1.>何种情况下使用仪表运放比其它运放具有更大优势?2.>仪表运放在应用设计中需注意哪些事项?3.>单电源的仪表运放在设计中应避免的事项?
1. (Differential input) Small signal with high common mode voltage. High source impedance.2. Pay attention to common mode range (say, if higher than +/-15V, then need AD628 or AD629 type difference amp), PCB layout (symitic layout, it”s easier for AD8221) to get high CMRR.3. Common mode voltage is positive, not go to negative (unless specified by datasheet). For examples, AD623 at +5V power supply, input range is -0.15V to 4.85V.
仪表放大器通常会受到无线频率干扰,请问如何减少这种干扰的?
Use EMI filter. AD8556 has some build in EMI filter.
请问,在仪表放大器的ref端直接接参考电压好,还是通过一个单运放构成的跟随器效果好?为什么?谢谢。
因为REF端并不需要大的输入电流,也不需要阻抗匹配,所以直接接参考电压就可以的。
仪表放大器的设计,与带放大器、AD转换器的单芯片信号调理器的设计,有什么区别?
您是指内部电路的设计,还是它们的应用之间的不同?如果是内部的设计,放大器+ADC的设计要考虑更多的相互干扰的问题。对于应用来说,集成的方案的尺寸会更小,但是性能相对于高精度的单仪表放大器来讲会差一些。
仪表放大器的差分输入,和传感器配合使用时,如何设定输入偏置电路?电阻数值如何选取?
If you mean set common mode voltage level, it”s better to set ((+V)-(-V))/2. VCM will affect output range. If the IIA is not good, it also affect CMRR. But good parts such as AD8221 will guaratee CMRR over a very big common mode voltage range. AD8221 CMRR>100dB at 1kHz at gain of 10 vover the tatal VCM = –10V to +10V range (+/-15V power supply).
在AD8221的输入端需要怎样设计滤波器才能最大限度降低噪声而又得到快速的响应时间?
一般情况下,AD8221的输入端不需要接滤波器,至于滤波等功能可以放在AD8221后去做。 仪表放大器对滤波器没有什么特殊的要求,就按照截止频率的需要设计滤波器就好。
怎样在仪表放大器端调整失调和增益。
Most IIA has a gain set resitor, you can choose the right resistors. That”s why it”s better than discrete circuit. Some parts has PGA (such as AD8251 G=1,2,4,8, AD8250 G=1,2,5,10), AD8555 (G=70~1280)
ADI的单片仪表放大器有那些型号?价格如何?
ADI的单片仪表放大器有很多产品,最新的高性价比产品有AD8221, AD8220,AD8230,AD8250,AD8251等等。价格也根据性能的不同有所变化,您可以到ADI网站上了解更多产品和价格的信息。www.analog.com/china
用仪表放大器构成压控恒流源 如何搭建。。
A normal AMP can built constand current circuit to put sensor resistor between load and GND. A IIA can build constand current circuit where the sensor resistor can be put any where in the load circuit. And as IIA has good CMRR over high common mode range, so it”s possbile to use small sensor resistors.
我现在想对一个频率为1KHZ,但幅度只有几十uv的微弱信号进行放大1000倍,请问现在ADI有什么放大器能尽量减少干扰并且方便使用呢,以前听说AD623,现在应该有更好的使用吧,请推荐和介绍。
因为您放大1000倍需要的增益带宽积为1M,最新推出的仪表放大器精度有所提高,但是大多数增益带宽积在700~800K,所以还是继续使用AD623比较好
AD8251和AD8250 现在样片出来了么?可以申请到么?
AD8250已量产。AD8251还未量产,请联系ADI代理商申请样片。
仪表放大器和传感器配合使用时,如何进行调零?
IIA normally has very low offset, so there is no need to add just the offset of the IIA (for example, AD8221 has 25 μV max input offset voltage, 0.3 μV/°C max input offset drift). For the sensor, if you can gurantee senor”s ouput is differential to IIA, then common mode voltage will be reject by IIA”s high CMRR.
ADI的仪表放大器的输入电流/电压失调以及共模抑制比,现在能达到什么样的水平?
Good new IIA has high CMRR at both DC and some frequency range (AD8221 spec at 10k HZ).AD8221 CMRR DC to 60 Hz with 1 k? Source Imbalance (VCM = –10 V to +10 V)G = 1 80(Agrade), 90(B grade) 80(C grade) dBG = 10 100 110 100 dBG = 100 120 130 120 dBG = 1000 130 140 130 dBCMRR at 10 kHz (VCM = –10 V to +10 V )G = 1 80 80 80 dBG = 10 90 100 90 dBG = 100 100 110 100 dBG = 1000 100 110 100 dB
电阻的匹配问题是指它的绝对值还是它们的比值?
它们之间的差值。差值决定了共模抑制比,绝对值决定了增益误差。
我们有一个产品中有9路AD采样,AD前的运方和滤波器件分别是OP200GS,MAX307CWI,AD795,AD797BR,ADC用的是AD7862,现在遇到的问题是9个通道的精度不够,导致9通道一致性不够,请问改从那个方面下手改进?谢谢!!
AD7862 is Simultaneous Sampling Dual 250 kSPS 12-Bit ADC with two 2:1 MUX. If every channel is exactly the same, then it should be OK. The issue may comes from MAX307 differential MUX because it has big on resistor (100 Ohm) and it drift with temperature and varied with frequecy, you need high input impedance after MAX307 (or ADG1207). Various in the amplifiers on each channel is also a issue (difference in gain by mismatch of resistors, big offset amplifiers has different offset, offset drifter, etc). A new part is AD7658 (6ch simulteneous sampling 12bit ADC, AD7656 is 6ch 16bits). If you use 2pcs, then no MUX need. Then it”s easier to get good channel match. Here you can use OP2177 (Low Offset Voltage: 60 μV Max,Very Low Offset Voltage Drift: 0.7 μV/°C Max)
如果要扩充单芯片仪表放大器的性能,如何处理输入级和输出级才能提高整体性能而不是降低性能?
If you use IC in your application, then choose a good part (such as AD8221). If you mean IC design, then it”s more important to make sure good match resistors, choose right input type and carefuly bias. Commplemtary design will get good performance, maybe higher cost.
请介绍以下OP482G的应用
OP482的功耗较低,同时输入阻抗高,偏置电流小,因此它可以应用在一些便携式的需要高阻抗的信号调理的应用上。
放大器如AD604,特别在高增益下会产生自激而引起干扰噪音,请问有何良策?
First, please do not use 1 AD604 to gain up one channel twice, it”s better to use 2pcs AD8331 if you need 2 stage gain. If you use each AD604 in 2 channel, then it”s ok. A new part is AD8332. Carefully PCB layout is very important. Make sure output is far away from input. Make sure good decoupling. Get a good low impedance ground plane.
仪表放大器由多个运放组成,它对运放性能的匹配性有何特别要求?
If you use 3 amplifiers to build the same function as IIA, then all resistors must be matched (exactly the same). It”s easier to use 1 integrated IIA (such AD8221). Please refer to presentation.
另外,ADI有没有输入和输出同为Rail to Rail的仪表放大器?请介绍一下!谢谢
您可以考虑AD623,他的输入和输出到轨的距离都只有150mV左右。
如何实现两个仪表放大器的同步工作?需要增加什么电路或元件?
I do not understand whay you want. The analog circuit will always gain all the input. If you circuit are exactly the same, the same length of input and output, same gain, then the 2 channel should be good matched (same amplitude, same phase delay). It”s better to use dual IIA (such as AD8222) than 2pcs single IIA (such as AD8221) because dual IIA in same package has the same temperature drift.
可不可问一个运放的问题?就是所谓深度负反馈的不稳定性,可不可以介绍一个经验值,比如闭环增益为多少倍可能会引起系统不稳定
If the AMP”s phase margin is less than 30 degree, then it”s trend to be unstable. It depends on feed back net work, no necessary high gain. Normally under high gain, we need consider parastics (for example, if you use a feed back resistor of 10M Ohm, then the leakage on PCB board maybe some impact, but when you use 10k Ohm feed back resitor, then the leakage maybe very small compare to feed back current). And, if the amplifier is current feed back resistor, please follow the recommandation feed back resistor suggested in datasheet. Normally 1 gain stage with a gain bigger than 40dB (A=100), you need consider stability issue.
如何拟制手机信号对仪表放大器或自建仪表放大器电路的干扰?
对于RFI干扰,您可以参考AD8221数据手册的图49
仪表放大器具有自动调零功能吗?它对频率特性有何影响?它又如何和信号通道隔离?
Most IIA has very low offest. If use chop technology, need consider the chop frequency if the part is not good designed (please refer to AD8628 self-zero amplfier datasheet for details). If it does, please add low pass filter to remove it”s impact.
仪表放大器的输入端和传感器的输出相连接,如何处理传感器的噪音问题?
可以加入滤波器滤除噪声。
仪表放大器和一般的高性能运算放大器有何不同?请专家给介绍一下!谢谢!
仪放的输入阻抗高,共模抑制比高,放大的是差分信号。
请介绍一下仪表放大器的主要应用在那些领域?
仪表,医疗,传感器信号调理等等。总的来说,它可以用在需要对大噪声和干扰下的高阻抗的微弱信号的检测的应用上。
i plan to measure bio signals. the signals r in micro V level. the BW is about 1MHz. i need 4 channel.give me some advice for amp.thanks
Most IIA is not faster enough to work at 1MHZ signal. But AD8250 (G=1,2,5,10) is fast enough (10MHZ) to gain it up. AD8250 has High CMRR (98 dB (min), *G = 10), Low gain drift(10 ppm/°C (max)), Low offset drift( 1.7 μV/°C (max), G = 10). If you need high gain and low noise, AD8334 is a good choice (0.74nv/sqrt(Hz), 100M BW). Another low noise part is ADA4899 (Ultralow noise: 1 nV/√Hz, 2.6 pA/√Hz bandwidth: 600 MHz (G = +1))
AD627的输入时Rai to Rail的么?它的合适的输入范围是多少?
AD627 is rail to rail out put, not rail to rail input. It”s input range is (?VS) ? 0.1 to (+VS)– 1 (-5.1V to 4V at +/-5V power supply)
我需要测量生物信号。微伏级到几十微伏。4个通道。带宽在1MHz。(信号放大后,用ADC同步纪录4个通道中信号的峰出现的时间,值)对放大器,我考虑用AD8250作前放,后接8334或8335。请教专家,这个方案如何?有没有更好的方案?我这里用8334还是8335好?谢谢。
This design depends on you AC or DC+AC signal. I assume you have big source impdance, AD8250 is good, the only issue is AD8250 has big noise (Low noise: 18 nV/√Hz, G = 10 (max)), suggest build a good 1MHZ Low pass fiter after AD8250, then to AD8334. If AC only and small source impdance, suggest AD8334″s LNA directly as it has low noise. AD8334 is better than AD8335 as it has lower noise, but no big difference if you have use AD8250 in first stage, as AD8250″s noise is much bigger. ADC, you need 4 channel simultenouse sampling, suggest 2pcs AD9216 (dual 10bit, PP port, use AD9238 if you need 12bit) or 1pcs AD9219 (quad, 10bit, LVDS output). ADA4899-1 has small input impedance as well.