will it depend on the filter topology?
Any help is appreciated!
Thanks
"opposite direction" - do you think inductive filters will produce a NEGATIVE delay?A capacitor filter will advance/ delay a signal, in the opposite direction from its sister inductive filter.
Thanks Audioguru for your reply. Would you mind sending me a ref that has those equations?The delay time of an lowpass RC filter is the phase shift that can be calculated. Of course if the filter has more RC's in it for a higher order then the phase shift and delay are
more.
I find my reply is not correct, or not always. I'm getting a refresher as I compare simulations of RC and RL high pass filters with the same rolloff curve.
Thanks BradtheRad and LvW for your comments, I would be happy to have your opinions on this as well."opposite direction" - do you think inductive filters will produce a NEGATIVE delay?
"opposite direction" - do you think inductive filters will produce a NEGATIVE delay?
I am aware that say a first order low-pass filter needs some time based on its time constant to settle properly. However, I am looking for a quantitative way to figure out the propagation delay and settling time for filters based on the order. Say if I have a 7th-order filter, I want to know how long I need to wait until I get the valid output. Besides, at the moment I am not sure if this delay time is topology dependent or not.
An RC lowpass filter cuts high frequencies. One RC produces a maximum phase shift delay of 90 degrees that is simply calculated from the frequency that is fed to it. It has no settling time but since high frequencies are reduced then the rise and fall times of transients are slowed.Thanks Audioguru for your reply. Would you mind sending me a ref that has those equations?
I am aware that say a first order low-pass filter needs some time based on its time constant to settle properly. However, I am looking for a quantitative way to figure out the propagation delay and settling time for filters based on the order. Say if I have a 7th-order filter, I want to know how long I need to wait until I get the valid output. Besides, at the moment I am not sure if this delay time is topology dependent or not.
An RC lowpass filter cuts high frequencies. One RC produces a maximum phase shift delay of 90 degrees that is simply calculated from the frequency that is fed to it. It has no settling time but since high frequencies are reduced then the rise and fall times of transients are slowed.
Active filters sharper than Bessel have ringing on transients that has a settling time.
I doubt if we can say that a phase shift is identical to a delay. A delay is given in seconds - and not in degree. Delay is given in seconds and not in degree!
More than that, for a simple RC stage the max. phase shift of 90 deg does exist for INFINITE frequencies only (that means: it will never be reached in reality).
Of course, even the first order RC block has a settling time.
@ mordak: What do really need to know?
If the frequency is 1kHz and the phase shift is 45 degrees then the delay is (1/1000Hz) x (45 degrees/360 degrees)= 125us.
You show a digital pulse where the source is saturated (not linear) so the propagation delay is caused by the source device coming out of saturation. A linear circuit responds immediately ......
Hi,
I am trying to design an analog low pass filter. I was wondering if there is any equation showing the relation between the filter spec, say order of the filter, and its settling time and propagation delay. And if there is any, will it depend on the filter topology?
Any help is appreciated!
Thanks
He showed a pulse. The slew rate affects its rise-time and fall-time.Gentlemen - why do you speak about the slew rate? I am afraid, this will puzzle the OP.
He is just asking for delay properties of an anlog filter - thats all.
Do you know any ref that formulates these relationships?Sorry, but this is not correct.
Each filter needs a certain "transient" time before it behaves as desired (filter action).
This time depends on the filter degree as well as on the Q value of the pole pair(s).
.
He showed a pulse. The slew rate affects its rise-time and fall-time.
The term slew rate seems to refer to non-linear amplifier behavior, in so far Audioguru's comment is substantiated. A linear filter doesn't show slew-rate, but the pulse response might look quite similar to the post #11 picture though.
A common way to describe the frequency dependent delay respectively phase shift of a linear filter is the group delay. It has a well defined characteristic for specific filter prototypes.
Gentlemen - why do you speak about the slew rate? I am afraid, this will puzzle the OP.
He is just asking for delay properties of an anlog filter - thats all.
I think the propagation delay is related to the filter order.
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