Balanced APD LiDAR Receiver for Relative Intensity 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 RIN, 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 attenuators to reduce RIN, the invention uses a dual-photodiode balanced detection architecture where the RIN is rejected through differential processing of the two photodiode signals, eliminating the need for expensive attenuator components.
Solution Approach 2:
The patent converts the harmful RIN effect into a beneficial common-mode signal that can be rejected. By feeding both photodiodes with signals containing the same RIN component and then subtracting the signals in differential mode, the RIN is converted from a harmful noise source into a rejectable common-mode component, improving SNR without additional attenuation.
2Power
If transimpedance amplifiers are used to amplify photodiode signals, then the signal amplitude is increased, but thermal and shot noise are introduced reducing SNR
Solution Approach 1:
The patent merges the signal amplification and noise rejection functions into a single differential processing stage. Instead of amplifying signals separately through TIAs (which introduces noise), the invention combines the photodiode outputs and performs differential amplification, which simultaneously amplifies the desired signal while rejecting common-mode noise through the balanced architecture.
Solution Approach 2:
The patent converts the amplification process from a noise-introducing operation (as in TIA) into a noise-rejecting operation. By using differential amplification of balanced photodiode outputs, the amplification gain is applied to the differential signal while common-mode noise is suppressed, turning the amplification function into a benefit rather than a harm source.
3Object-affected harmful factors
If balanced photodiode configuration is used to achieve common mode rejection, then the common mode rejection ratio is improved, but the device complexity increases
Solution Approach 1:
The patent segments the single photodiode detection function into two separate photodiodes working in parallel. Each photodiode handles a portion of the optical signal, and their outputs are combined differentially. This segmentation enables common-mode rejection while distributing the complexity across two simpler, identical channels rather than one complex channel.
Solution Approach 2:
The patent changes the operational parameter from single-ended detection to differential detection. By measuring the difference between two photodiode outputs rather than the absolute value of one, the system achieves common-mode rejection. This parameter change from single-channel to dual-channel differential operation improves noise rejection while maintaining manageable complexity through symmetry.
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 enhances the SNR and performance of the lidar system by balancing photocurrents, maintaining performance as RIN changes over time, and reducing manufacturing costs and noise, while avoiding the high costs and noise issues of optical attenuators and TIAs.
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.