ADS7040EVM-PDK Kit Operation
6.6
Offset Calibration
The ADS7040 device has the ability to calibrate its internal offset. The offset calibration can be initiated by
the user either on power-up or during normal operation. During offset calibration, the analog input pins
(AINP and AINM) are disconnected from the sampling stage and connected to an internal reference. The
result of the offset calibration in stored in an internal register. For subsequent conversions, the device
adjusts the conversion results provided on the SDO output with the value stored in this internal register.
The ADS7040 GUI implements offset calibration as described in the
Offset Calibration During Normal
Operation
section of ADS7040 datasheet (
).
depicts the
Offset Calibration
page of the
GUI.
Figure 18. Offset Calibration Page
The Offset Calibration test is best conducted with a DC input at the Analog Input Terminal of the
ADS7040EVM. Simply click the
Calibrate
button. The GUI first performs a histogram test for the device
described in
and populates the first of the two graphs. The pre-calibrated Mean code is
inserted in the indicator. Next, the calibration frame is sent to the ADS7040 device that enables the
internal offset calibration logic. The GUI performs the histogram test for a second time and the second
graph is populated and Post Calibrated Mean value computed. Finally, the difference between the first and
second computed mean is populated in the Calculated Offset Correction indicator.
The computed offset for all subsequent attempts to calibrate the device will always yield a result of within
the limits specified in the datasheet. This indicates that after the calibration is performed for the first time,
the offset is actually being applied on all subsequent conversions. This computed offset will remain fixed,
unless the device is reset or there is a significant change in operating temperature or analog supply
voltage.
16
ADS7040EVM-PDK
SBAU240 – November 2014
Copyright © 2014, Texas Instruments Incorporated
