Successive Approximation Register ADC 12-bit Resolution over 0-VDDA – KBA222392

Version 2

    Version: **

     

    Translation - Japanese: 0-VDDAでの 逐次比較レジスタ型ADC 12ビット分解能– KBA222392- Community Translated (JA)

     

    Question:

    How can I get a 12-bit resolution on PSoC® 4 successive approximation register (SAR) ADC when operated in a singleended unsigned mode for an input range of 0-VDDA?

     

    Answer:

    To get a 12-bit resolution from SAR ADC, connect the single-ended negative input to Vref. The range of the resultant register counts are listed in the table.

     

    Single/Differential

    Signed/Unsigned

    Single-ended Negative Input

    -Input

    +Input

    Result Register

    Single

    Signed

    Vss

    Vss

    Vref

    Vss

    -noise

    0x07FF

    0x0000

    0xFFxx

    Single

    Signed

    External

    Vneg

    Vneg+Vref

    Vneg

    Vneg-Vref

    0x07FF

    0x0000

    0xF800

    Single

    Unsigned

    Vref

    Vref

    2*Vref

    Vref

    Vss

    0x0FFF

    0x0800

    0x0000

    Single

    Signed

    Vref

    Vref

    2*Vref

    Vref

    Vss

    0x07FF

    0x0000

    0xF800

    Differential

    Unsigned

    N/A

    Vx

    Vx+Vref

    Vx

    Vx-Vref

    0x0FFF

    0x0800

    0x0000

    Differential

    Signed

    N/A

    Vx

    Vx+Vref

    Vx

    Vx-Vref

    0x07FF

    0x0000

    0xF800

     

    When the Vref select value is set to VDDA/2, the range translates to 0 to VDDA, which is the full 12-bit resolution.

     

     

    The SAR ADC is a fully differential architecture, optimized to provide 12-bit accuracy in the differential mode of operation. The input range of the SAR ADC is Vn ± Vref. The SAR ADC can be configured in a single-ended mode by fixing the negative input. When the negative input is fixed to VSS, conversions are only 11-bit accurate as the signal at the positive input cannot go below VSS. By fixing the negative input to VDDA/2, you will get the full 12-bit resolution on the range 0 to VDDA.