Suggestion from my side. maybe we can have an automated step function with adjustable step time for these tests? So then we can just write down values and not switching back and forth programs and edit values. I'm half dead right now
If ever we build a per value / per device calibration matrix, yes, we should have such auto-set macro function. Does not even have to be in the BP, can be in the PC.
Yes, boring and source of mistakes. If needed, I will do it. I already did this some years ago: automated calibration on a FG with a DMM and and an oscilloscope with SCPI commands from an excel sheet (do you guess why I was talking of a SCPI interface in the new firmware
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Anyway thank you for your time, both of you. The more values, the more ideas (and you have a lot), the more potential upgrades.
However, I think for now, all we need is some rough guidelines on what autoranges to select, and maybe some coarse global correct. So maybe one or two more person, then we are done for now.
Agreed on that. I will also run tests and that will be enough data at the moment.
It seems now obvious that we have first to deal with some hardware upgrades before finding software workarounds.
For now I will add static calibration only on the 3 ranges on amplitude and offset. This should be enough for low frequencies.
For higher frequencies, it will be time to think about it later on and decide, after fine tuning the opamp part, if this will be done in FPGA via digital filters (zov maybe?) or if something can be done via FP.
Also, I ran the wave all the way down to 0.01Hz, and the shape of the flattened top stayed the same. Meaning it is not a response time thing. Not even a current thing, because if the local capacitor would drain out, surely it would fall off more toward the trailing edge.
I wonder if it is something to do with the fact this OpAmp is described in the datasheet as a "CURRENT-FEEDBACK AMPLIFIER". I do not know what that means, normally when I mess with OpAmp I consider voltages. Need to read up on that.
From the THS3001 datasheet: "The ability to control the amplifier gain independent of the bandwidth constitutes a major advantage of current-feedback amplifiers over conventional voltage-feedback amplifiers"
A test I would suggest would be to use the feedback resistor value recommended in the THS3001 datasheet, that is 560 ohms for a gain around 5 instead of 1.5kohms. Then replacing the gain resistor with a 180 ohms one instead of the 499 ohms one. This would lead to a gain of 4.11 that could be compensated by the software calibration.
I have some THS3095 ready for tests as well as preproduction THS3491 but not time to do it now...
Also, I wonder if it can be resolve by, instead of replacing, *adding* an OpAmp.
Just leave the THS3002 in place, and add a pair of THS3001. They have the same behavior, the PCB traces are in place, de-soldering is harder then soldering.
All we need to do is add to the unpopulated footprint.
Good idea but as DerKammi said, we would have to add shared output resistors. May not be to difficult to modify traces for that... That is a typical design with THS3491.