Differential Passive Circuit Modelling with Pentapole Impedance Matrices Application to an Integrated Audio Switching Amplifier for Portable Devices

In this paper a novel method to model the passive parts of differential output system is presented. This approach, based on impedance matrices, models conducted EMI and takes into account component non-idealities. It is not only able to deal with common mode but also differential mode and with conversion between the two modes. This method is experimentally applied to the passive output part of an audio differential switching amplifier dedicated to mobile phone applications. Using a simple impedance-meter, results show good accuracy up to 110 MHz when associating the different parts of the system.