Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

how to increased the roll off rate

Status
Not open for further replies.
N

naspek

Member level 1
Member level 1
Joined
Feb 17, 2010
Messages
37
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,286
Activity points
1,546
hey there...
i wanted to modified my 1st order Butterworth low pass filter with K=1.
i want to increased the roll off rate.. but, after changing the resistor value,
the capacitor value and fo, i the roll of rate still the same..
how can i increased my roll off rate?
 

To change the roll-off rate you need to add an extra RC stage.

An nth order pole has a slope of -20*n dB/decade.
What you are doing is changing the critical frequency and not the slope..

google bode plot concepts!
 

    N

    naspek

    Points: 2
    Helpful Answer Positive Rating
abbeyromy said:
To change the roll-off rate you need to add an extra RC stage.
An nth order pole has a slope of -20*n dB/decade.
What you are doing is changing the critical frequency and not the slope..
google bode plot concepts!
Click to expand...

Just two small correction/supplements:
1.) An "extra RC stage" means in practice: A second order network instead of 1st order, because the series connection of two first order stages does allow a maximum pole Q only below 0.5 (Butterworth: Q=0,707)

2.) Not an "nth order pole" but an nth order transfer function has the mentioned slope of -20*n dB/dec.

_________

And - naspek - please don't speak anymore from a first order Butterworth response!
 

if i add another RC network, the roll off rate will be -40dB/decade..
which is decreasing from -20dB not increasing. am i right?
 

naspek said:
if i add another RC network, the roll off rate will be -40dB/decade..
which is decreasing from -20dB not increasing. am i right?
Click to expand...

Is -5 larger or smaller than -1 ?

A slope of -40dB/dec is smaller than -20dB/dec but the corresponding roll-off rate is larger, because the roll-off rate is considered to be positive! (The word "roll-off" contains already the negative slope). That´s the whole story.
But check your task! Are you interested in another roll-off rate only or do you like to design a filter with a certain transfer function resp. frequency response (like Butterworth, for example) ?
 

    N

    naspek

    Points: 2
    Helpful Answer Positive Rating
@LvW
Thanks for the corrections!!
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top