3/14/02: Minute Paper How do touch lamps work? Have you ever lick a 9V battery? If we have AC coming out of outlets, and light bulbs rely on DC to operate, is there some AC-DC conversion in the lamp socket, or does the light bulb run on AC? Does the HW grader give partial credit? Speaking about frequencies of TV… Now does a satellite dish receive the signal? What kind of signal does it use? What worse than seeing a worm in your apple? –Have a worm.

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.

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  ) CD PlayerAmplifierSpeaker (Source) (Circuit) (Load) VSVS ZSZS Z1Z1 Z2Z2 ZLZL

Filters Low-pass filters (LP)

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

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

High-pass Filters (HP) 1/  2

Concept Check: filters Which are the following circuits high-pass or low-pass filters? Answers: High-Pass Filters: (b) and (c) low-pass filters: (a) and (d)

Bode Plot: High-pass filter 3db point 20 dB/Decade