Sangwook Nam

Seoul National University, Sŏul, Seoul, South Korea

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Publications (195)163.93 Total impact


  • No preview · Article · Dec 2015
  • Duksoo Kim · Byungjoon Kim · Sangwook Nam
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    ABSTRACT: A linearization technique of a transconductor circuit is proposed in this brief. By adopting a two-path feedforward architecture, the Gm3 component of the transconductor vanishes and a highly linear V-to-I conversion is achieved. This technique consists of self-biased inverters only, and it can be applied to transconductors with differential inputs. It also has an advantage in process scaling and precise bias control is not necessary. A tunableGm.Chigh-pass filter for the baseband of a frequency-modulated continuous-wave radar system is implemented using these linearized transconductors. The filter is synthesized with a high-order admittance method. The designed filter is fabricated in a 0.13 μm CMOS process. The filter cutoff frequency can be tuned from 0.15 to 0.75 MHz with a current consumption value of 11-36 mA. An in-band input-referred third-order intercept point of +19.4 dBm and a 1-dB compression point of +5.35 dBm are measured, demonstrating a highly linear filter operation.
    No preview · Article · Nov 2015 · Circuits and Systems II: Express Briefs, IEEE Transactions on
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    ABSTRACT: This paper presents a 77-GHz radar system using a transmitter (Tx) and receiver (Rx) integrated with on-chip waveguide feeders in 65-nm CMOS. The newly proposed on-chip waveguide feeder shows the insertion loss of about 2 dB and more than 30% bandwidth. Additionally, both the Tx and Rx are integrated with internal ×10 frequency multipliers. Therefore, a radar system can be easily implemented without sensitive millimeter-wave packaging technology by mounting the Tx and Rx chips on the waveguide aperture. The interconnections for the low-frequency reference and baseband signals can be realized on the low-cost FR-4 printed circuit board. The radar system shows 9-dBm output power and 13-dB down-conversion gain from the waveguide port.
    No preview · Article · Sep 2015 · IEEE Transactions on Microwave Theory and Techniques
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    ABSTRACT: Implantable endovascular devices such as bare metal, drug eluting and bioresorbable stents have transformed interventional care by providing continuous structural and mechanical support to many peripheral, neural and coronary arteries affected by blockage. Although effective in achieving immediate restoration of blood flow, the long term re-endothelialisation and inflammations induced by mechanical stents are difficult to diagnose or treat. Here we present nanomaterial designs and integration strategies for the bioresorbable electronic stent with drug-infused functionalized nanoparticles to enable flow sensing, temperature monitoring, data storage, wireless power/data transmission, inflammation suppression, localized drug delivery, and hyperthermia therapy. In vivo and ex vivo animal experiments as well as in vitro cell studies demonstrate the previously unrecognized potential for bioresorbable electronic implants coupled with bioinert therapeutic nanoparticles in the endovascular system.
    Full-text · Article · Apr 2015 · ACS Nano
  • Dong-yeon Kim · Youngjoon Lim · Hee-Sung Yoon · Sangwook Nam
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    ABSTRACT: A W-band 8 × 8 slot array antenna is proposed and fabricated by electroforming for high-precision manufacturing. The external mutual coupling between radiating shunt slots is compensated for input impedance matching and a uniform held distribution. The overall antenna aperture area is 473.1 mm2 with slot spacings of 2.8 and 2.64 mm in the transverse and longitudinal direction, respectively. The measured maximum gain is 26.8 dBi and the corresponding antenna efficiency is 81.9% at 94 GHz. The measured impedance bandwidth when the VSWR is less than 2.0 (-10 dB) is 8.3%, with a range from 89.9 to 97.6 GHz.
    No preview · Article · Apr 2015 · IEEE Transactions on Antennas and Propagation
  • Jae-Hoon Song · Byung-Sung Kim · Sangwook Nam
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    ABSTRACT: In this letter, an adaptively biased class-C Voltage Controlled Oscillator (VCO) with a self-turn-off auxiliary class-B pair is presented for fast and robust startup in a 65-nm CMOS process. It consists of a main class-C core and an auxiliary class-B cross-coupled pair. The class-B auxiliary pair is used to solve the inherent startup problem of class-C VCOs. It works only during startup and turns itself off when the VCO reaches a steady state using an adaptive bias scheme. The dc current consumption of the VCO and bias circuit is 5 mA at 1.2 V ${rm V}_{rm DD}$. Here, a good phase noise level of $-132.41~{rm dBc}/{rm Hz}$ at a 1 MHz offset frequency from a 2.46-GHz carrier is shown, to yield a Figure-of-Merit (FOM) of 192.45.
    No preview · Article · Jan 2015 · IEEE Microwave and Wireless Components Letters
  • Sumin Yun · Dong-Yeon Kim · Sangwook Nam
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    ABSTRACT: A folded, cavity-backed crossed-slot antenna is proposed for antenna miniaturization. The cavity dimensions of a conventional cavity-backed crossed-slot antenna are about a half-guided-wavelength along each side, which is unsuitable in many applications like a handheld device or body area network (BAN). To reduce the size of the cavity, a folded cavity is proposed in this letter. The center plate that divides the cavity into the upper cavity and the lower cavity increases the effective length inside the cavity. Compared to the conventional cavity-backed crossed-slot antenna, a 72.8% size reduction can be achieved using the proposed structure. The proposed antenna also has circular polarization and wideband characteristics, which are the main advantages of a cavity-backed crossed-slot antenna. The proposed technique is especially useful for reducing the lateral dimensions of the cavity.
    No preview · Article · Jan 2015 · IEEE Antennas and Wireless Propagation Letters
  • Youngjoon Lim · Sangwook Nam

    No preview · Article · Dec 2014
  • Jongmin Park · Sangwook Nam

    No preview · Article · Oct 2014
  • Jaeyong KO · Kihyun KIM · Jaehoon SONG · Sangwook NAM
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    ABSTRACT: This paper describes the design method of a broadband CMOS stacked power amplifier using harmonic control over wide bandwidths in a 0.11 μm standard CMOS process. The high-efficiency can be obtained over wide bandwidths by designing a load impedance circuit as purely reactive as possible to the harmonics with broadband fundamental matching, which is based on continuous Class-F mode of operation. Furthermore, the stacked topology overcomes the low breakdown voltage limit of CMOS transistor and increases output impedance. With a 5-V supply and a fixed matching circuitry, the suggested power amplifier (PA) achieves a saturated output power of over 26.7 dBm and a drain efficiency of over 38% from 1.6 GHz to 2.2 GHz. In W-CDMA modulation signal measurements, the PA generates linear power and power added efficiency of over 23.5 dBm and 33% (@ACLR =-33 dBc).
    No preview · Article · Oct 2014 · IEICE Transactions on Electronics
  • Byungjoon Kim · Sangwook Nam · Hee-Ran Ahn · Jae-Hoon Song
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    ABSTRACT: This letter proposes a wideband compact DC block design technique. This DC block has a wide pass-band and wide stop-band and transforms termination impedances. It comprises a pair of coupled lines on a defected ground structure (DGS) with capacitor loading. A periodic DGS pattern increases coupling, and, consequently, a wideband DC block design is allowed with a microstrip process on a high dielectric low height substrate. A DC block with equal termination impedances of 50 Ω and another that transforms 50 into 30 Ω are fabricated. The measured fractional bandwidths are 48% and 47%. The size of the DC block is 16.8× 15 mm2(0.057λ0× 0.051λ0).
    No preview · Article · Sep 2014 · IEICE Transactions on Electronics
  • Yoon Goo Kim · Youngjoon Lim · Sumin Yun · Sangwook Nam

    No preview · Conference Paper · Jul 2014
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    ABSTRACT: In this paper, a prototype slot array antenna for dual polarized monopulse operation is proposed. The suggested monopulse antenna structure is composed of a dual polarized radiating part using substrate integrated waveguide (SIW) technology and a feed network using metallic rectangular waveguides for dual plane tracking. Radiation patterns of the fabricated prototype antenna are measured at elevation and azimuth cutting planes for each linear polarization. Measured realized sum (Σ) pattern gains are more than 22 dBi and the null depths (NDs) for difference (Δ) patterns are less than -27 dB at boresight direction at center frequency of Ku-band. However, the proposed prototype monopulse antenna has somewhat high sidelobe and cross polarization levels. The reasons for these drawbacks are discussed at the end of this paper.
    No preview · Conference Paper · Jul 2014
  • H.-R. Ahn · Byungjoon Kim · Sangwook Nam
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    ABSTRACT: A compact UHF 3 dB power divider (PD) is presented. It consists of two identical asymmetric impedance transformers (MCCTs) and one isolation circuit with resistance and capacitance. The MCCT is composed of two different transmission-line sections and one open stub, and good frequency performance may be achieved by the combination of transmission-line sections and open stub. One PD is fabricated at a design center frequency of 500 MHz, of which total transmission-line sections are only 39.68$^{circ}$ long. The measured bandwidth with 15 dB return loss is about 68%.
    No preview · Article · Jul 2014 · IEEE Microwave and Wireless Components Letters
  • Byungjoon Kim · Duksoo Kim · Sangwook Nam

    No preview · Article · Jun 2014
  • Kihyun Kim · Junghee Choi · Munkyo Seo · Sangwook Nam
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    ABSTRACT: A 500 MHz On-Off Keying (OOK) transmitter integrated with a high-efficiency wideband power amplifier (PA) is designed for low-power/high-data rate applications. The PA biased in Class C region, employs a bias current-reused and an RF current-combining structure to achieve a high-efficiency and high-data rate. The transmitter is fabricated using a 0.13 $mu$m CMOS process. The chip size is 0.6 mm$^{2}$ and the measured drain efficiency of the PA reaches 59.5% at 500 MHz with 1.62 dBm output power while consuming only 2.52 mW dc power from a 3 V power supply. The efficiency of the transmitter is 38.4% and the energy usage is 22 pJ/bit at a data rate of 100 Mbps with ${-}0.75$ dBm average output power.
    No preview · Article · Jun 2014 · IEEE Microwave and Wireless Components Letters
  • Yoon Goo Kim · Sangwook Nam
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    ABSTRACT: A method is presented to analyze the maximum power transfer efficiency of a wireless power transfer system and its electromagnetic fields via spherical modes. The Z-parameter and Y-parameter for two coupled antennas are derived using the antenna scattering matrix and an addition theorem. In addition, formulas for calculating the maximum power transfer efficiency and optimum load impedance are presented. A formula is derived to calculate the electromagnetic field generated by a wireless power transfer system from the antenna scattering matrix.
    No preview · Article · Jun 2014 · IEEE Transactions on Antennas and Propagation
  • Junhyuk Choi · Byungjoon Kim · Duksoo Kim · Jaeyong Ko · Sangwook Nam
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    ABSTRACT: This paper presents a dual band CMOS power amplifier (PA) for an S/X band high resolution radar system. Reconfigurable band-switchable matching networks and a dual band Wilkinson power combiner (impedance transformer) are used for an output matching network. The PA is fabricated using a UMC 0.13 μm CMOS process. It provides a saturated output power of 24.8 dBm and 25.3 dBm with the power-added-efficiency (PAE) of 27.2 % and 36.4 % at 8.4 GHz and 3.0 GHz, respectively. The 3-dB bandwidth is 2.5 GHz (7.4-9.9 GHz) and 2.3 GHz (2.7-5.0 GHz). This amplifier achieves a fractional bandwidth of 29% and 60 % at each band, and shows suitable performance for use in a high resolution radar system.
    No preview · Conference Paper · Jun 2014
  • Jae-Hoon Song · Byung-Sung Kim · Sangwook Nam
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    ABSTRACT: This paper includes 77 GHz VCO design using a coupled-line inductor with spiral-shaped electromagnetic bandgap (EBG) structure. The coupled-line inductor enhances Q due to its low substrate loss. Thus, phase noise performances of VCO can be improved. However, the length of coupled-line will be long owing to its low inductance per unit length. EBG structure is applied to reduce its size. The 3-D EM simulation is performed to show its enhancement of inductance and Q. The simulated inductance and Q of proposed coupled-line with EBG structure are 114.0 pH and 30.70 at 77 GHz, respectively. The VCO core is designed with proposed coupled-line inductor.
    No preview · Conference Paper · Apr 2014
  • Hee-Ran Ahn · Sangwook Nam
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    ABSTRACT: A 3-dB power divider (PD) terminated in equal complex impedances is presented. It consists of two identical 90 ° transmission-line sections and an isolation circuit, being composed of resistance and capacitance, or resistance and inductance, depending on the termination impedances. If the termination impedance has capacitance, the isolation impedance should consist of inductance, and therefore, the isolation circuit should be implemented with a chip inductor. However, the chip inductor contains additional stray capacitance and resistance, which lead to undesired frequency performance. To avoid the usage of the chip inductors, even with arbitrary termination impedances, three design methods by adding transmission-line sections, adding open stubs, and adding short stubs are introduced. The PDs designed by the three methods can have not only desired isolation impedances, but also the total size of the PDs can be reduced. To verify the suggested theory, three PDs are measured. For one PD with adding transmission-line sections, the measured reflection coefficients at all ports are -43.29, -41.55, and -51.69 dB, the isolation is 56.7 dB, and the power division is -3.042 dB at a design center frequency of 1 GHz, which agree quite well with those predicted.
    No preview · Article · Nov 2013 · IEEE Transactions on Microwave Theory and Techniques

Publication Stats

2k Citations
163.93 Total Impact Points

Institutions

  • 1996-2015
    • Seoul National University
      • • Department of Electrical and Computer Engineering
      • • School of Electrical Engineering and Computer Sciences
      Sŏul, Seoul, South Korea
  • 2008
    • Samsung Thales
      Sŏul, Seoul, South Korea
  • 2003
    • Soon Chun Hyang University Hospital
      Sŏul, Seoul, South Korea