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The result of the zero-scale calibration conversion is stored in the offset calibration registers for the appropriate ADC. The result of the full-scale calibration conversion is stored in the gain calibration registers for the appropriate ADC. With these readings, the calibration logic can calculate the offset and the gain slope for the input-to-output transfer function of the converter.

What is the Calibration logic used here?

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• Hi,

The calibration logic mentioned in the datasheet is part of the ADC block. It is for the computations during the ADC calibration. The calibration method for ADuC845 is to calibrate the offset by forcing a zero-scale voltage and the gain using a full-scale voltage.

Regards,
Karl

Is there any equation to find the calibrated output, if we have the gain error and offset error?

Is there any equation to find the calibrated output, if we have the gain error and offset error?

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• The ADuC845 datasheet has examples for the procedure of ADC internal and system calibration. Offset and gain calibration coefficients are stored in SFRs.

• Hi,

what are the steps I need to follow when I am using System Calibration? Also, In system Calibration the user gives input voltage to AIN+ and AIN- pins, So what will be the input voltage range that I can apply to the AIN+ and AIN- pins.

• Hi,

The typical procedure to perform system calibration is first to apply a differential voltage of 0V to the analog input, then a full-scale differential voltage. There is an example of the system calibration in the datasheet (Rev.D Page 35 of 110).

The input voltage range for the AIN+ and AIN- pins are -0.3V to AVdd+0.3V.

• Thanks for this piece of information.

when I use ADuC845 with chop enabled, By default it performs internal/self-calibration right?

However, when I need to perform system calibration and at what conditions like update rate, gain, etc.

• Chopping on delta sigma delta ADCs is a technique that can be used to cancel offset voltages and other low frequency errors. You can read more about it on the attached file.

For the ADC conditions during calibration, it is recommended to use the slowest possible update rate to optimize the calibration accuracy. For the gain, set it to the intended application.

• Hi,

I am doing the internal calibration. my conditions are chop disabled, gain=1 at 2.56V.

How can I notice if any changes are made in offset and gain registers?

What is the default value of offset and gain registers?

• The offset and gain calibration coefficients are held in the following ADC SFR:
OF0L/M/H
OF1L/H
GN0L/M/H
GN1L/H

You can monitor the registers if there are any changes.

The default offset and gain coefficients are specific to each device. The coefficients are overwritten once the user initiates a calibration procedure.

• I am using ADuC845. calibration conditions are chop disabled, unipolar, gain=1.

What is the default value of offset and gain registers? So that I can check the registers if any changes are made.

• The factory or default calibration registers are automatically downloaded to the ADC calibration SFRs at power-on or after a reset.

You can check the ADC SFRs before and after initiating the calibration procedure for any changes.