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DC coupled 2.7 GHz Active Probe Project - Now Available!

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joeqsmith:

--- Quote from: RFKev on September 05, 2023, 02:56:51 pm ---
--- Quote from: joeqsmith on September 01, 2023, 02:10:36 pm ---
--- Quote from: RFKev on September 01, 2023, 08:22:54 am ---
--- Quote from: joeqsmith on August 16, 2023, 05:05:00 am ---S11 & S21 for the blade probe using the PNA.  My homemade PCB waveguides are going to be useless.    Starts out at 500 ohms as and drops off rather quickly reaching 100 ohms at 6 GHz.   Mag isn't very stable  (when holding all the parts in my hands, moving them around...).  Then there is de-embedding the interconnect.   Consider it all just a gross measurement to give us some idea how it behaves.

--- End quote ---
What was the measurement setup and METAS VNA Data Explorer configuration to get the probe impedance with frequency?

--- End quote ---
I showed the screen shot of the METAS setup and used S11 to measure the impedance.  Guessing that is not what you are asking.  Maybe consider posting a more detailed question.

--- End quote ---
I can see the settings along the top of the METAS screenshot. Was there anything configured in the "Setup" dropdown?  My main question is how was the probe interfacing with the VNA.  Did you touch the probe on the port 1 connector, or probe a transmission line?  If you probed a line connected to port 1, was it terminated with a 50ohm load?

--- End quote ---
No, just S11. Everything is defaults except the top.   My comment about de-embedding the interconnect was the main point.  Ideally, I would have a custom jig for this.   You can't... well, er... you could probe an RF connector directly but nah....   I have a connector that matches with my home made standards and touched off on it.  This gets up roughly the correct reference plane.  Still, I expect some error.  There is nothing attached to the test connector besides the probe (which is what I am wanting to measure).   Think of it this way.  If the test connector were terminated to 50, then I  place the probe in parallel with that, we are not going to measure 500 ohms but rather 500 in parallel with 50, product over sum....

schratterulrich:
Your probe project is very impressive. It certainly took a lot of effort to achieve this high bandwidth.
I came across this post because I probably took a similar approach to building an active probe.
My intention was to get a probe with very high input impedance and low capacitance to test sensitive nets like oscillator signals and to get an high impedance amplifier for 50 Ohm instruments.
I chose the ADA4817 operational amplifier and got the following characteristics for the active probe. (With direct SMA connection)
500 MHz bandwith
660 ps Rise Time
1,3 pF input capacitance
95 MOhm Input impedance

lasmux:

--- Quote from: schratterulrich on September 10, 2023, 06:59:01 am ---Your probe project is very impressive. It certainly took a lot of effort to achieve this high bandwidth.
I came across this post because I probably took a similar approach to building an active probe.
My intention was to get a probe with very high input impedance and low capacitance to test sensitive nets like oscillator signals and to get an high impedance amplifier for 50 Ohm instruments.
I chose the ADA4817 operational amplifier and got the following characteristics for the active probe. (With direct SMA connection)
500 MHz bandwith
660 ps Rise Time
1,3 pF input capacitance
95 MOhm Input impedance

--- End quote ---
Hey, cool probe there :) Nice linear response out to 300MHz or so!

Thanks for the feedback. It definitely did take a lot of effort, and even more learning. I am currently waiting for the 9th revision PCB to arrive (!!!). Fortunately active probe PCBs are small and relatively cheap.

hpw:

--- Quote from: lasmux on September 14, 2023, 11:11:43 pm ---Fortunately active probe PCBs are small and relatively cheap.

--- End quote ---

And please do not forget any 2GHz differential mode(s)  ::)

LooseJunkHater:
What is the estimated price for the probe?

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