Pulsed-Coherent Lidar Front End Combining Coarse and Fine ToF
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing lidar systems struggle to simultaneously achieve high depth resolution and fast acquisition, with coherent detection being slow and pulsed detection having low resolution and limited by walk error.
Innovation Solution
A pulsed-coherent detection method combining coarse and fine ToF measurements, using a variable gain amplifier to maintain constant output amplitude and post-edge detection to reduce walk error, along with a phase-invariant variable-gain low-noise amplifier to enhance dynamic range and precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If coherent detection is used to achieve high resolution, then measurement precision is improved, but acquisition speed deteriorates
Solution Approach 1:
The patent segments the ToF measurement into two distinct parts: coarse ToF measurement using pulsed detection method and fine ToF measurement using coherent detection method. The coarse measurement captures the general time range with fast acquisition, while the fine measurement refines the resolution within a specific window. This segmentation allows the system to achieve both high resolution and fast acquisition by combining the strengths of both detection methods rather than using either one alone.
2Productivity
If pulsed detection is used to achieve fast acquisition, then productivity is improved, but measurement precision deteriorates
Solution Approach 1:
The measurement process is divided into two stages: first, pulsed detection is used for coarse ToF measurement to achieve fast acquisition and determine the general time range; second, coherent detection is applied for fine ToF measurement within the identified time window to achieve high depth resolution. This two-stage segmentation allows the system to leverage the speed advantage of pulsed detection and the precision advantage of coherent detection in sequence.
3Adaptability or versatility
If variable gain amplifier is used to control amplitude, then adaptability is improved, but device complexity increases
Solution Approach 1:
The patent implements an automatic gain control (AGC) loop that uses feedback to dynamically adjust the gain of the variable gain amplifier. The AGC circuit monitors the signal amplitude and automatically adjusts the amplifier gain to maintain optimal signal levels across a wide dynamic range. This feedback mechanism provides adaptability to handle varying signal strengths while managing complexity through an automated control system rather than manual adjustment.
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
The method achieves sub-mm resolution with 10-m dynamic range and fast acquisition, reducing walk error and improving measurement accuracy by combining pulsed and coherent detection techniques.
Implementation Method 1
a coherent detector configured to measure a fine ToF by detecting the phase difference (Δφ) between the clock signal (CKref) and the received signal (RFin)
Implementation Method 2
a pulse edge detector configured to measure a coarse ToF by detecting a falling edge (post-edge) of the received signal (RFin)
Implementation Method 3
the power of back-reflected light is detected using a square-law photodetector
Data Source
AI summary
Systems and methods for a light detection and ranging (lidar) system utilizing both coherent and pulsed detection for Time of Flight (ToF) measurement are disclosed. In one embodiment, a lidar system includes a reference clock providing a clock signal (CKref) with time period Tclk, an automatic gain control (AGC) loop that is triggered when a received signal RFin is greater than a threshold voltage Vth, a coherent detector measuring a fine ToF by detecting the phase difference (Δϕ) between the clock signal (CKref) and the received signal (RFin), a pulse edge detector measuring a coarse ToF by detecting a falling edge (post-edge) of the received signal (RFin) and counting cycles N to estimate an arrival time of N×Tclk, and a combiner that calculates total ToF by combining output of the coherent detector and pulse edge detector using the equation:ToF=[N+(ΔΦ2π)]×Tclk.