Adaptive Analog Subtraction Circuit for Light Sensing Mismatch Error
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Solution Overview
Problem
Ambient light sensors using photodetectors face challenges due to mismatch errors in current mirrors, which affect the accuracy of ambient light sensing, leading to suboptimal adjustments in display and keypad backlighting, and reduced battery life.
Innovation Solution
A mismatch correction circuit is introduced to adjust the gain of an adjustable gain current mirror, using an amplitude demodulator and digital filter to eliminate the mismatch error, thereby producing an accurate signal indicative of ambient visible light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a current mirror is used to replicate and subtract currents from photodetectors, then ambient light sensing is enabled, but mismatch errors reduce measurement precision
Solution Approach 1:
The patent implements a feedback mechanism where the third current (resulting from analog subtraction) is fed back through a digital-to-analog converter to adjust the gain of the current mirror. This feedback loop continuously compensates for mismatch errors, improving measurement precision while maintaining the reliability of the sensing system.
Solution Approach 2:
The patent dynamically changes the gain parameter of the current mirror based on detected mismatch errors. By adjusting the gain through a controlled current source, the system compensates for manufacturing variations and drift, thereby improving measurement precision without compromising system reliability.
2Use of energy by moving object
If manual backlight control is used without ambient light sensors, then device complexity is reduced, but energy consumption increases
Solution Approach 1:
The ambient light sensing system operates autonomously to control backlighting without requiring manual user intervention. The system self-adjusts display and keypad backlight intensity based on ambient light conditions, extending battery life while managing the complexity through automated operation.
Solution Approach 2:
The patent implements dynamic backlight control that automatically adjusts illumination levels based on real-time ambient light detection. This dynamic adjustment optimizes energy consumption by reducing backlight power in bright conditions and maintaining visibility in dim conditions, thereby extending battery life despite the added sensor complexity.
3Measurement precision
If analog subtraction is performed without mismatch correction, then circuit simplicity is maintained, but measurement precision deteriorates
Solution Approach 1:
The patent uses feedback to measure the mismatch error through the third current and then applies correction by adjusting the current mirror gain. This feedback-based correction improves measurement precision while adding minimal circuit complexity compared to completely redesigning the subtraction architecture.
Solution Approach 2:
The patent introduces an intermediary correction mechanism that uses the third current as a mediator to detect and compensate for mismatch errors. This intermediary approach improves measurement precision without requiring complete architectural changes, maintaining relative circuit simplicity while enhancing accuracy.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces and eliminates mismatch errors, enhancing the accuracy of ambient light sensing, improving display and keypad backlight control, and extending battery life by maximizing the dynamic range of the ADC.
Implementation Method 1
Photodetectors can be used as ambient light sensors (ALSs)
Implementation Method 2
A chopper circuit can be used to chop the first current at a chopping frequency
Data Source
AI summary
Circuits, methods, sub-systems and systems including adaptive analog subtraction for light sensing are described herein. In an embodiment, an analog circuit including a current mirror is configured to replicate a first current to produce a replicated version of the first current, and to subtract the replicated version of the first current from a second current to produce a third current. A mismatch correction circuit is configured to produce an adjustment signal, indicative of a mismatch error associated with the analog circuit, based on a digital version of the third current. This adjustment signal is used to reduce the mismatch error associated with the analog circuit.