When selecting components for an RFI filter, it is important to keep a few things in mind. First, the capacitors connected to ground on each input should be well matched. NPO/C0G or X2Y capacitors are recommended. Also, the RFI filter should not be too low in frequency. The higher the RFI filter cutoff, the less effect mismatches will have on AC CMRR. The choice of cutoff is a tradeoff between the AC CMRR required and how robust the RFI rejection should be. Additionally, board layout should be symmetrical and long traces avoided. A poorly laid out board can contribute significant parasitic capacitances.