Open source USB scope

  
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There are plans to make it 1Gsps in the future, using interleaved ADCs and staggered clock, but that`s beyond me at the moment, so the first iteration will only have 100Msps (fastest from single ADC). The part I`m most unsure about is the analog front end, as we haven`t done any high speed circuit design in classes yet, so most of my knowledge com
Open source USB scope - schematic

es from random places on the internet. Would be great if anyone wants to take a look Input from BNC probes go into a 1Mohm resistor in parallel with 20pF (so the probes can compensate for it). The signal is buffered by a wideband, unity-gain stable JFET op amp (OPA656), before being fed to a summer (the pre-amp of the programmable gain amplifier), that adds a bipolar offset from a DAC to the signal. Then it goes to a programmable gain amplifier, and finally the ADCs. The problem with that front end is that there is that the input overload protection will blow very easily. Any overvoltage input is directly shorted by the diodes - bad news! Perhaps, with modifications, it could be used as a digitizer card for SDR (software defined radio, GNUradio in particular) 100Msps is very fast for a continuous capture digitizer card. The analog requirements are much simpler - 50 ohm or 75 ohm input, perhaps only a 500mVpp to 5Vpp or so input amplitude range, and much less need for overload protection. In power electronics, transistors should ideally be either fully on or fully off, because a half-on transistor just makes a really poor imitation of Tiffany Yep. The problem with that front end is that there is that the input overload protection will blow very easily. Any overvoltage input is directly shorted by the diodes - bad news! I`m doing internship right now (as a software developer), so this is my evening and weekends project....



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