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LMH6518 differential input bias

Other Parts Discussed in Thread: LMH6518

Hello,all,


I am now confused by the input common mode bias mode of the chip LMH6518, the datasheet does mention whether we need to construct the bias for the input pins (pin 6 and 7, ac coupling from the previous stage) or the chip can bias itself.  Thanks.

  • Hi Zhaofei,
    Sorry, I did not see your post till now!
    The LMH6518 inputs do not generate their own biasing. So, you are correct in that you need to provide the biasing externally.

    For the circuit you've shown, you need to add the proper biasing (using resistors to Vcc and another one to ground as a voltage divider) on the right hand side of the two input capacitors to bias each input to around 2.5V (when using Vcc= 5V single supply for the LMH6518). However, you may want to review the low value cap (120pF) you have chosen, as you'll lose a large portion of your spectrum below the low frequency cut-off formed by this cap and the Thevenin equivalent of the biasing resistors (to be added).

    Regards,
    Hooman