Time-of-flight camera phase error compensation
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Solution Overview
Problem
Time-of-flight cameras face challenges in accurately measuring distances due to phase errors caused by temperature changes and aging of electronic components, which affect the precision of distance measurements.
Innovation Solution
Incorporating a time measurement unit, such as a time-to-digital converter, to measure the propagation time of pulses through drivers and adjust pulse durations to reduce phase errors, ensuring accurate distance calculations by synchronizing the start of measurement with pulse generation and storing temporal positions to compensate for signal propagation variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If phase error compensation is not implemented, then the device complexity remains low, but the measurement precision deteriorates due to temperature changes and aging effects
Solution Approach 1:
The patent applies preliminary action by measuring the propagation time of clock signals through drivers before actual distance measurement occurs. The system pre-characterizes the temporal positions of clock signals at different temperatures and stores these as compensation data. During operation, this pre-measured data is used to compensate for phase errors, eliminating the need for complex real-time correction mechanisms while maintaining high measurement precision.
Solution Approach 2:
The system uses its own internal clock signals to measure propagation time through the drivers, rather than requiring external reference equipment. The ToF camera generates test clock signals, measures their propagation time through the same drivers used for light source and shutter control, and uses this self-measured data to compensate for phase errors in distance measurements.
2Measurement precision
If propagation time measurement is implemented for all pixels, then the measurement precision improves, but the productivity decreases due to increased processing time
Solution Approach 1:
The patent extracts the phase error measurement function from individual pixel processing and implements it as a separate, dedicated time measurement unit. This unit specifically measures the propagation time of clock signals through drivers, independent of the main distance measurement process. By separating these functions, the system can compensate for phase errors without adding processing overhead to each pixel's distance calculation.
Solution Approach 2:
The time measurement unit serves multiple purposes: it measures propagation time for phase error compensation, characterizes driver behavior at different temperatures, and provides data for both near and far object measurements. This multi-functional approach allows a single measurement system to support various measurement scenarios without requiring separate processing paths for each object distance.
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 significantly reduces the influence of phase errors on distance measurements, enhancing the accuracy and reliability of time-of-flight cameras by compensating for signal propagation times and pulse duration changes, thereby improving measurement precision.
Implementation Method 1
measuring, with the time measurement unit, the propagation time of the pulses through the drivers
Implementation Method 2
measuring the propagation time of light between two points very precisely, it is possible to calculate the distance between them
Implementation Method 3
The light source emits a modulated light signal that reflects off objects in the scene, and the ToF camera measures the time between the emission and the arrival of the reflected light signal
Implementation Method 4
a sinusoidal modulation of the light signal can be used, in which case the distance values are derived from the phase shift between the outgoing and incoming light signals
Data Source
AI summary
A time-of-flight, ToF, camera for measuring distance information for objects of a scene includes a light source for emitting modulated light signals for illuminating the objects, an image sensor for capturing reflected light signals, and shutters for opening and closing the exposure of the image sensor. A pulse generator generates first pulses for switching the light source and second pulses for switching the shutters. A first driver amplifies the first pulses and outputs the same to the light source, and a second driver amplifies the second pulses and outputs the same to the shutters. A time measurement unit measures the propagation time of the pulses through the drivers and/or the pulse duration of the pulses output from the drivers. A processing unit generates a distance measurement image based on the captured reflected light signals to reduce the influence of phase errors on the distance measurement image.