Allegro ICs Based on Giant Magnetoresistance (GMR)
Allegro ICs Based on Giant Magnetoresistance (GMR)
By Bryan Cadugan，
亚博棋牌游戏
抽象
亚博棋牌游戏Allegro MicroSystems是一个发展，制造和营销高性能的世界领导者integrated circuits (ICs)，它包含高性能磁传感器。这款白皮书提供了对巨型磁阻（GMR）效应的基本理解，以及Allegro如何在市场领先的IC中使用这种技术，以满足当今的应用要求。
The Giant Magnetoresistance (GMR) Effect
The GMR effect was discovered in 1988 by both Albert Fert of Unité Mixte de Physique CNRS/Thales and Peter Grünberg of Institut für Festkörperforschung Forschungszentrum Jülich GmbH. Both of these individuals won the Nobel Prize for this discovery in 2007. The fundamental principle of the GMR effect is based on electron spins. In a magnetoresistor, electron scattering rates increase or decrease as a function of the interaction of the spin state of the electrons and the magnetic orientation of the medium in which the electrons are traveling. Electron scattering increases the mean free path of the electron flow, effectively altering the resistance of the medium. In summary, a magnetoresistor is a resistor that changes its resistance value in the presence of a magnetic field.
GMR transducers are manufactured by creating a sequence of very thin layers made of different magnetic and nonmagnetic materials. The sequence and thickness of these materials enable the stack of thin films (GMR stack) to change its resistance in the presence of magnetic fields.
随着时间的推移，GMR的进步导致了“旋转阀”型结构的开发，这是Allegro在其最新IC中使用的。在旋转阀中，两个磁性层中的一个被认为是“参考”并且以其定向固定或固定，另一个称为“自由”层，并且可以自由地与周围环境中的磁场对齐（见图1）。在典型的磁传感器应用中，该磁场由磁铁或电流产生，并且被亚博尊贵会员称为B.应用程序throughout the remainder of this document. The “spin-valve” is so named because it resembles a faucet, where the flow of water is related to the degree of rotation of the spigot. The open position for a GMR spin-valve relates to when themagnetic layers are aligned (as shown in Orientation A in Figure 1) where the resistance is lowest. The closed position (or low flow position) occurs when the magnetic layers are anti-aligned (as shown in Orientation B in Figure 1) where the resistance is highest. For any angular difference between the “reference” and “free” layers, the resistance of the GMR transducer is proportional to the cosine of this angle.
R = R闵+（r.闵– R最大）×cos（θ）
The % of change in resistance is called the MR%, or magnetoresistive percentage. Allegro’s GMR transducers typically have MR% in the range of 5% to 8% for the full range of field response. This level of response creates a signal about 50 times higher than Allegro’s Hall-effect transducers, enabling a higher signal-to-noise level in ICs using GMR transducers instead of Hall-effect transducers.
The GMR Response
The native response of the GMR to an applied field (B应用程序) in the plane of the resistor (and therefore the die surface or IC surface) is proportional to the cosine of the angle of the applied magnetic
领域。然而，GMR的电阻值并不总是表示场的强度。基本GMR换能器更多的是磁角传感器（如图1所示）。但是，在
many cases, a linear response to the field in one axis is desired from a GMR transducer. In order to create this linear response, an anisotropy is created 90 degrees from the “reference” layer that
像另一个磁场一样用施加的场（这个各向异性诱导的场，B一个，由图2中的黄色箭头表示）。然后，响应在零磁场的状态下具有线性区域。这种线性化响应的方法用于许多Allegro的IC。重要的是要注意现场响应范围的饱和响应。当在线性应用时，将最大操作范围指定以考虑杂散磁场和待感测的磁刺激。可以引用GMR产品数据表以指示操作边界条件。一项注意事项是Allegro霍尔效应解决方案没有这种本土饱和的响应。Allegro的Hall ICS基于应用程序或电路条件具有饱和的响应，而不是大厅技术本身的结果。
在IC应用中使用GMR
通常，GMR电阻器被创建并放置在惠斯通桥配置中。惠斯通桥的一半（图3中的元素A和C）位于一个磁性条件下
一个d the other half of the Wheatstone bridge (elements B and D) is positioned under another magnetic condition. Ideally, these conditions present an equal but opposite response, allowing for the maximum output signal from the bridge. As shown by blue arrows and text in Figure 3, elements A and C sense a field in an orientation pointing left (in an anti-parallel state in this example, denoted as R最大in Figure 1), and elements B and D sense a field in an orientation pointing right (in a parallel state in this example, denoted as R闵在图1中）。结果是电阻器A和C将处于高电阻状态，并且B和D中的那些将处于低电阻状态。然后差分输出将是正的。
With a Wheatstone bridge, the output is always scaled with the applied VCC., and with no magnetic field applied, centers the differential output at 0 V. The differential bridge output will then swing positively or negatively according to the direction of the applied magnetic field on the Wheatstone bridge. This bridge configuration allows for both a cancellation of temperature effects and also for a level of immunity to stray magnetic field.
For current sensors, field is steered over elements A and C of the Wheatstone bridge in one direction, and the field over elementsB and D of the Wheatstone bridge in the opposite direction (see
Figure 4). The output of the Wheatstone bridge is fed into a differential amplifier and then through Allegro’s normal sensitivity and offset correction circuits, and possibly more advanced signal processing circuits in the analog or digital domains. In other applications where the conductor is not integrated, the physical spatial separation of the GMR elements is used to affect a differential
信号，允许响应各种磁刺激。
GMR的另一个应用程序是用于环杂志net speed sensing applications such as ABS or transmission sensors. A ring of magnetic material is created with alternating north and south magnetization as shown in Figure 5. The GMR sensor may be placed under this material such that the plane of the die is horizontal. The spacing between the A and C GMR elements and B and D GMR elements creates a different magnetic field sensed by these sets of elements based on where the ring magnet is in its rotational cycle. When an N (north) pole is centered over the die, the magnetic field is pointing to the left over elements A and C and to the right over elements B and D. This will create a response on the GMR as noted in Figure 3, with a maximum positive response out of the GMR bridge. When over an S (south) pole, the response will be maximally negative. When between poles, the field is about equal for each element and the response of the bridge is near 0. This results in a sinusoidal output from the sensor as the ring magnet rotates. By counting the time between thresholds in the output over time, the speed of the ring magnet can be measured. The higher sensitivity of the GMR compared with traditional Hall sensors provides the capability for much higher air gap sensing, as well as much higher repeatability in the output for higher precision in the speed output.
Allegro有一个单片GMR解决方案
许多销售GMR解决方案的供应商使用多芯片方法：“传感器”芯片和“接口”芯片。Allegro是直接整合GMR技术的IC制造商中的一个非常少数的IC制造商之一
on top of their semiconductor wafers.
This integrated approach offers many advantages, including an improvement in reliability by avoiding additional die-to-die bonding, and allowing for a simpler overall design when integrating current carrying lines or positioning the elements versus an external reference.
Wafers into Packages
由于Allegro的GMR解决方案本质上是单片，因此GMR IC晶片以与Hall效果传感器IC晶片相同的方式管理。将制造的晶片磨削到它们的包装的适当厚度，并且将晶片切割成适当的模具尺寸。在此步骤之后，该部分包装在Allegro的标准范围的半导体IC封装中。
选择大厅解决方案或GMR解决方案
GMR传感器在Hall-ef带来一些好处fect transducers. However, it is very important to understand the desired application of these transducers, as in many cases a Hall solution is the better solution.
| Factor | Hall | GMR (based on 示例堆叠） |
| 敏感方向 | Through plane (1 axis) | 在平面（2轴）， 通常是1个小学 |
| Response | 完美的一个轴线性 | Cosine type response in 2 axes that is more 复杂解释 |
| 敏感度（本机） | ~10-20 μV / G | 0.5-2 mV / G (50+ X hall) |
| Linear range | 不受限制的 | ±55 g |
| Responsive range | 不受限制的 | ±100 g |
Conclusion
Allegro的新集成GMR技术为Designer的工具箱提供了一个额外的工具，以解决新的应用程序，并在现有应用程序中扩展其ICS的功能。亚博尊贵会员GMR提供了改善发出信号的能力，增加分辨率，或减少给定解决方案的所需现场等级（较小的磁铁，更大的空气间隙等）。此外，对晶片或IC表面的平面感测，可以通过平面敏感霍尔技术来创造新的更强大，差异磁解的能力，而不是可能的。Allegro将在所有相关磁传感器IC组合中释放产品，以利用GMR技术提供的新功能。