Optical Receiver LOS Detection Using Level Monitor and Squelching
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Solution Overview
Problem
Conventional optical receivers face challenges in reliably generating a Loss Of Signal (LOS) alarm due to secondary response issues and mis-assertion/mis-negation of alarms caused by noise and fluctuations, particularly in small-sized modules with limited lead pins, where additional circuits are required to detect signal levels before the coupling capacitor.
Innovation Solution
The optical receiver incorporates a receiver optical module with a photodiode, pre-amplifier, level monitor, and squelching unit in an AC mode, where the level monitor and squelching unit are in a secondary path, preventing secondary responses by fixing the output to a preset voltage when the signal is absent, and the main amplifier generates an LOS alarm when the signal magnitude falls below a preset level, all within a compact module with limited lead terminals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the optical receiver uses AC coupling mode with TIA and main amplifier, then the receiver can be compact with limited lead pins, but secondary response causes mis-assertion and mis-negation of LOS alarm
Solution Approach 1:
The patent divides the signal path into two separate segments: a primary path for signal amplification (PD-TIA-main amplifier) and a secondary path for LOS alarm detection (PD-level monitor-comparator). This segmentation allows the LOS alarm function to be monitored independently without being affected by the secondary response in the AC-coupled main signal path, thereby resolving the contradiction between compact size and alarm reliability.
Solution Approach 2:
The level monitor acts as an intermediary element that directly monitors the photocurrent from the PD before AC coupling occurs. By introducing this intermediate monitoring point, the system can detect LOS conditions based on the actual optical signal level without being influenced by the secondary response artifacts introduced by the AC coupling capacitors in the main signal path.
2Reliability
If additional circuits (peak-holding, bottom-holding, digital filter) are added to detect signal level before coupling capacitor, then LOS alarm reliability improves, but device complexity increases and additional lead pins are required
Solution Approach 1:
The patent extracts the LOS detection function from the complex signal processing chain by directly monitoring the photocurrent at the PD output. Instead of using peak-holding, bottom-holding, or digital filtering circuits, the invention takes out the essential LOS detection capability and implements it through a simple level monitor and comparator that compare the photocurrent against a reference level, thereby maintaining high reliability while minimizing circuit complexity.
Solution Approach 2:
The patent changes the detection parameter from monitoring the amplified voltage signal (which suffers from secondary response) to monitoring the photocurrent directly at the PD output. By changing what parameter is monitored (from voltage after AC coupling to current at PD output), the system achieves reliable LOS detection without requiring complex additional circuits or additional lead pins.
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 configuration effectively prevents secondary response issues and mis-assertion of LOS alarms, allowing for reliable detection of optical signal absence without additional circuits or lead pins, ensuring accurate alarm generation and compact module design.
Implementation Method 1
The PD, by being supplied with a bias voltage through the level monitor, converts the input optical signal into a photocurrent
Data Source
AI summary
An optical receiver able to generate the LOS alarm reliably is disclosed. The optical receiver module in the optical receiver provides a level monitor that monitors the average of the optical input, compares it with a reference and generates a decision signal that is provided to the squelching unit. The squelching unit, by receiving the decision signal, isolates the outputs of the output buffer from the inputs thereof and fixes the outputs of the receiver module in the level “0” or the level “1”. Even the main amplifier is coupled with the receiver optical module in the AC mode; no complicated response appears in the input of the main amplifier.