Integrated Electronic and Optoelectronic Circuits and Devices for Pulsed Time-of-flight Laser Rangefinding

The main focus of this work concerned with the development of integrated electronic and optoelectronic circuits and devices for pulsed time-of-flight laser rangefinding is on the construction of the receiver channel, system level integration aimed at realisation of the laser radar module and in integration of all the receiver functions of laser radar on one chip. Since the timing discriminator is a very important part of a pulsed time-of-flight laser rangefinder, two timing discrimination methods are presented and verified by means of circuit implementations, a leading edge discriminator and a high-pass timing discriminator. The walk error of the high-pass timing discriminator is ±4 mm in a dynamic range of 1:620 and the uncompensatable walk error of the leading edge discriminator is ±30 mm in a dynamic range of 1:4000. Additionally a new way of combining the timing discriminator with time interval measurement is presented which achieves a walk error of ±0.5 mm in a dynamic range of 1:21. The usability of the receiver channel chip is verified by constructing three prototypes of pulsed TOF laser radar module. The laser radar achieves mm-level accuracy in a measurement range from 4 m to 34 m with non-cooperative targets. This performance is similar to that of earlier realisations using discrete components or even better and has markedly reduced power consumption and size. The integration level has been increased further by implementing a photodetector on the same chip as the rest of the receiver electronics. The responsivity of the photodetector is about 0.3 A/W at 850 nm wavelength and the noise of the receiver is reduced by a factor of about two relative to realisations using an external photodetector, because of the absence of parasitic capacitances and inductances caused by packages, PCB wiring, bond wires and ESD and I/O cell structures. The functionality of a multi-channel pulsed TOF laser radar chip is demonstrated using the photodiode structure investigated here. The chip includes four photodetectors with receiver channels and a three-channel time-to-digital converter. The chip together with external optics and a laser pulse transmitter enables distances to be measured in three directions with a single optical pulse, thus showing the feasibility of implementing all the receiver functions of a pulsed time-of-flight imager on a single chip using a current semiconductor process.