<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"><HTML><HEAD><META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1"><TITLE>Newbie to the list - Question about Low Pass Filtering in VEE</TITLE><META content="MSHTML 6.00.2800.1141" name=GENERATOR></HEAD><BODY><DIV><SPAN class=197360216-12092003><FONT face=Arial><FONT color=#0000ff><FONTsize=2><SPAN class=625110416-12092003>Lol yes I feel for me having to use 4.0 aswell. I'm quite sure t</SPAN>he ringing is due to aimpedance mismatch. <SPAN class=625110416-12092003>Unfortunatelythere is no way for me to insert a load at the end of the line, ands</SPAN>witch<SPAN class=625110416-12092003>ing</SPAN> to 50 ohms mode kills thesignal amplitude & changes some of its characteristics. Fortunately, Idon't have to measure rise<SPAN class=625110416-12092003>/fall</SPAN>time - justtop, bottom, frequency and <SPAN class=625110416-12092003>duty cycle. Anyways, I will work on this - thanks for theinput.</SPAN></FONT></FONT></FONT></SPAN></DIV><BLOCKQUOTE dir=ltr style="MARGIN-RIGHT: 0px"> <DIV class=OutlookMessageHeader dir=ltr align=left><FONT face=Tahoma size=2>-----Original Message-----<BR><B>From:</B> andy_street@agilent.com [mailto:andy_street@agilent.com]<BR><B>Sent:</B> Friday, September 12, 2003 1:41 AM<BR><B>To:</B> BDavis@sjm.com; vrf@it.lists.it.agilent.com<BR><B>Subject:</B> RE: [vrf] Newbie to the list - Question about Low Pass Filtering in VEE<BR><BR></FONT></DIV> <DIV><SPAN class=063422108-12092003><FONT face=Arial color=#0000ff size=2>Hello Bjorn,</FONT></SPAN></DIV> <DIV><SPAN class=063422108-12092003><FONT face=Arial color=#0000ff size=2></FONT></SPAN> </DIV> <DIV><SPAN class=063422108-12092003><FONT face=Arial color=#0000ff size=2>VEE 4-0 - wow! Unfortunately, you will not be able to take advantage of the plethora of signal processing functions inherent in the VEE 6-0 Matlab engine. But aside from this, have you considered where the ringing is coming from - is there a mismatch between the scope input impedance and the output impedance of the source you are trying to measure. Is there some bandwidth limitation - if you are expecting a square wave output, but you are seeing lots of ringing, maybe you are losing some of the harmonics of the signal and thus the rise time and waveform shape is affected - Gibbs phenomena.</FONT></SPAN></DIV> <DIV><SPAN class=063422108-12092003><FONT face=Arial color=#0000ff size=2></FONT></SPAN> </DIV> <DIV><SPAN class=063422108-12092003><FONT face=Arial color=#0000ff size=2>Bottom line, my suspicion is that low pass filtering you signal may not be the thing you want to do! If you decide that it is (I suggest before you do this, maybe try switching the scope impedance high/50 ohms if possible), then consider some kind of averaging - averaging is akin to low pass filtering (e.g. check out the moving average function/smoothing in VEE)</FONT></SPAN></DIV> <DIV><SPAN class=063422108-12092003><FONT face=Arial color=#0000ff size=2></FONT></SPAN> </DIV> <DIV><SPAN class=063422108-12092003><FONT face=Arial color=#0000ff size=2>If you want the whole nine yards, then here is what you need to do:</FONT></SPAN></DIV> <DIV><SPAN class=063422108-12092003><FONT face=Arial color=#0000ff size=2>1. Design you low pass filter (FIR is simplest) - effectively you determine the tap weights of the FIR</FONT></SPAN></DIV> <DIV><SPAN class=063422108-12092003><FONT face=Arial color=#0000ff size=2>2. Take the impulse response of the filter - this is the array of tap weights and CONVOLVE this with your time domain signal</FONT></SPAN></DIV> <DIV><SPAN class=063422108-12092003><FONT face=Arial color=#0000ff size=2>3. Voila - you now have a filtered time domain signal.</FONT></SPAN></DIV> <DIV><SPAN class=063422108-12092003><FONT face=Arial color=#0000ff size=2></FONT></SPAN> </DIV> <DIV><SPAN class=063422108-12092003><FONT face=Arial color=#0000ff size=2>Hope this helps,</FONT></SPAN></DIV> <DIV><SPAN class=063422108-12092003><FONT face=Arial color=#0000ff size=2></FONT></SPAN> </DIV> <DIV><SPAN class=063422108-12092003><FONT face=Arial color=#0000ff size=2>Andy</FONT></SPAN></DIV> <BLOCKQUOTE> <DIV class=OutlookMessageHeader dir=ltr align=left><FONT face=Tahoma size=2>-----Original Message-----<BR><B>From:</B> Davis, Bjorn [mailto:BDavis@sjm.com]<BR><B>Sent:</B> 11 September 2003 18:57<BR><B>To:</B> VEE vrf<BR><B>Subject:</B> [vrf] Newbie to the list - Question about Low Pass Filtering in VEE<BR><BR></FONT></DIV> <P><FONT face=Arial size=2>Hi, this is my first post to the list. I'm using HP-VEE 4.0 and I'm measuring a digital signal from my oscilloscope. Anyways there is a terrible amount of ringing and I was wondering if anyone could maybe point me to some kind of Low Pass Filtering algorithm? Thanks for the help!</FONT></P> <P><FONT face=Arial size=2>-Bjorn</FONT> </P><BR> <P><FONT face=Arial size=2>***************************** </FONT><BR><FONT face=Arial size=2>This communication may contain information that is proprietary, privileged, confidential or legally exempt from disclosure. If you are not a named addressee, you are notified that you are not authorized to read, print, retain, copy or disseminate this communication without the consent of the sender and that doing so may be unlawful. If you have received this communication in error, please notify the sender via return e-mail and delete it from your computer. Thank you. 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