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Transimpedence amplifier

I need to simulate the example circuit given in the datasheet of LTC6269-10. For 20 K feedback resistance, the bandwidth is 210 MHz. But when I simulate the circuit am not achieving the correct bandwidth. Am attaching the LTspice file.

Simulation.asc

Please find the example circuit in the datasheet.

  • Hi ,

    I'd drop the compensation cap across RF significantly (from the 1pF you'd chosen). Your circuit was oscillating (if you look at its step response).

    LTspice shows about 300MHz -3dB BW with the lowered CF:

    Here is the simulation file I used:
    LTC6268 TIA EZ 4_27_22.asc

    Regards,

    Hooman

  • But in the datasheet it is given as 200 MHz, we are getting 300 MHz why is that so? And also practically how to achieve the feedback capacitance of 0.048 PF. Practically if i solder 0.048pF capacitance. Output is same irrespective of the feedback capacitance.

  • Hi ,

    It appears from the LTC6269 datasheet front page that two parallel 40k feedback resistors get you into the vicinity of the femto-Farad compensation capacitance you need:

    From the front page datasheet: "*TWO 40.2kΩ 0603 PACKAGE RESISTORS IN PARALLEL".

    Somehow this statement is missing from the LTC6269-10 datasheet!

    In this case, the parasitic capacitances of the two resistors produces enough compensation capacitance.

    As for the stated bandwidth: LTspice simulation may be close to what you get but the datasheet is the ultimate guide as to what performance you'll measure. Also, in this case, as you can see varying the capacitance by a few femto-Farads will make a difference. So, the response will be very much dependent on your actual setup / board.

    Regards,

    Hooman