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Decoupling Capacitors are normally capable of supressing EMI noise up to 75 MHz. Above that frequency a ferrite bead helps in supressing. My question is where should we place the ferrite ? After the capacitor or before the capacitor?
That way you have a (1-stage) low pass filter. If you assume you have a voltage source with low output impedance, then putting the cap before inductor wouldnt help as much (depending on its size). For filtering high frequency noise, always go from a high impedance to low impedance (i.e. inductor and then cap to ground).