Low-Side Laser Diode Driver With Servo-Controlled Sink Current
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Solution Overview
Problem
Existing low side drivers for laser diodes fail to maintain a constant sink current when the cathode potential is low, leading to increased power consumption and reduced battery autonomy due to the need for higher anode potentials to compensate.
Innovation Solution
A low side driver integrated circuit with a reference transistor, output transistor, switching transistor, matching transistor, and servo-control circuits to regulate drain and gate-source voltages, ensuring a precise sink current even at low cathode potentials, thereby reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the anode potential is increased to maintain constant sink current, then the sink current precision is improved, but the power consumption increases
Solution Approach 1:
The patent changes the control parameter from anode potential to cathode potential through the low-side driver configuration. By controlling the cathode potential directly via the output transistor, the system maintains precise current control without requiring high anode potentials, thus reducing power consumption while preserving current precision.
Solution Approach 2:
The patent introduces a low-side driver circuit as an intermediary between the power source and the laser diode. This driver circuit, comprising output transistor, reference transistor, and servo-control circuits, acts as a mediator that precisely controls the sink current through cathode potential regulation, eliminating the need for high anode potentials and thereby reducing overall power consumption.
2Use of energy by moving object
If the cathode potential is kept low to reduce power consumption, then the power consumption is reduced, but the sink current precision deteriorates
Solution Approach 1:
The patent implements feedback control through two servo-control circuits that continuously monitor and adjust the cathode potential. The first servo-control circuit applies the cathode potential to the reference transistor, and the second applies a static reference voltage to the source of the reference transistor. This feedback mechanism ensures precise sink current control is maintained even at low cathode potentials, preventing current drops while keeping power consumption low.
Solution Approach 2:
The low-side driver circuit is designed to self-regulate the sink current through its internal feedback mechanisms. The servo-control circuits automatically adjust the cathode potential to maintain constant current without external intervention, enabling precise current control at low potentials and thus reducing power consumption while maintaining performance.
3Use of energy by moving object
If the cathode potential is low, then the power consumption is reduced, but the sink current drops below the threshold
Solution Approach 1:
The feedback control through servo-circuits continuously monitors the sink current and adjusts the cathode potential to maintain it above the threshold level. This ensures reliable and stable current control even when operating at low cathode potentials, preventing current drops while minimizing power consumption.
Solution Approach 2:
The circuit incorporates prior cushioning by using the reference transistor and servo-control circuits to preemptively maintain the cathode potential at levels that ensure stable current operation. This preventive mechanism ensures the sink current remains above the threshold before any potential drop occurs, guaranteeing reliable operation at low power consumption levels.
Data Source
AI summary
In an embodiment, a low side driver integrated circuit for a laser diode includes a reference transistor, an output transistor having a gate coupled to a gate of the reference transistor, a first transistor having a gate for receiving a pulsed signal, a drain coupled to a drain of the output transistor and a source coupled to ground, a second transistor, for obtaining a source voltage of the output transistor equal to the source voltage of the reference transistor, a first servo-control circuit for applying a drain voltage of the output transistor to the drain of the reference transistor, and a second servo-control circuit for applying a static reference voltage to the source of the reference transistor.