Optical Receiver Positive Feedback Loop Photodiode Bias Control
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Solution Overview
Problem
Optical receivers face challenges in maintaining transmission quality at high speeds due to increased jitter caused by varying optical input power, particularly when using directly modulated laser diodes, which degrades bit error rates and communication systems.
Innovation Solution
An optical receiver design featuring a positive feedback loop between the photocurrent and bias, utilizing a current mirror and sensing amplifier to dynamically adjust the bias applied to the photodiode, ensuring stability and efficiency across different optical input levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the bias current is increased to operate the directly modulated laser diode at high speed, then the transmission speed is improved, but the optical output power becomes excessively large
Solution Approach 1:
The patent dynamically changes the bias current parameter based on the detected optical input power level. When optical input power is high, the bias current is reduced; when optical input power is low, the bias current is increased. This parameter adaptation allows the system to operate at high speeds without producing excessively large optical output power, resolving the contradiction between transmission speed and optical output power.
2Measurement precision
If the photodiode is set to receive low power optical signals, then the sensitivity is improved, but the tolerance for overload optical input power deteriorates
Solution Approach 1:
The patent implements a dynamic bias adjustment mechanism that adapts the photodiode's operating point in real-time based on the optical input power level. The bias current is dynamically increased when optical input power is high to prevent saturation and maintain overload tolerance, while allowing high sensitivity operation when optical input power is low. This dynamic adaptation resolves the contradiction between signal sensitivity and overload tolerance.
3Reliability
If the optical input power is increased to improve signal strength, then the signal-to-noise ratio is improved, but the jitter increases causing degradation in transmission quality
Solution Approach 1:
The patent employs a feedback mechanism where the optical input power level is detected and used to control the bias current applied to the photodiode. When optical input power is high (which improves signal strength), the feedback loop reduces the bias current to prevent jitter increase and maintain transmission quality. This feedback control resolves the contradiction between signal strength and transmission quality by automatically adjusting the bias current based on the actual operating conditions.
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 suppresses jitter degradation by increasing bias at higher optical input levels, maintaining transmission quality while optimizing power consumption and reducing the risk of self-breakdown in avalanche photodiodes.
Implementation Method 1
a photodiode (hereafter denoted as PD) to generate an electrical signal depending on optical power received thereby
Data Source
AI summary
An optical receiver is disclosed, in which a PD is biased by a positive feedback loop with respect to the photocurrent generated thereby. The optical receiver includes the PD, a current mirror to reflect the photocurrent into a mirror current, a current detector to convert the mirror current into a voltage signal, and a bias source stabilized by the negative feedback loop by sensing the output voltage thereof superposed with the voltage signal output by the current detector. The PD, the current mirror, the current detector and the bias source comprises the positive feedback loop for the photocurrent.