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 ILASER results in an ineffective modulation of the pulse width tP and limits the distance resolution lP(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 VD 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 tPand 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 ILASER by adjusting the VBUS 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 ILASER rise and fall times in tens of nanoseconds.