Balanced APD LiDAR Receiver Biasing for RIN Noise Rejection
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Solution Overview
Problem
Lidar receivers face challenges in achieving high signal-to-noise ratio (SNR) due to relative intensity noise (RIN) from lasers, which increases over time, and existing methods like optical attenuators are expensive and generate additional noise, while transimpedance amplifiers (TIAs) introduce thermal and shot noise, reducing SNR.
Innovation Solution
A lidar system using a pair of avalanche photodiodes with a processor to determine and apply biases to balance photocurrents, achieving a common mode rejection ratio (CMRR) near one, thereby improving SNR without additional noise generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If optical attenuators are used to reduce laser intensity noise, then the relative intensity noise is reduced, but the device cost increases and additional noise is generated
Solution Approach 1:
The patent extracts and removes the optical attenuator component from the system entirely. Instead of using optical attenuators to reduce laser intensity noise, the invention uses a dual-photodiode balanced detection architecture where the noise rejection is achieved through differential signal processing, eliminating the need for expensive optical attenuators and their associated noise.
Solution Approach 2:
The patent replaces the mechanical/optical attenuation method with an electrical/differential detection method. By substituting the optical attenuator with a balanced photodiode detection system, the invention achieves noise reduction through electrical signal differentiation rather than optical attenuation, thereby eliminating the drawbacks of the optical attenuator approach.
2Ease of operation
If transimpedance amplifiers are used to convert photodiode signals, then the signal conversion is achieved, but thermal and shot noise are introduced reducing SNR
Solution Approach 1:
The patent merges the signal paths from two photodiodes into a single differential output. By combining the signals in a balanced configuration where common-mode noise (including thermal and shot noise) appears equally on both paths, the differential extraction process rejects this noise while preserving the differential signal, thus achieving signal conversion without introducing additional thermal and shot noise.
Solution Approach 2:
The patent converts the harmful thermal and shot noise that would normally be introduced by transimpedance amplifiers into a benefit through common-mode rejection. The noise components that appear as harmful factors in conventional single-photodiode systems become common-mode signals that are rejected by the balanced detection architecture, thereby improving signal-to-noise ratio.
3Difficulty of detecting and measuring
If conventional photodetectors are used, then the detection function is achieved, but signal-to-noise ratio is limited due to RIN
Solution Approach 1:
The patent segments the detection function into two separate photodiode channels instead of using a single photodetector. By dividing the detection task across two photodiodes operating in parallel with balanced detection, the system can separately process and differential extract the signals, thereby rejecting common-mode RIN noise while maintaining the detection function.
Solution Approach 2:
The patent introduces asymmetry in the signal processing path while maintaining symmetry in the optical input. The two photodiodes receive symmetric optical inputs but process signals through asymmetric differential extraction, where the difference between the two signals is extracted. This asymmetric processing of symmetric inputs enables common-mode rejection of RIN noise while preserving the differential signal information.
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 solution effectively balances photocurrents to enhance SNR, maintain performance across temperature changes, and reduce manufacturing costs by avoiding expensive optical attenuators and noise-prone TIAs, while maintaining lidar system performance.
Implementation Method 1
a first photodiode to generate a first analog signal that is based at least in part on the reflection of the optical beam; a second photodiode to generate a second analog signal that is based at least in part on the reflection of the optical beam
Implementation Method 2
Light detection and ranging receiver with avalanche photodiodes
Data Source
AI summary
A light detection and ranging (lidar) receiver may include a first photodiode, a first amplifier connected to the first photodiode, and a first analog-to-digital converter (ADC) connected to an output of the first amplifier. The lidar receiver may include a second photodiode, a second amplifier connected to the second photodiode, and a second ADC connected to the second amplifier. The lidar may include a processor connected to an output of the first ADC and an output of the second ADC and a direct-current-to-direct-current converter connected to an output of the processor and to the first photodiode and the second photodiode. The processor may determine, based on the output of the first ADC and the output of the second ADC, a first bias to apply to the first photodiode and a second bias to apply to the second photodiode.