The effect and solution of EMI caused by 217 Hz TDMA switching from compact size GSM security system

This paper portrays the effect and solution of radiation interference from antenna to the base-band audio circuit. The 217 Hz TDMA modulation of GSM module constitutes a form of switching noise and causes the EMI problem in audio frequency. Differential and single-end PCB layout architectures are simulated and compared by full 3D EM simulator, GEMS, for observing the appearance of common mode noise cancellation mechanism. The actual two-way voice communication testing is also operated to verify the efficacy of noise cancellation by this differential architecture.