Magnetic sensors are used in many applications, such as navigation systems, data storage devices (HD), biomagnetic fields detection, etc. Usually, magnetometers are rugged and reliable alternatives compared to other technologies. In special, measuring biomagnetic fields – very low intensity fields – requires magnetometers with high sensitivity. Recent studies demonstrated that the GMI (Giant Magnetoimpedance) magnetometer based on the impedance phase characteristics of the sensor is an adequate option to this purpose. The goal of this project is the development of a phase detector to be used in this kind of transducer, improving its resolution and making it capable of measuring cardiac magnetic fields.