AD7738 Zero and Full scale System Calibration

AD7738 circuit details:

REFIN+ and AINCOM connected to 2.5V reference, REFIN- connected to ground.

Analog input voltage ranges selected as +/- 1.25V.

MUXOUT+=ADCIN+ and MUXOUT-=ADCIN-

AVDD connected to 5V

What is the range (min and max) of external voltage that can be connected to perform

  1. Zero scale System calibration
  2. Full scale System Calibration

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  • 0
    •  Analog Employees 
    on Sep 18, 2017 3:47 AM

    Hi Sunil Kumar,

       Apologies for the late response. The system zero scale and system full scale calibration determines the offset or gain cause by the system. A good way to do a system zero scale calibration is to short the input pins Ain+ and Ain- when differential or connect to ground when in single ended mode. The AD7738 expects a zero output on this connection, so any voltages that the ADC sees during calibration is considered an offset which is contribute by the system which the ADC will calibrate or compensate when performing the conversion. Meanwhile for full-scale system calibration, the ADC expects an input that produces and full scale output. For a +/-2.5V range, When performing system calibration a 2.5V input voltage must be force on the analog input., the ADC expects this voltage, the ADC then converts the input voltage. Any deviation on calibration result from the ideal or expected full scale conversion is an error, therefore AD7738 will need to adjust its conversion output based from the calibration result.

    Regards,

    Jonathan

Reply
  • 0
    •  Analog Employees 
    on Sep 18, 2017 3:47 AM

    Hi Sunil Kumar,

       Apologies for the late response. The system zero scale and system full scale calibration determines the offset or gain cause by the system. A good way to do a system zero scale calibration is to short the input pins Ain+ and Ain- when differential or connect to ground when in single ended mode. The AD7738 expects a zero output on this connection, so any voltages that the ADC sees during calibration is considered an offset which is contribute by the system which the ADC will calibrate or compensate when performing the conversion. Meanwhile for full-scale system calibration, the ADC expects an input that produces and full scale output. For a +/-2.5V range, When performing system calibration a 2.5V input voltage must be force on the analog input., the ADC expects this voltage, the ADC then converts the input voltage. Any deviation on calibration result from the ideal or expected full scale conversion is an error, therefore AD7738 will need to adjust its conversion output based from the calibration result.

    Regards,

    Jonathan

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