You could use a Tektronix P6247 or P6248 if you're looking For a TekProbe interface.
Common mode range of +-7V
To zoom in on the ripple, apply a constant 5V from a reference to the negative input of the probe.
Make sure the ground side of the reference is hooked up to the ground of the cap on the DUT supply that you are measuring your ripple across. Add a local bypass cap for the reference and either twist your leads or use coax for the feed.
I'm wondering if this isn't an overly obfustigated way of measuring ripple. One of the problems I see is that the 5V offset must be ripple free as well over a large frequency band. Just look at the Jim Williams appnote linked to above which uses a DC blocking capacitor and a coax cable soldered directly to the point of interest.
If you’re on a tight budget, why not go old school and pick up a Tek p6046?
If you’re on a tight budget, why not go old school and pick up a Tek p6046?
+1 on P6046 if the OP only on hobbyist budget.
Its also the example probe in the official standard ATX document.
I wonder what the common mode rejection versus frequency and isolation of that J2113A actually is; Picotest does not say.
I wonder why their J2102A transformer isolates so poorly below 1kHz.
Also I find another great improved version of that amplifier int that AN http://www.analog.com/media/en/technical-documentation/application-notes/an159fa.pdf
Also I find another great improved version of that amplifier int that AN http://www.analog.com/media/en/technical-documentation/application-notes/an159fa.pdf
The amplifier described in an159 look really interesting. I will definitely try to build one of those!
Do you mean the one shown in figure 15? That can work but the specific example was intended for measuring the noise at the output of a linear regulator and has a lot more gain than required.
This sort of things works well if it is just built into the original board layout and only populated for testing.
So I guess if the amplifier is not close enough to the measurement point it will pickup a lot of external noise?
So I guess if the amplifier is not close enough to the measurement point it will pickup a lot of external noise?
All of the usual probing rules apply which is why building the test circuit into the layout is advantageous.
Maintaining a good common mode rejection up to 20MHz and beyond is not trivial either and unless calibration is performed, external dividers become a problem. I have not tried them but I was thinking parts like the LT1187, LT1189, or LT1193 video difference amplifiers would work well in these applications but like all video amplifiers, they are pretty noisy and too noisy to measure linear regulators although they could be used with a low noise preamplifier. They have the advantage of getting rid of the external feedback networks back to the inputs so common mode rejection should be easier to maintain without calibration and their datasheets show about 40dB CMRR at 20MHz.
Googling further led me to Patrick Coleman, who has forked Levido's design and posted all the details on his Github page here:
https://github.com/blinken/power-rail-probe/tree/main
Coleman even sells a fully assembled device, complete with a matte black enclosure professionally overlaid with white text:
https://paradar.co.uk/products/low-noise-oscilloscope-power-rail-probe
£249 (US$317) fully assembled
£45 (US$57) for blank PCB & enclosure (must buy components on BOM separately yourself)