Passive RL Filter

Today we continued resonance circuits. Last time we went over series resonance circuits. This time we did parallel resonance circuits. It turns out they have the same formula for resonance frequency. Here is a table of the formulas

Then we went over passive filters. There are four types of passive filters. They are lowpass, highpass, bandpass and bandstop

Here are the transfer functions of different passive filters
Lowpass

Highpass

Bandpass

Then we did a lab on passive RL filter. We found the resonance frequency to be 100000 rad/s. We applied different frequencies on the AC voltage input.

ωc/10 ωc/8

ωc/4

ωc/2

ωc

2ωc

4ωc

8ωc

10ωc

Summary: For RL passive filters. If the voltage across the inductor is taken as the filter output, the circuit will act as a high-pass filter. However, if we take the voltage across the resistor as the filter output, the circuit acts as a low-pass filter. The higher the frequency is, the more voltage will be allocated to the inductor and the less voltage will be allocated to the resistor. The lower the frequency is, the more voltage will be allocated to the resistor and the less voltage will be allocated to the inductor. Also, when the frequency is higher, the phase shift of the resistor is higher and the phase shift of the inductor is lower. When the frequency is lower, the phase shift of the resistor is lower and the phase shift of the inductor is higher.