Cmos Based Lensless Imaging Systems And Support Circuits
While much progress has been made in various fields of study in past few decades, leading to better understanding of science as well as better quality of life, the role of optical sensing has grown among electrical, chemical, optical, and other physical signal modalities. As an example, fluorescent microscopy has become one of the most important methods in the modern biology. However, broader implementation of optical sensing has been limited due to the expensive and bulky optical and mechanical components of conventional optical sensor systems. To address such bottleneck, this dissertation presents several cost-effective, compact approaches of optical sensor arrays based on solid state devices that can replace the conventional components. As an example, in chapter 2 we demonstrate a chip-scale (<1 mm2 ) sensor, the Planar Fourier Capture Array (PFCA), capable of imaging the far-field without any off-chip optics. The PFCA consists of an array of angle-sensitive pixels manufactured in a standard semiconductor process, each of which reports one component of a spatial two-dimensional (2D) Fourier transform of the local light field. Thus, the sensor directly captures 2D Fourier transforms of scenes. The effective resolution of our prototype is approximately 400 pixels. My work on this project  includes a circuit design and layout and the overall testing of the imaging system. In chapter 3 we present a fully integrated, Single Photon Avalanche Detector (SPAD) using only standard low- voltage (1.8V) CMOS devices in a 0.18m process. The system requires one highvoltage AC signal which alternately reverse biases the SPADs into avalanche breakdown and then resets with a forward bias. The proposed self-quenching circuit intrinsically suppresses after-pulse effects, improving signal to noise ratio while still permitting fine time resolution. The required high-voltage AC signal can be generated by resonant structures and can be shared across arrays of SPADs . An ideal light sensor to provide the precise incident intensity, location, and angle of incoming photons is shown in chapter 4. Single photon avalanche diodes (SPADs) provide such desired high (single photon) sensitivity with precise time information, and can be implemented at a pixel scale to form an array to extract spatial information. Furthermore, recent work has demonstrated photodiode-based structures (combined with micro-lenses and diffraction gratings) that are capable of encoding both spatial and angular information of the incident light. In this chapter, we describe the implementation of such grating structure on SPAD to realize a pixel-scale angle-sensitive single photon avalanche diode (A-SPAD) using a standard CMOS process. While the underlying SPAD structure provides the high sensitivity, the diffraction gratings consisting of two sets of metal layers offers the angle-sensitivity. Such unique combination of the SPAD and the diffraction gratings expand the sensing dimensions to pave a path towards a lens-less 3-D imaging and a light-field timeof-flight imaging. In chapter 5, we present a 72 x 60, angle-sensitive single photon avalanche diode (A-SPAD) array for lens-less 3-D fluorescent life time imaging. A-SPAD pixels are comprised of (1) a SPAD to resolve precise timing information, to reject high-powered UV stimulus, and to map the lifetimes of different fluorescent sources and (2) integrated diffraction gratings on top of the SPAD to extract incident angles of incoming light, enabling 3-D localization at a micrometer scale. The chip presented in this work also integrates pixel-level counters as well as shared timing circuitry, and is implemented in conventional 180nm CMOS technology without any post-processing. Contact-based read- out from a revolving MEMS accelerometers is problematic therefore contactless (optical) read-out is preferred. The optical readout requires an image sensor to resolve nanometer-scale shifts of the MEMS image. Traditional imagers record on a rectangular grid which is not well-suited for efficiently imaging rotating objects due to the significant processing overhead required to translate Cartesian coordinates to angular position. Therefore, in chapter 6 we demonstrate a high-speed ( 1kfps), circular, CMOS imaging array for contact-less, optical measurement of rotating inertial sensors. The imager is designed for real-time optical readout and calibration of a MEMS accelerometer revolving at greater than 1000rpm. The imager uses a uniform circular arrangement of pixels to enable rapid imaging of rotational objects. Furthermore, each photodiode itself is circular to maintain uniform response throughout the entire revolution. Combining a high frame rate and a uniform response to motion, the imager can achieve sub-pixel resolution (25nm) of the displacement of micro scale features. In order to avoid fixed pattern noise arising from non-uniform routing within the array we implemented a new global shutter technique that is insensitive to parasitic capacitance. To ease integration with various MEMS platforms, the system has SPI control, on-chip bias generation, sub-array imaging, and digital data read-out. My work on this project  includes a circuit design and lay- out and some testing including, a FPGA based controller design of the imaging system. In the previous chapters, compact and cost effective imaging sys- tems have been introduced. Those imaging systems show great potential for wireless implantable systems. A power rectifier for the implant provides a volt- age DC power with a small inductor, for small volume, from a small AC voltage input. In the last chapter we demonstrate an inductively powered, orthogonal current-reuse multi-channel amplifier for power-efficient neural recording. The power rectifier uses the input swing as a self-synchronous charge pump, making it a fully passive, full-wave ladder rectifier. The rectifier supplies 10.37[MICRO SIGN]W at 1.224V to the multi-channel amplifier, which includes bias generation. The prototype device is fabricated in a TSMC 65nm CMOS process, with an active area of 0.107mm2 . The maximum measured power conversion efficiency (PCE) is 16.58% with a 184mV input amplitude. My work on this project  in- cludes the rectifier design and overall testing to combine "orthogonal currentreuse neural amplifier" designed by Ben Johnson.
Angle sensitive SPAD; SQFBR; PFCA
Molnar, Alyosha Christopher
Lal, Amit; Afshari, Ehsan
Ph.D. of Electrical Engineering
Doctor of Philosophy
dissertation or thesis