Photodiode Light-to-Frequency Modulation With Residual Charge Sensing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing light-to-frequency modulator circuits face limitations in accuracy due to the inability to account for residual charge at the end of the integration time, leading to incomplete light intensity measurement.
Innovation Solution
The proposed optical sensor system includes a photodiode, integrator, comparator, reference charge circuit, and a resistance coupled between the integrator input and a reference voltage node. At the end of the integration time, the photodiode is disconnected, and a reference voltage is applied to the integrator, allowing for the measurement of residual voltage by monitoring the time until the comparison signal switches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed integration time is used in the LTF engine, then the device complexity is reduced and operation is simplified, but the measurement precision deteriorates due to unaccounted residual charge
Solution Approach 1:
The patent applies preliminary action by performing a residual charge measurement during the integration phase itself, before the integration time expires. A monitoring circuit continuously checks the integrator output voltage and detects when it approaches the threshold voltage. This allows the system to account for residual charge that would otherwise be lost, improving measurement precision without adding complex post-integration processing steps.
2Productivity
If the integration time is reduced to improve productivity, then the light intensity measurement speed increases, but the measurement precision deteriorates due to increased noise and unaccounted residual charge
Solution Approach 1:
The patent implements feedback by using the monitoring circuit to detect the integrator output voltage during integration and compare it with the threshold voltage. This feedback mechanism allows the system to determine when residual charge is present and adjust the pulse count accordingly. This enables shorter integration times with maintained precision because the residual charge is actively monitored and accounted for rather than being lost.
3Device complexity
If a well-defined charge package is used for threshold crossing, then the device complexity is reduced, but the measurement precision deteriorates due to loss of residual charge information
Solution Approach 1:
The patent introduces an intermediary monitoring circuit that acts as a mediator between the integrator and the comparator. This monitoring circuit detects the integrator output voltage during integration and identifies when it approaches the threshold voltage. It provides information about residual charge to the control logic, enabling the system to account for charges that would otherwise be lost with fixed charge packages, thereby improving precision without complicating the charge package structure.
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 enhances the accuracy of light intensity measurement by accounting for residual voltage, improving accuracy at low signal counts and enabling reduced integration times without increasing noise.
Implementation Method 1
a photodiode having a photodiode output for providing a current of a first polarity
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
A method of measuring light intensity comprising exposing a photodiode to light to cause the photodiode to provide a current of a first polarity, supplying said current to an integrator to integrate said current to provide an integrated output voltage, and comparing the output voltage with a threshold voltage. Charge packages of opposite polarity are applied to said first polarity to reset the integration voltage prior to the start of the integration time. At the end of the integration time, the photodiode is disconnected from said integrator and a reference voltage coupled to the integrator input, whilst a resistance is coupled into the circuit until the comparison signal switches. The comparison signal is monitored to measure a time between the end of the integration time and the switching of the comparison signal to provide a measure of a residual voltage.