Simulation and implementation of a two-mode-operation transconductance regulator with a Gallium Nitride High-Electron-Mobility Transistor

A GaN high-electron-mobility transistor (HEMT) with a wide-bandwidth operational amplifier was employed to implement and develop a two-mode-operation transconductance regulator (TMOTR). Using the proposed TMOTR, the laser diode can be operated in either the continuous constant-current mode to fulfill a continuous-wave laser or pulse-width modulation (PWM) to achieve a narrow-pulsed laser. When the laser diode is operated in PWM mode and at high frequency, the parasitic elements of the GaN HEMT, laser diodes, printed circuit board, and power wires must be considered, because these parasitic elements can influence the rising-edge slope of the laser diode driving current resulting in narrow-pulsed duty cycle diminution. This study applied equivalent circuit models of a GaN HEMT and laser diode to determine the parasitic parameters in accordance with device packages; therefore, the simulation circuit of the TMOTR with its parasitic element could be implemented to obtain the critical simulation waveform. The parasitic element parameters of the laser diode and GaN HEMT were calculated in detail and used simulation software to verify the TMOTR's characteristics. Finally, the TMOTR prototype was implemented, and the experimental waveforms were measured to confirm simulations, equivalent circuits, and dynamic responses; the GaN HEMT and MOSFET were experimented to compare their differences.