Categories

Homebrew highspeed lo-Z scope probe

Posted on Wednesday, January 16th, 2013 in DIY, oscilloscope by the machinegeek

loz_probe
Paulo Oliveira was experimenting with probing high speed signals with his oscilloscope. You might think that a 500 MHz probe would be adequate to probe a 125 MHz clock signal, but he demonstrates why this is not the case. He wrote a detailed article on building your own high-speed oscilloscope probe, demonstrating how a surprisingly simple and affordable DIY passive probe can outperform even the best 10X passive probes for this particular application.

You can read his observations and probe construction details on Paulorenato.com.

Via the contact form.

This entry was posted on Wednesday, January 16th, 2013 at 4:13 am and is filed under DIY, oscilloscope. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.

3 Responses to “Homebrew highspeed lo-Z scope probe”

  1. artag says:

    This idea is described in the book http://www.ivorcatt.org/digital-hardware-design.htm

    I’m not implying that Paulo copied it or anything of that sort – but it’s a good idea, and if you like it you might find the rest of the book interesting. Catt was slightly controversial later on but the topics in that are the foundation of modern high speed logic and pcb design, which is not often described.

  2. Drone says:

    There are sooo may problems with this… First, the Author’s post says he’s using RG-58 with an SMA connector (wrong, looks like flex RG-174?). Then, the Author uses an SMA/BNC adapter to connect with the scope – which by the way must support an in-device 50 Ohm input option (many low-cost, and even mid-cost scopes don’t these days). Then, unless you spend a lot of money on proper connectors/adapters/cables and the expensive tools to mate the cables to the connectors, your results will vary widely. The biggest mine-field to traverse in this adventure involves horrific Chinese-made coaxial adapters, connectors and coaxial cables. Also, there’s an issue of whether your scope has a 75 Ohm BNC input connector or a true 50 Ohm BNC connector (yes, they are different, not to mention using the proper-impedance BNC connector to connect to the scope). And we haven’t even scraped the surface of probe compensation and calibration issues… I’m spewing – enough already (sorry).

  3. AMS says:

    As covered in some of the Jim Williams app-notes, you should use a composition resistor for these as they’re lower inductance and capacitance than a film-based (spiral path on radial components) resistor as used here.

Leave a Reply

Notify me of followup comments via e-mail. You can also subscribe without commenting.

Recent Comments

  • T.O.: For $29 I can get 10 STM32F1 mini boards plus external debugger, free shipping. $0.99 would get me bare microcontroller if I need own board....
  • KH: However innocent it may be, I'm not impressed by the choice made by the creator of the image. Now, I'm not the most politically correct...
  • cyk: A simple google search for "free arm ide" lists CooCox on the first page: http://www.coocox.org/index.html Supports a ton of different ARM M0/3/4 micros and all...
  • Stennly: Despite the popularity of STM32s, it may not be the best place to start. As mentioned already, the Silicon Labs gecko family is cheap to...
  • Pete Juliano: Since this posting on my blog I have received an excellent suggestion on how to quickly disconnect the 48 VDC from the amp so you...