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Richard Erlacher
04/04/13 10:55
Read: 959 times
Denver, Co

#189613 - What information do you want to extract?
Responding to: Joseph Hebert's previous message
Like you, I'm one who believes in squeezing every nickel until the buffalo sh*ts, so I certainly understand your desire not to overinvest.

Now, I haven't done anything with these parameters for years and years, but I'm curious what you want to know about your circuit that isn't apparent from the static parameters by means of which you could calculate the impedance using methods described in the MECL System Design Handbook.

Further, I'd suggest you consider a TEKTRONIX TM500-series (yes, I know that requires a mainframe) calibration generator, as those are quite precise and also quite inexpensive. I bought one (just to give you an idea of how long it's been since I last used it, I can't even remember the exact device number, but I think it's a PS506 or something like that.) in order to calibrate a TEK 475A oscilloscope. In order to generate a short-enough pulse, you can use an xor gate as a delay and another one to produce the pulse, and while it's not as short as some of the multi-k-buck devices on the market, you can work with it. If you're intending to find discontinuities, or if you're trying to optimize terminations, this can do it. High-speed gates either High-Speed CMOS, ECL or GaAs, will give you pretty short pulses.

It generates a sharp risetime on a fast pulse, which lets you examine the waveform along the transmission path you're studying. (The real challenge is to sort out what comes from the circuit and what comes from the probe. I used to wrap the probe in aluminum foil and ground both ends, having put the circuit under test in a Faraday cage made of 3/8" hardware cloth (mesh).) This required careful attachment of the probes to the circuit and grounding both the mesh and the foil to a common ground, and that means lots of time per measurement.

I don't know how often you'll have to make such measurements, but sometines it's worth renting the exact instrument you need. Typically that will cost 10% of what a purchase costs, but if you can save 90%, your client may be willing to bear the cost in order to solve his problem.


List of 19 messages in thread
Measuring trace impedance with a TDR?      Joseph Hebert      04/01/13 08:53      
   Maybe there's help here ...       Richard Erlacher      04/01/13 09:23      
      Thanks. Hardware/model specific      Joseph Hebert      04/01/13 10:22      
         Beauty contest      Steve M. Taylor      04/03/13 05:32      
            Growing your own      Joseph Hebert      04/03/13 16:56      
               What information do you want to extract?      Richard Erlacher      04/04/13 10:55      
                  desired information      Joseph Hebert      04/04/13 14:04      
                     "pre-loved"      Steve M. Taylor      04/05/13 12:27      
                        Pre "loved"      Joseph Hebert      04/05/13 16:40      
                        Resolution      Joseph Hebert      04/06/13 13:42      
                           ???      Steve M. Taylor      04/09/13 16:38      
                              Plenty, I'm sure, but ...       Richard Erlacher      04/09/13 21:03      
                              cost      Joseph Hebert      04/11/13 17:31      
                                 Though this is a large and cumbersome instrument ...      Richard Erlacher      04/12/13 10:24      
                     Better than standard solutions?      Oliver Sedlacek      04/08/13 01:59      
                        How do they do so?      Joseph Hebert      04/08/13 10:59      
                           Magic?      Oliver Sedlacek      04/09/13 01:43      
                           signal integrity      Andy Peters      04/16/13 15:23      
                              Exactly      Joseph Hebert      04/16/13 18:41      

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