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vrf Waveform Analysis

Question asked by VRFuser on May 7, 2008
Craig,

Speed of your waveforms must be taken into account. You could write a rise/fall time function based on absolute voltages thresholds, this gets around any ringing, overshoot, or undershoot that could affect where the 10%-90% levels are at especially if the waveform does not have a stable VOH or VOH level to extrapolate % levels (typical for very high speed or signals prone to cross talk). Another funtion could be created using time intervals to average stable areas of  VOH/VOL.

 

Shirley

 

From: Street, Andy M [mailto:andy.street@tycoelectronics.com]
Sent: Wednesday, May 07, 2008 12:40 PM
To: VRF
Subject: RE: [vrf] Waveform Analysis

 

Hi Craig,

 

I agree with Rufus.  VEE does not have any native rise/fall time functions, so you would have to write your own.  This can become quite challenging, quite quickly.  For instance, say you want the 10-90% rise time.  Chances are, you will not have samples at those points.  So you will end up interpolating/extrapolating, based on a subset of points that form your rise time.  What kind of interpolation should you use - e.g. spline, linear etc (VEE's Matlab's has a nice spline interpolation, so you could maybe send your rising edge into this interpolator and then find your 10-90% levels, within a given tolerance...). 

 

However, if you have the chance, I would try and get the metrics you are looking for from the instrument itself (oscilloscope).  All the scope manufacturers have years of know how and IP tied up in the measurement algorithms, which will/should be robust and QA'd.

 

But, if all you have if an array to work from, then I would start by looking at the Matlab example for interpolation and also read up on the 'find' function in Matlab - as this will get you your threshold points...

 

Good luck,

 

Andy

 

  _____  

From: Warren, Rufus [mailto:Rufus.Warren@Herley.Com]
Sent: Wednesday, May 07, 2008 1:20 PM
To: VRF
Subject: RE: [vrf] Waveform Analysis

Craig,

 

My first impression is that you really want to measure rise and fall directly.  Take a look at Agilent’s Frequency Counters.  If you must use the data, your measurements are going to be off by the digitization error and whatever other errors you have in the data collection.  So you are not going to get very accurate results; but to answer your question, no, none that I know.

 

 

Rufus

  _____  

From: Olbinski, Craig A (GE Healthcare) [mailto:Craig.Olbinski@med.ge.com]
Sent: Wednesday, May 07, 2008 12:15 PM
To: VRF
Subject: [vrf] Waveform Analysis

 

I need to calculate rise time, fall time, and the plateaus of positive and negative going square waves. I have the waveform data contained in an array. Are there any function within Vee that will do this?

 

Thanks,

Craig

GE Healthcare
___________________________

Craig A. Olbinski
Repair Development Engineering
Global Parts and Repair Solutions
Phone:  (414) 615-6873  Fax:  (414) 615-6979
Pager:  (414) 440-1747   Mail Stop: GA-43
E-Mail:  craig.olbinski@med.ge.com
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