1. Frequency Responses Up to now, we have learnt –ac circuit analysis with periodic sources (fixed frequency, if multiple frequencies, use superposition principle) –Transient analysis Now, frequency responses: filters and resonant circuits.

2. Transfer Function Since we are interested in frequency responses, we use phasors (frequency domain). V L (j  ) is a phase-shifted and amplitude- scaled version of V S (j  )

3. Filters Low-pass filters (LP)

4. Low-Pass Filters Cutoff frequency  o =1/RC, H V =1/  2 working example quick determination of filter type

5. Concept Check: filter Which of the following circuits is a low-pass filter? (a)(b)(c) Answer: (c)

6. High-pass Filters (HP) 1/  2

7. Concept Check: high-pass filter