supply op amp can work at a narrow voltage range, e.g. 0V to 5V and dual supply op amp needs a wide operating voltage range. When using a dual supply op amp at single supply, pay attention on the CMVR and the output swing that the op amp can operate properly. | [2004-2-27 16:29:23] |
| [问：dtwh1588] | 在弱信号放大器中，如何降低电源引起的噪声？如何保持信号放大后的不失真？ | |
| [答：Ricky] | Please try to use de-coupling cap to reduce power supply noise. During the layout, please place these cap as close as the V+ pin as possible.Also, you may try to put guard-ring on the pcb at the pos / neg input pins.If it"s possible, try to use 2 stages of opamps instead of one opamp. With min gain of the 1st opamp or called "preamp", the distortion can be less significant to your system. | [2004-2-27 16:29:31] |
| [问：yl5139] | 怎样用一个运放构成具有上下限比较翻转的电路？ | |
| [答：KK] | Not sure if I understand your question correct. Sound like you need a window comparator circuit. | [2004-2-27 16:30:08] |
| [问：percy] | 怎么样加入短路保护功能？ | |
| [答：KK] | Usaully the short circuit protection circuit is built inside the op amps but only some have it. Pls check the datasheet to see if the op amp you choose with the protection circuit built-in. | [2004-2-27 16:32:00] |
| [问：tjlhj] | WEBENCH软件是否免费？ | |
| [答：KK] | Yes, it is absolutely free of charge. Feel free to use it. | [2004-2-27 16:32:25] |
| [问：boboluckey] | 请问？我要将50Hz的交流信号整形成同频的方波信号，该怎样选择芯片？怎样设计原理图？谢谢！！ | |
| [答：Ricky] | It is very difficult. Multiple stage of complex filters are needed. Please visit our web page for filter introduction.www.nationa.comSearch for AN-779 apps note. Thanks. | [2004-2-27 16:33:16] |
| [问：qin] | 请问当放大器放大线性度不好时应如何调节 | |
| [答：KK] | It really depends on the op amp circuit design. You may need to choose an op amp with better Harmonic Distortion spec. But limiting the input signal to the Analog ground will help improve the linearity of the output signal. | [2004-2-27 16:34:48] |
| [问：wyy2002] | 运算放大器的负载能力与哪些因素有关？如何提高运算放大器的负载能力？ | |
| [答：KK] | The output capability of an op amp depends on the output stage circuit design. In case you really need to drive a heavy load, we recommend that you should use an external transistor. | [2004-2-27 16:37:27] |
| [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。 | [2004-2-27 16:38:07] |
| [问：zhangjsh] | 请提供WEBENCH设计工具的详细取得方法，及操作说明。1、贵公司宽温度放大器的可选型号2、放大器温度补偿方法有何见解。 | |
| [答：Ricky] | For webench simulation, please visit our web.www.nationa.com for details.1.) We have many part available for wide temp range. There are 3 temp ranges that you can choose from -- commercial (0to70C), industrial (-40to85C)& military(-55 to 125C)I suggest you to choose military grade device.2.) Usually, you should select high precison opamp with high grade resistors.My suggestion: LMV771, LMV772, LMV774, LMC606x & LMC608x. | [2004-2-27 16:38:14] |
| [问：xueYxue] | 请问对于一些敏感电阻所产生的信号采用什么放大的方式会使输出信号更加纯净？谢谢！ | |
| [答：Ricky] | We call it " error amplifier" | [2004-2-27 16:39:30] |
| [问：jason_wang] | 您好：将传感器压电陶瓷的信号（电荷信号）转化为电平信号，如何选用运算放大器？ | |
| [答：KK] | CMOS op amp should be used because of the high input impedance. | [2004-2-27 16:39:31] |
| [问：kwqiang] | 放大器设计工具能模拟放大器那些性能?精确度如何? | |
| [答：Ricky] | It"s difficult to measure the accuracy of this simulation tools. I"m unsure about the data but I believe it"s good tool to give you brief idea that how the opamp performed in your system. | [2004-2-27 16:43:56] |
| [问：walkcman] | 请专家讲解一下什么叫"轨至轨"?谢谢！ | |
| [答：KK] | Rail-to-Rail input means that the op amp can work with an input signal coming from very close to or equal to both the +ve supply rail and -ve supply rail. Rail-to-rail means that the op amp can output a siganl swing very close to both the +ve supply rail and -ve supply rail. The Rail-to-rail feature is important in the single supply (i.e low voltage) applications. | [2004-2-27 16:46:13] |
| [问：shenglichun] | 对于抑制高次谐波，差分放大与单端放大那个好？ | |
| [答：Ricky] | It depends if your system is signal supply or dual supply with negative supply. Also, how you design the ground & power make big difference. Usually, I like diff amp 差分 better. | [2004-2-27 16:47:42] |
| [问：qin] | 请说明提高转换率的方法.是否需要外接另外一个运放来获得更好的驱动能力 | |
| [答：KK] | The slew rate is fixed for a particular op amp once its design is finished.Usually op amp is designed for signal conditioning but not for driving very high current. Power transistor or specific amplifier (e.g. Audio amp like our Boomer series) are recommend for high power applications. | [2004-2-27 16:50:19] |
| [问：kwqiang] | 放大器设计工具对元件的分布参数/寄生参数有何考虑? | |
| [答：Ricky] | These data is not included in this webench tool because parasitic parameters always releated to your pcb material...number of layer, trace width, etc. These uncertain is not completed..also not important for you to start design at the very beginning stage. | [2004-2-27 16:51:53] |
| [问：kwqiang] | 放大器设计工具能在什么样的环境下运行?价格如何? | |
| [答：Ricky] | It"s free! Please visit our web page.www.nationa.com | [2004-2-27 16:53:39] |
| [问：张振坤] | 双极运放和CMOS运放在性能有何差别? | |
| [答：KK] | Biploar op amp usually has a lower input impedance and high input bias current, high current noise, also has a faster speed.CMOS op amp usually has a higher input impedance and lower input bias current, high voltage noise, lower speed (BW) but consume very low current. | [2004-2-27 16:53:40] |
| [问：qin] | 运放的输出短路保护能力如何?在设计上如何考虑过载能力? | |
| [答：Ricky] | Usually, there is current limitor circuitry inside the opamp in order to protect the IC. However, in case of safety, please refer to datasheet / specification for max value. | [2004-2-27 16:55:46] |
| [问：ecnan jing_EBY7E] | NS的运放的电压灵敏度最大能到多少? | |
| [答：KK] | Voltage Sensitivity ? It seems this is the spec of the end system but not of an op amp. | [2004-2-27 16:56:44] |
| [问：imbird] | NS的op amp设计工具，可不可以和其它电路仿真工具(如cadenc）共享设计资源？ | |
| [答：Ricky] | For this particular webench tool, I don"t think they are compatible with each other. However, NS amplifier group offer spice models for OrCAD to use. Please visit our amplifier group web page.http://amplifiers.national.com | [2004-2-27 16:58:35] |
| [问：张振坤] | 运放的输入电流/电压失调,现在能达到什么样的水平? | |
| [答：KK] | The offset volage of an op amp can be trimmed at just a few uV range by various techniques like Chopper-stable or Laser trim in the production. | [2004-2-27 16:59:02] |
| [问：张振坤] | 运放作为单元电路已集成在许多电路中,是否是单独运放的应用范围在缩小? | |
| [答：KK] | Usually for new system, a lot of op amp will be used as integared solution is not ready. Also, discrete op amp is always used as some rememdy of some circuit problem. Therefore the demand for discrete op amps is actually incrasing. | [2004-2-27 17:01:04] |
| [问：fireheart] | 用webench模拟出来的结果与实际硬件电路会有多大的差异呢？ | |
| [答：Ricky] | It depends on the design of your other system such as power supply. In gerenal, the webench simulation can reach 90% accuracy to actual result. | [2004-2-27 17:01:14] |
| [问：huacc121] | 請問如何有效的實際測量op的特性 | |
| [答：Ricky] | All of the IC from our company are tested before we ship out. Basically, datasheet/spec is a very good reference for device performance. The actual measurement can be done by customer depends on the actual configuration. In general, I will suggest to use as buffer / voltage follower to test the opamp. | [2004-2-27 17:05:11] |
| [主持人：ChinaECNet] | 现在听众提问较多，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。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。 | [2004-2-27 17:05:56] |
| [问：wyy2002] | 国半有没有低功耗的运放？如何提高低功耗运放的负载能力？谢谢！ | |
| [答：KK] | Yes. Some low power op amp examples are LMC6442, LPV321. Low power op amp means it "Quiescent current" (i.e. no load) is very low, say a few uA. When it is used to drive heavy low - high current output, the low quiescent current will not make sense any more. Therefore, low power op amp usually cannot support high output. | [2004-2-27 17:07:38] |
| [问：chengjing] | 放大小的AC信号时,双端输入和单端输入在抑制噪音方面有什么不同xixi | |
| [答：Ricky] | No, should be about the same. The most important is the power supply design & grounding. | [2004-2-27 17:08:06] |
| [问：Lewiswen] | i use LM4910 for headphone amplifier,there always have noises,what"s the reason? | |
| [答：KK] | LM4910 is an audio amp but not an op amp. | [2004-2-27 17:09:27] |
| [问：ajanzhong] | 请专家介绍一下： 在电路设计时使用运算放大器，基本的原则是什么？需要注意纳方面的问题？ | |
| [答：Ricky] | Just brifely.Power supply range.Input range.Output range.Gain of the amplicationOutput loadingIf RRIO is needed?enough GBWP to cover whole freq range... | [2004-2-27 17:10:46] |
| [问：Byron] | What"s the diffence for the design between Crurent Op Amp & voltage OP Amp.? | |
| [答：KK] | Pls refer to our Application notes OA30 and OA31. | [2004-2-27 17:11:10] |
| [问：stick] | 现在运算放大器的单位增益带宽能做到多高？ | |
| [答：KK] | A few hundred MHz. | [2004-2-27 17:12:14] |
| [问：xueYxue] | 我用光敏电阻产生的电流放大后会不会产生干扰信号？谢谢！ | |
| [答：Ricky] | Basically, it should not be any problem. | [2004-2-27 17:12:45] |
| [问：Gemlee] | If NSC has CMOS technology AMP? | |
| [答：KK] | Yes, our LMC op amp series are all CMOS op amps. | [2004-2-27 17:12:47] |
| [问：hzh4656] | 请问是否有4路以上输出的运算放大器？多路输出信号是否同步放大？ | |
| [答：KK] | National doesn"t support more than 4 channel Op amps. Each channel works independently. | [2004-2-27 17:13:56] |
| [问：qin] | 如何减少差分输入的信号干扰 | |
| [答：Ricky] | Try add guard-ring at the positive & negative inputs of the opamp when you design your PCB layout. | [2004-2-27 17:14:26] |
| [问：张振坤] | 单电源运放和双电源运放在结构上和性能上有何差别?是否可以互用? | |
| [答：KK] | Pls refer to my answer to a previous question from "lineare@126.com" | [2004-2-27 17:17:17] |
| [问：张振坤] | 在什么情况下,需要特别注意运放的CMRR和PSRR参数? | |
| [答：Ricky] | CMRR is the ratio of the offset voltage over common mode voltage. As a result, be carefull if you have large offset opamp with small common voltage inputs. | [2004-2-27 17:18:34] |
| [问：lzhyi] | 集成运算放大器是否都需要调零呢？那些不需要调零，失调有多大？ | |
| [答：KK] | It depends on application. Today most generally purpose op amp doesn"t provide the offset trim pins. But you can still do it externally if it is needed. For simplicity, you can choice precision op amp for your precision application. | [2004-2-27 17:20:15] |
| [问：dtwh1588] | 运算放大器用于微伏级信号放大，如何解决放大倍数和噪声控制？ | |
| [答：Ricky] | Try to use small gain only for the preamp stage in order to protect the input signal before the real gain stage...mean two stages of opamp is the solution for very small input signal. Also, choose low noise part number..Suggestions: lmv721, lmv722, lmv751, lmv771, lmv772 & lmv774. | [2004-2-27 17:21:56] |
| [问：yjems] | 设计传感器接口电路时，运放的输入阻抗是不是越高越好？为什么？ | |
| [答：KK] | In general, Yes.Usually the current or voltage from a sensor is very little and therefore the input bias current is a major error source. The little the input bise current, the less error. | [2004-2-27 17:22:53] |
| [问：fred975] | 1.对于传感器上的信号，如何去除低频信号。我现在在对PSD（位置敏感探测器）的输出信号进行运算放大处理，但是总去除不了其中的干扰（低频部分）。2.对于负反馈系统，如何配置其反馈电阻Rf谢谢您的解答 | |
| [答：Ricky] | For 1.) You may try to place a high-pass filter to block low frequency signal such as DC. For example, a 0.1uF cap in series at the input.For 2.) You may try to use our webench simulation tool | [2004-2-27 17:27:01] |
| [问：kwqiang] | 用运放组成的有源滤波器和数字滤波器相比,有何差别和优缺点? | |
| [答：KK] | For some simple (low order) filter, active analog filter is easy to implement and low cost. But high order active analog filter design can be very difficult. In implementing Digital filter, you need to converter the analog signal to digital signal first and also you need to have a MCU or DSP to do all the calculation. That could be expensive. | [2004-2-27 17:27:23] |
| [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。 | [2004-2-27 17:27:40] |
| [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。 | [2004-2-27 17:27:59] |
| [主持人：ChinaECNet] | 现在请填写调查问卷，谢谢参与。 | [2004-2-27 17:28:29] |
| [主持人：ChinaECNet] | 恭喜您，tongwb_00a！经过计算机抽奖您在本次座谈中获得一部MP3播放器。请网名为 tongwb_00a 的用户与中电网联系(8610-82888222-7009 或 lilin@chinaecnet.com)。 | [2004-2-27 17:28:50] |
| [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。 | [2004-2-27 17:29:04] |
| [问：tjlhj] | 放大器前端需要射极跟随器吗？ | |
| [答：Ricky] | Not necessary. | [2004-2-27 17:29:50] |
| [问：kwqiang] | 能否提供少量的样片呢？ | |
| [答：KK] | Yes, You can apply samples at our Web. | [2004-2-27 17:30:59] |
| [问：seasize] | 在LCD TV板上，如何克服音频放大回路对视频的影响 | |
| [答：Ricky] | High pass filters are necessary to block audio frequency. | [2004-2-27 17:31:42] |
| [问：kwqiang] | 运算放大器的参数互相制约,请举例说明如高精度放大器,选择运放所依据的主要原则. | |
| [答：Ricky] | For high precison amp 高精度放大器, the most important is low offset voltage at the input. Also, offset voltage drift over the whole temperture range should be small enough. | [2004-2-27 17:34:25] |
| [问：qin] | 多级放大器设计时,级联间的电平和阻抗匹配如何考虑 | |
| [答：Ricky] | Mid-range of the total power range...Ex. 5V if power supply is 10V. Impedance is not that important. | [2004-2-27 17:35:51] |
| [问：gxynet] | NS have instrument op? | |
| [答：KK] | No, currently we don"t have instrument amps. | [2004-2-27 17:43:10] |
| [问：zjuhrw] | 如何在小信号时通过器件的选择滤掉噪声 | |
| [答：Ricky] | Low pass filter may help | [2004-2-27 17:44:52] |
| 非在线问答: | ||
| [问：] | 1。现在市面上常用的运放型号有哪些？<br> 2。我想利用运放制作一个双门限比较器，但是只知道原理没见过器件的我不知道如何下手，求助！ | |
| [答：] | 1.)Like our LMV321,358,354 & LMV341/2/4 & LMV821/2/4 2.) Please download our apps note AN-74 for comparator with hysteresis. | |
| [问：] | opamp在温度补偿方面有何改进？能否提供本次讲座详细资料？ | |
| [答：] | Opamp doesn't do temp compensation over the system. It does provide the user a very min offset drift over the full temp range if it is precison amplifier. | |
| [问：] | webench适用运放的设计吗？ | |
| [答：] | Yes! Please visit www.national.com | |
| [问：] | what should i take care when using op to drive pZT(PZT:压电陶瓷） | |
| [答：] | Since PZT is a capacitive load depends on the cross-section area, stability issue of close loop design maybe difficult. Also, noise & EMI may affect the system performance as well. | |
| [问：] | 放大器的频率有多宽，怎样拓宽频宽？谢谢 | |
| [答：] | On every datasheet of our part, max bandwidth is posted for referenc and this is max. | |
| [问：] | 放大器漂移问题该如何考虑和解决? | |
| [答：] | There are internal & external offset nulling can be done for offset error compensation. For internal approach, purchase a opamp with null adjust. For external approach, depends on the config of the circuit. Usually extra resistor within the feedback loop will help fine tuning the accuracy. | |
| [问：] | 和LM741价格相仿，性能更好的放大器，请举几个？谢谢 | |
| [答：] | How about LM321 or even better LMV321? | |
| [问：] | 哪种放大器适用于正反馈? | |
| [答：] | Generally, every opamp can be used as positive feedback system. Schmitt trigger, Hysteresis & window comparator are examples of positive feedback. | |
| [问：] | 您好，我想了解一下仪用放电器的选型注意事项？ | |
| [答：] | Low noise, Low offser & High precision part numbers. Like our LMV77x, LMC606x, LMC608x, LMV93x & LMV98x | |
| [问：] | 请教专家:用运放做带通滤波器,一般设计几级最稳定?谢谢! | |
| [答：] | 2nd-oder band pass filter should be good for general purpose. Except for some cases that very detail is needed, you may need up to like 6th order. | |
| [问：] | 请介绍宽带设频放大器，它的性能及通常价格水平? | |
| [答：] | Because of the fast slew rate & good ac performance, most of the wideband opamps are more expensive than general purpose opamps..USD 0.5 & up. | |
| [问：] | 请介绍运放的最新技术？ | |
| [答：] | Please visit our web page http://amplifiers.national.com | |
| [问：] | 请问，普通运算放大器开环增益有多大？ | |
| [答：] | Open loop gain approx. 200,000 generally. | |
| [问：] | 请问:我要将50Hz的交流信号整形成同频的方波信号，该怎样选择芯片？怎样设计原理图？谢谢！！ | |
| [答：] | Please download LM101A datasheet & review info of application section. | |
| [问：] | 请问NS的代理商是那些？我是在无锡的，就近有吗？ | |
| [答：] | We have 4 disty office at Nanjing. Please visit http://www.national.com/contacts/Details/0,1596,China,00.html for details. | |
| [问：] | 请问一般运放的输出接口是什么接口？能够带动多大的电流？如何选择上拉、下拉电阻？ | |
| [答：] | Mostly push-pull output stage is formed by a pair of bipolar transistors ..NPN & PNP. Max output current is choosen by design depends on specific application. | |
| [问：] | 请问一下：设计运放时，CMRR,输入输出阻抗、噪声、线性度、输出摆幅、功耗等几种参数，通常如何把握? | |
| [答：] | Trade-off always exists. Usually, prelim. Spec is chosen by product marketing, customer's input & industry trend…including technologies. | |
| [问：] | 请问有没有对数运算放大器？ | |
| [答：] | Yes! But it's not general purpose part. For low cost approach, you may try to LM394 which is good match BJT as transdiode device. Good performance! | |
| [问：] | 请问运放现在的主要发展趋势和应用前景? | |
| [答：] | Smaller size, less power…main application..handset, LCD panel, consumer, etc. | |
| [问：] | 请问运算放大器用于有源滤波器应注意和考虑的参数有哪些?请推荐几种运放型号.谢谢! | |
| [答：] | Low noise, low distortion...LMV721/2, LMV751, LMV771/2/4, LMV821/2/4 | |
| [问：] | 我在一项工程设计中要设计一个输出电压幅值高稳定度的、30MHz正弦振荡器，其输出功率为2W。请问：选择高速运放时需考虑那些指标？请推荐贵公司高速运放的合适型号。 | |
| [答：] | Please visit our web page http://amplifiers.national.com for our high speed series LMHxxxx. | |
| [问：] | 有没有运算放大器的的基本应用介绍？ | |
| [答：] | Please visit our web page http://amplifiers.national.com | |
| [问：] | 运放输出电压幅度是不是不能超过运放的正负工作电压？ | |
| [答：] | Correct! | |
| [问：] | 运算放大器的型号太多了，特别是性能相近的运放的型号也很多，请问实际应用中是不是随便选则就可以，还是根据经验，还是有其他的标准？ | |
| [答：] | It depends on your actual need. Sometimes a wrong choice is still functional but you can not obtain the best performance by the device itself. Experience & knowledge are the most important. | |
| [问：] | 运算放大器的指标？如何选购？ | |
| [答：] | Please visit http://amplifiers.national.com | |
| [问：] | '运算放大器基本介绍. 资料在那里 | |
| [答：] | Please visit http://amplifiers.national.com | |
| [问：] | 怎样实现放大器的反电压输出? | |
| [答：] | You have to get voltage reference together with opamp to form negative voltage regulator. | |
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