Simple RC filters phase question

In summary, the conversation discusses the confusion of finding the phase equation of a lossy low pass filter and compares it to a normal low pass filter. The person has tried subbing in values and comparing to a bode plot but is getting different results. It is then pointed out that they had mistakenly multiplied by the negative of the conjugate, which was causing the discrepancy. Once corrected, the results matched.
  • #1
jonni
2
0

Homework Statement


I'm a bit confused about how to find the phase equation of a lossy low pass filter
eg.
r6yf51.jpg


Homework Equations


For a normal low pass filter it's just arctan(wRC)



The Attempt at a Solution



jja1is.jpg


So I am comparing this by subbing in values and comparing to a bode plot of an actual circuit on a breadboard and a spice version of the circuit. But this is nothing like what i get in spice, I've checked for errors but I think its something wrong with the way I am actually calaculating it... but can't figure out why?
 
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  • #2
You multplied by the negative of the conjugate. This will screw up your phase equation.
 
  • #3
Oh thanks so much! Worked out fine now. I feel so stupid haha, i soooo wasn't thinking when i did that! I get the exact same thing except in the last line it's +1 not -1. Makes a big difference though.
 

1. What is a simple RC filter?

A simple RC filter is a type of electronic filter that uses a combination of a resistor (R) and a capacitor (C) to filter out unwanted frequencies in a circuit. It is commonly used in audio and power supply circuits.

2. How does a simple RC filter work?

A simple RC filter works by using the capacitance of the capacitor to block certain frequencies from passing through the circuit. The resistor and capacitor are connected in series, and the output is taken from the capacitor. The cutoff frequency, or the frequency at which the filter starts to attenuate the signal, can be adjusted by changing the values of R and C.

3. What is the phase response of a simple RC filter?

The phase response of a simple RC filter refers to how the filter affects the phase of the output signal compared to the input signal. In a simple RC filter, the phase shift is directly proportional to the frequency of the input signal. At the cutoff frequency, the phase shift is 45 degrees, and as the frequency increases, the phase shift approaches 90 degrees.

4. How do you calculate the cutoff frequency of a simple RC filter?

The cutoff frequency of a simple RC filter can be calculated using the formula fc = 1/(2πRC), where fc is the cutoff frequency, R is the resistance in ohms, and C is the capacitance in farads. This formula assumes that the input signal is a pure sine wave.

5. What are the advantages of using a simple RC filter?

Some of the advantages of using a simple RC filter include its simplicity, low cost, and effectiveness in removing unwanted high-frequency noise from a signal. It also has a relatively flat frequency response in its passband, making it suitable for audio applications.

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