Analysis of RF Noise in LDO and Establishment of Noise Immunity

This paper presents the mechanism of RF noise propagation in a low-dropout regulator (LDO). Two dips in the output voltage in the range from 100 MHz to 1 GHz were confirmed by a direct power injection (DPI) method and a transverse electromagnetic (TEM) cell method. These characteristics were reproduced in simulation, and we observed that the inductance of the device wiring, parasitic elements of the pass transistor and the non-linearity of the OPAMP greatly contribute to the output drops. We established a method that is not affected by nonlinearity and succeeded in eliminating the drops in the output voltage.