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https://designers-guide.org/forum/YaBB.pl Design >> Analog Design >> Q of the low pass filter https://designers-guide.org/forum/YaBB.pl?num=1128318106 Message started by Analoger on Oct 2nd, 2005, 10:41pm |
Title: Q of the low pass filter Post by Analoger on Oct 2nd, 2005, 10:41pm Hi all, I was a bit confused. I understand that quality factor "Q" is an important spec of bandpass filter. But what does quality factor mean for low pass filter? Why do we need to care about it? Thank you! |
Title: Re: Q of the low pass filter Post by Analoger on Oct 4th, 2005, 8:23pm Any comments, pls? |
Title: Re: Q of the low pass filter Post by Anuranjan Jha on Oct 10th, 2005, 11:19pm For a low pass filter, Q does not make sense unless you specify the frequency. You may say Q is a function of frequency because the loss in the circuit depends on it. Anuranjan |
Title: Re: Q of the low pass filter Post by Analoger on Oct 15th, 2005, 9:26pm Anuranjan , no offense, but i don't think you really understand the question and the definition of quality factor - which has different meanings under different circumstance. |
Title: Re: Q of the low pass filter Post by Paul on Oct 17th, 2005, 12:12am Hi, I'm not sure who misunderstands the signification, in any case your question is ambiguous. I guess you are questioning the pole quality factor, not the filter quality factor. The pole quality factor defines who much damping your transient response shows, respectively how much peaking your frequency response exhibits. It essentially depends on the ration between the real and the imaginary parts of the poles. For a two-pole filter, you can find the math in any convenient text book. The following document discusses both quality factors: http://www-inst.eecs.berkeley.edu/~ee247/fa04/lectures/L2_f04.pdf Paul |
Title: Re: Q of the low pass filter Post by Analoger on Oct 17th, 2005, 10:31am Hi Paul, I understand the pole quality factor concept. The imaginary part of the pole determines the oscillation frequency, and the real part determines the damping. I remembered I saw it somewere that "Q" of a low-pass filter is given as a spec. That's why I'm asking. Thank you. |
Title: Re: Q of the low pass filter Post by Paul on Oct 19th, 2005, 12:32am Quote:
But that certainly is the pole quality factor and not the filter quality factor. Best Paul |
Title: Re: Q of the low pass filter Post by Juddy on Oct 23rd, 2005, 6:55pm By the way, I have also a question on Q of the LPF. when we design a cascaded (two-stage) filter with each stage two poles, how to design the Q- of each stage, should the Q value of two-stages increase of decrease, thanks in advance!!! |
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