Finding the Needle in a Haystack: Measuring small differential voltages in the presence of large common-mode voltages

大海捞针：存在于高共模电压的小差分电压测量

Introduction ||概述

Differential Signals Versus Common-Mode Signals || 差分信号vs共模信号

Common-Mode Rejection (CMR) || 共模抑制

Galvanic Isolation || Galvanic隔离

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作者： ic921 于 2006/1/17 0:48:00 发布： 研讨翻译：大海捞针----存在于高共模电压的小差分电压测量 -2/2- High Impedance Versus Galvanic Isolation || 高阻抗vs Galvanic隔离 [09] [09] Many applications need the ability to sense a small differential voltage in the presence of a high common-mode voltage, but do not require the intrinsic safety or the ability to break ground loops that are provided by galvanic isolation. These applications require a high-CMR AMPLIFIER that can accept high common-mode voltage. This type of AMPLIFIER, sometimes called a “poor man’s isolation AMPLIFIER,” isolates the sensor from the SYSTEM with a high impedance, rather than with a galvanic isolation barrier. While not isolation in the true sense, it can serve the same purpose in some applications at much lower cost. In addition, a dc-to-dc converter is not required, since the whole SYSTEM is POWERed from the same POWER supply. 许多应用需要这样的能力，以感测存在于高共模电压中的小差分电压，但它并没有本质安全的要求或在提供galvani隔离的情况下允许切断地环路。此类应用就需要能接受高共模电压的高共模抑制的放大器。这种类型的放大器，有时称之为“穷人的放大器”，以高阻抗将传感器与系统隔离而不用galvanic隔离栅。如果实际的感测不隔离就在某些情况下可以以较低的费用获得同样的效果。不要DC-DC转换器的另一种情形，是因为整个系统都由同一电源供电。 ［译者语］While not isolation in the true sense 中，true一词似乎有特殊的意义，那种情景/情形实在想象不出！ [10] [10] Figure 2 shows the AD629, a high-common-mode-voltage difference AMPLIFIER that was designed for these types of applications. It seems simple enough. It’s “just” an op amp and five resistors. Can’t users “roll their own?” Yes, but the resistors would have to be matched to better than 0.01% and would have to track to better than 3 ppm/℃. RESISTOR self-heating would degrade dc CMR, while capacitive strays would degrade ac CMR. Performance, size, and cost would all be sacrificed compared to what could be obtained in an 8-lead DIP or SOIC. 如图2所示的高共模电压差分放大器AD629就是为这种类型的应用而设计的。它显得足够简单，正好是1个运算放大器加5个电阻。Can’t users “roll their own?”是的，但电阻的匹配度优于0.01%，且有优于3ppm/℃的(温度循迹效果)。电阻自热会降低直流共模抑制DC-CMR，而杂散电容(capacitive strays)则会降低交流共模抑制AC-CMR。牺牲性能、尺寸、价格compared to what could be obtained in an 8-lead DIP or SOIC。 ［译者语］Can’t users “roll their own?”这句不会译。 另，杂散电容一般是stray capacitive，这里capacitive strays有什么不同吗？ [11] [11] Applications such as simple industrial process-CONTROL loops with ANALOG inputs and OUTPUTs that require galvanic isolation could use the AD202/AD204. These are complete isolation AMPLIFIERs with galvanic isolation between the input and OUTPUT stages. Transformer coupling means that they can also provide isolated POWER to the input stage, eliminating the need for an external dc-to-dc converter. The AD202/AD204 provide an uncommitted op amp for input signal conditioning, have CMR of 130 dB at a gain of 100, and 2000-V-peak CMV isolation. Figure 3 shows an AD202 CIRCUIT* to measure a ± 5-V full-scale signal riding on a common-mode voltage of up to 2000 V. For applications that require isolated BRIDGE excitation, cold-junction compensation, linearization, and other signal-conditioning functions, the 3B, 5B, 6B, and 7B series provide a family of complete, well-isolated signal conditioners. 象有需要模拟galvanic隔离输入输出的简单工艺控制环这样的应用，可以用AD202/AD204。这些是输入级和输出级之间完全隔离的galvanic隔离放大器。变压器耦合意味着给输入级提供电源隔离，免去了额外的DC-DC转换器。The AD202/AD204 provide an uncommitted op amp for input signal conditioning，在增益为100时有130dB的共模抑制和2000V的峰值电压隔离。如图3的AD202电路*测量±5V的满度信号所承受(riding)的共模电压高达2000V。 在需要隔离桥激励、冷端补偿、线性化和其它信号调理功能的应用，the 3B, 5B, 6B, and 7B series provide a family of complete, well-isolated signal conditioners. ［译者语］前一个保留未译的一句，主要是对uncommitted的含意不解。后一句可能与产品系列有关，未详查，故未译。 [12] [12] *These Figures are illustrative examples; they are not detailed schematics of tested applications. Please consult PRODUCT data sheets for more information. You will also find the online seminar notes, Practical ANALOG Design Techniques, and the book, Practical Design Techniques for Sensor Signal Conditioning (available from ADI), to be useful sources of design information. Use extreme caution when working with high-voltage CIRCUITs. *这些图只是具体的实例，但不详细描述它们的测试应用原理。要获取更多更详尽的信息，请参考产品数据手册。你也可以查找在线研讨会笔记《Practical ANALOG Design Techniques》和索取《Practical Design Techniques for Sensor Signal Conditioning》一书(ADI有)的有用信息。Use extreme caution when working with high-voltage CIRCUITs. Figure 2. AD629 High-common-mode-voltage-difference AMPLIFIER. Figure 3. AD202/AD204 used in application requiring galvanic isolation and ANALOG OUTPUTs. [13] [13] Some industrial sensor applications require galvanic isolation, combined with the DIGITAL OUTPUT of a SMART sensor. DIGITAL isolation, rather than ANALOG isolation, could be used more cost-effectively but an external dc-to-dc converter is required. An example of this sort of application is in motor CONTROL, where a fault condition in the motor could destroy the CONTROL ELECTRONICS. The AD7742 synchronous voltage-to-frequency converter could be used, together with an opto-coupler and a dc-to-dc converter, as shown in Figure 4. A remote AD7742 can be interfaced with a SYSTEM microprocessor or microCONTROLler to complete the A/D conversion. For stand-alone applications the serial-OUTPUT AD7715 ANALOG front end, a 16-bit sigma-delta A/D converter, could be used, but it has five DIGITAL lines to isolate, rather than the SINGLE DIGITAL OUTPUT from the V/F converter. However, instead of five opto-couplers and a dc-to-dc converter, an AD260 five-channel high-speed LOGIC isolator with its own on-board transformer could be used. Figure 5 shows the AD7715 and AD260. 部分工业传感器应用要求有galvanic隔离，并和智能传感器的数字输出结合到一起。用数字隔离而不用模拟隔离可以更节省但需要外加DC-DC转换器。以马达控制一类的应用为例，马达故障情况下就会损坏控制器件。如图4，将AD7742同步电压频率转换器和光耦合器、DC-DC转换器用到一起。由系统微处理器或微控制器接口就能完成A/D转换。可用有模拟前端（处理的）串行输出的16位Σ-Δ模数转换器AD7715，但它有5个数字线要隔离，不单是V/F转换那样只有一条数据信号的输出。然而，用AD260则可以代替5个光耦和一个DC-DC转换器。 ［译者提示］同步VFC（AD7742）和异步VFC（如ADVFC32）是不同的。请阅读器件数据手册加以区别。 Figure 4. AD7742 used in application requiring galvanic isolation and DIGITAL OUTPUTs. Figure 5. AD7715/AD260 used in application requiring galvanic isolation and DIGITAL OUTPUTs. Figure 6

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作者： iC921 于 2006/1/18 17:32:00 发布： 共模增益不能用差模电压计算VDIFF 只能计算VCM的增益。 ------------------ 你分数有500分(我没看)帖图的方法是 1 点击编辑框下面的“普通” 2 等待片刻后，粘贴复制好的内容进去就可以了。 我现在就这样做。 Figure 1. Measurement SYSTEM with differential and common-mode voltages. 图1：有差分和共模电压的测量系统 ------------------ 另一种方法是：将图片链接放到下面的“链接图片”栏中，这不受分数限制。