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> 1 GHz DIY differential probes

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dietert1:
Where did you get that number "6.3"? Can't find that in the LMH3401 datasheet.
The evaluation board manual describes a 50/200 Ohm configuration (gain = 4), so i unterstood that was supposed to be stable.

Marco:
Why not build an AC differential amplifier from a pair of RF transistors?

tggzzz:

--- Quote from: Marco on October 15, 2018, 11:40:12 am ---Why not build an AC differential amplifier from a pair of RF transistors?

--- End quote ---

Or from a few bits of coax and a combiner, e.g. http://emcesd.com/pdf/cd94scr.pdf

Note: I haven't tried such a probe!

nctnico:

--- Quote from: dietert1 on October 15, 2018, 10:37:09 am ---Where did you get that number "6.3"? Can't find that in the LMH3401 datasheet.
The evaluation board manual describes a 50/200 Ohm configuration (gain = 4), so i unterstood that was supposed to be stable.

--- End quote ---
The number 6.3 is from the specs on the website. That corresponds with a gain of 16dB. I just checked the evaluation kit manual but I can't find any mention of configuring the chip for a gain of 4x. Creating an opamp with a high bandwidth which is stable at a gain of 1 is very hard because it needs compensation to be stable but at the same time the compensation eats into the bandwidth.

dietert1:
Yes, they use 16 dB as a basic configuration of the LMH3401 in the specs. But that is not a stability limit, see for example Figure 2 in the datasheet, which is for 12 dB and extends well up to 5 GHz. Schematic is in Figure 51. The 12 dB configuration is also mentioned in the evaluation board user manual, paragraph 4.4.
As far as i understand one advantage of the LMH3401 over the LMH5401 mentioned before is the internal feedback path which helps for stability.

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