SparkX Pi-Filter

It’s 2pm on a Tuesday and you find yourself at the test house with a design failing an emissions test. You quickly determine that you need to hack a filter onto your design but there is no space to do so. If only you had a simple board you could attach to the product. Introducing the Pi-Filter! This simple board gets the name Pi-Filter from its shape which resembles the Greek letter Pi. It has two shunt capacitors with an inductor in between. In this C-L-C configuration a person can quickly implement a low pass filter.Why is this filter so popular? Simplicity and usefulness! With these three components unwanted noise on a signal or power line can often be filtered out rather quickly. One very popular use for Pi-filters is in regulatory testing for conductive emissions. Conductive emission is when noise from electronics couples onto the interconnecting cables and passes into other equipment.To relate an experience when taking a new product through regulatory testing for FCC and CE Mark certifications the product was failing conductive emissions due to noise from the switching power regulator. Hacking together a Pi-Filter on the DC voltage input signal the noise was filtered out. While the PCB design had to be revisited to add the Pi-Filter footprint that experience provided the inspiration to design a simple filter board for others to have in their test bag of tricks to resolve noise issues.