Current-Domain LIDAR Frontend With DC/AC Cancellation Loops
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Solution Overview
Problem
Current direct time-of-flight (dTOF) LIDAR systems face challenges in achieving high dynamic range and noise performance due to the fundamental coupling of bandwidth and noise in trans-impedance amplifiers (TIAs), which limits their range performance and complicates hardware implementation, especially for long-range automotive LIDARs with low object reflectivity.
Innovation Solution
A current-domain analog frontend (AFE) circuit is introduced, featuring a photo detector, current feedback DC servo loop, feedback network, and floating class AB output stage, which decouples noise and bandwidth, enabling flexible operation across 4 orders of magnitude dynamic range and supporting alternative modulation schemes like intensity modulation phase-coded bursts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If trans-impedance amplifiers are used to amplify the reflected optical signal, then the signal can be detected, but the bandwidth and noise performance are fundamentally coupled, limiting dynamic range
Solution Approach 1:
The patent divides the signal processing into separate DC and AC paths. The DC component is processed through a servo loop that can be optimized for low noise, while the AC component (containing the TOF signal) is processed through a high-bandwidth path. This segmentation allows each path to be optimized independently for its specific function, resolving the fundamental coupling between noise performance and bandwidth in traditional TIAs.
2Length of moving object
If high peak optical power is used to maximize range, then the achieved range improves, but the average power must be maintained at maximum permissible level by reducing pulse-width, imposing system challenges
Solution Approach 1:
The patent implements a DC servo loop with feedback that automatically adjusts to cancel the DC component of the photodetector current. This feedback mechanism enables the system to handle the high dynamic range signals resulting from long-range operation without requiring complex hardware modifications, thus resolving the contradiction between extended range and system complexity.
3Device complexity
If the DC component of the photodetector current is not canceled, then the circuit is simpler, but the AC signal path is limited by the DC level, reducing dynamic range
Solution Approach 1:
The patent introduces a DC servo loop as an intermediary system that separates the DC cancellation function from the AC signal path. The servo loop acts as a mediator that removes the DC component without interfering with the high-bandwidth AC signal, thereby enabling both high dynamic range and relatively simple circuit implementation.
4Power
If high-speed power semiconductor components are used to deliver large power in short time, then the transmitted laser pulse performance improves, but the cost and complexity increase
Solution Approach 1:
The patent replaces the need for complex high-speed power semiconductor components with an electrical circuit solution (DC servo loop with capacitive coupling) that achieves the same effect of enabling high peak power transmission with reduced complexity. The electronic feedback circuit substitutes for the need for specialized high-speed power devices.
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 current-domain AFE optimizes noise and recovery speed, allowing for high dynamic range and bandwidth performance without clipping, enabling accurate time-of-flight and intensity measurements, and reducing system complexity and cost.
Implementation Method 1
a photo detector configured to source a current
Data Source
AI summary
A circuit for filtering a signal corresponding to a time of flight (TOF) of light from a laser reflected off an object to a photo detector, the circuit includes a preamplifier, a DC cancelation loop, and an AC cancelation loop. The preamplifier may be configured to receive the signal from the photo detector corresponding to an output of the laser reflected off an object remote from the laser and photo detector. The DC cancelation loop includes a current feedback DC servo loop. The AC cancelation loop includes a feedback network driven by a floating class AB output stage, and the preamplifier configured to drive the floating class AB output stage, wherein the preamplifier is driven by an error signal of the feedback network and creates an AC signal path with the feedback network and floating class AB output stage.