ADS131B04-Q1: ADC measurement accuracy

Hi Neal,

Thank you for your interest in the ADS131B04-Q1.

Can you be more specific regarding which specifications you are interested in? Most of the Electrical Characteristics table is populated. For noise performance across gain and data rate, please refer to Tables 7-1 and 7-2.

Regards,

Hi Neal,

the specifications in the ADS131B04-Q1 datasheet are input referred, that means they include the errors of the complete signal chain inside the device (PGA, ADC, VREF, etc.).

The data rate primarily only effects the noise performance of the device. Faster data rates mean that less averaging can happen inside the delta-sigma ADC which means the input-referred noise increases. You can see that by looking at the noise table 7-1 in the datasheet.

At faster data rates the input-referred noise will be larger than the actual offset of the device. This means you would have to average multiple readings in the MCU in order to see the true offset performance of the device.

Regards,

Hi

1. Does ADS131B04 have built-in self-calibration

2. It is described in the manual that the correction factor should be stored in external non-volatile memory. How to determine the correction factor?

3. What is the correction method for ADC internal offset error and gain error?Can you explain it in detail, or is there any material for reference?

Thanks!

Hi Neal,

the ADS131B04-Q1 does offer some sort of internal offset calibration support.

In order to determine the offset of one of the ADC channels you would short the inputs using the MUXx[1:0] = 01b settings.
The MCU would then take multiple readings from this channel and average the results. This averaged value would then be the offset calibration value. You can store this value in the ADS131B04-Q1 offset calibration registers (CHx_OCAL_MSB, CHx_OCAL_LSB). The device will then subtract that value automatically from every conversion. Alternatively the subtraction could also be performed in the MCU.

If you only do the offset calibration one time at end of line in production, then you would have to store the offset calibration value somewhere in non-volatile memory in the MCU. All registers in ADS131B04-Q1 are volatile, means they get cleared to default values whenever there is a reset.
Many customers would however perform periodic offset calibration during run time to remove offset drift.

In case the global-chop mode is used you might not even have to perform an offset calibration because the offset error is very very small already when using global-chop mode.

Gain calibration is unfortunately a little harder to implement. For gain calibration you will have to provide an external precision calibration test signal to the ADC channels. The test signal should be set a little lower than the full-scale range of the ADC channel. Let's say at 95% of FS. Or alternatively use a value which is close to the maximum signal that can occur in the application - as long as it is <95% of FS.
The MCU would then take multiple readings from the ADC channel with this test signal applied and average the results. The gain calibration factor would then be the ratio between the ideal output code for the applied test signal and the measured average code.

Because a precision test signal is required, a gain calibration is usually only implemented at end of line in production. The gain calibration factor then needs to be stored on non-volatile memory. You can write the gain calibration factor to the gain calibration registers (CHx_GCAL_MSB, CHx_GCAL_LSB) after every reset, or do the gain error compensation in the MCU.

Regards,