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vrf Newbie to the list - Question about Low Pass Filtering

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 6.00.2712.300" name=GENERATOR></HEAD><BODY><DIV><SPAN class=063422108-12092003><FONT face=Arial color=#0000ff size=2>HelloBjorn,</FONT></SPAN></DIV><DIV><SPAN class=063422108-12092003><FONT face=Arial color=#0000ffsize=2></FONT></SPAN> </DIV><DIV><SPAN class=063422108-12092003><FONT face=Arial color=#0000ff size=2>VEE4-0 - wow!  Unfortunately, you will not be able to take advantage of theplethora of signal processing functions inherent in the VEE 6-0 Matlabengine.  But aside from this, have you considered where the ringing iscoming from - is there a mismatch between the scope input impedance and theoutput impedance of the source you are trying to measure.  Is there somebandwidth limitation - if you are expecting a square wave output, but you areseeing lots of ringing, maybe you are losing some of the harmonics of the signaland thus the rise time and waveform shape is affected - Gibbsphenomena.</FONT></SPAN></DIV><DIV><SPAN class=063422108-12092003><FONT face=Arial color=#0000ffsize=2></FONT></SPAN> </DIV><DIV><SPAN class=063422108-12092003><FONT face=Arial color=#0000ff size=2>Bottomline, my suspicion is that low pass filtering you signal may not be the thingyou 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 considersome kind of averaging - averaging is akin to low pass filtering (e.g. check outthe moving average function/smoothing in VEE)</FONT></SPAN></DIV><DIV><SPAN class=063422108-12092003><FONT face=Arial color=#0000ffsize=2></FONT></SPAN> </DIV><DIV><SPAN class=063422108-12092003><FONT face=Arial color=#0000ff size=2>If youwant 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 tapweights 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 andCONVOLVE 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=#0000ffsize=2></FONT></SPAN> </DIV><DIV><SPAN class=063422108-12092003><FONT face=Arial color=#0000ff size=2>Hopethis helps,</FONT></SPAN></DIV><DIV><SPAN class=063422108-12092003><FONT face=Arial color=#0000ffsize=2></FONT></SPAN> </DIV><DIV><SPAN class=063422108-12092003><FONT face=Arial color=#0000ffsize=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. St. Jude Medical, Inc. </FONT></P>  <P><FONT face=Arial size=2>*****************************</FONT> </P>---<BR>You  are currently subscribed to vrf as: andy_street@agilent.com<BR>To subscribe  send a blank email to "join-vrf@it.lists.it.agilent.com".<BR>To unsubscribe  send a blank email to "leave-vrf@it.lists.it.agilent.com".<BR>To send messages  to this mailing list, email "vrf@it.lists.it.agilent.com". <BR>If you need  help with the mailing list send a message to  "owner-vrf@it.lists.it.agilent.com". </BLOCKQUOTE></BODY></HTML>  

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