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Measurements >> RF Measurements >> bandwidth estimation
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Message started by dandelion on Oct 10^th, 2006, 6:08pm

Title: bandwidth estimation
Post by dandelion on Oct 10^th, 2006, 6:08pm

Hi,
I found some datasheet gives the below information:

"Rise time figures are calculated from tr = 0.35/bandwidth. Or tr = 0.41/bandwidth"

I know the bandwidth can be estimated through the time domain characerristics, but why it is 0.35 or 0.41?

Would pls. anyone can explain it to me?

Thanks

Title: Re: bandwidth estimation
Post by Ken Kundert on Oct 10^th, 2006, 10:27pm

The 0.35 number comes from assuming the produces a Gaussian response (it looks like a Gaussian filter). It is the 10%-90% risetime. See http://en.wikipedia.org/wiki/Rise_time. I found this by typing "Rise time 0.35 bandwidth" into Google. An actual derivation for the single pole case is given in http://freespace.virgin.net/ljmayes.mal/circuittheory/Riserc.htm.

I am not sure where the factor of 0.41 comes from, but my best guess is that it is the rise time of a 2nd order maximally flat envelope delay (bessel) filter.

-Ken

Title: Re: bandwidth estimation
Post by dandelion on Oct 12^th, 2006, 5:51am

Ken Kundert wrote on Oct 10^th, 2006, 10:27pm:

Hi Ken,
Thanks for the help.

You's are right also on the explaination on the 0.41 coefficient, since I found the note in th edata sheet as below

"The conversion factor for the rise time to bandwidth is 0.41 since the HFBR-24x6 has a second order bandwidth limiting characteristic."