Laser Diode Driver Precharge Circuit for Low-Grey Bandwidth
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional laser diode drive methods face limitations such as reduced bandwidth with reduced peak current, pulse performance interference between pixels, non-linear load optimization, and the need for optical factory equipment calibration to achieve perfect blacks and high resolution in Laser Phosphor Displays.
Innovation Solution
The method involves increasing the bias current to a threshold level below the actuation level of the laser diode, using a resistor in parallel to charge a capacitance, and employing a precharge pulse method to maintain high bandwidth and prevent pulse interference, thereby simplifying calibration and optimizing driver circuit loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the peak current level is reduced, then the bandwidth of the driver reduces, but reducing peak current is necessary for low grey region operation
Solution Approach 1:
The patent applies preliminary action by pre-charging the laser diode capacitance before the main drive pulse arrives. This pre-charge prepares the circuit in advance, ensuring that when the main pulse comes, the driver maintains high bandwidth response even at low peak current levels. The pre-charge current is applied through a dedicated path that does not load the main driver, thus preserving driver bandwidth while enabling low grey region operation.
2Illumination intensity
If the peak current level is reduced, then bandwidth reduces and rise/fall times slow down, but this makes optical power control difficult in low grey region
Solution Approach 1:
The pre-charge mechanism prepares the laser diode and circuit capacitance in advance, ensuring that when the main drive pulse arrives, the system responds with fast rise and fall times. This preliminary preparation eliminates the sluggish response that would otherwise occur at low peak current levels, maintaining precise optical power control in the low grey region.
Solution Approach 2:
The patent introduces a pre-charge current path as an intermediary mechanism that prepares the system state before the main control pulse. This intermediary action separates the bandwidth-critical main pulse from the capacitance charging function, allowing the main driver to operate at full bandwidth while still enabling low grey region control.
3Stability of the object's composition
If a dc bias current is raised to improve linearity in low grey region, then linearity improves, but the phosphors still receive sufficient illumination resulting in grey black levels
Solution Approach 1:
The patent segments the current delivery into two distinct paths: a pre-charge path that prepares the circuit capacitance without illuminating the phosphor, and a main drive pulse path that controls optical output. This segmentation allows the system to achieve linearity improvement through proper timing and current shaping without the unwanted effect of continuous DC bias illumination on the phosphor.
Solution Approach 2:
The patent uses periodic pulsed action with a pre-charge phase followed by the main drive pulse. This periodic structure replaces the continuous DC bias approach, providing the linearity benefits of prepared circuit state while avoiding continuous phosphor illumination. The pulsed nature ensures black levels remain truly black while maintaining control linearity.
4Manufacturing precision
If pixels are close together, then high resolution is achieved, but the peak level of driver pulse may be affected by previous pulse or pulses
Solution Approach 1:
The pre-charge mechanism ensures that each pixel's drive circuit is prepared in advance with a known initial state, independent of previous pulses. This preliminary preparation resets or stabilizes the circuit capacitance before each main pulse, preventing carryover effects from previous pulses even when pixels are closely spaced and operated at high frequencies.
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 allows for zero 'off' current while maintaining high bandwidth pulse control, reducing 'history effect' between pixels, and simplifying calibration, resulting in improved brightness control and uniformity across the display.
Implementation Method 1
charging a capacitance to a precharge capacitance of a circuit including the laser diode, wherein the precharge capacitance is below a capacitance actuation level of the laser diode
Data Source
AI summary
A method and apparatus to drive a laser diode are disclosed comprising increasing a bias current to the laser diode to a threshold level, wherein the threshold level is below an actuation level of the laser diode and wherein a resistor is placed in parallel to the laser diode, charging a capacitance to a precharge capacitance of a circuit including the laser diode, wherein the precharge capacitance is below a capacitance actuation level of the laser diode; and actuating the laser diode.