Resonant H-Bridge Laser Driver Circuit for High Current Nanosecond Pulses
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Solution Overview
Problem
Existing laser diode driver circuits struggle to achieve high current levels at narrow pulse widths, particularly in long-range LIDAR applications, often requiring larger transistor sizes and limited by the relationship between pulse width and power, which restricts the ability to generate high-intensity, short pulses for accurate distance measurement while adhering to eye safety limits.
Innovation Solution
The resonant H-bridge laser diode circuit topology utilizes parasitic inductors and an external capacitor to create a resonant circuit in parallel with the load, enabling the generation of pulse widths from 1 nsec to 10 nsec, allowing for higher current levels at narrower pulse widths using smaller transistors, and allowing the voltage across the load to exceed the supply voltage, thereby achieving higher di/dt without the need for large switches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional laser diode driver circuits are used, then the circuit can operate with standard transistor sizes, but high current levels at narrow pulse widths cannot be achieved
Solution Approach 1:
The patent implements a resonant circuit that dynamically oscillates at a specific frequency, allowing the circuit to naturally generate narrow pulse widths through the resonant oscillation of the LC tank circuit. This dynamic behavior enables high current levels at narrow pulse widths without requiring oversized transistors, as the resonant oscillation inherently limits the pulse duration while maintaining peak current.
Solution Approach 2:
The patent changes the operating parameters by introducing a resonant frequency determined by the inductance and capacitance values. By adjusting the LC resonant parameters, the circuit can achieve different pulse widths and current levels, breaking the conventional trade-off between current magnitude and pulse duration that limits standard driver circuits.
2Power
If larger transistor sizes are used to achieve high current levels, then the current capability is improved, but the device size and power consumption increase
Solution Approach 1:
The resonant circuit uses the natural oscillation dynamics of the LC tank to generate high current pulses. The inductor and capacitor work together to create a self-sustaining oscillation that delivers high peak currents without requiring large transistor sizes. The resonant frequency and Q-factor of the tank circuit determine the pulse characteristics, allowing standard-sized transistors to achieve high current levels that would otherwise require much larger devices.
3Adaptability or versatility
If pre-charging architectures are used, then the circuit can be simplified, but pulse widths from 1 nsec to 10 nsec cannot be obtained
Solution Approach 1:
The patent achieves wide pulse width adjustment (1 nsec to 10 nsec) by varying the resonant circuit parameters, specifically the inductance and capacitance values. The resonant frequency formula f = 1/(2π√LC) shows that by changing L or C, the pulse width can be precisely controlled across the desired range. This parameter-based control provides versatility without requiring complex multi-architecture switching.
Solution Approach 2:
The resonant circuit provides inherent dynamic control over pulse characteristics through its oscillation behavior. The natural ringing of the LC tank circuit produces pulses whose width is determined by the damping and Q-factor, allowing continuous adjustment across a wide range without discrete architecture changes. This dynamic approach simplifies the overall design compared to switching between different pre-charging architectures.
4Speed
If the voltage across the load is limited to the supply voltage, then the circuit operation is simplified, but higher di/dt cannot be achieved
Solution Approach 1:
The resonant circuit dynamically generates voltage swings that exceed the supply voltage through the inductive kickback effect. When the switching transistor turns off, the collapsing magnetic field in the inductor generates a voltage spike that adds to the supply voltage, creating peak voltages significantly higher than the rail voltage. This dynamic voltage multiplication enables high di/dt without requiring complex voltage control circuits or multiple supply rails.
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 solution enables the generation of high-intensity, short laser pulses necessary for accurate long-range distance measurement while reducing the size and power requirements of the transistors, allowing for more efficient and safer operation within eye safety limits.
Implementation Method 1
The resonant H-bridge topology of this disclosure can utilize parasitic inductors that are unavoidable in conjunction with an external capacitor to create a resonant circuit in parallel with the load
Data Source
AI summary
A resonant H-bridge laser driver circuit topology is described that can achieve high current levels at narrow pulse widths while using smaller transistor sizes. The resonant H-bridge topology can utilize parasitic inductors in conjunction with an external capacitor to create a resonant circuit in parallel with the load.