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AMC1311-Q1: How to connect AMP and ADC.

Koji Hayashi92
Mastermind 7030 points
Part Number: AMC1311-Q1
Other Parts Discussed in Thread: ADC121S101-Q1, ADC121S101

Hi TI-team

My customer wants to know how to connect AMP and ADC.
P.1 of the data sheet has a Simplified Schematic  with "ADC121S101-Q1" connected as ADC of AMC1311B-Q1.
In Simplified schematic, AMC1311B-Q1 differential outputs (VOUTP, VOUTN) are input to ADC121S101-Q1.
Specifically, how is it recommended to connect ?
 
Best Regards,
Koji Hayashi
  • 0
    TI__Guru 55342 points

    Hi Koji,

    Sounds like you want to do a differential to single-ended conversion. 

    This cookbook circuit performs a similar function: http://www.ti.com/lit/an/sbaa317/sbaa317.pdf

    This tech note as well: http://www.ti.com/lit/an/sbaa229/sbaa229.pdf

    I'm not familiar with the ADC121S101, so ask your customer to verify the common-mode limits of the ADC when designing this circuit. 

  • 0 in reply to Alexander Smith
    Mastermind 7030 points

    Hi Alex-san

    Thank you for quick response.

    What does "common mode limits" mean?

    Please teach me. 

    Best Regards,
    Koji Hayashi

  • 0 in reply to Koji Hayashi92
    TI__Guru 55342 points

    Hello Hayashi-san,

    Common mode limitation refers to the acceptable input range for an individual channel. For example, many amplifiers are not truly rail-rail, meaning that the acceptable input range is somewhere within the power rail as some headroom is needed. 

    For example, say I'm powering a differential amplifier from 5V and GND. The amplifier requires 300mV of headroom from either rail, and therefor the acceptable input range is 300mV to 4.7V. This is the common-mode input range. For this type of amplifier, typically you would set the negative input to be midsupply (2.5V) and swing the positive input around the mid supply voltage.

    Looking at the ADC121S101-Q1, I do not believe this is a concern because the analog input can range from VA to GND, which is rail to rail.