Hi,
triggered by Your thread I quickly built a probe based on the circuit suggested by Tommi Otsavaara in his thesis "1 GHz Power Rail Probe".
Seemingly he orientated on the Keysight N7020 probe that Sharia kindly dared to open up for us
![Wink ;)](https://www.eevblog.com/forum/Smileys/default/wink.gif)
The major differences to the Levido DIY-probe seems the higher output resistor of the LF-path of 590R which requires the second inverting stage to have a gain of -11.8, and the increased Offset range of up to 50V
I had some OP270 lying around, which is a low en-noise dual OP27, which in simulation results in very nice low noise, but it´s decompensated and faster brother OP37 would be better suited to the second inverter gain stage.
In the Levido probe where the second inverter is just a buffer with a gain of -1 the OP27 may get problems due to the required higher load currents.
As alternatives TI lists some ´Soundplus audio-OPAs´ like the OPA1655/1656 with lownoise, sufficient GBW and high current outputs.
If higher supply lines are possible the JFET-Input OPA827 appears interesting.
Due to the overall high offset-gain of 118 the Otsavaara probe´s offset-setting becomes critically sensitive and rather requires multiturn-potis even though potis are used for coarse and fine tuning already.
Another point is the lowpass filtering of the LF-path.
The Otsavaara relies on simple RC-Filtering, which in this case leads to a shelving-filter character.
In simulation this adds ~0.3dB of output signal level to the HF-path.
The Levido probe on the other hand utilizes a RLC-filter that follows a LP-filter curve much closer, hence attenuates the LF-path alot better.
@tszaboo
increasing the Offset range from +-24V to +-50V or even more (R&S claims up to 60V) seems easy ... just a bit of shuffling values of the Potis and the offset-input resistor.
Do You plan on offering a probe with higher offset range also?
regards
Calvin