1. Series & Parallel Resonance Passive Filter

2. The series resonant circuit
Resonance
Resonance is a condition in an RLC circuit in which the capacitive and inductive reactances are equal in magnitude, thereby resulting in a purely resistive impedance.
The series resonant circuit

3. Series Resonance Input impedance:
Resonance occurs when imaginary part is 0
Resonant/center frequency:

4. Series Resonance At resonance:
The impedance is purely resistive, Z = R
The voltage and the current are in phase, pf=1
The magnitude of transfer function H(w) = Z(w) is minimum
The inductor voltage and capacitor voltage can be much more than the source voltage

5. Series Resonance
Average power dissipated by the RLC circuit:
Where:

6. The current amplitude vs. frequency for the series resonant circuit
Series Resonance
The current amplitude vs. frequency for the series resonant circuit
Maximum power:
Power at certain frequency:

7. Series Resonance
Half power frequency:

8. Series Resonance
The “sharpness” of the resonance in a resonant circuit is measured quantitatively by the quality factor Q
The quality factor of a resonant circuits is the ratio of its resonant frequency to its bandwidth

9. The higher the circuit Q, the smaller the bandwidth
Series Resonance
Relation between Q and bandwidth B:
The higher the circuit Q, the smaller the bandwidth

10. Series Resonance High Q circuit if,
and half power frequency can be approximated as:

11. Example 1 R=2Ω, L=1mH, C=0.4μF. Determine :
The resonant frequency and the half-power frequency
The quality factor and bandwidth
The amplitude of the current at ω0, ω1 and ω2

12. The parallel-resonant circuit
Parallel Resonance
The parallel-resonant circuit

13. Parallel Resonance Input admittance:
Resonance occurs when imaginary part is 0
Resonant frequency:

14. Parallel Resonance
Half power frequency:

15. Parallel Resonance

16. Parallel Resonance High Q circuit if,
and half power frequency can be approximated as:

17. Example 2 R=8 kΩ, L=0.2 mH, C=8 μF. Determine :
The resonant frequency, quality factor and bandwidth
The half-power frequencies
The power dissipated at ω0, ω1 and ω2

19. Filters
A filter is a circuit that is designed to pass signals with desired frequencies and reject or attenuate others.
4 types of filters:
Lowpass filter: passes low frequencies and stops high frequencies
Highpass filter: passes high frequencies and rejects low frequencies
Bandpass filter: passes frequencies within a frequency band and blocks or attenuates frequencies outside the band
Bandstop filter: passes frequencies outside a frequency band and blocks or attenuates frequencies within the band

20. Ideal frequency response of four types of filters:
a) lowpass
b) highpass
d) bandstop
c) bandpass

21. Lowpass Filters
A lowpass filter is designed to pass only frequencies from dc up to the cutoff frequency ωc

22. Lowpass Filters
Transfer function:
Cutoff frequency:

23. Highpass Filter
A highpass filter is designed to pass all frequencies above its cutoff frequency ωc

24. Highpass Filters
Transfer function:
Cutoff frequency:

25. Bandpass Filter
A bandpass filter is designed to pass all frequencies within a band of frequencies, ω1 < ω0 < ω2

26. Bandpass Filters
Transfer function:
Center frequency:

27. Bandstop Filter
A bandstop filter is designed to stop or eliminate all frequencies within a band of frequencies, ω1 < ω0 < ω2

28. Bandstop Filters
Transfer function:
Center frequency:

29. Example 3 Bandstop filter rejects 200 Hz while passing other
frequencies. For R=150 Ω and bandwidth 100 Hz,
determine: L C

30. Exercise 1 For a series RLC bandstop filter, R=2 kΩ, L=0.1 mH,
C=40 pF. Determine :
The center frequency
The bandwidth
The half-power frequencies
The quality factor