Testing of the Noise Measurement System for GMR Sensors

Giant Magnetoresistive (GMR) sensors have high sensitivity and a quick response in the presence of the low magnetic field, taking an increasing part in many applications such as speed and position sensing, current sensing, detection of the nanoparticles from biological systems and even in fundamental studies of superconductivity [1]. However, the sensor`s intrinsic noise is a crucial parameter in terms of low field applications. The GMR sensor delivers a small output signal and in this case its resolution can be limited significantly if the intrinsic noise is high. The magnetoresistive devices generate different types of noise, namely thermal noise, low-frequency noise and magnetic noise [2]. In this context, the main purpose of this paper is to present the noise measurement system used for this kind of sensor. The system will be tested for thermal noise measurement because it is an easy noise source to calculate and it is dominant in all passive resistive elements. The noise measurements were performed at room temperature T = 300K and in a frequency range of 10 Hz to 100 kHz. The results show the significant influence of the input impedance of the low noise amplifier in the noise measurement, especially in the case of high values of the resistances.