TOF Sensor Pixel Circuit Individual Exposure Control
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Solution Overview
Problem
Current distance measurement devices using the time of flight (TOF) method face limitations in achieving high measurement accuracy due to variations in light reception across different pixels, leading to inconsistent exposure times and noise in distance calculations.
Innovation Solution
The implementation of a control circuit with transistors and comparators in a distance measurement device that individually sets exposure times for each imaging pixel based on accumulated voltages, allowing for precise control of light reception and improved signal processing through signals TRG0 and TRG180, enabling enhanced measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional TOF distance measurement device is used, then the basic distance measurement function is provided, but the measurement accuracy is insufficient due to variations in light reception across different pixels
Solution Approach 1:
The imaging unit is divided into multiple imaging pixels, each with independent exposure time control through dedicated transistors (first transistor with first gate signal line, second transistor with second gate signal line). This segmentation allows each pixel to independently adjust its exposure time based on accumulated voltage, ensuring consistent light reception across different pixels and improving measurement accuracy.
Solution Approach 2:
The exposure time for each imaging pixel is dynamically adjusted by changing the timing of gate signals applied to the transistors. The control circuit modifies exposure time parameters based on accumulated voltage levels, allowing each pixel to optimize its light reception and reduce variations between pixels, thereby improving measurement accuracy.
2Measurement precision
If exposure times are not individually controlled for each pixel, then the device structure remains simple, but variations in light reception cause noise in distance calculations
Solution Approach 1:
The control circuit is segmented into multiple independent control paths, each associated with specific imaging pixels. Each control path includes transistors and comparators that operate independently to control exposure timing for their designated pixels. This segmented approach reduces noise in distance calculations while keeping each control unit relatively simple.
Solution Approach 2:
Accumulated voltage serves as an intermediary parameter that bridges the light reception signal and the exposure time control. The comparator uses the accumulated voltage to determine when to switch transistors, creating an intermediate control mechanism that reduces noise without requiring complex direct control logic, thus balancing measurement precision and device complexity.
3Measurement precision
If consistent exposure times are enforced across all pixels, then noise is reduced, but the device requires complex individual control mechanisms for each pixel
Solution Approach 1:
Multiple control functions are merged into a unified control circuit architecture that uses shared components (comparators, signal lines) across pixel groups. The first and second transistors with their respective gate signal lines are controlled by a common control circuit that manages exposure timing for multiple pixels, reducing overall device complexity while maintaining consistent exposure times across pixels.
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 approach enhances measurement accuracy by ensuring consistent exposure times across pixels, reducing noise and improving the signal-to-noise ratio, thereby providing more precise distance measurements.
Implementation Method 1
the distance measurement device emits light, and detects the reflected light reflected by an object to be measured
Data Source
AI summary
There is provided a time of flight sensor. The time of flight sensor includes a light receiving element PD, a first signal line TRGO and a second signal line TRG180, a first transistor TGA in electrical communication with the light receiving element, the first transistor comprising a first gate in electrical communication with the first signal line TRGO, a second transistor TGB in electrical communication with the light receiving element, the second transistor comprising a second gate in electrical communication with the second signal line TRG180, and a control circuit P200 comprising at least one comparator 102A, 102B, wherein the control circuit is in electrical communication with the first and second signal lines TRGO, TRG180. The transistors TGA and TGB of the pixel circuit P100 are turned on and off so that any one of the transistors TGA and TGB is turned on, and the electric charges generated by the photodiode PD are selectively accumulated at the floating diffusion FDA and the floating diffusion FDB. First and second voltages VSLA, VSLB depending on voltages at first and second floating diffusions FDA, FDB, respectively, are compared to a reference voltage VREF. The first signal TRGO is a logical product of a clock signal SCK and the comparator output QO, and the second signal TRG180 is the logical product of the inverted clock signal SCK and the comparator output QO. A distance measurement device has an imaging unit including a pixel array of a plurality of imaging pixels P arranged in a matrix. One control circuit P200 is provided for one pixel circuit P100. The control circuit P200 controls the exposure time in the pixel circuit P100. The pixel circuit P100 supplies the voltages VSLA and VSLB to the control circuit P200, and the control circuit P200 generates the signals TRGO and TRG180 on the basis of the voltages VSLA and VSLB, and supplies these signals TRGO and TRG180 to the pixel circuit P100. Thus, since the exposure time can be individually set in each of the plurality of imaging pixels, the measurement accuracy in distance measurement can be enhanced.