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LTC6560 with substantial input capacitance (MPPC)


at first glance, the LTC6560 TIA seem very attractive also for single pulse processing of Multi Pixel Photon Counters (MPPC), e.g But even the smallest MPPCs have input capacitance of about 100 pF, 50 times higher than typical values shown in the LTC6560 datasheet. Is there any experience available for the LTC6560 at such input capacitance?


  • Hi,

    Input capacitance limits the bandwidth of the TIA circuits. You might need a wider bandwidth opamp with that big input capacitance from the sensors alone. LTC6560 bandwidth is specified with Cin total of 2pF which is far from your requirement since the MPPC sensor alone contributes 100pF. Please keep in mind also that the Cin total is a combination of photodiode capacitance, amplifier input capacitance and stray board capacitances. 

    Also, the amplifier noise voltage is an important factor in choosing the opamp for transimpedance circuits with high input capacitance because this noise dominates at higher frequencies. With that, a opamp with very low noise voltage is recommended.

    To help you in choosing the suitable opamp for your TIA circuit, Analog Devices has a tool called Photodiode Wizard where you can input the parameters of the photodiode you want to use and the tool will suggest a corresponding opamp and compute the values of the feedback components on your TIA. Here is a video tutorial for this tool.