This is one reason that LC circuits are the typical networks used for impedance matching in antennas they can provide impedance matching in narrow bandwidths while providing strong filtration of EMI simultaneously. Similarly, they are intended to ensure impedance matching along an interconnect if needed. In particular, they are intended to prevent filtering around a desired signal bandwidth while filtering noise at other frequencies.

The circuits shown below are intended to provide multiple functions. These filters are shown in the image and table below. A C filter is just a bypass capacitor that is shunted to ground. There are three primary methods to placing low-pass filters from passives on critical circuits these are called C, LC, CL, Pi, and T filters. With analog signals, one strategy is to use a bandpass filter that is centered at the signal’s frequency. Using a passive that presents higher impedance to noise signals will reduce their impact on circuit performance.Īs high frequency noise induces a stronger back EMF than low frequency noise, the typical strategy is to use low-pass filtering on the input in a critical circuit with high cutoff frequency. Noise that is received from EMI will typically be inductive, which passes a back EMF into the circuit, and higher frequencies will pass a stronger EMF. The most common type of EMI filter is a passive component, which will provide higher impedance against noise at certain frequencies. Passing EMC certification and ensuring a device works properly requires taking steps to reduce EMI in your PCB. Passive Components as EMI Filter Circuits Here’s how you can incorporate an EMC filter and other EMI suppression strategies in your next PCB. That being said, an EMI filter is still an important part of an EMC compliance strategy for new products. However, this is not the whole story, as you also need to suppress EMI emission from these circuit blocks. Placing an EMI filter on each critical circuit or component is one strategy for providing EMI immunity. The last thing you need is for a device to fail to operate properly when brought near your cell phone. EMI emission should be suppressed from a device under test, and it should have a minimum required level of immunity to external EMI. EMI, EMS, and EMC tests are important parts of device qualification, especially if you want to ensure FCC/IC/CE compliance.

T and pi filter design