Current Source Calibration Using Temperature-Tracking CAL DACs
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current current source calibration methods fail to maintain stable and fixed current output relative to each other due to temperature and bias current changes, as existing calibration techniques do not track these environmental variations, leading to erroneous calibrations and the need for frequent recalibration.
Innovation Solution
A trim circuit and calibration method that includes multiple CAL DACs whose output currents change with bias current and temperature, allowing for accurate tracking and compensation of current mismatch between current sources, using a combination of operational amplifiers, current mirrors, and voltage DACs to generate currents proportional to transconductance and bandgap voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single CAL DAC with fixed scale factor is used for calibration, then the calibration is simple and the device complexity is low, but the calibration becomes erroneous when temperature or bias current changes occur
Solution Approach 1:
The calibration DAC is divided into multiple independent calibration DACs, each responsible for compensating specific components of the current mismatch under different operating conditions. This segmentation allows each CAL DAC to handle particular aspects of temperature and bias current variations, improving overall calibration accuracy without requiring a single complex circuit
Solution Approach 2:
The calibration system transitions from a fixed scale factor approach to a dynamic multi-CAL-DAC architecture where the compensation characteristics can adapt to varying temperature and bias current conditions. Each CAL DAC is designed with specific transconductance relationships that enable dynamic tracking of mismatch variations across different operating points
2Measurement precision
If calibration is performed under specific temperature and bias current conditions, then the initial calibration precision is high, but the current sources fail to maintain stable output when environment changes
Solution Approach 1:
The calibration system utilizes parameter changes in transconductance with respect to temperature and bias current to enable tracking of mismatch variations. By designing CAL DACs whose output characteristics change with these parameters, the system maintains calibration accuracy across varying operating conditions while preserving high initial calibration precision
Solution Approach 2:
The multiple CAL DACs provide continuous compensation feedback that tracks and counteracts mismatch variations caused by temperature and bias current changes. This feedback mechanism ensures that current sources maintain stable output relative to each other throughout operating condition variations, building upon the high initial calibration precision
Data Source
Figure 1A
Figure 1B
Figure 2~3
AI summary
In an example embodiment, a circuit is provided that includes a calibrated trim circuit comprising a bias circuit configured to generate a bias current that varies with temperature, and a calibration digital to analog converter (CAL DAC), wherein a bias voltage of the CAL DAC is driven by the bias current, and wherein the CAL DAC is configured to set an output current of the trim circuit, and wherein a bias voltage of the CAL DAC is set by the bias current such that the output current of the trim circuit varies with temperature.