At Under a Dollar, New GaN Laser Drivers Indicate Ubiquitous LiDAR Is On Its WayFebruary 23, 2021 by Jake Hertz
Bringing indirect time-of-flight (IToF) to cell phones, tablets, drones, and even toy robots may now be possible with a highly-integrated GaN laser driver IC.
While LiDAR and direct time-of-flight devices often shine in the spotlight for their role in autonomous vehicles, indirect time-of-flight technology is making headway in consumer applications, as we see in autonomous vacuums.
While direct time-of-flight LiDAR is most commonly associated with ADAS, indirect time-of-flight is making its way into consumer devices that only require short-range mapping. Image (modified) used courtesy of EPC
Many technologies hinge on improvements in LiDAR, but LiDAR itself hinges on improvements at an even lower component level. Specifically, advances in GaN transistors have proven integral to developing highly-sophisticated LiDAR systems.
A leader in the field, Efficient Power Conversion (EPC) has been developing GaN for LiDAR for years but has now taken its work a step further, bringing accessible GaN-based LiDAR technology into a consumer arena. All About Circuits spoke with EPC CEO Alex Lidow to hear about the company's newest laser driver IC and how he thinks it will revolutionize LiDAR.
Why GaN Is the Way to Go With LiDAR
LiDAR systems send pulses of light out from a vertical-cavity surface-emitting laser (VCSEL), requiring high-power electrical control that’s very fast with tight rise and fall times. This is one of the reasons that GaN benefits LiDAR systems. Offering significantly faster switching times than silicon FETs, GaN allows for short pulse widths at high currents.
This feature is vital for LiDAR since shorter pulse width leads to higher resolution while a high pulse current allows LiDAR systems to see further.
GaN offers higher resolution LiDAR solutions than silicon. Screenshot used courtesy of EPC
GaN also offers better thermal performance. "The thermal limit is always set by the laser," Lidow remarks. "You run the laser to its thermal limit and when that occurs, these gallium nitride devices are not even warm."
Lidow notes that while you can make a LiDAR system with silicon, the performance of these devices is no better than radar.
"A bad LiDAR system is not worth more than a good radar system," Lidow says. "But a good radar system is always going to be cheaper today because there are so many of them out there."
The Trouble With Conventional LiDAR Drivers
In a conventional LiDAR system, you would typically find a silicon driver IC, which drives a GaN FET and, in turn, pumps current into the LiDAR laser system.
Interfacing these components turns out to be one of the limiting factors of the whole system since the inductance in the interconnects severely slows down the control signals. This means slower rise and fall times and ultimately wider pulse widths—meaning poorer resolution.
Conventional LiDAR system. Screenshot used courtesy of EPC
"The problems come from the fact that the silicon driver is interfaced to the GaN FET. That becomes the rate-limiting part of this whole circuit," Lidow explains. "First of all, silicon is not as fast as GaN, but secondly, there is inductance in (the interconnect) between these two. That inductance is the thing that slows the signal down. And we're talking about tens of picoseconds.”
A New Integrated Laser Driver for Indirect Time-of-Flight
EPC's solution to this problem: integration.
The company's new product, the EPC21601, integrates a GaN driver with a GaN FET onto a single IC, eliminating the interconnect inductance and removing the rate-limiting aspect of conventional LiDAR circuits. EPC envisions the 10 A, 40 V laser driver IC being useful in indirect time-of-flight (IToF) applications.
Coming in at 1.5 mm x 1.0 mm, the new IC is said to provide a solution that is 36% smaller on a PCB than conventional solutions.
A conventional LiDAR system with a silicon driver IC vs. EPC's integrated LiDAR system with a GaN driver and GaN FET in a single IC. Image (modified) used courtesy of EPC
According to EPC, this integrated solution has measurable metrics of speed and performance improvement, too. “It reduces the inductance from about 50 picohenries to just a couple of picohenries," Lidow says. "Pulses are 1.4 nanoseconds wide, where the fall time is 245 picoseconds and the rise time is 470 picoseconds, which is getting near to the limit of your ability to measure.”
By integrating LiDAR driving circuitry onto a single IC, EPC is aiming to make LiDAR more affordable and accessible while raising the bar for performance. With the chip costing about $1, Lidow predicts that the race for affordable LiDAR may be over, and sophisticated LiDAR will start to creep up in products across the board.
Functional block diagram of the EPC21601. Image used courtesy of EPC
Elaborating on possible use cases, Lidow expressed, “What I'm particularly excited about is that now you don't have to worry about multiple chips, and you can get them for under a dollar."
"This laser driver IC opens up the consumer market, and it blows open the use of three-dimensional awareness and LiDAR through cell phones, tablets, drones, or anything else you want. If you're making a toy robot, you can now put a LiDAR system in it.”