ToF Image Sensor Ramp Control for Adaptive A/D Range
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Solution Overview
Problem
Image sensing devices face challenges in flexibly adjusting the analog to digital (A/D) conversion range according to varying use environments or conditions when measuring depth information using time-of-flight technology, which affects the accuracy and efficiency of depth measurement.
Innovation Solution
The image sensing device includes a plurality of current cells that can be adjusted based on enable signals and selection signals, a current-voltage conversion circuit, and control circuits to generate a ramp signal whose slope is adjusted according to the ratio of reflected light to background light, allowing for flexible A/D conversion range adjustment while maintaining a fixed swing range of the ramp signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the A/D conversion range is fixed, then the device structure is simple, but the device cannot adapt to varying use environments or conditions when measuring depth information
Solution Approach 1:
The patent implements dynamic adjustment of the A/D conversion range by controlling the number of active current cells in the ramp signal generator. The conversion range is changed in real-time based on environmental conditions (reflected light to background light ratio), transforming a static system into an adaptive one without requiring multiple fixed-range converters
Solution Approach 2:
The patent changes the key parameter of the ramp signal (slope) by adjusting the number of active current cells. This parameter change directly controls the A/D conversion range, allowing the system to adapt to different environments by modifying the ramp signal characteristics rather than changing the entire conversion architecture
2Adaptability or versatility
If the number of current cells is increased to expand A/D conversion range, then the conversion range is extended, but the power consumption and circuit complexity increase
Solution Approach 1:
Instead of using all current cells continuously, the patent dynamically activates only the necessary number of cells based on the current measurement requirements. This dynamic activation reduces power consumption while maintaining the ability to expand the conversion range when needed by activating additional cells
Solution Approach 2:
The patent adjusts the operational parameter (number of active cells) to match the required conversion range. When a smaller range is sufficient, fewer cells are activated, reducing power consumption. When a larger range is needed, more cells are activated, expanding the conversion range without permanently increasing power consumption
3Measurement precision
If the ramp signal slope is adjusted to optimize depth measurement accuracy, then the measurement precision is improved, but DC offset may occur affecting signal integrity
Solution Approach 1:
The patent employs a control circuit that monitors the ramp signal generation process and provides feedback to adjust the number of active current cells. This feedback mechanism ensures that the ramp signal slope is optimized for depth measurement accuracy while preventing conditions that would generate DC offset, thereby maintaining signal integrity
Solution Approach 2:
The patent carefully adjusts the ramp signal slope parameter within optimal ranges that maximize depth measurement accuracy without exceeding thresholds that would cause DC offset. By controlling the parameter change magnitude and range, the system achieves high precision while maintaining signal reliability
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 enables improved performance by optimizing the A/D conversion range based on the use environment, preventing DC offset and enhancing the accuracy of depth measurement in image sensing devices using time-of-flight technology.
Implementation Method 1
a pixel array suitable for generating a plurality of pixel signals based on incident light
Implementation Method 2
a current-voltage conversion circuit suitable for converting a plurality of unit currents, which are supplied from current cells used among the plurality of current cells, into a ramp signal
Data Source
AI summary
Disclosed is an image sensing device including a plurality of current cells whose total number to be used is adjusted based on a plurality of enable signals, and which are sequentially controlled based on a reset signal and a plurality of selection signals; a current-voltage conversion circuit suitable for converting a plurality of unit currents, which are supplied from current cells used among the plurality of current cells, into a ramp signal; and a first control circuit suitable for generating the plurality of enable signals based on a maximum conversion code value corresponding to a slope of the ramp signal.