Changhyuk Lee

On the origin of periodic surface structure of laser‐annealed semiconductors

Observations on laser‐irradiated GaAs are reported in which the phenomenon of induced surface periodicity is related to a nonlinear interaction between simultaneously oscillating axial modes of the laser. It is suggested that during surface melting and regrowth material is distributed along nodal lines of a standing acoustic wave pattern corresponding to the axial mode beat frequencies. The several patterns observed are not consistent with an interference effect at optical frequencies.

400‐Å high aspect‐ratio lines produced in poylmethyl methacrylate (PMMA) by ion‐beam exposure

We report preliminary results on the fabrication of 400‐ and 2600‐A deep lines in polymethyl methacrylate (PMMA) by means of H+ exposure through a holographically produced fine conformal gold mask.

A microscale camera using direct Fourier-domain scene capture

We demonstrate a chip-scale (<1 mm(2)) 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.

Effects of LO harmonics and overlap shunting on N-phase passive mixer based receivers

This paper presents an overview of two loss mechanisms in multi-path passive mixers: 1) the up-conversion of harmonic images due to the square shape of the LO sampling pulses, and 2) the overlap between LO pulses. Both these mechanisms can be modeled by a shunting impedance on the mixer input and we explore two methods to mitigate their effects. We expanded a passive-mixer first receiver to N>;8 phases and characterized gain, noise and input impedance tuning range. Additionally, we included hardware to directly measure the effect of overlapping LO pulses on the gain and input impedance of these receivers. Finally, we propose a method to use integrated inductors to suppress the currents which flow when two mixer switches are on at the same time, alleviating this loss mechanism.

Robustness of planar Fourier capture arrays to colour changes and lost pixels

Planar Fourier capture arrays (PFCAs) are optical sensors built entirely in standard microchip manufacturing flows. PFCAs are composed of ensembles of angle sensitive pixels (ASPs) that each report a single coefficient of the Fourier transform of the far-away scene. Here we characterize the performance of PFCAs under the following three non-optimal conditions. First, we show that PFCAs can operate while sensing light of a wavelength other than the design point. Second, if only a randomly-selected subset of 10% of the ASPs are functional, we can nonetheless reconstruct the entire far-away scene using compressed sensing. Third, if the wavelength of the imaged light is unknown, it can be inferred by demanding self-consistency of the outputs.

A fully integrated Software-Defined FDD transceiver tunable from 0.3-to-1.6 GHz

An ideal Software Defined Radio (SDR) requires a reconfigurable, intergrated, widely-frequency-tunable transceiver able to support different RX/TX duplex schemes. Here we present an integrated transceiver capable of supporting both TDD and FDD operation with >25dB integrated RX-TX isolation from 0.3-1.6GHz without any off-chip switches or filters. The transceiver uses an artificial transmission line (TL) and distributed PA to separate TX and RX. TX noise in the RX band is further suppressed by >13dB an RX-tracking PA degeneration circuit.

A Low-Power Edge Detection Image Sensor Based on Parallel Digital Pulse Computation

An all-digital low-power CMOS edge detection image sensor array is presented. Each pixel contains a voltage-controlled ring oscillator to achieve low-power and cost-efficient digital-only edge detection. While conventional edge detection methods require high computing power and large chip area to process intensity maps, this work implements an all-digital parallel processing algorithm that detects differences between neighboring pixel pairs on chip, hence reducing the aforementioned power and cost overheads. In particular, a simple column-shared frequency comparator enables low-power operation by eliminating arithmetic computations with large memory requirement. Such a simple edge detection algorithm allows the processor area to be less than 16% of the entire image sensor, therefore maximizing the proportion of active optical area. The prototype image sensor presented in this work is fabricated using a four-metal 180-nm CMOS image sensor process and contains 105 × 92 pixels. An individual pixel size is 8 × 8 μm2 with a fill factor of 11.69%, while the total chip area is 1 × 1.3 mm2. The image sensor exhibits a frame rate of 30 frames/s and a power consumption of 8 mW, which is 27.7 nW/pixel/frame at VDD of 1.6 V.

An on-chip 72×60 angle-sensitive single photon image sensor array for lens-less time-resolved 3-D fluorescence lifetime imaging

We present a 72×60, angle-sensitive single photon avalanche diode (A-SPAD) array, able to perform lens-less 3-D fluorescent lifetime imaging. A-SPAD pixels are comprised of (1) a SPAD to resolve precise timing information, reject high-powered UV stimulus, and map the lifetimes of different fluorescent sources and (2) integrated diffraction gratings over the SPAD to extract the incident angle of light, enabling 3-D localization at a micrometer scale. The chip integrates pixel-level counters and shared timing circuitry, and is implemented in unmodified 180nm CMOS.

A Wideband Fully Integrated Software-Defined Transceiver for FDD and TDD Operation

Although there is much active research on software-defined radios (SDRs) with receive (RX) or transmit (TX) functionality, little work has been done on SDR transceivers supporting frequency division duplex (FDD). In this paper, we present a new circuit concept in which a distributed TX circuit cancels the transmitted signal at a reverse RX port through destructive interference while adding signal constructively at a forward TX port. We pair the distributed transmitter with a receiver-tracking PA degeneration technique to suppress the injected noise from TX circuits in the RX band. The system does not require off-chip filters or circulators, but still achieves both SDR flexibility and both FDD and time division duplex function. Measurements from the transceiver implemented in 65-nm CMOS show a frequency tuning range of 0.3–1.6 GHz with TX–RX isolation >23 dB and transmitted power up to 19 dBm.

Self-quenching, Forward-bias-reset for Single Photon Avalanche Detectors in 1.8V, 0.18µm process

We present a fully integrated, Single Photon Avalanche Detector (SPAD) using only standard low-voltage (1.8V) CMOS devices in a 0.18µm process. The system requires one high-voltage 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.