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IVC 102 for Faraday cup measurements

Ishara Mudalige
Intellectual 280 points

Other Parts Discussed in Thread: IVC102, LMP7721

Hi TI,

I am working on an aerosol sensor which is basically a Faraday cup, and it gives really low current signal depending on the charged particles concentration condensed on to it. This current is really low as 1fA to 10fA range, can be measured by using a good electrometer. However, I want to make this instrument portable by using IVC102 chip to measure this current. ( I am a fluid mechanics guy only have basic knowledge in elec. stuff)

  1. Can IVC102 capable of measuring this low current?
  2. Which measurement technique might be suit to this application? (Basic reset-and-integration or the switched input measurement)
  3. If answer to the above is switched input measurement, do I need to include a sensor capacitance externally? (Data sheet Fig 3a)

Note: My sensor resistance (Faraday cup) is also low as 100-500

 

  • 0
    Prodigy 180 points

    Dear Ishara,

    I am not working for TI, but it happens that I've used the IVC102.

    1. IVC102 has 750fA maximum Ibias so if you try to amplify your signal which is in the range of 1 to 10fA the bias current will dominate your signal.
    2. I personally prefer switched input because by subtracting the two samples I get (with ADC and uC), I get an offset correction. But perhaps someone else will know better for your sensor
    3. I do not think so, the capacitance shown in the datasheet is part of the sensor (photodiode)

    For that range of currents perhaps LMP7721 could be better (i bias ).

    Also by portable you mean battery powered?

    Because you have to consider the power supply voltages. IVC102 needs negative supply between -18V and -10V

    I hope I helped,

    Gabriel

  • 0 in reply to Gabriel Koutilellis1
    Intellectual 280 points

    Dear Gabriel,

     

    Thanks for the reply. I really appreciate it. Now it makes more sense. I would not be able to use IVC102 for 1-10fA range, unless if I can increase the sensor current which is doable.

     I should use the word compact instead of portable.

    By the way, is there any good source to start these femto- amp measurements by using trans impedance amplifiers (or generally op-amp) for beginners (non electronics & electrical engineers)?

     

    Thanks again. 

    ~Ishara