Design of low cost common and differential mode noise diagnostic circuit

Conducted Emission measurement with LISN gives a combined emission of common mode and differential mode. All standards give the limits for this. By conducted emission, we mean the combined emission of common mode and differential mode on the power line from an Equipment Under Test (EUT). It is vital to be able to separate this common mode (CM) and differential mode (DM) noises in the conducted emission. For this we propose new discriminators which are low cost and easy to design. In the end, we also propose a relatively low cost approach using oscilloscope. The time domain measurement is performed and transformed into frequency domain using FFT. This can be easily designed, manufactured and used to measure conducted emission and analysed. The analysed test result of CM & DM emission is useful to design fixes to reduce emission as per required standard limits. The method of using oscilloscope is helpful for design engineers, as it saves money and time of testing with costly EMI receivers.