howard johnson passive probe

Does somebody have some literature about designing a probe, from DC-5GHz bandwidth range, suitable for sampling/real time oscilloscopes?

Did anybody try to build it by himself?

rfmw

Perhaps this 1 GHz probe description helps.

This doesn't directly answer your question, but it's related.

"The Truth About The Fidelity of High Bandwidth Voltage Probes, AN 1404"
http://cp.literature.agilent.com/lit...988-6515EN.pdf

"Restoring Confidence in Your High-Bandwidth Probe Measurements, AN 1419-01"
http://cp.literature.agilent.com/lit...988-7951EN.pdf

"Improving Usability and Performance in High-Bandwidth Active Oscilloscope Probes, AN 1419-02"
http://cp.literature.agilent.com/lit...988-8005EN.pdf

Thanks for your links. In the meantime I've made a passive probe. It has approximately flat response from DC to 3 GHz. Is someone is interested I can post some pictures with measurements...

Hi rfmw,

I am very interested in your probe's pictures, and measurements.
Please post them.
Thanks.
g579

Really interesting the passive probe...
What about impedance of it? Is still high at high freq?
Do you have a model or an expression for it?

Bye
Mazz

I bought some nice old Tektronix P6056 and P6057 probes on eBay. Some specs from the instruction manual:

The P6056 is a 450 ohm series resistor, so it is a x10 probe. 3.5 GHz bandwidth. Input capacitance about 1 pF. 500 ohms DC to 300 MHz decreasing to 250 ohms at 1 GHz.

The P6057 is a 4950 ohm series resistor, so it is a x100 probe. 1.4 GHz bandwidth. Input capacitance about 1 pF. 5000 ohms DC to 350 MHz decreasing to 1500 ohms at 1 GHz.

there is an article in Elektor(india), january issue about construction of 1 Ghz fet probe.

@Mazz

response (S21) of the probe is approx -21 dB flat to approx 3 GHz. Then it rises up because of parallel capacitance of input resistor.

I'll try to put some pictures and S21 measurement asap...

bye,
rfmw

EDIT: about it's circuit... it's the same as that passive probe described in book of Black Magic

Hi rfmw,

I am waiting your pictures and S21 on the probe.
In the meantime please clarify your reference on Black Magic, as below.

"about it's circuit... it's the same as that passive probe described in book of Black Magic"

Thanks
g579

Hi g579,

I'm refering to the High-Speed Digital Design, A Handbook of Black Magic by Howard W. Johnson.

For his probe look at Chapter 3, pages 97-101.

Hi rfmw,

The book is worhwhile to see. Somehow this book went out of my attention. Thanks.
Waiting your pictures and S21 on your probe too.
Thanks
g579.

hi g579,

here're the measurements and a couple of photos... I'd like to hear your comments ;)

Hi rfmw,

Thanks for the S21 datas and realization pictures.
Just one question. Have the S21 datas been measured at an 50 ohm through-line enviroment ?
Thanks
g579

Yes, one port of network analyzer was connected to the 50 ohm microstrip transmission line terminated with the 50 ohm load. The second port was connected to the probe and i was holding its tip on the 50 ohm load at the end of the microstrip transmission line...

Very nice idea.
I would like to understand what is the input impedance of the probe to understand if the inserted probe affects the transmission line.
A test could be measuring the S21 of the microstrip with and without the probe inserted.
Thanks.
Mazz