AMR technology for more accurate current detection

Advanced systems require accurate, efficient, and reliable sensors to obtain appropriate feedback to regulate system operations. Power Electronics News recently discussed current detection with John Newton, vice President of ACEINNA, and Mike Horton, chief technology officer.



Current detection is a widely used technology found in almost all types of electronics, Newton says. At present the mainstream of current detection method mainly has three, one of the most common is the use of operational amplifier of shunt resistance (shunt resistor) which can adjust the signal; The current value can be obtained by measuring the voltage drop of the shunt resistance.

The second way is to use a current transformer, which is actually very much like a current transformer. The advantage of this, notes Newton, is that it is itself isolated, meaning that there is no electrical connection between the current being measured and the output signal, but current converters tend to be bulky. Another disadvantage is that it does not always respond to DC, so it can only be used to measure AC current.

A third common approach is to use magnetic sensors, usually Hall components, to measure the magnetic field generated by the current. The advantage of this approach is that it is isolated, can be small, and can always respond to DC; The disadvantages are inaccuracy and limited bandwidth, usually within 100KHz or less.


There are a few drawbacks to using a detection resistor, Newton points out: "first, the voltage must be lowered in order to measure the current. Therefore, when measuring a large current, the power consumption is relatively large. This is even more problematic if you want to measure currents with a certain dynamic range. Because the resistance must now be resized so that it has a sufficient voltage drop at a low current level to achieve the desired accuracy. This means that at the higher end of the current range, I2R dissipates even more. Another problem is that you need a lot of external components, especially if you want to do isolation current detection, because now you have to have a whole set of extra circuits to create isolation layers.

In view of the above two shortcomings of resistance detection, ACEINNA's method is to use new technology to detect current. It's also magnetic, but using anisotropic magnetoresistance, or AMR, rather than a hall piece. According to Newton, the advantage of this AMR technology is that it is more sensitive, less noisy and has higher bandwidth, so it is a high  -  performance magnetic sensor technology that can solve the problem of current detection.


AMR has another advantage. The current detection module based on hall effect is sensitive to magnetic field in z direction. Therefore, if another current is flowing through the hall assembly in the system, it will be sensed because the magnetic field will be perpendicular to the circuit board on which the sensor is located. The AMR component is sensitive on the x axis and parallel to the PCB surface, so any stray current positioned laterally in the system will generate a magnetic field that is not on the sensitive axis, so it is more resistant to external interference than the hall component.

Newton said, AMR sensor structure is a resistive bridge (resistive bridge), so what has happened is a bridge resistance changes with applied magnetic field. The bridge structure is very symmetrical in nature, completely different from the hall component topology. Horton added that AMR components are not just a change in topology, but a change in accuracy, speed, and cost. Because of the material, the sensor is more accurate and the hall assembly is very insensitive.

Horton further pointed out that, as Newton said, first of all, the sensitive axis of hall component is not correct, so some solutions must be adopted. But more importantly, hall is just a kind of magnetic sensing technology with low sensitivity and very low sensitivity: "hall components can measure real large current in a binary way, such as in an encoder, or make a rough measurement of the current, but not in a high resolution, such as a 16-bit ultra-high resolution sensor, which has relatively high noise. So from a pure precision and bandwidth point of view, it can be said that the AMR material is better and has better physical properties.


According to Horton, in addition to AMR technology, advanced materials and unique circuit designs are needed to take advantage. The basic physical characteristics of AMR give it high bandwidth and better sensitivity than hall components. Therefore, the hall sensor cannot be seen in the high  -  performance compass, because its sensitivity is not high enough to measure the weak micro  -  gaussian horizontal magnetic field of the earth; AMR sensors can detect these very small currents, as well as very large currents, with high resolution and high bandwidth, which hall sensors cannot do.

ACEINNA's current sensor locking requires high bandwidth, high speed, good isolation, good dynamic range and accuracy; Thus, Newton points out that high performance power in a server or telecommunications equipment power module is a good application. In addition, high  -  voltage, high  -  bandwidth and large  -  dynamic range applications are also targeted markets, such as inverters, uninterruptible power systems (UPS), motor drivers, and high  -  performance electric motors, etc., with more stringent requirements for performance and current detection applications. Article source network, if you have any questions, please contact yibai