Current Trimming Circuit Using Cascaded Scaling for Accurate Small Currents
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Solution Overview
Problem
Conventional trim circuits face challenges in generating small trim currents accurately, as large resistors occupy space and introduce noise, and current mirrors with large scaling ratios compromise matching and can operate in the sub-threshold region, leading to unpredictable behavior.
Innovation Solution
A trim system that uses a differential voltage generator and trim current generator to produce a trim signal that ratiometrically tracks a control signal, allowing for precise correction of operational parameters by adjusting the ratio of resistors and transistors, enabling the generation of small trim currents without the need for huge resistors or large current mirror ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If large resistors are used to generate small trim currents, then the trim current accuracy is improved, but the circuit area increases and noise is introduced
Solution Approach 1:
The patent changes the operating parameters by using a current mirror with a scaling ratio of approximately 2:1 repeated in cascade, rather than using a single large scaling ratio current mirror or large resistors. This allows generating small trim currents (e.g., 10 nA) through multiple stages of moderate scaling, maintaining accuracy while reducing area and noise.
2Quantity of substance
If current mirrors with large scaling ratios are used to generate small trim currents, then the trim current magnitude is reduced, but the matching is compromised and sub-threshold operation occurs
Solution Approach 1:
The patent segments the current scaling into multiple stages, each with a moderate scaling ratio (approximately 2:1), rather than using a single large scaling ratio. This segmentation maintains transistor matching and ensures operation in the saturation region, avoiding sub-threshold effects while achieving the required small trim current magnitude.
Solution Approach 2:
The patent introduces dynamic element matching (DEM) techniques to actively compensate for mismatches in the current mirror structures. This dynamic approach maintains high matching accuracy even with multiple scaling stages, ensuring reliable operation in the saturation region while generating the required small trim currents.
Data Source
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AI summary
A trimming resource includes an adjustable driver resource, a differential voltage generator, and a trim current generator. The adjustable driver resource produces an output signal. The differential voltage generator receives the output signal from the adjustable driver resource and produces a differential drive signal. The trim current generator derives a trim signal from the differential drive signal received from the differential voltage generator. According to one configuration, the trim current generator outputs the trim signal to an electronic component, correcting an operational parameter of the electronic component.