Laser Diode Driving Circuit Using Probability Density Function
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Solution Overview
Problem
Conventional driving circuits for semiconductor laser diodes face challenges in precisely controlling driving current due to overshoot and undershoot in photocurrent signals, which are influenced by noise and lead to erroneous peak level detection, making it difficult to maintain stable output power and extinction ratio.
Innovation Solution
A driving circuit that uses a comparator, signal mixer, and averaging unit to generate a control signal based on a superposed signal with a predetermined distribution, such as Gaussian or uniform, to accurately reflect the ratio of photocurrent to a preset reference level, thereby avoiding overshoot and undershoot issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a peak hold circuit is used to detect and hold peak levels of the monitor signal, then the driving current can be controlled to maintain constant output power, but the circuit produces erroneous results when the monitor signal contains noises, overshoot, or undershoot
Solution Approach 1:
The invention extracts only the essential information from the monitor signal by using a comparator to generate binary signals that indicate whether the signal exceeds a reference level. This extraction process removes the harmful overshoot and undershoot components while retaining the necessary control information, thereby resolving the contradiction between measurement precision and reliability under noise conditions.
Solution Approach 2:
The comparator performs preliminary action by converting the analog monitor signal into binary signals before further processing. This preliminary conversion eliminates the impact of overshoot and undershoot that would otherwise affect subsequent peak detection and holding operations, ensuring reliable control even in noisy conditions.
2Device complexity
If conventional peak hold circuit is used, then the circuit structure is relatively simple, but it cannot precisely control the driving current when overshoot or undershoot occurs in the monitor signal
Solution Approach 1:
The invention introduces binary signals as an intermediary between the monitor signal and the peak hold circuit. These binary signals, generated by the comparator, serve as a mediator that translates the analog signal into a form that is immune to overshoot and undershoot, thereby improving measurement precision without significantly increasing device complexity.
Solution Approach 2:
The invention changes the parameter domain from analog voltage levels to binary digital signals. By transforming the monitor signal into binary form through the comparator, the system achieves precise driving current control that is insensitive to overshoot and undershoot, while maintaining relatively simple circuit structure.
Data Source
AI summary
The present invention provides a laser diode driving circuit that enables to precisely control the amplitude of the driving current with suppressing the overshoot and the undershoot appeared in the monitor signal of the optical output from the laser diode. The driving circuit of the invention includes a signal mixer, a comparator, an averaging unit and a current generator. The signal mixer superposes an additional signal on the monitor signal. The amplitude of the additional signal varies in accordance with a preset distribution function. The comparator compares thus superposed signal with a reference level and outputs a binary signal. The averaging unit integrates this binary signal and the current generator provides the driving current based on the averaged binary signal.