Ki-Jin Kim

Bio: Ki-Jin Kim is an academic researcher from KAIST. The author has contributed to research in topics: Amplifier & CMOS. The author has an hindex of 9, co-authored 33 publications receiving 574 citations.

Wideband planar monopole antennas with dual band-notched characteristics

Abstract: Wideband planar monopole antennas with dual band-notched characteristics are presented. The proposed antenna consists of a wideband planar monopole antenna and the multiple cup-, cap-, and inverted L-shaped slots, producing band-notched characteristics. In order to generate dual band-notched characteristic, we propose nine types of planar monopole antennas, which have two or three cap (cup or inverted L)-shaped slots in the radiator. This technique is suitable for creating ultra-wideband antenna with narrow frequency notches or for creating multiband antennas

The high isolation dual‐band inverted F antenna diversity system with the small N‐section resonators on the ground plane

Abstract: The high isolated dual-band inverted-F diversity systems for portable devices, operating in 2.4 GHz band (2400–2484 MHz) and 5.2 GHz band (5150–5350 MHz), are presented. To reduce the mutual coupling and get high isolation between two internal dual-band antennas, we proposed the small N-section resonators in the form of slots on the ground plane. The optimized small size resonators for high isolation, antenna radiation efficiency, and high effective diversity are analyzed. Because of their small size, N-section resonators can be widely used in small diversity systems that require high isolation between antennas. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 731–734, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22238

High Isolation Internal Dual-Band Planar Inverted-F Antenna Diversity System with Band-Notched Slots for MIMO Terminals

Abstract: Internal dual-band planar inverted-F antenna (PIFA) diversity system for portable devices, operating in the 2.4-GHz band (2400-2484MHz) and 5.2-GHz band (5150-5350MHz), is presented. To reduce the mutual coupling and get the high isolation between the two internal dual-band antennas, we proposed the band-notched lambda/4 slots on the ground plane. The optimized band-notched slots for high isolation, high radiation efficiency and high effective diversity gain are analyzed. The band-notched slots can be used to the small MIMO terminals which require high isolation between antennas

A 60 GHz Wideband Phased-Array LNA With Short-Stub Passive Vector Generator

Abstract: This letter presents 60 GHz 5 b phased-array low noise amplifier (LNA) implemented in 90 nm CMOS for a short range wireless application. The design consists of common source two-stage LNA, short-stub vector generator, I/Q modulator with 5 b digital to analog converter and differential to single amplifier. All the proposed amplifiers are designed using a transformer coupled method which results in wideband operation to meet the frequency requirement of the standard. The proposed circuit provides 360 phase controllability over 50-70 GHz band while achieving 12.5 dB gain, 6.55 dB NF and consuming 50 mA from 1.2 V. The measured rms phase error is in the phase accuracy limitation (differential phase array) and gain variation is quite low (<; 0.92 dB) over 5 b control range.

A Sign-Equality-Based Background Timing-Mismatch Calibration Algorithm for Time-Interleaved ADCs

Abstract: A background timing-mismatch calibration algorithm is proposed, which detects and corrects the sampling time mismatches in time-interleaved analog-to-digital converter (ADC) channels by analyzing the sign-equality of a reference slope and a timing-mismatch-induced error value. The sign of the ideal derivative along the input is estimated through the adjacent channel outputs, thus not requiring an additional time-shifted ADC channel. The sign of the reference slope, which is the estimated sign of the ideal derivative at the sampling edge of the reference ADC, is matched against the sign of the error value to determine if the timing mismatch is leading or lagging the sampling edge of the reference ADC. The proposed algorithm aligns the sampling edge of each subchannel to that of the reference ADC by handling only two sign bits and thus reduces the timing mismatches with only negligible hardware overhead consisting of simple logic gates.

An Overview of Signal Processing Techniques for Millimeter Wave MIMO Systems

Abstract: Communication at millimeter wave (mmWave) frequencies is defining a new era of wireless communication. The mmWave band offers higher bandwidth communication channels versus those presently used in commercial wireless systems. The applications of mmWave are immense: wireless local and personal area networks in the unlicensed band, 5G cellular systems, not to mention vehicular area networks, ad hoc networks, and wearables. Signal processing is critical for enabling the next generation of mmWave communication. Due to the use of large antenna arrays at the transmitter and receiver, combined with radio frequency and mixed signal power constraints, new multiple-input multiple-output (MIMO) communication signal processing techniques are needed. Because of the wide bandwidths, low complexity transceiver algorithms become important. There are opportunities to exploit techniques like compressed sensing for channel estimation and beamforming. This article provides an overview of signal processing challenges in mmWave wireless systems, with an emphasis on those faced by using MIMO communication at higher carrier frequencies.

Hybrid MIMO Architectures for Millimeter Wave Communications: Phase Shifters or Switches?

Abstract: Hybrid analog/digital multiple-input multiple-output architectures were recently proposed as an alternative for fully digital-precoding in millimeter wave wireless communication systems. This is motivated by the possible reduction in the number of RF chains and analog-to-digital converters. In these architectures, the analog processing network is usually based on variable phase shifters. In this paper, we propose hybrid architectures based on switching networks to reduce the complexity and the power consumption of the structures based on phase shifters. We define a power consumption model and use it to evaluate the energy efficiency of both structures. To estimate the complete MIMO channel, we propose an open-loop compressive channel estimation technique that is independent of the hardware used in the analog processing stage. We analyze the performance of the new estimation algorithm for hybrid architectures based on phase shifters and switches. Using the estimate, we develop two algorithms for the design of the hybrid combiner based on switches and analyze the achieved spectral efficiency. Finally, we study the tradeoffs between power consumption, hardware complexity, and spectral efficiency for hybrid architectures based on phase shifting networks and switching networks. Numerical results show that architectures based on switches obtain equal or better channel estimation performance to that obtained using phase shifters, while reducing hardware complexity and power consumption. For equal power consumption, all the hybrid architectures provide similar spectral efficiencies.

Hybrid MIMO Architectures for Millimeter Wave Communications: Phase Shifters or Switches?

Abstract: Hybrid analog/digital MIMO architectures were recently proposed as an alternative for fully-digitalprecoding in millimeter wave (mmWave) wireless communication systems. This is motivated by the possible reduction in the number of RF chains and analog-to-digital converters. In these architectures, the analog processing network is usually based on variable phase shifters. In this paper, we propose hybrid architectures based on switching networks to reduce the complexity and the power consumption of the structures based on phase shifters. We define a power consumption model and use it to evaluate the energy efficiency of both structures. To estimate the complete MIMO channel, we propose an open loop compressive channel estimation technique which is independent of the hardware used in the analog processing stage. We analyze the performance of the new estimation algorithm for hybrid architectures based on phase shifters and switches. Using the estimated, we develop two algorithms for the design of the hybrid combiner based on switches and analyze the achieved spectral efficiency. Finally, we study the trade-offs between power consumption, hardware complexity, and spectral efficiency for hybrid architectures based on phase shifting networks and switching networks. Numerical results show that architectures based on switches obtain equal or better channel estimation performance to that obtained using phase shifters, while reducing hardware complexity and power consumption. For equal power consumption, all the hybrid architectures provide similar spectral efficiencies.

A Compact Ultrawideband Antenna With 3.4/5.5 GHz Dual Band-Notched Characteristics

Abstract: We propose a compact planar ultrawideband (UWB) antenna with 3.4/5.5 GHz dual band-notched characteristics. The antenna consists of a beveled rectangular metal patch and a 50 Omega coplanar waveguide (CPW) transmission line. By etching two nested C-shaped slots in the patch, band-rejected filtering properties in the WiMAX/WLAN bands are achieved. The proposed antenna is successfully simulated, designed, and measured showing broadband matched impedance, stable radiation patterns and constant gain. An equivalent circuit model of the proposed antenna is presented to discuss the mechanism of the dual band-notched UWB antenna. A UWB antenna and a single band-notched one are also provided for references.

Planar Ultrawideband Antennas With Multiple Notched Bands Based on Etched Slots on the Patch and/or Split Ring Resonators on the Feed Line

Abstract: Three types of ultrawideband (UWB) antennas with triple notched bands are proposed and investigated for UWB communication applications. The proposed antennas consist of a planar circular patch monopole UWB antenna and multiple etched slots on the patch and/or split ring resonators (SRRs) coupled to the feed line. Good agreement is achieved between the simulated and measured results. These techniques are significant for designing UWB antennas with multiple narrow frequency notched bands or for designing multiband antennas.