High speed and intensity laser diode drivers for Time-of-Flight 3D ranging and Pico-Projectors

In the last decade, the ability to drive lasers with high frame-rate (higher than standard video-rate), with very faint illumination, has become more and more important in many fields, like ambient surveillance, road safety, identification of people and objects, biomedical imaging, studies on physics of materials as well as commercial applications such as gaming, laser-based projection and augmented virtual reality glasses. There is a growing interest in devices capable of projecting or acquiring high framerate 2D or 3D videos. This work presents the design of a 4-channel integrated laser diode driver (LDD) fabricated in 160 nm BCD technology for a low-power pico-projector application based on micro-electromechanical systems (MEMS) micro-mirrors and the design of a high-power and intensive single chip LDD in the same technology for direct time of flight (TOF) measurement in Light Detection and Ranging (LiDAR) application. The embedded 10-bit current DAC in pico-projector LDD known as video DAC, can produce 300MHz sharp current pulses with 1ns rise/fall time, less than 7% overshoot, 3-4ns settling time while the full-scale range (FSR) is also programmable through a static 10-bit current DAC, known as scale DAC, in the range of 160uA up to 160mA. These performances are guaranteed thanks to the novel active bootstrap presented in this work. TOF LDD, as the second part of this Ph.D. thesis, can produce a fully programmable sharp current pulses up to 20A with less than 1ns duration and a repetition rate of 40MHz. to reach such high performances, a new driving topology is proposed which has brought new challenges in the design that must be mitigated by innovative solutions. ‎Chapter 1 illustrates a general introduction about both applications, pico-projection and time of flight measurements, focusing on the lase driving part and introducing well-known solutions, their drawbacks and possible improvements as would be explained in detail in this work. ‎Chapter 2 presents a brief overview of the laser principles, specifically the semiconductor laser diode operation. This section is written to be more generic to cover both applications, but the main focus is on the ToF application as it is more sensitive to Laser behavior due to the high-frequency requirements. It gives a fundamental background about the laser operation and behavior according to the driving pulse, threshold current, temperature variation, and current pulse shapes. ‎Chapter 3 focuses on the pico-projection LDD. The operation principle in system level and the laser driving role in such a system. The high-frequency compatibility, low power, high range FSR programmability, dynamic performances such as rise time, fall time, settling time are the challenges of the design that must be studied carefully. The solutions for such challenges end up with innovative solutions that are illustrated in detail within this chapter. The simulation and measurement results are shown in this chapter for each dedicated block. ‎Chapter 4 focuses on the time of flight LDD. The dToF principle and its differences with respect to indirect ToF (iToF) are well described and its distinct design considerations such as optical pulse width, repetition rate, rise time, optical power are clarified as design challenges for such LDD. To improve the conventional laser driving approach, which is a limiting point to get further improvement in the dToF specs, a new driving topology is introduced. The new topology has some challenging drawbacks that require innovative solutions to deal with, such as, clamping circuit, PVT compensated monostable, eye-safety fault detection and out sync drift-less level shifter to drive TDC. In this chapter, the proposed solutions and their validations are described in detail and testified by means of simulations.

In the last decade, the ability to drive lasers with high frame-rate (higher than standard video-rate), with very faint illumination, has become more and more important in many fields, like ambient surveillance, road safety, identification of people and objects, biomedical imaging, studies on physics of materials as well as commercial applications such as gaming, laser-based projection and augmented virtual reality glasses. There is a growing interest in devices capable of projecting or acquiring high framerate 2D or 3D videos. This work presents the design of a 4-channel integrated laser diode driver (LDD) fabricated in 160 nm BCD technology for a low-power pico-projector application based on micro-electromechanical systems (MEMS) micro-mirrors and the design of a high-power and intensive single chip LDD in the same technology for direct time of flight (TOF) measurement in Light Detection and Ranging (LiDAR) application. The embedded 10-bit current DAC in pico-projector LDD known as video DAC, can produce 300MHz sharp current pulses with 1ns rise/fall time, less than 7% overshoot, 3-4ns settling time while the full-scale range (FSR) is also programmable through a static 10-bit current DAC, known as scale DAC, in the range of 160uA up to 160mA. These performances are guaranteed thanks to the novel active bootstrap presented in this work. TOF LDD, as the second part of this Ph.D. thesis, can produce a fully programmable sharp current pulses up to 20A with less than 1ns duration and a repetition rate of 40MHz. to reach such high performances, a new driving topology is proposed which has brought new challenges in the design that must be mitigated by innovative solutions. ‎Chapter 1 illustrates a general introduction about both applications, pico-projection and time of flight measurements, focusing on the lase driving part and introducing well-known solutions, their drawbacks and possible improvements as would be explained in detail in this work. ‎Chapter 2 presents a brief overview of the laser principles, specifically the semiconductor laser diode operation. This section is written to be more generic to cover both applications, but the main focus is on the ToF application as it is more sensitive to Laser behavior due to the high-frequency requirements. It gives a fundamental background about the laser operation and behavior according to the driving pulse, threshold current, temperature variation, and current pulse shapes. ‎Chapter 3 focuses on pico-projection LDD. The operation principle in system level and the laser driving role in such a system. The high-frequency compatibility, low power, high range FSR programmability, dynamic performances such as rise time, fall time, settling time are the challenges of the design that must be studied carefully. The solutions for such challenges end up with innovative solutions that are illustrated in detail within this chapter. The simulation and measurement results are shown in this chapter for each dedicated block. ‎Chapter 4 focuses on the time of flight LDD. The dToF principle and its differences with respect to indirect ToF (iToF) are well described and its distinct design considerations such as optical pulse width, repetition rate, rise time, optical power are clarified as design challenges for such LDD. To improve the conventional laser driving approach, which is a limiting point to get further improvement in the dToF specs, a new driving topology is introduced. The new topology has some challenging drawbacks that require innovative solutions to deal with, such as, clamping circuit, PVT compensated monostable, eye-safety fault detection and out sync drift-less level shifter to drive TDC. In this chapter, the proposed solutions and their validations are described in detail and testified by means of simulations.