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ADC14C105: input impedance needed

lowtzow
Prodigy 40 points
Part Number: ADC14C105
Other Parts Discussed in Thread: PGA870

Hello,

I didn't found the input impedance for this ADC in the datasheet. For some calculation and matching with a PGA870 I'm intessted in this data.

Do you can provide me this data.

thanks

Alex

  • 0
    TI__Mastermind 43910 points

    Hi Alex

    I did an initial look but haven't found any s-parameter or other information regarding the input impedance of this device.

    The analog inputs are primarily capacitive. The capacitance value of each input (Cin) is listed in the specification table on page 7 of the datasheet. The values are 8.5pF when CLK is low and 3.5 pF when CLK is high.

    I'll check some more and post again if I find any other information.

    Best regards,

    Jim B

  • 0 in reply to Jim Brinkhurst1
    Prodigy 40 points

    thank you for your feedback.

    Yes this data I checked, but there is now information about the input resistance. I'm wondering why this information is missing.

    regards

    alex

  • 0 in reply to lowtzow
    TI__Mastermind 43910 points
    Hi Alex
    There will be a small amount of series resistance between the input and sampling capacitance due to wire-bond and sample switch resistance, but unfortunately I don't have any information on the magnitude of either.
    There is no on-chip termination resistance between Vin+ and Vin-. This is effectively high impedance other than the capacitance.
    Best regards,
    Jim B