LED Driving Circuit Peaking Current Control for Optical Fiber Links
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Solution Overview
Problem
Existing LED driving circuits for optical fiber links face challenges in reducing current consumption and achieving high-speed light emission, with differential drive type circuits experiencing difficulty in reducing current consumption and single drive type circuits struggling to control peaking current effectively, leading to delayed response times and potential distortion.
Innovation Solution
A light emitting diode driving circuit incorporating a current mirror circuit with interconnected MOS transistors and a peaking circuit to precisely control the driving and peaking currents, allowing for synchronized rising and falling edges and adjustable peaking current values, thereby enhancing response speed and reducing current consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a differential drive type LED driving circuit is used to achieve high-speed light emission, then the response speed is improved, but the current consumption increases due to constant bias current flow
Solution Approach 1:
The patent applies periodic action by using pulsed driving current instead of constant bias current. The LED is driven with periodic pulses at frequencies matching the digital signal rate (e.g., 155 Mbps), allowing the LED to respond quickly during pulse periods while remaining off during non-pulse periods, thus reducing average current consumption while maintaining high-speed response capability
Solution Approach 2:
The patent implements dynamics by making the bias current adjustable and time-variable rather than fixed and constant. The bias current can be dynamically set to optimal values based on operating conditions, and the circuit transitions between different current states (off state, bias state, driving state) to optimize both speed and power consumption under varying conditions
2Use of energy by moving object
If the driving current is completely reduced to zero when the LED is off to reduce current consumption, then the current consumption is reduced, but light emission is delayed when the LED needs to turn on
Solution Approach 1:
The patent applies preliminary action by maintaining a small bias current in the LED during the off state before full driving is needed. This bias current keeps the LED in a partially activated state, so when a driving pulse arrives, the LED can transition to full emission faster than if it were completely off, thus reducing emission delay while still maintaining lower average power consumption
3Speed
If peaking current is used to accelerate the response speed of the LED, then the response speed is improved, but the circuit complexity increases due to additional current control requirements
Solution Approach 1:
The patent merges the peaking current generation function with the existing driving circuit components. The peaking current is generated by utilizing the same switching transistors and circuit elements already present in the driving circuit, rather than adding completely separate peaking circuitry. This integration reduces the overall circuit complexity while still achieving the beneficial peaking effect for accelerated LED response
4Use of energy by moving object
If a single drive type LED driving circuit is used to reduce current consumption, then the current consumption is reduced, but the peaking current control becomes difficult leading to distorted light emission
Solution Approach 1:
The patent applies segmentation by separating the current control functions into distinct stages: bias current control stage and driving current control stage. The bias current is controlled through one path while the driving current (including peaking current) is controlled through another path. This segmentation allows independent optimization of each current type, enabling precise peaking current control in a power-efficient single-drive architecture
Data Source
AI summary
An LED driving circuit includes: (a) a current mirror circuit having N-channel MOS transistors whose respective gates are connected with each other, (b) a constant current source for supplying an LED driving current to an N-channel MOS transistor 4, (c) an LED connection terminal, connected with the N-channel MOS transistors, for connecting the LED, (d) an inverter and an input-terminal respectively for inputting, to a source of the N-channel MOS transistor, an ON/OFF signal for controlling ON/OFF of the LED, and (e) a peaking circuit, connected with a drain and source of the N-channel MOS transistor, for generating a peaking current used in peaking a current flowing into the LED. With this arrangement, it is possible to provide an LED driving circuit that easily realizes low current consumption and high-speed emission for the LED. With such an LED driving circuit, an optical transmitter for use in an optical fiber link can also be realized.