Switchable Current Mirror Trimming for Low-IQ Bandgap References
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current technologies face challenges in precisely trimming low-IQ current mirrors, particularly in bandgap voltage references, due to limitations in measurement precision and the impact of measurement equipment on the circuit, which affects the accuracy and power consumption of analog integrated circuits.
Innovation Solution
A trimmable and switchable current mirror system that adjusts the effective width-to-length ratios of transistors using a mirror trim code, allowing for indirect measurement and trimming of current mirrors, minimizing mismatch errors through a closed-loop control and multiplexer-based selection of transistors, enabling precision beyond standard automated test equipment capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct measurement methods are used to trim current mirrors, then measurement precision can be improved, but the measurement equipment impacts the circuit and increases power consumption
Solution Approach 1:
The patent introduces an intermediary measurement approach where instead of directly measuring the low current (200 nA) which requires high-precision equipment and consumes power, the system measures a related voltage parameter that can be indirectly correlated to the current mirror performance. This intermediary measurement allows trimming without directly loading the low-current circuit, thus reducing power consumption and equipment impact.
2Extent of automation
If standard automated test equipment is used for trimming, then the trimming process can be automated, but the measurement precision is insufficient for low-IQ current mirrors
Solution Approach 1:
The patent transforms the measurement from the current domain to the voltage domain. Instead of measuring the difficult-to-detect low current directly, the system measures a voltage that is functionally related to the current mirror operation. This dimensional transformation allows standard automated test equipment to achieve the required precision by measuring voltage rather than current, thereby maintaining automation while achieving sufficient measurement precision.
3Use of energy by moving object
If low-IQ current mirrors are used to reduce power consumption, then power efficiency is improved, but trimming precision becomes difficult to achieve
Solution Approach 1:
The patent applies preliminary action by performing measurements and adjustments at a higher current level before finalizing the low-IQ operation. The trimming process is conducted when the current mirror is operating at a more favorable current level where measurements are easier and more precise, and then the results are applied to achieve accurate low-IQ operation. This preliminary trimming action ensures precision is achieved before the circuit operates in its final low-power state.
Data Source
AI summary
A trimmable and switchable current mirror can be used in a bandgap voltage reference to calibrate the voltage reference without requiring access to measurement of the quiescent current IQ of the voltage reference. Trimmable transistors within the current mirror are alternately selectable as the diode-connected transistor via a mirror switch signal. A bandgap voltage difference is computed for two bandgap voltage values measured for alternate switched configurations of the current mirror. A set of such differences is computed and stored for different trim configurations of the mirror transistors, and the trim configuration corresponding to the lowest absolute value bandgap voltage difference can be selected as the optimal trim configuration. Following mirror transistor trim adjustment, a bandgap resistor trim can be adjusted to further calibrate the bandgap voltage reference.