Photosensor Circuit Dynamic Output Switching for Saturation Prevention
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Solution Overview
Problem
Existing photosensor circuits either saturate at high light intensities due to linear output characteristics, limiting dynamic range, or exhibit poor sensitivity in low-intensity light conditions with logarithmic output characteristics, often resulting in afterimages due to increased impedance.
Innovation Solution
A photosensor circuit design that includes a photoelectric conversion element, a first MOS transistor for logarithmic voltage conversion, a charge-storing capacitor, and a control section for managing gate and drain voltages to efficiently transfer electrical charge between capacitors, allowing for linear or logarithmic output characteristics based on light intensity, enhancing sensitivity and dynamic range while preventing saturation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If linear output characteristics are used in photosensor circuit, then sensitivity in low-intensity light condition is improved, but sensor saturation occurs at high light intensity, limiting dynamic range
Solution Approach 1:
The patent applies dynamics by making the output characteristics changeable based on light intensity conditions. The photosensor circuit dynamically switches between linear and logarithmic output characteristics: using linear characteristics for low-intensity light to maintain sensitivity, and logarithmic characteristics for high-intensity light to prevent saturation. This dynamic adaptation allows the circuit to optimize performance across varying light conditions, achieving both high sensitivity and wide dynamic range.
2Adaptability or versatility
If logarithmic output characteristics are used in photosensor circuit, then dynamic range is improved, but sensitivity in low-intensity light condition deteriorates and afterimages occur
Solution Approach 1:
The patent applies local quality by providing different output characteristic types (linear and logarithmic) for different light intensity ranges. Instead of using a single uniform characteristic across all conditions, the circuit selectively applies linear characteristics when sensitivity is needed (low light) and logarithmic characteristics when dynamic range is needed (high light). This localized optimization resolves the contradiction by matching the appropriate characteristic type to the specific operating condition.
3Measurement precision
If electrical charge transfer is enhanced in photosensor circuit, then sensitivity is improved, but operational complexity increases
Solution Approach 1:
The patent applies preliminary action by performing charge transfer optimization in advance through specific voltage control sequences. The control section pre-establishes optimal voltage conditions (Vg1, Vg2, Vd) for charge transfer before measurement, and systematically manages the charging and discharging phases of capacitors C1 and C2. This structured preliminary preparation of voltage states simplifies the overall operation while maximizing charge transfer efficiency and sensitivity.
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 improved sensitivity and dynamic range by efficiently transferring electrical charge, minimizing afterimages and operational differences with other circuits, and maintaining high signal-to-noise ratios in low-intensity light conditions.
Implementation Method 1
a photodiode PD provided as a photosensor element (i.e., photoelectric conversion element) for detecting incident light (light signal) L1 and converting the detected incident light L1 into an electrical signal
Data Source
AI summary
Photosensor circuit includes: a photoelectric conversion element; a first MOS transistor for converting a current signal into a voltage signal, a first capacitor element; a second capacitor element; a second MOS transistor for controlling charge transfer from the first capacitor element to the second capacitor element; and a control section for supplying gate voltages and drain voltages to the first and second MOS transistors. The control section performs initial setting and voltage control such that the charge transfer can be carried out efficiently for setting of the gate voltages and drain voltages to be supplied the first and second MOS transistors. Time length of the charge transfer is set so as not to exceed 100 μsec.