Employing simplified resistance–inductance–capacitance equivalent circuits to analyze and confirm a gallium nitride-based current linear regulator for laser diode controls

In this study, a gallium nitride (GaN)-based current linear regulator (GBCLR) was developed and implemented to control 450 nm laser diodes, and the laser beams could be concentrated by the fiber optic cable. The GBCLR consisted of a GaN high-electron-mobility transistor (HEMT) and wide-bandwidth operational amplifiers. When using the GBCLR, the driving current of the laser diode can be operated in either continuous constant-current mode for a continuous-wave laser or pulse-width modulation mode to achieve a short-pulsed time laser. In the high-frequency pulse-width modulation mode of the GBCLR, the parasitic elements of the GaN HEMT, laser diodes, and printed circuit board must be evaluated because they can cause the gate–source voltage to overshoot and influence the laser operating current; however, few studies have analyzed these phenomena. This study adopted the complex equivalent circuits of the GaN HEMT and laser diode to establish a complete GBCLR simulation schematic with the same physical configurations and packages; thus, the GBCLR simulation circuit was able to obtain the critical simulation waveform, and the unknown parasitic element parameters could be inferred for the GBCLR design. However, the complete equivalent circuit of the GBCLR was quite complex; therefore, this study proposed a new simplified model and method to demonstrate that this method was practicable. Finally, a GBCLR prototype was developed, and the critical experimental waveforms were measured to verify the simulations and analyses.