Integrated current sensor using giant magneto resistive (GMR) field detector for planar power module

A planar power module was developed, and a gate-driver circuit with an over-current protection was planned to integrate into the module. After reviewing several current-sensing methods, the giant-magneto-resistive (GMR) sensor was chosen as a current-sensing method. However, there were several factors that hindered accurate measurement. The high junction temperature of the power dice gave high influence to the operating temperature of the GMR sensor, and the magnetic-flux distribution seen by the GMR sensor was also non-uniform due to skin effect. The temperature response of the GMR sensor was analyzed by experiments, and the GMR sensor showed about 3.45% errors when it sensed 80 Adc and the operating temperature changed by 60°C. To further improve the measurement capability over wide range of operating temperature, an active temperature-compensation method is described. The optimal position of the GMR sensor was found based on FEA simulation as the midpoint of two current paths. At that location, the GMR sensor could consistently sense both current excitations. A test module was fabricated, and preliminary measurement result showed excessive noise that had to be filtered out for accurate measurement. A signal-conditioning circuit was designed using an instrumentation amplifier, and the current measurement between the GMR sensor and a high-bandwidth current probe showed consistent result. The current sensor with signal-conditioning circuit was integrated into the gate-driver circuit, and the concept was verified by experiments.