Simple Resistor Circuit

Thread Starter

mig78

Joined Mar 30, 2006
8
[attachmentid=1328]The attached network is at the input of a digital channel, the output is later routed to a comparator. Can anyone explain why they need to let the signal through [attachmentid=1328]this network. Whats is the application of this circuit?

Appreciate some feedback

Thanks

mig78
 

paultwang

Joined Mar 8, 2006
80
Originally posted by mig78@Mar 30 2006, 06:16 AM
[attachmentid=1328]The attached network is at the input of a digital channel, the output is later routed to a comparator. Can anyone explain why they need to let the signal through [attachmentid=1328]this network. Whats is the application of this circuit?

Appreciate some feedback

Thanks

mig78
[post=15623]Quoted post[/post]​
Looks like a slightly complicated frequency filter to me. You can derive a transfer function, make a Bode plot, and see what it does.




Please do not upload bmp images as it is very size inefficient.
 

nanobyte

Joined May 26, 2004
120
No. It's definitely a High Pass Filter because a capacitor comes before the resistors in the circuit. High Pass Filters go capacitorsa first then resistors. Low Pass Filters are the opposite way around.
 

Papabravo

Joined Feb 24, 2006
14,404
Originally posted by nanobyte@Mar 31 2006, 06:28 PM
No. It's definitely a High Pass Filter because a capacitor comes before the resistors in the circuit. High Pass Filters go capacitorsa first then resistors. Low Pass Filters are the opposite way around.
[post=15662]Quoted post[/post]​
Its a cute saying but improperly applied. Is there not a DC path from In to Out? If there is, then it cannot be a highpass circuit! Boom! Done!
 

dbwgwee

Joined Mar 30, 2006
14
Originally posted by Papabravo@Mar 31 2006, 04:34 PM
Its a cute saying but improperly applied. Is there not a DC path from In to Out? If there is, then it cannot be a highpass circuit! Boom! Done!
[post=15664]Quoted post[/post]​
Great! Pass the lotion!
 

Ron H

Joined Apr 14, 2005
7,014
The Bode plot is more meaningful if you plot it out past where the zero cuts in.
The step response is also interesting.
 

Thread Starter

mig78

Joined Mar 30, 2006
8
Originally posted by JoeJester@Apr 1 2006, 11:33 AM
It's a low pass filter.

Here's a redrawn circuit with bode plot.
[post=15675]Quoted post[/post]​
Thanks for your input it looks definitely more like a low pass filter.
The redrawn circuit makes it look more clearer.
 

Thread Starter

mig78

Joined Mar 30, 2006
8
Originally posted by Ron H@Apr 1 2006, 02:22 PM
The Bode plot is more meaningful if you plot it out past where the zero cuts in.
The step response is also interesting.
[post=15679]Quoted post[/post]​

hi Ron,

I couldn't understand what you mean "plot it past where the zero cuts in"

Can you spend some time to xplain. Appreciate them.

By the way how can I figure out what is the bandwidth of this filter up to -3db roll off.
 

Papabravo

Joined Feb 24, 2006
14,404
Originally posted by mig78@Apr 6 2006, 08:18 AM
hi Ron,

I couldn't understand what you mean "plot it past where the zero cuts in"

Can you spend some time to xplain. Appreciate them.

By the way how can I figure out what is the bandwidth of this filter up to -3db roll off.
[post=15897]Quoted post[/post]​
Systems, like your filter, have transfer functions. A transfer function maps an input function in the frequency domain to an output function in the frequency domain. Most all the transfer functions you will ever see, besides all the ones you won't, are rational functions.

What is a rational function you say? It is a quotient of two polynomial functions. The poynomial functions can be of different orders. You may remember that polynomial functions have roots. What happens to a polynomial at a root? It's vale is goes to zero. But wait, there's more.

If the poynomial in the numerator is zero, the value is called a "ZERO" of the transfer function.
If the polynomial in the denominator goes to zero, the value is called a "POLE" of the transfer functiion.

POLES and ZEROS interact to produce the behavior captured in the Bode Plot, which has two parts, MAGNITUDE and PHASE. Don't forget the PHASE when trying to understand things.

Does this help, or are you now even more confused?
 

Thread Starter

mig78

Joined Mar 30, 2006
8
Originally posted by Papabravo@Apr 6 2006, 10:44 PM

Does this help, or are you now even more confused?
[post=15903]Quoted post[/post]​
Hello PapaBravo,

Man....I'm even more confused. Can you address me to a good reference link that you know of that xplains BodePlot and Poles & Zeros. Pls help.

Thanks.

By the way can you also let me know how to calculate the cutoff frequency for this filter?

Appreciate your reply,

Thanks!
 
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