Figure 5 demonstrates the asymmetrical (common mode) 50Ω/50Ω (mode B) simulation. To wit, Rsource and Rload have three combinations of impedances: 50Ω/50Ω (mode A), 0.1Ω/100Ω(mode C) and100Ω/0.1Ω(mode D). Symmetrical (differential mode) performance can be analyzed by using AC analysis. From the manufacturer’s datasheet, we know the off-the-shelf filter is a multi-stage filter shown in Figure 3.įigure 3 Electric schematics of the off-the-shelf filterĪ simplified simulation model is built as shown in Figure 4. In our particular situation, a filter is modeled using SIMetrix (the model can be easily built using other simulation tools such as LTSPICE). As a result, manufacturers sometimes provide insertion loss results in four representative topologies, as shown in Figure 2.įigure 2 Insertion loss shown in the datasheet, four set-ups were tested, mode A-DĪ simplified simulation model in SPICE simulation toolĪ SPICE-based simulation tool provides a quick and cost-effective way of filter performance analysis. It is understood that CISPR 17 provides a measured impedance that provides an optimal filter performance prediction (in reality the impedance of neither the source nor the load is 50Ω). Understanding filter performance measurement per CISPR 17Īccording to, CISPR 17 defines the measurement set-ups for filters. This article summarizes our approach to build a sufficiently accurate filter simulation, step by step. Once the simulation model is proved to be accurate enough, we can then quickly design our own filter and gain a good confidence level with an implemented design of our choosing. However, we can use this filter as a benchmark and can aim for a simulation that would agree with experimental results. In this case, we have the datasheet from the manufacturer that provides a reasonable result. Unfortunately, when it comes to EMC, due to the prevalence of parasitic parameters and the nonlinearity associated with frequency, simulation modeling often takes a long time to develop and may not predict a result that agrees with the experiment. However, a simulation model needs to be accurate enough so that the result does not over-predict or under-predict the filter performance (which is usually characterized as insertion loss). Naturally, the question came, how effective is our own filter compared with this off-the-shelf part?įigure 1 An off-the-shelf filter from Schaffner used in troubleshooting stageĪ quick simulation can give design engineers a good confidence level when designing a customized filter solution. After proving that the filter was effective, the next job was to design our own filter so we can fit the filter in the product with a reasonable size and cost. This was a quick-fix and was implemented as a proof of concept. Recently, when I was helping a client with EMI issues on their automotive product, I bought an off-the-shelf filter from a well-known manufacturer.

Dual pi filter design