Low pass filter (arctan domain)

Click For Summary

Discussion Overview

The discussion revolves around the phase characteristic of a low pass filter (LPF) and the interpretation of the arctan function's domain and range in this context. Participants explore the relationship between the phase shift and the arctan function as it applies to filter behavior.

Discussion Character

  • Homework-related
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions why the domain range of the arctan function is stated as [0, 90] degrees, suggesting that it should be between [-π/2, π/2].
  • Another participant clarifies that the phase shift is related to the range of the function, not the domain, and explains that the phase shift for a single-pole LPF varies from 0 to -90 degrees.
  • A further reply indicates that the confusion may stem from the graphical representation of the phase response, suggesting that the plot may not accurately depict the arctan function's behavior in this context.
  • The same participant notes that as frequency increases, the phase response reflects only half of the arctan function, which goes negative due to the sign.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of the arctan function's domain and range, indicating that the discussion remains unresolved regarding the graphical representation and its implications for understanding phase characteristics.

Contextual Notes

There is a potential misunderstanding regarding the graphical representation of the arctan function in relation to the phase shift of the LPF, which may depend on how the phase response is plotted.

TheGood
Messages
2
Reaction score
0

Homework Statement


when I'm trying to calculate and show the graphic of the phase characteristic i don't understand why the domain range of the arctan function is [0,90] :


Homework Equations


aa4a.gif





image392.gif



The Attempt at a Solution


shouldn't be the domain of arctan function between [-Pi/2,Pi/2]?
z_tri59.png
 
Last edited:
Physics news on Phys.org
The value of the phase shift is the range of the function, not the domain. The domain is the input range to the function and the range is the output values of the function.

The phase shift for a single-pole LPF varies from 0 to -90 degrees, as shown in the diagram. It is 0 at low frequencies in the passband of the filter, and drops to -90 degrees past the cutoff of the LPF.
 
I see that you've edited your post to add the red arctan curve. I think it may be the shape of the phase response in the first plot that is confusing you. I don't think it is plotted very well -- it make is look like the full arctan() curve, when it is really only half of it.

When ω = 0, you get the arctan(0) which is zero. As the frequency increases, you get half of the arctan() function, going negative because of the sign being negative.

Does that make more sense now?

http://www.electronics-tutorials.ws/filter/filter_2.html

.
 
thank you, the link was helpful too!
 

Similar threads

  • · Replies 11 ·
Replies
11
Views
4K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 16 ·
Replies
16
Views
2K
  • · Replies 4 ·
Replies
4
Views
1K
  • · Replies 10 ·
Replies
10
Views
2K
  • · Replies 6 ·
Replies
6
Views
4K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 6 ·
Replies
6
Views
3K
  • · Replies 11 ·
Replies
11
Views
4K
Replies
13
Views
5K