1. RLC Band-pass Filters

2. Band Stop (Notch) Filter

3. Another Example

4. AM Radio Receiver
“Selectivity” is very important – relates to a parameter “Q” for the filter.

5. Series RLC Band-pass Filters in more detail
Max |HV|=1 at
High Q  more selective

6. Quality Factor Q Dw: note abs magnitude is
Looking at the roots of both equations:

7. Quality Factor: Cont.
The lower the R (for series R) the sharper the peak

8. RLC at Resonance At resonance: current is max. Zeq =R
current and voltage are in phase.
the higher Q, the narrower the resonant peak.

9. Concept Check: ac Circuit Resonance
The current in an RLC series circuit leads the ac voltage source. To bring the circuit to resonance, should the capacitance be increased or decreased?
Answer: ICE, it is capacitive, reduce the impedance of the capacitor, i.e. increase the capacitance. Alternatively, inductance can be increased to offset the impedance of the capacitor.