FMCW LiDAR Time-Domain AGC for ADC Dynamic Range Limits
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Solution Overview
Problem
FMCW LIDAR systems face challenges in dynamic range limitations, leading to signal distortion and noise interference, which are not effectively addressed by increasing the number of bits in ADCs and digital datapaths due to power, area, and cost constraints.
Innovation Solution
Implementing automatic gain control (AGC) across optical, analog, or digital paths to adjust the dynamic range of FMCW LIDAR systems, using variable gain elements to reduce signal distortion and noise interference while maintaining power, area, and cost efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If bits are added to ADCs and digital datapaths to increase dynamic range, then dynamic range is improved, but power consumption increases
Solution Approach 1:
The patent applies preliminary action by performing automatic gain control on the analog signal before it reaches the ADC. Variable gain amplifiers adjust the signal amplitude in advance, ensuring the signal falls within the optimal dynamic range of the ADC. This preliminary adjustment eliminates the need for additional bits in the ADC to handle varying signal amplitudes, thereby maintaining power efficiency while preserving dynamic range performance.
Solution Approach 2:
The patent introduces variable gain amplifiers as intermediary components between the optical front-end and the ADC. These amplifiers act as mediators that condition the analog signal by adjusting its amplitude to match the ADC's optimal input range. This intermediary adjustment allows the system to maintain high dynamic range performance without requiring the ADC to have excessive bit depth, thus avoiding the power penalty associated with high-resolution ADCs.
2Measurement precision
If bits are added to ADCs and digital datapaths to increase dynamic range, then dynamic range is improved, but circuit area increases
Solution Approach 1:
By performing gain control in advance before the signal enters the digital domain, the patent prevents the need for wide datapaths throughout the digital signal processing chain. The variable gain amplifiers prepare the signal with appropriate amplitude, allowing subsequent digital processing to use narrower, more area-efficient datapaths while still maintaining the ability to handle the full dynamic range of the input signal.
Solution Approach 2:
The variable gain amplifiers serve as intermediary components that condition the signal in the analog domain before digital conversion. This analog-domain adjustment eliminates the need for high-bit-width digital datapaths, thereby reducing the overall circuit area required for digital processing components without sacrificing dynamic range performance.
3Measurement precision
If bits are added to ADCs and digital datapaths to increase dynamic range, then dynamic range is improved, but system cost increases
Solution Approach 1:
The patent applies preliminary gain control in the analog domain to optimize the signal amplitude before digital conversion. This approach allows the system to use lower-resolution, cost-effective ADCs and digital datapaths while still achieving the required dynamic range performance, thereby reducing the overall system cost compared to using high-bit ADCs without preliminary signal conditioning.
Solution Approach 2:
By introducing variable gain amplifiers as intermediary components, the patent enables the use of more cost-effective ADCs and digital processing components. The analog-domain signal conditioning performed by these intermediaries eliminates the need for expensive high-resolution digital components, thus reducing the overall system cost while maintaining dynamic range performance.
4Device complexity
If optical or analog components are used, then system complexity is reduced, but dynamic range is limited
Solution Approach 1:
The patent applies dynamics by using variable gain amplifiers that can dynamically adjust their gain based on the input signal amplitude. This dynamic adjustment capability allows the system to maintain optimal signal levels across a wide dynamic range without requiring complex high-resolution ADCs. The system remains relatively simple in architecture while achieving enhanced dynamic range through the dynamic gain control mechanism.
Solution Approach 2:
The patent changes the amplitude parameter of the analog signal dynamically using variable gain amplifiers. By adjusting the gain parameter in response to signal conditions, the system extends its effective dynamic range without introducing complex high-resolution digital components. This parameter-based approach maintains system simplicity while overcoming the dynamic range limitations of fixed-gain analog components.
Data Source
AI summary
A light detection and ranging (LIDAR) system includes an automatic gain control (AGC) unit to reduce the dynamic range, reducing processing power and saving circuit area and cost. The system detects a return beam of a light signal transmitted to a target, having a first dynamic range in a time domain. An analog to digital converter (ADC) generates a digital signal based on the return beam. A processor can perform time domain processing on the digital signal, convert the digital signal from the time domain to a frequency domain, and perform frequency domain processing on the digital signal in the frequency domain. The AGC unit can measure a power of the return beam, and apply variable gain in the time domain to reduce a dynamic range of the return beam to a second dynamic range lower than the first dynamic range.