Noise coupling path analysis for RF interference caused by LCD noise modulation

RF interference caused by liquid crystal display (LCD) noise modulation in a mobile phone was investigated and its noise coupling path was demonstrated. In the frequency division duplex communications, mobile phones can send (uplink) and receive (downlink) at the same time. When an antenna transmits high power signal, the baseband noise from an LCD panel is modulated into an RF band and causes interference in a receiving antenna. A noise coupling path between an antenna and a display driver IC, which drives the LCD panel, was experimentally demonstrate. In addition, a simple noise source model was proposed to represent modulation mechanism. A network analysis with the modulation model showed good correlation with the measured spectra of the modulated noise in a receiving antenna.