GPON Preamble Detection Circuit Using Segmented Pulse Counters
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Solution Overview
Problem
In gigabit passive optical networks (GPON), identifying the preamble of burst mode transmissions is challenging due to asynchronous, out-of-phase, and amplitude-varied optical signals from multiple ONUs, requiring precise time-critical circuitry which is complex and costly.
Innovation Solution
A signal detection circuit using multiple counters to monitor different portions of a time interval, reducing false triggers and enabling simpler, less time-critical measurements to confirm a valid preamble, thereby compensating for signal variations and ensuring accurate phase alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If precise time-critical circuitry is used to measure time between consecutive edges for preamble detection, then measurement precision is improved, but device complexity increases and cost increases
Solution Approach 1:
The patent divides the time interval into multiple segments and uses separate counters for each segment. Instead of using one complex time-critical circuit to measure the entire interval, multiple simpler counters measure individual segments. This segmentation reduces the time-critical requirements for each counter while maintaining overall measurement precision for preamble detection.
Solution Approach 2:
The patent replaces complex time-critical electronic measurement circuitry with a simpler counting-based approach. By using multiple counters that increment on clock cycles rather than requiring precise time interval measurement, the system substitutes a mechanically simpler counting mechanism for complex timing circuitry, reducing both complexity and cost.
2Reliability
If multiple counters are used to monitor different portions of time interval, then false triggers are reduced, but device complexity increases
Solution Approach 1:
The patent segments the time interval measurement into multiple portions, each monitored by a separate counter. This segmentation allows the system to verify that edges occur in the correct sequential pattern across multiple time segments, significantly reducing false triggers caused by noise or irregular signals. The complexity increase is minimal since each counter uses identical simple logic.
Solution Approach 2:
The patent implements feedback logic that monitors the outputs of multiple counters and uses their combined results to validate preamble detection. The feedback mechanism checks whether the counting patterns from different segments are consistent with expected preamble characteristics, providing reliable false trigger reduction through cross-verification of multiple independent measurements.
Data Source
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AI summary
A circuit detects a digital pattern with a first counter having an input receiving a digital pattern, and an output providing an output signal after detecting a first number of pulses during a first time period. A latch has an input coupled to the output of the first counter for latching the output signal of the first counter. A second counter has an input receiving the digital pattern, and an output providing an output signal after detecting a second number of pulses during a second time period. A logic gate has a first input coupled the output of the first counter, and a second input coupled to the output of the second counter, and an output coupled to the input of the latch. An amplitude detection circuit has an input coupled for receiving the digital pattern and an output coupled to the input of the first counter.