Design of a Sub-harmonically Injection-Locked TDC Array for Space Applications

Abstract

Over the past two decades, successful orbital missions undertaken to map the Earth, Mars, Mercury and the Moon have proved that light detection and ranging (LIDAR) measurements are powerful catalysts in space exploration. LIDAR based technologies help evaluate the topography of a land and its surface features along with gathering data to understand the habitability of planetary bodies by creating depth maps. In systems which involve time-of-flight (TOF) techniques, depth maps are created by sending a laser pulse to a target and detecting the reflected pulse by an appropriate photodetector. The detected signal is then supported by electronic circuitry which records the TOF and estimates the distance between the target and the laser source. Bound by the amount of measurements that a LIDAR should perform, there are many technical challenges due to varying system requirements like payload constraints, operating conditions in space, instrument size and power budget. In this thesis, two major tasks were carried out, targeting imaging application in Ultraviolet (UV) and visible spectral range. A front-end readout circuit specifically designed for III-Nitride based UV avalanche photodiodes (APDs) is presented. Specific challenges of the readout are discussed in detail followed by measurement results. Further, a time-correlated single-photon counting (TCSPC) based TOF sensor is presented with silicon based single-photon avalanche diodes (SPADs) at the detector end. The sensor is fabricated in a 65 nm 3D IC CMOS technology, where the SPADs are integrated in the top tier and the processing electronics in the bottom tier. The 8x8 time- to-digital converter (TDC) array used to measure the TOF achieves a resolution of about 60 ps, thus providing a minimum measurable range of about 9 mm. The maximum achievable dynamic range is 150 m. The array incorporates concepts like coupling and injection locking to minimise the overall system jitter and provide a superior phase noise performance.