• Ferrite bead low pass filters

    09/21/2017 at 03:39 0 comments

    First and second generation ferrite bead filters - the later one is to the left, where the beads sit inside slots in the PCB. The left one is just the inductors for a 7th order filter - I didn't add the caps as I want to change the layout to use two strings per L. The 'flat' style reduces the height and increases the Q as there's less superfluous copper in circuit. However the impedance here is so low that all the extra copper joining the caps together influences the performance. Hence the need for 3rd gen where the caps are all close together. The termination impedance here is about 1ohm - even 10mohm of resistance reduces the Q to below 100.