Mixed-Signal Analog Auto-Calibration for Input Offset Drift
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Integrated circuits with analog input devices face challenges in minimizing input offset voltage, particularly due to inherent DC input offset voltage in operational amplifiers, which requires costly calibration during manufacturing and is not adaptable to changing environmental conditions.
Innovation Solution
An auto-calibration circuit that includes a digitally controlled input offset voltage compensation circuit with a volatile trim register, allowing for online calibration in end-user systems to compensate for input offset voltage across various operating conditions, including temperature and voltage changes, without the need for factory calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If factory calibration is performed to minimize input offset voltage, then manufacturing precision is improved, but manufacturing cost and time increase
Solution Approach 1:
The system performs self-calibration automatically at the end-user site using the microcontroller's existing test equipment, eliminating the need for external factory calibration services. The auto-calibration circuit works cooperatively with the microcontroller to minimize input offset voltage without requiring additional manufacturing steps or specialized testing equipment.
Solution Approach 2:
The calibration data is stored in a volatile trim register that is automatically initialized and prepared during system startup. The system performs preliminary calibration actions at power-on, ensuring that the analog input device is calibrated before actual use, rather than requiring separate factory calibration steps.
2Manufacturing precision
If calibration is performed at one operating point during manufacturing, then initial precision is improved, but adaptability to changing environmental conditions deteriorates
Solution Approach 1:
The system enables dynamic recalibration at the end-user site under different operating conditions. The auto-calibration circuit can be re-triggered by the microcontroller when environmental conditions change, allowing the system to adapt to temperature variations, voltage changes, and other operational parameters rather than being fixed at a single calibration point.
Solution Approach 2:
The system uses feedback from the analog input device's performance under various operating conditions to trigger recalibration. The microcontroller monitors system operation and can initiate auto-calibration when drift or performance degradation is detected, ensuring continuous optimization across changing environmental conditions.
3Measurement precision
If separate testing equipment is used for digital microcontroller and analog functions, then testing accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The system merges the calibration functionality into the existing microcontroller unit by utilizing its built-in test equipment and processing capabilities. The auto-calibration circuit integrates with the microcontroller's analog-to-digital converter and existing test interfaces, eliminating the need for separate dedicated calibration equipment while maintaining measurement accuracy through coordinated operation.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Auto-calibration of the analog circuits occurs when requested by a user and/or the occurrence of an event(s). The user may invoke an auto-calibration on demand through an auto-calibration (ACAL ) input to the mixed-signal integrated circuit. An external voltage calibration (VCAL ) input may be used for auto-calibration of the mixed-signal integrated circuit to a user-supplied common-mode voltage reference. Auto-calibration of the mixed- signal integrated circuit may also be initiated upon the occurrence of any one or more of the following events: 1 ) detection of auto-calibration data corruption, e.g., parity checking of auto-calibration data values digitally stored in the mixed-signal integrated circuit; 2) an internal timer that causes a calibration request after a programmable timeout period, 3) change in the internal integrated circuit die temperature as determined by a temperature sensor, and 4) a change in the power supply and/or internal supply voltage(s).