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| > 1 GHz DIY differential probes |
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| joeqsmith:
--- Quote from: tronde on August 19, 2016, 12:51:39 am ---I don't want to break Elektor's copyright, but this is the specs: Technical specification • Attenuation: 10:1 with a differential signal and 50 ? termination in the ‘scope • Differential input resistance: 5 k? • Single-ended input resistance: 2.5 k? • Output resistance: 50 ? • Bandwidth: 1.9 GHz (–3 dB) • Rise/fall time: 300 ps • Power supply: ±8 to 12 V DC. They also write: For readers who are interested the author offers ready-to-use and tested PCB modules, also a kit consisting of case, RF cable with BNC connector and power supply lead with plug. Further information from: alfred_rosenkraenzer@gmx.de. --- End quote --- Looked to see if they had a website or something with more info. Do you have a link besides the email address? |
| Cerebus:
--- Quote from: joeqsmith on August 19, 2016, 03:19:41 am --- --- Quote from: tronde on August 19, 2016, 12:51:39 am ---I don't want to break Elektor's copyright, but this is the specs: Technical specification • Attenuation: 10:1 with a differential signal and 50 ? termination in the ‘scope • Differential input resistance: 5 k? • Single-ended input resistance: 2.5 k? • Output resistance: 50 ? • Bandwidth: 1.9 GHz (–3 dB) • Rise/fall time: 300 ps • Power supply: ±8 to 12 V DC. They also write: For readers who are interested the author offers ready-to-use and tested PCB modules, also a kit consisting of case, RF cable with BNC connector and power supply lead with plug. Further information from: alfred_rosenkraenzer@gmx.de. --- End quote --- Looked to see if they had a website or something with more info. Do you have a link besides the email address? --- End quote --- I finally managed to find a copy of this to look at. There's very little to this probe. An ADA4927-1 op amp, input and feedback resistors for it, two 7xL05 regulators and associated decoupling. That is pretty much all. The amp only has an input common mode range of +/- 3.5V. The most concerning thing from my perspective is that there is not even a nod to input protection - the author relies on 2297 ohms of input resistance and whatever the chip has on board as input protection. Given there is a differential output already available from the amplifier so some sort of bootstrapped protection network wouldn't have been too taxing to design. I'm pretty comfortable that posting just the schematic for study and discussion falls under fair use, so here it is: |
| JohnG:
Interesting. I would not have guess that you could do the differential to single-ended conversion that way. Also, a 300 ps rise and fall time does not correspond to a 1.9 GHz BW. That is more what I would expect from a ~1.2 GHz probe. Either the frequency response is not approximately single-pole near the BW, or 1.9 GHz is for small-signal only. I'll look up the specs on the chip. John |
| Marco:
--- Quote from: JohnG on August 19, 2016, 01:14:17 pm ---Interesting. I would not have guess that you could do the differential to single-ended conversion that way. --- End quote --- I'd like to see some CMRR measurements. As I said before the datasheet CMRR might be a result of errors in the differential output canceling out. |
| alfredr:
Hi, my name is Alfred Rosenkraenzer. I am the designer of this active high speed probe described in Elektor 2016. This version is no longer available, but there is a new one described in ELEKTOR 3/2017(DE) using a USB power supply. The analog specs are similiar. I am selling loaded and tested pcb and finished probes (no blank boards). More info under alfred_rosenkraenzer@gmx.de |
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