Optical Sensor Calibration Circuit Without Band-Gap Reference
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Solution Overview
Problem
Existing optical sensors that use band-gap voltage references consume a large area and high power on integrated circuits, making them inefficient for precise brightness measurement.
Innovation Solution
An optical sensor arrangement that eliminates the need for a band-gap voltage reference by using a current source and an adjustable current source with a trimming signal, coupled with a charge-balancing analog-to-digital converter, to perform calibration and measurement phases, reducing power consumption and area requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a band-gap voltage reference is used for brightness measurement, then measurement precision is improved, but area consumption and power consumption increase
Solution Approach 1:
The patent extracts and removes the band-gap voltage reference from the optical sensor system. Instead of using a band-gap reference, the invention employs a current source with trimming capability that can be calibrated externally. This extraction eliminates the large area-consuming band-gap circuit while maintaining measurement precision through alternative calibration methods using a small test current source and stored correction values.
Solution Approach 2:
The current source in the patent serves multiple functions: it provides the primary measurement current, generates a small test current for calibration, and can be trimmed to compensate for variations. This multi-functionality replaces the specialized band-gap voltage reference, achieving both area reduction and maintained precision through a more versatile component.
2Measurement precision
If a band-gap voltage reference is used for brightness measurement, then measurement precision is improved, but power consumption increases
Solution Approach 1:
The patent removes the power-hungry band-gap voltage reference circuit and replaces it with a low-power current source architecture. The current source uses trimming and calibration techniques that consume minimal power compared to the continuous operation of a band-gap reference, thereby reducing overall power consumption while preserving measurement accuracy.
Solution Approach 2:
The patent performs calibration in advance by measuring with a known test current source and storing correction values in memory. This preliminary calibration action eliminates the need for continuous high-power reference voltage generation during normal operation, as the system uses stored calibration data to maintain precision at lower power levels.
3Area of stationary object
If a current source with trimming signal is used instead of band-gap reference, then area and power consumption are reduced, but device complexity increases
Solution Approach 1:
The patent combines the current source, trimming circuitry, and calibration functionality into a single integrated block. By merging these functions that would otherwise require separate components (including the band-gap reference), the design reduces overall area and simplifies the system architecture while maintaining the ability to perform precise calibrated measurements.
4Measurement precision
If calibration phase is added before measurement phase, then measurement precision is improved, but measurement time increases
Solution Approach 1:
The patent performs calibration as a preliminary action using a small test current source and stores the calibration data in memory for future use. This one-time preliminary calibration eliminates the need for repeated calibration during normal operation, thereby improving precision without significantly impacting ongoing measurement time, as the stored calibration data is reused.
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
This solution enables precise measurement of brightness with reduced power consumption and area usage, allowing for efficient implementation in consumer electronics and other applications without the need for a band-gap voltage reference.
Implementation Method 1
a light sensor (11) which generates a sensor current (IPD)
Data Source
AI summary
An optical sensor arrangement (10) comprises a light sensor (11), a current source (41), an analog-to-digital converter (12) and a switch (44) which selectively couples the light sensor (11) or the current source (41) to an input (14) of the analog-to-digital converter (12).