Optical Receiver Post-Distortion Circuit for Wider Dynamic Range
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Solution Overview
Problem
Optical receivers for analog RF video systems have limited dynamic range, making it difficult to maintain signal quality across varying optical path losses, as they struggle to balance noise and distortion while keeping costs low, especially in deployments like FTTP systems where the desired dynamic range is between 10 to 28 dB but current receivers only support about 7 or 8 dB.
Innovation Solution
The implementation of a post-distortion network in optical receivers that compensates for gain errors, ensuring a composite output voltage is linear with respect to input current, allowing for increased dynamic range by canceling out distortion and enabling higher values of feedback resistors to reduce noise without increasing distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the value of feedback resistors is increased to reduce noise, then noise performance is improved, but distortion increases
Solution Approach 1:
A post-distortion network is introduced as an intermediary component between the trans-impedance amplifier and the output. This network acts as a mediator that corrects the distortion generated by the amplifier, allowing the use of higher feedback resistor values for noise reduction without suffering from increased distortion. The post-distortion network compensates for the amplifier's non-linearities, effectively decoupling the noise-distortion tradeoff.
Solution Approach 2:
The patent employs feedback mechanisms within the post-distortion network to sense and correct distortion in real-time. By monitoring the output signal and applying corrective feedback, the system maintains low distortion levels even when using high feedback resistor values in the trans-impedance amplifier, thus resolving the contradiction between noise reduction and distortion control.
2Adaptability or versatility
If the optical dynamic range is increased to support varying path losses, then adaptability is improved, but distortion and noise performance become harder to balance
Solution Approach 1:
The optical receiver is segmented into functionally distinct blocks: a trans-impedance amplifier for signal amplification and a separate post-distortion network for distortion correction. This segmentation allows each block to be optimized independently - the amplifier can use high feedback resistors for low noise, while the post-distortion network handles distortion correction, enabling wide optical dynamic range without compromising performance.
Solution Approach 2:
The patent utilizes parameter changes in the post-distortion network to dynamically compensate for distortion across the wide optical dynamic range. By adjusting the operating parameters of the post-distortion network based on the input signal level, the system maintains optimal distortion and noise performance throughout the extended dynamic range, supporting adaptability without increasing complexity.
3Object-generated harmful factors
If larger transistor active area is used to minimize distortion, then distortion is reduced, but power consumption and cost increase
Solution Approach 1:
The post-distortion network serves as an intermediary that corrects distortion without requiring larger transistor active areas in the main amplifier. This allows the amplifier to use smaller, more power-efficient transistors while the post-distortion network handles the distortion correction, thereby reducing power consumption and cost without sacrificing distortion performance.
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 results in a lower distortion optical receiver with improved noise performance, enabling operation over a wider optical dynamic range and extending the permissible optical operating range, thus simplifying deployments by tolerating higher optical input conditions before distortion budget is exceeded.
Implementation Method 1
The amplitude-modulated optical signal is then demodulated into an electrical signal by a photo-detector
Data Source
AI summary
An optical receiver with increased dynamic range includes a photodetector, a photodetector biasing network, an amplifier and a post-distortion network. The post-distortion network compensates for gain error in the amplifier, such that a composite output voltage is relatively linear with respect to input current. The dynamic gain responses of the amplifier and the post-distortion network are equal in magnitude and opposite in phase. Additionally, a signal from at least one internal node of the amplifier may be connected to the post-distortion network, in order to further improve performance.