运算放大器基本介绍（台湾地区）National Semiconductor

简介：这次研讨会为需要使用运算放大器的工程师提供一个数据详尽的“速成课程”,重点介绍运算放大器的基本运作原理和电路设计的问题以及运算放大器的应用.

问：What are better for the input step of transister and JFET?
答： It depends the input impedance of your circuit. JFET has even larger input impedance but noisy.

问：如何实现运算放大器电路中噪声的最小化?
答： Please choose low noise opamp...like LMV721, LMV751, LMV771/2/4

问：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： 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..

问：贵公司的Op-Amp什么型号的产品可以提供CMRR大于100？
答： 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 C

问：電容性的負載有哪些，可否以實際電路舉例一下
答： 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.

问：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： To use Rail to Rail input and output OP Amp can increase the  动态范围.

问：现在运放的增益-带宽积可以达到多少？
答： 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.

问：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： Please take a look on our low offset voltage parts...LMV771 & LMV2011.

问：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： National Semiconductor or distributors can hold a seminar for your company to describle more details about different kind of OP Amps and their Specs.

问：opa可以放大電流嘛?
答： Yes, OP amp can be config as buffer amplifier - Current gain but No voltage gain.