OLED current detection using tunneling magnetoresistance sensor

The brightness, color gamut, Mura and other characteristics of the organic light-emitting diode (OLED) display are closely related to its driving current. In order to realize the nondestructive detection of OLED current after packaging, this paper establishes a magnetic detection method which is based on tunneling magnetoresistance (TMR) effect. First, according to the relationship between the brightness and its driving current of OLED display, it is obtained that the driving current is about 40 mA when one row pixels are light on. Through simulation and analysis of the spatial magnetic field distribution of 40 mA current, the sensitivity index requirements of TMR magnetic sensor are estimated. Then, TMR2922 is selected as the magnetic sensor. By lighting two row pixels, the relationship between display magnetic field and current is studied. To research the electromagnetic interference of the display, multi-row pixels are lighted. To determine the ability of TMR2922 current detection, one column of pixels is lighted. Finally, the magnetic field data of TMR2922 and the optical data of Hyperion colorimeter under different driving currents are compared and analyzed. The simulation shows that the noise of the magnetic field sensor should be better than 1. 1 nT/root Hz when the distance is 1. 5 mm. Experimental results show that TMR2922 can detect OLED row current without shielding, which is about mA level, but can not detect column current in mu A level, which requires a magnetic sensor with higher sensitivity.