Optical Transceiver Coupling Circuit for Common-Mode Voltage Matching
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Solution Overview
Problem
In optical line termination systems, existing methods for coupling optical transceivers and processing modules face challenges due to differing common mode voltage levels, leading to issues like inappropriate DC response in burst mode operations and signal jitter introduction, and are not adaptable to different types of optical transceivers.
Innovation Solution
A coupling module that uses high-pass and low-pass filters in parallel, with operational amplifiers and feedback circuits, to adjust and stabilize the common mode voltage of differential signals, ensuring compatibility and minimizing phase shift across a wide frequency range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If capacitive coupling is used to shift common mode voltage, then voltage level compatibility is improved, but DC response becomes inappropriate and burst mode operation fails
Solution Approach 1:
The patent introduces an intermediary circuit between the optical transceiver and processing module that performs both voltage level shifting and DC coupling. This intermediary uses operational amplifiers configured as voltage followers to buffer the signal while maintaining DC continuity, thereby achieving compatibility without sacrificing DC response or burst mode capability.
Solution Approach 2:
The patent changes the electrical parameters of the coupling circuit by using operational amplifiers with adjustable gain and offset controls. This allows the circuit to adapt the voltage level and DC offset dynamically, maintaining both voltage compatibility and proper DC response across different operating conditions including burst mode.
2Adaptability or versatility
If bus transceivers are used to shift common mode voltage, then voltage level compatibility is improved, but signal jitter is introduced
Solution Approach 1:
The patent replaces the mechanical/buffered signal conversion approach of bus transceivers with a direct analog signal path using operational amplifiers. This substitution maintains the signal in its original domain longer, avoiding the digital conversion and re-transmission process that introduces jitter, while still achieving voltage level compatibility through analog buffering and level shifting.
3Device complexity
If a fixed coupling method is designed for a single type of optical transceiver, then simplicity is improved, but adaptability to different transceiver types deteriorates
Solution Approach 1:
The patent designs a universal coupling circuit using operational amplifiers that can accommodate multiple types of optical transceivers. The circuit includes adjustable parameters such as gain control and offset adjustment that can be configured for different transceiver output characteristics, making a single circuit design compatible with various transceiver types without requiring redesign.
Solution Approach 2:
The patent introduces dynamic adjustment capabilities to the coupling circuit, allowing it to adapt its parameters based on the connected transceiver type. This may include programmable gain control or automatic level detection that adjusts the circuit behavior in real-time, providing both simplicity of a single design and adaptability to different devices.
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 jitter-free communication of high-speed signals with simultaneous DC coupling and wide bandwidth, maintaining signal integrity and adaptability to various common mode voltages, thus addressing the limitations of previous coupling methods.
Implementation Method 1
The split signals for both the positive differential signal path and the negative differential signal path can then be provided to a high-pass filter and a low-pass filter that are connected in parallel
Implementation Method 2
the common mode voltage outputs of the low-pass filters can be measured by a feedback circuit that then provides an appropriate input to the low-pass filters such that the common mode voltage output from the low-pass filters is at the appropriate level
Implementation Method 3
The low-pass filter can have an inverting configuration such that the output from the low-pass filter is inverted with respect to the input
Data Source
AI summary
A coupling module can be used to communicate high speed signals between an optical transceiver and a processing module of an optical communication device, such as an optical line termination (OLT) or an optical network unit (ONU). The coupling module can adjust the common mode voltage level of a differential signal output by the optical transceiver to the common mode voltage level required by the processing module. In addition, the coupling module splits each of the differential output signals from the optical transceiver and passes the split signals to both a high-pass filter and a low-pass filter that are connected in parallel. The outputs of the high-pass filter and the low-pass filter from different paths of the differential signal are cross-coupled and combined to provide a differential signal to the processing module.