Lidar Chirp Shutter Sampling for Ambient Light Noise Rejection
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Solution Overview
Problem
LIDAR systems face challenges in accurately measuring distances due to interference from ambient light and varying power consumption, which affect signal-to-noise ratio and image uniformity.
Innovation Solution
Implementing chirp modulation with synchronized chirp shutter signals, dividing chirp sections into windows for signal integration, and using switched circuits like Track-and-Hold or Sample-and-Hold to reduce noise and stabilize power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional LIDAR systems use continuous illumination without chirp modulation, then the system structure is simpler, but the Signal-to-Noise Ratio deteriorates due to ambient light interference
Solution Approach 1:
The patent applies chirp modulation to the illumination signal, transforming it from a static continuous wave into a dynamic frequency-modulated signal. The frequency of the illumination signal varies linearly over time according to the chirp function, enabling the system to distinguish reflected signals from ambient light through frequency analysis, thereby improving SNR while maintaining manageable system complexity through software-based signal processing
Solution Approach 2:
The patent changes the frequency parameter of the illumination signal over time using chirp modulation. By varying the frequency according to a predetermined chirp function, the system creates a unique frequency signature for each time window, allowing differentiation between target reflections and ambient light through frequency-domain analysis, thus improving reliability without excessive complexity
2Stability of the object's composition
If LIDAR systems use fixed power consumption design, then power management is simpler, but image uniformity deteriorates due to varying ambient light conditions
Solution Approach 1:
The patent implements periodic modulation of the illumination signal using chirp functions applied in alternating time windows. The illumination is turned on during odd-numbered time windows and off during even-numbered windows, creating a periodic pattern that enables differential measurement. This periodic action allows the system to maintain stable image uniformity by compensating for ambient light variations while managing power consumption through controlled illumination cycles
Solution Approach 2:
The system dynamically adjusts the illumination state between on and off states in alternating time windows, and dynamically varies the frequency of the illumination signal using chirp modulation. This dynamic behavior enables the system to adapt to varying ambient light conditions, maintaining image uniformity while optimizing power consumption through intelligent control of illumination timing and frequency characteristics
3Reliability
If LIDAR systems divide chirp sections into multiple windows, then noise from ambient light is reduced, but the device complexity increases
Solution Approach 1:
The patent divides each chirp section into multiple time windows, with each window corresponding to a specific depth range. By segmenting the measurement process into discrete time windows and applying chirp modulation to each, the system can selectively process signals from different depth ranges, reducing ambient light noise through time-gated detection. The segmentation approach manages complexity by organizing signal processing into structured, manageable time segments
Solution Approach 2:
The patent extracts and processes only the relevant frequency components corresponding to each time window through Fourier transform analysis. By taking out and analyzing specific frequency bins associated with each time window, the system isolates target signals from ambient light noise. This extraction approach reduces noise while managing complexity by focusing computational resources only on relevant frequency ranges rather than processing the entire spectrum
4Use of energy by moving object
If LIDAR systems use ascending and descending chirp shutter signals, then average power consumption is maintained constant, but the system complexity increases
Solution Approach 1:
The patent applies both ascending and descending chirp shutter signals simultaneously to the illumination, creating counterbalancing frequency variations. The ascending chirp increases frequency over time while the descending chirp decreases frequency over time, and their combined effect maintains the average frequency and thus the average power consumption at a constant level. This counterweight approach balances power consumption while managing the complexity through symmetric signal design
Solution Approach 2:
The patent merges the ascending and descending chirp shutter signals into a single illumination output. By combining both chirp functions in the illumination path, the system achieves constant average power consumption through the complementary nature of the two signals. The merging of these signals simplifies the overall control architecture compared to using separate independent control systems for each chirp type
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
Improves signal-to-noise ratio, enhances distance measurement accuracy, and maintains consistent power consumption, resulting in improved LIDAR system performance.
Implementation Method 1
The photodetectors are configured to receive optical radiation reflected from the scene and to output respective signals in response to the received optical radiation
Implementation Method 2
The shutter is configured to modulate the signals output by the photodetectors by applying a chirp shutter function, having a selected chirp period, to the signals
Data Source
AI summary
A LIDAR system includes a transmitter, a receiver, and a processor. The transmitter directs a sequence of illumination pulses toward a scene. The receiver including an array of photodetectors, which receive optical radiation reflected from the scene and output respective signals in response to the received optical radiation, a shutter which modulates the signals output by the photodetectors by applying a chirp shutter function, having a selected chirp period, to the signals, and a readout circuit, which samples and digitizes the modulated signals in each of a plurality of sampling windows, which span the chirp period, thereby generating a corresponding plurality of digitized output signals. The processor selects respective sampling windows for the photodetectors, and processes the digitized output signals in the selected respective sampling windows to generate a depth map of the scene.