Wide Dynamic Range CMOS Receiver Techniques for a Pulsed Time-of-Flight Laser Rangefinder

A pulsed time-of-flight (TOF) laser range finding system resolves the distance by measuring the transit times of short and energetic laser pulses sent towards the target and then reflected back to the radar receiver. The distance can be calculated using the known speed of light (~30 cm/ns). A TOF system utilizing the envelope detection of the echo pulse (linear detection) is more robust to the interferences introduced by background light (e.g., Sunlight) than single-photon detection-based systems, which is an essential advantage in outdoor applications. However, in this type of laser radar, the strength of the reflected echo can vary in an extensive range of 1:10,000 or more, depending on the distance and the target properties. This variation introduces a considerable systematic error (timing walk error) to the measured time interval.

The aim of this thesis work was to develop receiver electronics for this kind of pulsed Time-of-Flight (TOF) laser radar. In particular, the receiver electronics were intended to cover a wide dynamic range of at least 1:10,000 of the input optical pulses with a high level of accuracy and precision without separate timing walk error post-compensation or gain control techniques. The timing discrimination scheme proposed is based on the conversion of the unipolar optical pulse to a bipolar current signal immediately at the input of the optical receiver and marking the zero-crossing point of the bipolar signal as the timing point. It is shown that the proposed timing discrimination technique can cover a dynamic range of more than 1:50,000 of input echo amplitudes with a residual walk error of ±100 ps (equivalent to 1.5 cm in distance). The proposed technique is expected to suit well for long-range outdoor applications of pulsed TOF laser radars, i.e., traffic monitoring, autonomous driving and robotics, for example.