Photodetector Current Replicator for High Bandwidth Gain Regulation
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Solution Overview
Problem
Optical communication networks face issues with power transients and variations in signal power and optical signal-to-noise ratio (OSNR) due to network reconfiguration, particularly at high bit rates, where typical current replicators lack sufficient bandwidth for effective gain regulation.
Innovation Solution
A high bandwidth photodetector current replicator circuit that includes a photodetector, a transimpedance amplifier with a feedback resistor, and a logarithmic amplifier, capable of generating a second current that is linear with optical power in dB, with offset cancellation and a resistor ratio to scale currents, ensuring a bandwidth of at least 1 MHz irrespective of photodetector current levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a typical current replicator is used in optical communication networks, then the device complexity is reduced, but the bandwidth is insufficient for effective gain regulation at high bit rates
Solution Approach 1:
The current replicator is divided into multiple independent operational amplifiers (first op-amp, second op-amp, third op-amp) that process different aspects of the signal separately. The first op-amp generates the TIA output voltage, the second op-amp generates a first current proportional to the photodetector current, and the third op-amp generates a second current proportional to the TIA output voltage. This segmentation allows each amplifier to be optimized for its specific function, achieving high bandwidth while maintaining manageable device complexity.
2Adaptability or versatility
If network reconfiguration is performed to transmit different individual channels, then the adaptability of the optical network is improved, but power transients and variations in signal power and OSNR occur
Solution Approach 1:
The patent implements a feedback mechanism where the optical monitoring signal is converted to electrical signals through photodetectors, processed through the current replicator circuit with multiple operational amplifiers, and used to generate control signals that regulate the gain of optical amplifiers. This closed-loop feedback system continuously monitors and adjusts signal power levels, compensating for transients caused by network reconfiguration and maintaining stable signal power and OSNR despite changes in network topology or channel allocation.
3Power
If the photodetector current is increased to improve signal strength, then the signal power is improved, but the bandwidth of the TIA voltage decreases
Solution Approach 1:
The patent introduces an intermediary transimpedance amplifier (TIA) stage that converts the photodetector current to a voltage signal before further processing. The TIA output voltage serves as an intermediary that can be processed by subsequent operational amplifiers to generate the final control signals. This intermediary conversion allows the system to maintain high bandwidth by keeping the photodetector operating at optimal current levels while achieving the necessary signal power through the voltage conversion and subsequent amplification stages.
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
The solution effectively stabilizes signal power and OSNR by providing a high bandwidth current replication, enabling accurate gain regulation and minimizing transient gain effects, even at low input currents, thus enhancing network throughput and transmission distance.
Implementation Method 1
receiving, at a photodetector, an optical signal having a plurality of wavelengths and an optical power. Responsive to the optical signal received, the method may include generating a photodetector current when the photodetector is reverse biased with a bias voltage
Data Source
AI summary
Methods and systems for replicating high bandwidth current outputs from a photodetector or another current source include using a transimpedance amplifier (TIA) to directly generate a TIA voltage that is linear with optical power at the photodetector. The TIA voltage is used to generate a current that flows to a log amp, which generates a voltage that is linear with the optical power in dB. Additionally, offset cancellation is used at the TIA and at the log amp.