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THS4275: LOW gain trans-impedance amplifier, low noise

David D
Intellectual 580 points
Part Number: THS4275
Other Parts Discussed in Thread: THS4271, TINA-TI

Hi,

I'm designing a photo-diode interface: Iout(diode)=~4mA, Fout=~40MHz, Cdiode=~5pF.

The output current from the diode in my case is relatively high  so the required gain is rather small (~1V/A).

Such a scenario is not covered in literature.

Noise is also a consideration, so the 3nV/sqrt(Hz) of THS4275 seem marginal.

Could you advise on the best topology and opamp for this scenario?

Currently I'm thinking of this:

What do you think?

Thanks,

David.

  • 0
    TI__Genius 15975 points

    Hi David,

    The circuit that you have shown is normally what is used for converting current input to voltage output. I have attached a TINA-TI circuit using THS4271 that could be used for 4mA I-to-V conversion at 40MHz using a diode capacitance of 5pF.

    Even though the input current is around 4mA, I would still recommend using a higher value gain than 1V/A as it only fetches 4mV swing at the amplifier output (too low of a signal swing at the detector for most applications). As a result, I have used an Rf of 250ohms that gives an output swing of 2Vpp which is close to full scale of most ADCs readily available in the market.

    Best Regards,

    Rohit

    THS4271_TIA.TSC