Applet showing how square wave appears after filter

That would depend on the filter, and there are an unlimited number of filters, analog and digital.

You could use LT Spice, but creating the filters would be a bit of a chore. But educational!

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics

Do you have access to a 'scope and function generator?

George H.

what you are asking is known as the "step response" of the filter. the exact answer depends on the exact shape of the filter amplitude __and phase__ response so there is no simple answer.

it can round off the edges and/or add ringing.

I think you may find what you are after by Googling "Gibbs phenomenon" m

In data marzo 2019 alle ore 17:29:57, ha scritto:

Thanks, the question origin was to show to some guys online ,in an amateur electronic group,what they could expect when measuring a square wave generated by decently fast

logic with a "slower" oscilloscope. They have their oscilloscope and generator,so i was simply trying to demonstrate that the showed waveform was steep as expected,confirming the

guidelines in the book "HIGH-SPEED DIGITAL DESIGN" Thanks for your attention

Diego

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http://www.avg.com

l

ff

Oh, get them to wire up one of those fast inverters (I can't recall the number XX-14... Someone was using it to make a TDR edge.*) And see how good their 'scope is. If it's a digital 'scope that can push the BW limit button too.

George H.

*I've got a link that uses an 74AC14, but this was faster... I can look up the number if no one else chimes in.

74lvc family are faster and have a decent drive capability, but need good decoupling.

I've seen 3*(74lvc+143ohms) in parallel drive 50ohms through 2.5V in 250ps.

Right! I ordered this one SN74LVC1G04.

Given what you want to do then direct Fourier synthesis in a spreadsheet would be one quite informative way to do it and allow you to try various filters manually.

Column A

A1 = n A2 = Filter A3 = t A4 = 0 A5 = PI()/1024 A6 = =A5+A$5

Column B

B1 = 1 B2 = 1 B3 = ="sin("&B1&"t)" B4 = =B$2*sin(B$1*A$4)/B$1

Column C

C1 = B1+2 C2 = EXP(-C1*C1/$AA2)

Copy the formulae to populate A5..Z2500

Column AA

AA1 = 0 AA2 = 2000 AA3 = Summation AA4 = SUM(B4..Z4)

Copy this down to AA2500

Select A3..AA2500 range and Insert XY scatter diagram lines only.

You will see the resultant square wave summation and all the components that go into it up to the 50th harmonic. Most people are surprised just how much the brick wall cutoff to zero filter rings.

Try AA2 = 2000 or thereabouts to get realistic scope waveforms.

or for a flat response until some frequency cutoff try

C2 = IF(C1

In data marzo 2019 alle ore 10:17:52, Martin Brown ha scritto:

Thanks to you all for hints about 74LVC logic family and the spreadsheet. I copied the last message,I hope to be able to implement it correctly. Diego.

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http://www.avg.com