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Question asked by VRFuser on Sep 11, 2003
<!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.comvrf@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. 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