Ambient-Light Sensor Bootstrap Control for Low-Loss Auto-Zeroing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing ambient-light sensors face significant errors in measuring ambient light due to high information losses through the capacitive element during the integration time, which is exacerbated by the need for complex and expensive low-loss auto-zero switches with high threshold voltages.
Innovation Solution
Incorporating a bootstrap circuit that generates an adapted logic control signal with positive and negative voltage levels to control the auto-zero switch, reducing losses and eliminating the need for high-threshold voltage transistors, thereby simplifying and cost-reducing the manufacturing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a low-loss auto-zero switch with high threshold voltage is used, then measurement precision is improved, but device complexity and manufacturing cost increase due to additional masks
Solution Approach 1:
The patent changes the voltage level parameters of the control signal from single-positive to dual-level (positive and negative) to modify the switching behavior. This parameter change enables the use of standard-threshold transistors instead of high-threshold transistors, reducing manufacturing complexity while maintaining low signal loss during integration
Solution Approach 2:
The patent applies preliminary action by pre-charging the capacitive element to a positive voltage level before the integration phase. This preliminary charging action, combined with the negative control signal during integration, ensures the switch remains in a low-loss state throughout the measurement period without requiring complex high-threshold transistors
2Measurement precision
If a low-loss auto-zero switch with high threshold voltage is used, then measurement precision is improved, but manufacturing cost increases due to additional masks
Solution Approach 1:
The patent modifies the control signal voltage parameters to include negative voltage levels, which changes the switching characteristics to be compatible with standard-threshold transistors. This parameter modification eliminates the need for additional manufacturing masks, reducing production costs while maintaining measurement precision
Solution Approach 2:
The patent replaces expensive high-threshold transistors (which require additional masks) with standard-threshold transistors that use conventional manufacturing processes. The bootstrap circuit's voltage management compensates for the lower threshold, achieving the same low-loss performance with cheaper, more manufacturable components
3Device complexity
If standard auto-zero switch is used, then device complexity is reduced, but information loss increases during integration time
Solution Approach 1:
The patent introduces a bootstrap circuit as an intermediary between the control signal source and the auto-zero switch. This intermediary circuit generates the adapted dual-level control signals that enable standard switches to operate in low-loss mode, mediating between simple hardware and performance requirements
Solution Approach 2:
The bootstrap circuit performs preliminary action by pre-charging the capacitive element and establishing appropriate voltage levels before the integration phase begins. This preliminary setup ensures that when the standard auto-zero switch operates during integration, it does so in a low-loss state without requiring complex transistor designs
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 effectively reduces measurement errors in ambient light sensing without requiring additional masks for high-threshold voltage transistors, improving the operational efficiency of the auto-zero switch during integration time.
Implementation Method 1
a photodiode configured to generate an electrical signal according to an ambient light
Implementation Method 2
an amplifier comprising an operational amplifier looped by a capacitive element
Data Source
AI summary
According to one aspect, an ambient-light sensor includes a photodiode configured to generate an electrical signal according to an ambient light, a capacitive-feedback transimpedance amplifier connected at its input to the photodiode for receiving a signal generated by the photodiode and for generating as an output an amplified signal from the signal generated by the photodiode, and an auto-zero switch at the input of the capacitive-feedback transimpedance amplifier. The ambient-light sensor further includes a control circuit including a bootstrap circuit configured to receive an initial positive- or zero-voltage logic control signal, and then generate, from this initial logic control signal, an adapted logic control signal having a first positive voltage level and a second negative voltage control level for controlling the auto-zero switch.