Self-Powered Ambient Light Sensor With On-Chip Photovoltaic Cells
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Solution Overview
Problem
Existing ambient light sensors require an external power source, consuming power even in standby mode, making them unsuitable for power-critical devices like 'internet-of-things' sensor packs and wearables, and difficult to implement in hazardous environments.
Innovation Solution
An integrated circuit with isolated photovoltaic cells generating power through a series connection, coupled with a light-to-frequency oscillator and decoupling capacitors, powers an ambient light sensor without external power, using a photodiode to generate a signal dependent on ambient light levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If an external power supply is provided to the ambient light sensor, then the sensor can generate a usable output voltage/current value, but the device requires power supply infrastructure and consumes power even in standby mode
Solution Approach 1:
The sensor integrates a photovoltaic cell that converts ambient light directly into electrical power, enabling the sensor to power itself without external power supply infrastructure. This self-powered mechanism eliminates standby power consumption while maintaining reliable operation through direct energy conversion from the environment.
Solution Approach 2:
The patent changes the operational parameters by using a light-to-frequency conversion scheme where the output frequency directly represents the ambient light level. This parameter transformation allows the sensor to operate passively without active power consumption, as the measurement is derived from natural light frequency modulation rather than active signal generation requiring power.
2Adaptability or versatility
If photovoltaic cells are integrated on the substrate, then power can be generated without external supply, but isolation from the substrate is required to prevent interference
Solution Approach 1:
The photovoltaic cell is segmented and isolated from the substrate using deep trench isolation structures. This segmentation separates the power generation function from the sensor circuitry, preventing electrical interference while maintaining power independence. The isolation trenches create distinct functional zones on the substrate.
Solution Approach 2:
An insulation layer is introduced as an intermediary between the photovoltaic cell and the substrate. This intermediate layer provides electrical isolation and prevents direct interaction between the power generation element and the sensor circuitry, enabling both power independence and circuit compatibility.
3Power
If multiple photovoltaic cells are coupled in series to generate sufficient supply voltage, then adequate power voltage is achieved, but the area ratio of the cells must be optimized to maintain current generation
Solution Approach 1:
The photovoltaic cells coupled in series have asymmetric area ratios optimized for their specific positions in the series connection. This asymmetric design allows each cell to contribute optimally to the overall voltage and current output, with larger area cells positioned to maximize current generation while smaller cells provide the necessary voltage increment.
Solution Approach 2:
The patent optimizes the area ratio parameter of the photovoltaic cells based on their series connection configuration. By adjusting the area ratio to specific values (e.g., 1:1/k^n where k is between 1.1 to 2), the system achieves the required supply voltage while minimizing the total area occupied by the photovoltaic cells.
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 enables ambient light sensing without power consumption, allowing operation in power-critical devices and hazardous environments, with low current consumption and effective signal generation across varying light levels.
Implementation Method 1
a generator comprising a plurality of photo-voltaic cells (401, 403, 405) coupled in series to generate a supply voltage (Vdd)
Implementation Method 2
a sensor powered by the supply voltage generated by the generator, the sensor comprising a photodiode (409) configured to generate an output signal dependent on ambient light levels
Data Source
Figure 1a
Figure 1b
Figure 1c
AI summary
An integrated circuit comprising a substrate, the integrated circuit comprising: at least one photo-voltaic cell implemented on the substrate, the at least one photo-voltaic cell configured to generate a supply voltage; and circuitry implemented on the substrate, the circuitry powered by the supply voltage.