Fast GaN transistor drives laser in time-of-flight range sensor eval board

The intended application is ‘time-of-flight’ range measurement, and the chosen GaN transitor (EPC2216 ) is AEC Q101-qualified, allowing the circuit to be used in automotive lidar projects.

A novel aspect of this board is the ability to mount a wide variety of lasers via simple small PCB-based interposers that can be soldered onto the 5x5mm square of four copper pads (right hand side of photo).

The interposers are supplied on a snap-off strip (left). Under each is a 2 x 2 pattern to match the evaluation board’s 5x5mm footprint. According to EPC, the interposer selecton board “is revised as needed to accommodate
new lasers and other loads as needed”.

“The printed circuit board is designed to minimise the power loop inductance while maintaining mounting flexibility for the laser diode or other load,” according to ECP. “It includes multiple on-board passive probes for voltages, and is equipped with MMCX connections for input and sensing.”

The speed of the driver and FET means that turn-on can be as fast at 500ps and turn-off can be in 250ps, even at ~10A.

Input command pulses are coupled in through a 50Ω terminated MMCX, which is followed by a logic level translator (shipped, tset for 3.3V logic, but modifiable for other levels (differential drive is also possible).

After the level translator, the input pulse goes through a narrow pulse generator circuit, set to ~5ns when shipped but variable across 1.2 to 20ns using an on-board trimpot. The lower limit set by the on-board LMG1020 gate driver IC.

The power feed to the board needs to be 15V.

As well as laser diode driving, said the firm, it can also be used for other applications requiring a ground-referenced eGaN FET – Class E amplifiers, for example.

The accompanying instruction manual is clearly written and worth a look if you are tempted.