Example for linear phase filter

[gggould]

Hi all,

Can anyone gives me an example of what is linear phase filter?

Also, is a simple 1st order RC low pass filter a linear phase filter???

Thanks

 

[LvW]

Hi all,

Can anyone gives me an example of what is linear phase filter?
Also, is a simple 1st order RC low pass filter a linear phase filter???
Thanks

A linear phase filter is a filter with a linear phase function. Sorry for this simple answer, but that's the truth.
A linear phase is interesting because of the group delay which would be constant for such a filter. "Would be" means: In analog technology its not possible to create such a filter - only an approximation is in use: Thomson-Bessel lowpass.
(Hint: The transfer function for an ideal linear phase filter is exp(-sTo) )

 

[gggould]

Thanks for the response.

Since the phase of RC filter is -atan(w/wp). The derivative, or group delay, is not constant. so it is not a linear phase filter. Am I right?

 

[flatulent]

Most correct. A FIR filter, if the tap weights are symmetrical about the center of the delay line, is linear phase no matter what amplitude response you make by varying the tap weights.

 

[permute]

a linear phase filter has symmetric coefficients, which comes from the requirement that the impulse response be symmetric.

this means that ONLY FIR filters can have true linear phase. Why? an IIR filter has an infinately long impulse response. Thus to be a linear phase IIR filter, it would need to respond to an input an infinate amount of time before it happens.