Receiver Optical Assemblies With Remote Photo-Detector
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Solution Overview
Problem
Conventional receiver optical sub-assemblies (ROSAs) designed for long-haul applications are costly and not suitable for short-haul active optical cables, making them unfeasible for consumer applications due to high component costs and noise immunity issues, despite offering increased bandwidth and low noise performance.
Innovation Solution
The design of receiver optical assemblies (ROAs) with a photo-detector remotely located from a transimpedance amplifier (TIA) and a differential TIA circuit with higher input impedance, using impedance-controlled transmission circuits to reduce ringing effects and capacitance, allowing for higher bandwidth operation and cost reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional ROSA designs are used with photo-detector intimately connected to TIA, then bandwidth and noise performance are improved, but device complexity and cost increase
Solution Approach 1:
The patent divides the conventional integrated ROSA into separate modules: the photo-detector remains in the optical header packaging while the TIA circuit is relocated to a separate PCB location. This segmentation allows independent optimization of each component's function and reduces the complexity of intimate connections while maintaining performance through controlled impedance transmission lines.
Solution Approach 2:
The TIA circuit is extracted from the optical header packaging and placed on the PCB at a remote location. This extraction eliminates the need for complex intimate connections and expensive bonding assembly techniques, thereby reducing device complexity and cost while maintaining noise performance through proper transmission line design.
2Speed
If conventional ROSA designs are used with intimate photo-detector to TIA connection, then bandwidth is improved, but manufacturing cost increases
Solution Approach 1:
The patent employs standard PCB trace transmission lines instead of expensive specialized bonding assembly techniques. These conventional PCB traces are cheaper to manufacture while still achieving the required bandwidth performance through proper impedance control, making the overall system more cost-effective despite the remote TIA location.
Solution Approach 2:
The patent changes the TIA input impedance parameter to a higher value (at least 10 ohms) which allows for relaxed transmission line requirements. This parameter change enables the use of simpler, cheaper PCB trace implementations while maintaining the necessary bandwidth performance, thereby reducing manufacturing cost.
3Ease of manufacture
If photo-detector is remotely located from TIA, then manufacturing cost is reduced, but transmission circuit capacitance and ringing effects increase
Solution Approach 1:
The patent increases the TIA input impedance to at least 10 ohms, which reduces the time constant (tau = RC) formed by the transmission line capacitance and TIA input impedance. This parameter change allows for longer transmission lines with higher capacitance while maintaining bandwidth performance, thereby enabling cost-effective remote TIA implementations.
Solution Approach 2:
The patent uses standard PCB trace transmission lines that are conventional and well-understood in the industry, rather than requiring specialized low-capacitance interconnect structures. These standard PCB traces simplify manufacturing while the impedance matching and TIA input impedance selection compensate for the inherent capacitance.
4Adaptability or versatility
If TIA input impedance is increased to reduce ringing, then short-haul applications become viable, but traditional long-haul performance may be affected
Solution Approach 1:
The patent optimizes the TIA input impedance specifically for short-haul applications by setting it to at least 10 ohms, which reduces ringing effects in the transmission circuit. This local optimization for short-haul conditions allows the same circuit design to be universally applied across different application scenarios without requiring separate optimized designs for long-haul and short-haul uses.
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 enables the use of short-haul active optical cables in consumer applications by reducing costs and maintaining high bandwidth and low noise performance, making them more viable and cost-effective compared to traditional copper cables.
Implementation Method 1
a photo-detector configured to detect and convert input optical signals into output electrical signals
Data Source
AI summary
Embodiments disclosed herein include receiver optical assemblies (ROAs) having a photo-detector remotely located from a differential transimpedance amplifier (TIA). Related components, circuits, and methods are also disclosed. By providing the photo-detector remotely located from a TIA, additional costs associated with design constraints of providing the photo-detector intimate with a TIA may be avoided, thereby reducing cost of the ROA. In this regard as a non-limiting example, the ROAs according to the embodiments disclosed herein allow shorter haul active optical cable applications for use in consumer applications from a cost standpoint with the added benefits of increased bandwidth and low noise performance of optical fiber. In this regard, the ROAs disclosed herein provide higher input impedance differential TIA circuits and transmission circuits inhibiting or reducing ringing effects and maintain a sufficiently low resistance-capacitance (RC) time constant for differential TIA circuit to allow for higher bandwidth operation of the ROA.