Burst Optical Receiver AGC Using Preamble-Based Settling Control
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Solution Overview
Problem
The optical line terminal (OLT) in a passive optical network faces challenges in handling data bursts of varying signal strengths from different optical network units (ONUs) due to different optical path lengths, requiring rapid adjustment of amplification levels and system parameters during short intervals, while being insensitive to manufacturing tolerances and environmental variations.
Innovation Solution
A system comprising a photodiode, transimpedance amplifier, and a signal preamble detector that adjusts gain and settling time based on detected signal levels, using a switched capacitor circuit and a comparator to detect transitions in the data stream, allowing for adaptive control of the automatic gain control (AGC) system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the AGC system uses a fixed settling time constant, then the circuit design is simple, but the system cannot adapt rapidly to varying signal strengths of different data bursts from different ONUs
Solution Approach 1:
The patent applies dynamics by making the settling time constant variable rather than fixed. The AGC system switches between a first settling time constant during preamble reception and a second settling time constant during data payload reception, allowing the system to adapt its response characteristics to different operational phases and signal conditions.
Solution Approach 2:
The patent uses preliminary action by detecting the preamble pattern before the main data payload and adjusting the settling time constant in advance. The system identifies the preamble, switches to the appropriate settling time constant beforehand, and ensures the AGC is properly settled before the actual data reception begins.
2Speed
If the settling time is shortened for fast adaptation during preamble, then the AGC responds quickly to signal strength changes, but the system becomes sensitive to instantaneous signal level variations and noise
Solution Approach 1:
The patent dynamically adjusts the settling time constant based on the operational phase. During preamble reception, a shorter first settling time constant enables fast adaptation to signal strength changes. During data payload reception, a longer second settling time constant filters out instantaneous variations and noise, improving reliability.
Solution Approach 2:
The patent implements periodic action by alternating between different settling time constants based on the periodic structure of the received signal (preamble followed by data payload). The system switches settling time constants periodically according to the signal structure, optimizing performance for each phase.
3Measurement precision
If the AGC system adapts to each individual data burst, then the signal recovery is optimized, but the system complexity and adjustment time increase
Solution Approach 1:
The patent uses preliminary action by performing AGC adaptation during the preamble period before the main data payload. The system adjusts the gain and settles the AGC circuit using the first settling time constant during the preamble, ensuring optimization is completed before actual data reception begins, thus minimizing loss of time.
Solution Approach 2:
The patent segments the data reception into distinct phases (preamble and data payload) with different AGC optimization strategies. Each phase uses an appropriate settling time constant optimized for its specific requirements, allowing precise signal level measurement without excessive adaptation time for the entire data burst.
4Reliability
If the system uses a long settling time constant for stable signal reception, then the AGC is less sensitive to instantaneous variations, but the system cannot adapt quickly to different signal strengths of successive data bursts
Solution Approach 1:
The patent makes the settling time constant dynamic, switching between a longer second settling time constant during data payload reception for stability and a shorter first settling time constant during preamble reception for rapid adaptation to signal strength changes of successive bursts.
Solution Approach 2:
The patent applies periodic action by alternating between different settling time constants according to the periodic structure of the received signal. The longer settling time constant is used periodically during data payload reception to ensure stability, while the shorter constant is used during preamble periods to enable rapid adaptation.
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
Enables fast and accurate adaptation of the AGC system to varying signal strengths and data rates, minimizing errors and ensuring optimal signal recovery during both preamble and data payload phases.
Implementation Method 1
a photodiode; a transimpedance amplifier coupled to said photodiode
Implementation Method 2
an integrator or filter for smoothing said first control signal
Implementation Method 3
an integrator or filter for smoothing said first control signal
Data Source
AI summary
An assembly of electronic components for reception of data using an optical fiber wherein data is received in bursts, the assembly including: a photodiode; a transimpedance amplifier coupled to said photodiode, wherein a gain of the transimpedance amplifier is adjusted based on a level of a gain control signal; a received input signal sensor configured to sense a received input signal level; and a signal preamble detector configured to detect the end of at least one of said preamble patterns in a data burst conveyed in said received signal and further configured to generate said settling control signal as an output.