inverted input for adc

Discussion in 'General Electronics Chat' started by himadri117, Dec 12, 2014.

  1. himadri117

    Thread Starter New Member

    Nov 11, 2014
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    I am using ADC122S625 (Datasheet: http://www.ti.com/lit/ds/symlink/adc122s625.pdf).

    The ADC has a differential input per channel. My signal is from a RF devide with 3V peak to peak and 1.5V DC offset. I want to use the ADC in Single-Ended Input Operation. So I have choosen a Reference Voltage of 1.5V. Now my question is what should I use for the Inverted ADC input?

    First I thought I will pull it to Ground as a normal Single input ADC would use 0 to Va input range. But after reading the Datasheet (page. 15) it seems that I need to feed the Vref (1.5V) to the inverted inputs.

    From Datasheet (copied)::

    "Single-Ended Input Operation For single-ended operation, the non-inverting inputs of the ADC122S625 can be driven with a signal that has a maximum to minimum value range that is equal to or less than twice the reference voltage. The inverting inputs should be biased at a stable voltage that is halfway between these maximum and minimum values. In order to utilize the entire dynamic range of the ADC122S625, the reference voltage is limited at VA / 2. This allows the non-inverting inputs the maximum swing range of ground to VA. Figure 35 shows the ADC122S625 being driven by a full-scale single-ended source. Even though the design of the ADC122S625 is optimized for a differential input, there is very little performance degradation while operating the ADC122S625 in single-ended fashion."

    [​IMG]
    Please suggest to clear my understanding about the Inverted input.
     
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    I would suggest you do the following:

    [​IMG]
     
  3. himadri117

    Thread Starter New Member

    Nov 11, 2014
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    You mean pull to ground? But the Table 1 says Vref is equal to Vcm
     
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