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TINA/Spice/ADS1218: ads1218

simi jose
Prodigy 40 points
Part Number: ADS1218
Other Parts Discussed in Thread: TINA-TI,

Tool/software: TINA-TI or Spice Models

can i get the equivalent front end circuit for simulating front end of ADS1218 with buffer ON. Is there any bias voltage at input pins

  • 0
    TI__Guru** 112765 points

    Hi Simi,

    Unfortunately we do not have any Tina or Spice models for the ADS1218 device.  One of my colleagues did write an application note that describes the input behavior.  In section 3 of the app note there is a discussion regarding the input impedance with the buffer on.

    http://www.ti.com/lit/an/sbaa090/sbaa090.pdf

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 40 points

    the application note mentions ,"Unlike the equivalent model in the non-buffer case, there is only a differential resistive component and no common-mode resistive components". However no mention about bias voltages on the input pins. can you please clarify if there are any bias voltages on input bins in buffer on and internal vref of 2.5V.

  • 0 in reply to simi jose
    TI__Guru** 112765 points

    Hi Simi,

    When using the buffers (much like an op amp buffer), the inputs see a much higher overall impedance.  You will see some bias current from the chopper for offset correction, but this is an impedance ( similar to a resistance at the chopping frequency) which reduces the overall impedance of the input even with the buffer enabled.  The buffer cannot drive all the way to the rails, so the actual input range becomes limited as compared to the non-buffered input but the input impedance will still be much higher using the buffer.  There is no bias voltage on the input, only the voltage applied to the analog inputs.

    The reference input is un-buffered, and will see a bias current relative to the sampling frequency due to the switched cap input (12pf at the modulator frequency).  The voltage on the input will be the voltage applied for the reference itself.

    Best regards,

    Bob B