| APPLICATION AND SELECTION OF SMT FEEDTHRU CAPACITOR FILTERS EMI suppression and receiver noise reduction can be achieved most effectively with efficient filtering methods. Attenuations of over 100 dB are achievable depending on the complexity and size of the filters involved. However, before filtering is discussed, another EMI reduction method is noise limiting, using a series element (inductors or resistors). This method is easy to implement and inexpensive. The problem it poses is that it can only reduce noise by -3 to -10 dB. Because of that, series element EMI reduction is primarily used where there is a poor ground. SMT feedthru filter capacitors can actually replace discrete L/C filter networks (depending on the frequency response needed). The SMT filter capacitors should first be chosen for its specific frequency response. Then the voltage rating, DCR, and current capability must be evaluated for circuit suitability. If there is not a match on voltage, current and DC resistance ratings, the designer must select the closest available frequency response available on parts that will meet the design's power spec. The top 5 applications for SMT feedthru filter capacitors are: 1. Digital to RF interface filtering. 2. Control line high frequency decoupling. 3. Data and clock high frequency decoupling. 4. Power line high frequency decoupling. 5. High gain and RF amplifier filtering. |