Charbel G. Rizk

Flexible readout and integration sensor (FRIS): a bio-inspired, system-on-chip, event-based readout architecture

We present a bio-inspired system-on-chip focal plane readout architecture which at the system level, relies on an event based sampling scheme where only pixels within a programmable range of photon flux rates are output. At the pixel level, a one bit oversampled analog-to-digital converter together with a decimator allows for the quantization of signals up to 26 bits. Furthermore, digital non-uniformity correction of both gain and offset errors is applied at the pixel level prior to readout. We report test results for a prototype array fabricated in a standard 90nm CMOS process. Tests performed at room and cryogenic temperatures demonstrate the capability to operate at a temporal noise ratio as low as 1.5, an electron well capacity over 100Ge-, and an ADC LSB down to 1e-.

A bio-inspired event-driven digital readout architecture with pixel-level A/D conversion and non-uniformity correction

We present a bio-inspired readout integrated circuit (ROIC) for visible and infrared image sensors. At the system level, the architecture relies on an event based readout scheme where only pixels within a programmable range of photon flux rates are output. At the pixel level, a one bit oversampled analogto-digital converter together with a decimator allows for the quantization of signals up to 26 bits. Furthermore, digital non-uniformity correction of both gain and offset errors is applied at the pixel level prior to readout. We present results from a prototype 126×128 array fabricated in a standard 90nm CMOS process.

Noise analysis and comparison of analog and digital readout integrated circuits for infrared focal plane arrays

We analyze the traditional analog ROIC architecture and an oversampled Σ - Δ modulator/decimator architecture. We show how the latter has superior characteristics i.e. an improved maximum signal to noise ratio (SNRMAX). This is a result of effectively increasing the well capacity by a factor equal to the oversampling ratio (OSR). We also provide a high fidelity noise model for both an analog and the digital ROIC and show that the equivalent electron noise at the output of the digital ROIC is much less compared to the traditional analog ROICs.

Reducing memory requirement of cell state space based fuzzy logic controller design approaches using k-d trees

The memory requirement makes cell state space based fuzzy logic controller (FLC) design approaches prohibitive for high order systems. The paper presents a specially modified k-d tree data structure to minimize memory requirements. Based on the k-d tree representation of the cell state space, an optimal control table (OCT) can be built and further be used to optimize a Takagi-Sugeno (TS) type FLC with least mean square (LMS) learning algorithm. However, for high order systems, due to physical memory limit and the complexity of system dynamics, even with k-d trees, an OCT may not have desirable resolution that is critical in FLC optimization. A method to overcome this problem is presented. The method involves interpolating the control actions in an OCT to obtain some optimal trajectories. A FLC will learn from the sampling data along the trajectories instead of learning from the OCT. A 4D inverted pendulum is studied in the paper. The performance of the FLC designed with the new approaches compares favorably with a linear quadratic regulator.

Bioinspired polarization vision enables underwater geolocalization

A novel bioinspired polarization-sensitive imager enables passive underwater geolocalization with an accuracy of 61 km. With its never-ending blue color, the underwater environment often seems monotonic and featureless. However, to an animal with polarization-sensitive vision, it is anything but bland. The rich repertoire of underwater polarization patterns—a consequence of light’s air-to-water transmission and in-water scattering—can be exploited both as a compass and for geolocalization purposes. We demonstrate that, by using a bioinspired polarization-sensitive imager, we can determine the geolocation of an observer based on radial underwater polarization patterns. Our experimental data, recorded at various locations around the world, at different depths and times of day, indicate that the average accuracy of our geolocalization is 61 km, or 6 m of error for every 1 km traveled. This proof-of-concept study of our bioinspired technique opens new possibilities in long-distance underwater navigation and suggests additional mechanisms by which marine animals with polarization-sensitive vision might perform both local and long-distance navigation.

High-performance, event-driven, low-cost, and SWaP imaging sensor for hostile fire detection, homeland protection, and border security

The advanced imagers team at JHU APL and ECE has been advocating and developing a new class of sensor systems that address key system level performance bottlenecks but are sufficiently flexible to allow optimization of associated cost and size, weight, and power (SWaP) for different applications and missions. A primary component of this approach is the innovative system-on-chip architecture: Flexible Readout and Integration Sensors (FRIS). This paper reports on the development and testing of a prototype based on the FRIS concept. It will include the architecture, a summary of test results to date relevant to the hostile fire detection challenge. For this application, this prototype demonstrates the potential for this concept to yield the smallest SWaP and lowest cost imaging solution with a low false alarm rate. In addition, a specific solution based on the visible band is proposed. Similar performance and SWaP gains are expected for other wavebands such as SWIR, MWIR, and LWIR and/or other applications like persistent surveillance for critical infrastructure and border control in addition to unattended sensors.

Underwater geolocalization via polarization information (Conference Presentation)

Polarization information is abundant in nature, including the underwater environment. Polarization of light in the underwater environment is due to light coming from both the sun and from the sky. Hence, the underwater polarization is primarily determined by light’s transmission from air to water and in-water scattering. In this talk, we will present a new framework to solve sun’s position (heading and elevation) using background underwater polarization information. Based on this data, the underwater geo location of an observer can be determined passively. Extensive experimental data will be presented in the talk to demonstrate the accuracy of this method.

End-fire silicon optical phased array with half-wavelength spacing

We demonstrate an optical phased array with emitting elements spaced at half the operational wavelength. The device is a one-dimensional array fabricated on an integrated silicon platform for operation at a wavelength of 1.55 μm. Light is emitted end-fire from the chip edge where the waveguides are terminated. The innovative design and high confinement afforded by the silicon waveguides enables λ/2 spacing (775-nm pitch) at the output thereby eliminating grating lobes and maximizing the power in the main lobe. Steering is achieved by inducing a phase shift between the waveguide feeds via integrated thermo-optic heaters. The device forms a beam with a full-width half-maximum angular width of 17°, and we demonstrate beam steering over a 64° range limited only by the element factor.

Characterization of RTN noise in the analog front-end of digital pixel imagers

The interest for more digital functionality in the readout circuits for imagers is growing rapidly. Similarly, there are advantages to having the pixel pitch smaller from visible to long wave IR. The front end is the dominant source of electronic noise for an in-pixel digital design. Limiting the real estate considerably would force the design to smaller feature size, which may worsen the random telegraph signal or noise (RTS/RTN) that will likely be the dominate source for noise for these imagers. This paper summarizes initial results for RTN sensitivities at room temperature to various device types, geometries, and flux rates, evaluated on a digital pixel on 65- and 55-nm CMOS processes.

End-fire silicon waveguide array as a platform for high power beam shaping and steering

We demonstrate a scalable array of end-firing silicon waveguides as a platform for high-speed, high-power operation beam-steering applications. We fabricate devices, culminating in 16×1 arrays with a measured central lobe FWHM of 7°±0.6°.