Photodetection Pixel Circuit With Replica Feedback for Stable Pulse Width
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Solution Overview
Problem
The variation in threshold voltage of inverter elements due to process, voltage, and temperature fluctuations affects the output pulse width, leading to decreased photodetection accuracy in distance measurement systems using the time of flight method.
Innovation Solution
A photodetection device with a pixel circuit and a pixel replica circuit, along with a control circuit that adjusts the threshold voltage and pulse width based on pixel signal counts, to maintain consistent pulse widths and improve accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the threshold voltage of the inverter element is used for pulse generation, then the distance measurement system can operate with simple circuit configuration, but the output pulse width varies due to process, voltage, and temperature fluctuations, decreasing photodetection accuracy
Solution Approach 1:
The patent introduces a replica circuit that copies the pixel circuit configuration including the photoelectric conversion element and inverter element. The replica circuit generates a reference pulse signal that experiences the same PVT variations as the actual pixel circuit, allowing for accurate compensation without requiring complex additional compensation circuits.
Solution Approach 2:
The patent implements a feedback mechanism where the reference pulse signal from the replica circuit is used to calibrate and adjust the threshold voltage of the inverter element in the actual pixel circuit. This feedback loop continuously compensates for PVT variations, maintaining consistent pulse widths and ensuring photodetection accuracy despite environmental changes.
2Adaptability or versatility
If the threshold voltage varies with process, voltage, and temperature, then the inverter element can adapt to different operating conditions, but the output pulse width becomes unstable, affecting histogram shape and measurement accuracy
Solution Approach 1:
The replica circuit is designed to exactly copy the pixel circuit's inverter element configuration, ensuring that the reference pulse signal experiences identical PVT variations. This copying approach allows the system to maintain pulse width stability by using the reference signal to compensate for variations in the actual measurement circuit across different operating conditions.
Solution Approach 2:
The patent dynamically adjusts the threshold voltage parameter of the inverter element based on the reference pulse signal characteristics. By changing the threshold voltage parameter in response to PVT variations, the system maintains stable pulse width output while still adapting to different operating conditions through the feedback mechanism.
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 stabilizes pulse widths, enhancing photodetection accuracy and distance measurement precision by compensating for variations in process, voltage, and temperature.
Implementation Method 1
a photoelectric conversion element that photoelectrically converts incident light
Data Source
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AI summary
The present disclosure provides a photodetection device and a distance measuring system capable of suppressing a decrease in photodetection accuracy. A photodetection device (30) according to an embodiment of the present disclosure includes: a photoelectric conversion element (331a) that photoelectrically converts incident light; a comparator (331c) that compares an output voltage of the photoelectric conversion element with a threshold voltage (Vth); a pulse generation circuit (335) that uses a pixel signal (OUT_REP) indicating a comparison result by the comparator to generate a pulse signal (TRIG) having a pulse width shorter than a pulse width of the pixel signal; and a switch (336) that is connected to the photoelectric conversion element (331a) and is turned on and off on the basis of the pulse signal (TRIG).