Non-Intrusive Optical Power Measurement via Current Mirror
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Solution Overview
Problem
Conventional optical input power measurement solutions in high-bit-rate burst-mode optical networks, such as GPON, face limitations including excessive response time, limited dynamic range, and accuracy issues, which affect system performance and quality of service.
Innovation Solution
The implementation of a non-intrusive optical input power measurement system using current mirror circuitry, power measurement circuitry, and analog-to-digital conversion, which provides faster response, greater dynamic range, and improved accuracy by isolating the power measurement from the data path and utilizing a DC current load for temperature compensation and logarithmic amplification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional TIA or LimAmp-based optical input power measurement is used, then the measurement can be performed with simple circuitry, but the response time exceeds 1 millisecond which is unacceptable for burst-mode systems
Solution Approach 1:
The patent segments the power measurement function from the data path by introducing a separate DC current load and current mirror circuitry. This allows the power measurement to be performed independently during burst mode operations, enabling faster response time without compromising the data reception functionality.
Solution Approach 2:
The patent introduces an intermediary current mirror circuitry that copies the photodiode current to a separate measurement path. This intermediary mechanism enables the power measurement to be decoupled from the data path, allowing simultaneous operations and reducing measurement response time to sub-millisecond levels.
2Device complexity
If linear current-to-voltage conversion is used for power measurement, then the circuit implementation is simple, but the dynamic range is limited and accuracy deteriorates at low power levels
Solution Approach 1:
The patent changes the conversion parameter from linear current-to-voltage conversion to logarithmic conversion. By using a logarithmic amplifier, the circuit compresses the dynamic range of the photodiode current into a manageable voltage range, improving measurement accuracy at low power levels while maintaining simplicity in circuit implementation.
Solution Approach 2:
The patent replaces the conventional linear TIA conversion mechanism with a logarithmic amplification approach. This substitution enables better handling of wide dynamic range signals, improving measurement precision without significantly increasing circuit complexity.
3Measurement precision
If high-resolution ADC is used to meet accuracy requirements at low power levels, then measurement accuracy improves, but cost and conversion time increase
Solution Approach 1:
The patent applies preliminary action by using logarithmic amplification to pre-compress the dynamic range before the ADC conversion. This preliminary processing reduces the required ADC resolution, allowing standard-resolution converters to achieve high measurement accuracy without increasing cost or conversion time.
4Device complexity
If TIA transimpedance is used to determine current-to-voltage gain, then power measurement can be performed, but accuracy deteriorates due to significant temperature variation
Solution Approach 1:
The patent introduces feedback mechanisms through the current mirror circuitry that continuously monitors and compensates for temperature variations in the transimpedance gain. This feedback approach maintains measurement accuracy despite temperature changes while keeping the conversion circuit simple.
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 solution enables accurate and efficient optical input power monitoring, allowing for system parameter adjustments that enhance performance in high-bandwidth optical networks by reducing response time, increasing dynamic range, and improving measurement accuracy.
Implementation Method 1
a primary function of use of one of these devices in an Optical Line Termination (OLT) application is to convert high-frequency photodiode current to digital voltage levels
Implementation Method 2
The current mirror circuitry is connected between the DC current load, the power measurement circuitry and the upstream data path circuitry
Implementation Method 3
DC current load for temperature compensation and logarithmic amplification
Data Source
AI summary
An optical line termination comprises a DC current load, power measurement circuitry, upstream data path circuitry and current mirror circuitry. The current mirror circuitry is connected between the DC current load, the power measurement circuitry and the upstream data path circuitry. The DC current load is connected in parallel with a photodiode of the upstream data path circuitry. The DC current load exhibits a substantially fixed load. The current mirror provides a copy of an aggregate current to the power measurement circuitry. The aggregate current is a summation of a current draw by the DC current load and a current draw by the photodiode. The power measurement circuitry is configured for outputting a power level dependent upon the aggregate current. Accordingly, the optical line termination provides for a non-intrusive solution for measuring optical input power and, thereby, enables the measured optical power to be monitored.