TOF Image Sensor Phase Offset Calibration Circuit
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Solution Overview
Problem
Conventional time-of-flight (TOF) image sensing devices face challenges in accurately determining depth information due to ambient light interference and increasing depth errors with greater distances, making it difficult to compensate for depth errors and achieve high-resolution depth measurements.
Innovation Solution
The proposed solution involves an image sensing device that adjusts the initial phase offset between a modulated signal and a phase control signal based on acquired depth information, using an offset calculating circuit to select a reference phase closest to the depth phase and generate a phase offset signal, which is then used to compensate for depth phase errors, thereby minimizing depth errors and enhancing accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional TOF sensing is used without phase offset adjustment, then the device structure remains simple, but depth measurement precision deteriorates due to ambient light interference and increasing depth errors at greater distances
Solution Approach 1:
The system performs preliminary calibration by setting reference phases and calculating phase offset values before actual depth measurement. The offset calculating circuit pre-determines the phase offset based on reference phase measurements, which is then used to correct subsequent depth measurements, thereby improving precision without adding complex real-time processing
Solution Approach 2:
The system changes the phase parameter of the modulation signal to multiple reference phases (e.g., 0°, 90°, 180°, 270°) and measures depth at each phase. By analyzing the phase offset across different reference phases, the system calculates an optimal phase offset value that compensates for ambient light interference and improves measurement precision
2Measurement precision
If phase offset adjustment is implemented to improve depth accuracy, then depth measurement precision improves, but device complexity increases due to additional offset calculating circuit and control logic
Solution Approach 1:
The phase offset calculation and correction mechanism is designed to be universally applicable across different operating conditions (varying distances, ambient light levels). The same offset calculating circuit and control logic handle all depth measurement scenarios, making the added complexity worthwhile by providing consistent precision improvement without requiring multiple specialized subsystems
Solution Approach 2:
The system implements feedback by using the calculated phase offset to adjust and compensate depth measurements in real-time. The offset calculating circuit continuously monitors reference phases and updates the phase offset value, which is then fed back to correct the depth measurement, creating a closed-loop system that maintains high precision
3Measurement precision
If multiple reference phases are measured to calculate phase offset, then depth information accuracy improves, but measurement time increases due to additional measurement steps
Solution Approach 1:
The system uses periodic modulation signals at multiple reference phases (e.g., 0°, 90°, 180°, 270°) to measure depth. By periodically switching through these reference phases and measuring at each, the system efficiently extracts phase offset information without requiring continuous or excessive measurement time, as the periodic nature allows for rapid sequential measurement
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 allows for accurate and precise depth information acquisition by minimizing depth errors and optimizing signal-to-noise ratio, even in bright sunlight environments or at greater distances, by setting the phase difference between the reflected signal and phase control signal to optimal values such as 0, 90, 180, or 270 degrees.
Implementation Method 1
A TOF system calculates a distance from an origin to an object by measuring a flight time of light or a signal
Data Source
AI summary
An image sensing device includes an optical emitter outputting a modulated signal to a target object; an optical receiver generating, according to a phase control signal, pixel signals corresponding to a reflected signal from the target object; an image processor calculating a depth phase based on the pixel signals and compensating for the depth phase according to a phase offset signal to output a depth information signal; a driving control circuit generating the phase control signal corresponding to a phase of the modulated signal and setting an initial phase difference between the modulated signal and the phase control signal according to the phase offset signal; and an offset calculating circuit setting a plurality of reference phases, selecting a reference phase closest to the depth phase among the set reference phases and generating the phase offset signal representing a phase difference between the selected reference phase and the depth phase.