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DDC112: DDC112 current measurement limit/precision

Vahe Ghazikhanian
Prodigy 30 points
Part Number: DDC112

Does anyone know what the practical lower current measurement limit of DDC112 is using the 12.5 pF internal capacitor at Tint = 333 us?

I would like to measure a current in the range 1 pA to 200 nA. Given the input bias current and noise limitations of the DDC112 analog front end is this realistic? My detector capacitance is ~ 10 pF.

  • 0
    TI__Mastermind 49176 points
    Hello Vahe,

    Apologize for the delay in the response.
    Let me check with the team and will get back to you shortly.
  • 0
    TI__Expert 4590 points

    Honestly, I don't know but looks tight... Just quick calcs...

    The most sensitive range is the one you selected (12.5pF feedback) which will saturate at 50pC. So, it is a bit short of supporting your 200 nA x 333us = 66.6pC

    But anyhow, assuming you can waive that, the challenge is to be able to measure down to 1 pA (x 333us = 0.3fC). From input bias it seems that the typical is 0.1pA. Can't see a range associated to it, but probably does not scale much with range, so, may be good enough. The concern is that it may be bigger (in fact the max is much bigger) but it is probably some kind of margin due to tester limitations, although you can never be sure. Regardless, maybe you can calibrate it out. As long as your temp is stable, maybe you are fine... (0.01pA/C).

    Nevertheless, from noise perspective, looking at the graph, it seems to be 5ppm of FSR, so, that is 0.25fCrms, on the order of what you want to measure... In a single shot you would have quite amount of error. Using averaging you could reduce it...

    Just my two cents,

    Edu

  • 0 in reply to Eduardo Bartolome
    TI__Mastermind 18275 points
    Vahe,

    We hope that Eduardo was able to answer your question. We will close the thread, but if you need more assistance feel free to reply