29.6 A Digital-Type GaN Driver with Current-Pulse-Balancer Technique Achieving Sub-Nanosecond Current Pulse Width for High-Resolution and Dynamic Effective Range LiDAR System

In automotive applications, short laser pulse {I-{LASER}} widths through GaN FET control methods and effective assurance of accurate {I-{LASER}} are major challenges in highresolution light detection and ranging (LiDAR) systems (top of Fig. 29.6.1). Figure 29.6.1 shows two main laser-diode driver circuits for pulsed LiDAR applications [1]. A well-controlled pulse that accepts the parasitic inductance {L-{stray}} simplifies control in capacitor discharge driver circuit [2]. But, the fixed pulse shape of the {I-{LASER}} results in an ineffective modulation of the pulse width {t-{P}} and limits the distance resolution {l-{P}} (left of Fig. 29.6.1). Under a high pulse repetition frequency (PRF), incomplete pulses and insufficient power will reduce the effective detection range since the {V-{BUS}} is near hundred volts during the off time of each command cycle {T-{command}}. Although the FET control driver [3] with a low supply voltage {V-{supply}} allows complex command sequences, the structure needs a large inductor current in the front-end DC/DC converter throughout the {T-{command}} to ensure sufficient power and high dv/dt transition at {V-{BUS}}, which means extremely low driving efficiency. To further increase the resolution, a lower {V-{BUS}} is applied and the parasitic capacitance gain at the drain {V-{D}} of the GaN FET is smaller. Meanwhile, chip scale packaging or laser diode mounting minimizes {L-{stray}} and significantly reduces rise time {t-{R}} and fall time {t-{F}}, achieving subnanoseconds {t-{P}} and tens of centimeters distance resolution (right of Fig. 29.6.1). Under high speed {V-{command}}, the gate resistor prevents the device being damaged [4], but it limits the switching frequency and increases losses. The adaptive triple-slope gate driver [5] is not free from process, voltage, and temperature (PVT) variations and the falling slope is indeterminate. If a short pulse width is applied to [4] [5], a slight imbalance between {t-{R}} and {t-{F}} will cause the average laser current {I-{LASER, Avg}} to change, which changes {V-{BUS}} and distorts {I-{LASER}}, and then DC/DC takes a long time to regulate {V-{BUS}}. Therefore, this paper proposes a digital-type GaN driver with a laserdiode-peak-current-correction (LDPCC) loop and a current-pulse-balancer (CPB) loop for LiDAR systems. Even with parasitic resistance changes in the power path, the LDPCC loop ensures a constant {I-{LASER}} by adjusting the {V-{BUS}} over a wide range of PRF (maximum 200MHz) to enhance pulse-to-pulse reliability. In addition, with the proposed asynchronous-binary-driver (ABD), the CPB loop optimizes driver speed, and reduces pulse width to 0.9ns. To prevent {V-{BUS}} transient, the CPB balances {I-{LASER}} rise and fall times in tens of nanoseconds.