High-resolution Millimeter-wave Impulse-based MIMO 3D Imaging Radar in Silicon
Master of Science
The research on millimeter-wave (mm-wave) silicon-based integrated 3D imaging radar has gained tremendous attention in academia over the past decade. Compared with conventional 2D imaging, 3D imaging captures both 1D depth information and 2D intensity maps. Impulse-based 3D imaging radar can also obtains more constitutional information of objects, like spectroscopy, so as to potentially have material identification functionality with 3D imaging simultaneously. The main objectives in the roadmapping of silicon integrated 3D imaging radar are higher image resolution, a larger image range and shorter acquisition time. With the dramatically improved performance of silicon transistors, mm-wave circuits using CMOS and BiCMOS technologies can generate picosecond-level impulses but with small RF power. Shorter impulses provide higher image resolution, but small RF power limits image range. Spatially coherent impulse combining from multiple silicon circuits is the solution to this problem. Compared with narrow-band phased-arrays that perform only 2D spatial filtering and have range-ambiguity problems, impulse-radiating arrays are capable of performing 3D spatial filtering that enhances the imaging sensitivity of a certain point in 3D space without sacrificing image resolution. Therefore, impulse-based MIMO imaging radar can achieve both high resolution and a large image range simultaneously. In this present work, a 60ps impulse radiator with an on-chip antenna is implemented in the IBM 130nm SiGe BiCMOS process technology. The impulse radiator is the core element of the synthetic arrays that are used to perform 3D imaging in this thesis. A pulsed-VCO-based architecture is designed based on an asymmetric cross-coupled pulsed VCO to convert a digital input signal to radiated impulses. The deliberate asymmetry in the pulsed VCO is introduced to minimize the timing jitter of the radiated impulses in order to achieve spatially coherent impulse combining with high efficiency. The radiated impulses have a record RMS jitter of 178fs with 64 averaging when the input trigger signal has a RMS jitter of 150fs. Two widely spaced impulse radiators are used to perform spatially coherent impulse combining with an efficiency of 98.7%. As the first step in demonstrating impulse-based MIMO 3D imaging radar, in this work, custom synthetic array imaging systems were built based on the proposed silicon-based integrated impulse radiator. 3D imaging of metallic and dielectric objects (rocks immersed in oil) have been performed successfully. A depth accuracy of 27um, a depth resolution of 9mm and a lateral resolution of 8mm at 10cm distance in the air have been achieved. To the author’s knowledge, this work demonstrates the first high-resolution 3D images that are generated by using synthetic array imaging systems based on a fully-integrated impulse radiator in silicon. Future work includes implementing fully integrated impulse transceivers and fully integrated impulse-based MIMO 3D imaging radar with independent time-delay controls.
3D imaging; BiCMOS; Impulse radiator