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Current to Voltage Converter(Trance-impedance amplifier)

Sidda Raju
Prodigy 30 points
Other Parts Discussed in Thread: LMP7721

Hi Everyone,

I have a Custom single electrode MEMS based gas sensor it's output in the range of few nA to mA. So please suggest me any Current to voltage converter with highest gain and Precision.

  • 0
    TI__Expert 6250 points
    Hi Sidda,
    Working with nA, I'd suggest an ultra-low input bias current part such as the LMP7721. You'd have to configure this as a transimpedance amplifier externally, but that would give you the most flexibility for gain.

    A challenge involved in this is that at nA, PCB leakage, construction, and layout start to become very big concerns. Solder flux can easily contribute nA or more of leakage unless thoroughly cleaned.

    Dynamic range is also likely to be a problem. You may need to support multiple resistor values for the transimpedance amplifier to support the full nA to mA range (6 orders of magnitude).
  • 0 in reply to Alexander Davis
    Prodigy 30 points

    Hi Alex Davis,

    Output current of the MEMS gas sensor randomly vary from pA to nA  or nA to mA. so please let me know using LMP7721 how can i convert current to voltage in b/w the ranges without loss, please let me know any application note related on this.

  • 0 in reply to Sidda Raju
    TI__Expert 6250 points
    Hi Sidda,

    www.ti.com/.../sboa220.pdf discusses a transimpedance circuit for a photodiode application.

    Designing a single circuit which can work from pA to mA is going to be very difficult, as it will require multiple ranges and very low leakage switching to select between them. Design, component choice, PCB layout, PCB materials, board cleanliness, and other factors will become increasingly important (and difficult) in the nA range and below.

    If you simply need to gather data from this MEMS sensor, another option would be to buy or rent a commercially made picoammeter, which would already implement this functionality.

    If you have to build up a system like this, a good starting point would be schematics from commercially made picoammeters, as they have already faced these issues and found solutions to them.