Burst-Mode PON Receiver With Fast Threshold Setting

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Solution Overview

Problem

In high data rate passive optical networks (PON) systems, determining the threshold voltage for converting analog signals from light pulses to binary electrical signals is challenging due to varying light pulse magnitudes from optical network units (ONUs), leading to increased bit errors.

Innovation Solution

A receiver system utilizing a switchable low pass filter with a fast RC time constant during the preamble phase to quickly establish the threshold voltage, followed by a stable RC time constant during payload data reception, enabled by a reset signal from the media access controller, ensures accurate conversion of analog signals to digital signals.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a standard RC time constant is used for threshold voltage determination, then the threshold voltage is stable, but the establishment time is too long causing bit errors at high data rates

Engineering Contradiction:

Improvebit error rateVSAvoidthreshold voltage establishment time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent applies dynamics by making the RC time constant adjustable rather than fixed. The circuit switches between a first RC time constant during preamble reception and a second RC time constant during payload reception, allowing the threshold determination circuit to adapt its response time to different operational phases, thus resolving the contradiction between fast establishment and stability

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent uses preliminary action by determining the threshold voltage during the preamble phase before the actual payload data reception begins. The preamble serves as a preparation period where the threshold is established in advance using a longer RC time constant, ensuring accurate threshold determination is ready before critical data processing starts

Inventive Principle:

Principle #10Preliminary action

2Loss of time

If a fast RC time constant is used during preamble, then threshold voltage is established quickly, but the threshold voltage becomes unstable during payload reception

Engineering Contradiction:

Improvethreshold voltage establishment timeVSAvoidthreshold voltage stability

Core Design Contradiction:

Loss of timeVSStability of the object's composition

Solution Approach 1:

The patent switches the RC time constant dynamically based on the reception phase. During preamble reception, a first RC time constant is used for quick establishment, then during payload reception, a second RC time constant is switched in to maintain stability, resolving the contradiction between speed and stability through temporal separation of functions

Inventive Principle:

Principle #15Dynamics

3Stability of the object's composition

If threshold voltage determination is delayed, then stability is maintained, but bit errors increase due to slow response to varying light pulse magnitudes

Engineering Contradiction:

Improvethreshold voltage stabilityVSAvoidbit error rate

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

The threshold voltage is determined in advance during the preamble phase before payload reception begins. This preliminary determination ensures the threshold is established and stable before critical data processing starts, preventing bit errors while maintaining stability during the actual data reception

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The reception process is segmented into distinct phases: preamble reception for threshold determination and payload reception for data processing. This segmentation allows different RC time constants to be optimized for each phase, with a longer time constant during preamble for stability and a faster response during payload for accuracy

Inventive Principle:

Principle #1Segmentation

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 allows for rapid and accurate determination of threshold voltage, reducing bit errors and ensuring reliable data conversion in high-speed PON systems by stabilizing the threshold voltage before payload data reception.

Implementation Method 1

establishing a threshold voltage for determining whether the analog signal is a logical one or a logical zero

Methodology Applied

Scientific EffectLow pass filter: Filter (electronic)

Implementation Method 2

converting the magnitude of a light pulse to a proportional analog current

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS7920798B2PON burst mode receiver with fast decision threshold setting

Publication Date: 2011.04.05 MICREL INC

AI summary

A receiver converts an analog signal, derived from light pulses in a GPON fiber optic system, to clean digital electrical signals. A photodetector and transimpedance amplifier (TIA) convert the light pulses to analog electrical signals. A reset signal generated by a media access controller (MAC) in the GPON system signifies the start of a new burst of data. The receiver has a switchable low pass filter that establishes the threshold voltage for determining whether the analog signal is a logical 1 or a logical 0. At the very start of a new burst, the low pass filter has a fast time constant to quickly establish the threshold voltage for the burst. At a later time during the burst, the low pass filter is switched to have a slow time constant to create a relatively stable threshold voltage.