Resonant Laser Diode Pulse Circuit With Low-Inductance Commutation
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Solution Overview
Problem
Existing pulse generator circuits for laser diode arrays face challenges in generating high-intensity, narrow pulses with precise control over pulse duration and rise/fall times due to parasitic inductances and spurious activation of non-selected diodes, especially in common cathode configurations, which limits their effectiveness in applications like LIDAR systems.
Innovation Solution
A pulse generator circuit design that excludes energy storage capacitance from the commutation loop, using a resonant tank driven by a Gallium Nitride switch to generate sinusoidal currents, allowing for fast commutation and control of pulse current amplitude, with separate switches for each laser diode to prevent spurious activation and reduce parasitic inductance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If energy storage capacitance is included in the commutation loop, then energy storage is provided, but parasitic inductance increases and pulse duration control precision deteriorates
Solution Approach 1:
The energy storage capacitance is extracted from the commutation loop and placed in a separate charging path. This removes the source of parasitic inductance from the critical commutation path while preserving energy storage functionality through the inductive element in the charging path.
Solution Approach 2:
The circuit is segmented into two separate paths: a charging path with energy storage capacitance and inductive element, and a commutation loop without energy storage components. This segmentation isolates parasitic inductance sources from the pulse generation path, enabling precise pulse duration control.
2Duration of action of moving object
If conventional switching is used, then circuit simplicity is maintained, but rise and fall times are too long (1ns) to generate narrow pulses
Solution Approach 1:
The circuit uses resonant oscillation at a specific frequency to generate periodic current flow through the laser diode. By controlling the resonant frequency and Q-factor, narrow pulses with precise duration control are achieved, transforming continuous switching into controlled periodic energy delivery.
Solution Approach 2:
The circuit exploits electrical resonance analogous to mechanical vibration, where the inductive and capacitive elements oscillate at their natural frequency. This resonant oscillation produces the desired narrow pulse shape with fast rise and fall times, replacing conventional linear switching mechanisms.
3Device complexity
If common cathode configuration is used, then device integration is improved, but spurious activation of non-selected diodes occurs
Solution Approach 1:
Each laser diode channel is equipped with its own dedicated switching element and associated inductive element, creating locally optimized commutation paths. This local differentiation ensures that only the selected diode receives the resonant pulse current, eliminating spurious activation while maintaining integration benefits.
4Object-affected harmful factors
If interconnection length is reduced, then parasitic inductance decreases, but circuit layout complexity increases
Solution Approach 1:
Multiple functional elements (switching elements, inductive elements, and laser diodes) are merged into an integrated circuit structure where interconnections are minimized and optimized. This integration reduces parasitic inductance by eliminating external traces and connectors while managing layout complexity through systematic design rules.
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 design achieves fast switching with rise and fall times in the order of 100ps, enabling controlled generation of pulses with current amplitudes in the tens of amperes, reduces parasitic inductance, and allows for lower supply voltage, effectively addressing the limitations of conventional systems.
Implementation Method 1
a resonant tank (Lr, Cr) is provided, the resonant tank comprising a series connection of an inductance (Lr) and a capacitance (Cr)
Implementation Method 2
using a Gallium Nitride switch to generate sinusoidal currents, allowing for fast commutation
Data Source
Figure 1~1A
Figure 2
Figure 2A~2E
AI summary
A pulse generator circuit, for driving an array of laser diodes (LD_1, ..., LD_n) in a LIDAR system, for instance, comprises an LC resonant circuit (Lr, Cr) coupled between a first node (12) and a reference node (GND) as well as charge circuitry (16) configured to charge the capacitance (Cr) in the LC resonant circuit (Lr, Cr). A first electronic switch (S1) is coupled between the first node (12) and the reference node (GND), and one or more second electronic switches (S2_1, ..., S2_n) are coupled between the first node (12) and respective drive nodes (121, ..., 12n) in turn configured to be coupled to respective electrical loads (LD_1, ..., LD_n). The circuit comprises drive circuitry (18, 182_1, ..., 182_n; 201, 202, 203) configured to repeat pulse generation cycles comprising: closing the first electronic switch (S1), to enable the LC resonant circuit (Lr, Cr) to oscillate with an increasing current flowing in the inductance (Lr) therein, in response to the current flowing in the inductance (Lr) reaching a threshold value, opening the first electronic switch (S1) wherein, as a result of one second electronic switch (S2_1, ..., S2_n) being closed for a respective pulse duration time (Ton_S2_1, ..., Ton_S2_n), the current in the inductance (Lr) is commutated towards the aforesaid second electronic switch (S2_1, ..., S2_n) and the respective drive node (121, ..., 12n), opening the at least one second electronic switch (S2_1, ..., S2_n) at the expiration of said respective pulse duration time (Ton_S2_1, ..., Ton_S2_n).