Design Con 2015
Breaking News
Comments
Newest First | Oldest First | Threaded View
MeasurementBlues
User Rank
Blogger
Re: Source impedance
MeasurementBlues   9/18/2013 11:55:05 PM
NO RATINGS
Doug Smith has several articles about how to make probes for all kinds of measurements. Here's one: DC to 1GHZ Oscilloscope Probe Plans

Steve.Picotest
User Rank
Blogger
Re: Source impedance
Steve.Picotest   9/17/2013 1:15:02 AM
NO RATINGS
1 saves
Thanks for sharing your comments.  You are correct and made some good points.  While I have made homebrew divider probes, I can't usually get good pulse performance above 1GHz.  I do use the Lecroy P65 and P66 transmission line probes.  These are much better matched than I could do myself, so I can achieve 7.5GHz and 47pS rise time with 0.75pF loading.  If you can tolerate the low impedance, and in most power applications you can, these are a great way to go.  I also like that they aren't keyed, so they work with any 50 Ohm equipment. 

Tektronix offers a great 1GHz passive 3.9pF probe and their TPP0850 800V/800MHz passive probe, with 1.4pF.  I measured the rise time of the TPP0850 at 970pS. 

I also have the Lecroy ZS2500 and ZS4000 active probes, which are excellent when you need the speed and these are very low loading at <1pF. 

I published an article recently in Power Electronics on measuring ripple that covers more on this subject of probing and cable matching.  There is also a chapter dedicated to it in my upcoming measurement book, which should be available in late 2014 with the tentative title Power Integrity: Measuring, Optimizing and Troubleshooting Power-Related Parameters in Electronics Systems

 

 

jnissen
User Rank
Manager
Source impedance
jnissen   9/16/2013 11:23:28 PM
NO RATINGS
1 saves
You gave some fair advice but failed to mention why certain probe types work best in some situations. Source impedance often dictates what type of probe you can and should use. I often find myself creating my own resistor divider probes with simple coax and a couple SMT resistors. Very low capacitance and minimal loading on high impedance outputs. Active probes are great but sometimes you don't need them or want them. Been fooled lots of times relying on an active probe. Particularly nasty if you think you can use them for power supply ripple and droop analysis.



Flash Poll
Top Comments of the Week
Like Us on Facebook
EE Times on Twitter
EE Times Twitter Feed

Datasheets.com Parts Search

185 million searchable parts
(please enter a part number or hit search to begin)
EE Life
Frankenstein's Fix, Teardowns, Sideshows, Design Contests, Reader Content & More
Max Maxfield

Book Review: Deadly Odds by Allen Wyler
Max Maxfield
8 comments
Generally speaking, when it comes to settling down with a good book, I tend to gravitate towards science fiction and science fantasy. Having said this, I do spend a lot of time reading ...

Martin Rowe

No 2014 Punkin Chunkin, What Will You Do?
Martin Rowe
Post a comment
American Thanksgiving is next week, and while some people watch (American) football all day, the real competition on TV has become Punkin Chunkin. But there will be no Punkin Chunkin on TV ...

Rich Quinnell

Making the Grade in Industrial Design
Rich Quinnell
13 comments
As every developer knows, there are the paper specifications for a product design, and then there are the real requirements. The paper specs are dry, bland, and rigidly numeric, making ...

Martin Rowe

Book Review: Controlling Radiated Emissions by Design
Martin Rowe
1 Comment
Controlling Radiated Emissions by Design, Third Edition, by Michel Mardiguian. Contributions by Donald L. Sweeney and Roger Swanberg. List price: $89.99 (e-book), $119 (hardcover).