Yongchae Jeong

Chonbuk National University, Tsiuentcheou, Jeollabuk-do, South Korea

Are you Yongchae Jeong?

Claim your profile

Publications (77)73.98 Total impact

  • Phirun Kim, Girdhari Chaudhary, Yongchae Jeong
    [Show abstract] [Hide abstract]
    ABSTRACT: This article presents the design of an impedance transformer (IT) with wide out-of-band suppression characteristics. The wide out-of-band suppression characteristics can be obtained by loading several transmission zeros in the lower and upper out-of-bands. For experimental validation, a 50-to-10 Ω IT was implemented at a center frequency (f0) of 2.6 GHz for the long term evolution signal. The measured results are in good agreement with the simulations, showing a return loss higher than 20 dB over a passband bandwidth of 0.35 GHz (2.35–2.7 GHz) and out-of-band suppression better than 18 dB from DC to 1.78 GHz and from 3.45 to 6.97 GHz. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1600–1603, 2015
    Microwave and Optical Technology Letters 07/2015; 57(7). DOI:10.1002/mop.29144 · 0.62 Impact Factor
  • Namsik Ryu, Bonghyuk Park, Yongchae Jeong
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper proposes a CMOS linear power amplifier (PA) design scheme for IEEE 802.11g (WLAN) application. The proposed PA consists of a programmable gain amplifier and a high power stage which is composed of a main amplifier with class AB bias and an auxiliary amplifier with class C bias. Based on the un-even bias scheme, the power stage can improve linearity and reduce current consumption in the low power region. It is fabricated with a TSMC 40 nm standard RF CMOS process. The measurements show that the designed PA reaches a 1 dB gain compression output power of 24.6 dBm and a peak drain efficiency of 38% with a 3.3 V power supply at 2.4 GHz operating frequency range. When the PA was tested with an IEEE 802.11g OFDM signal of 20 MHz channel bandwidth, the obtained EVM compliant output power and drain efficiency are 18.5 dBm and 14%, respectively.
    IEEE Microwave and Wireless Components Letters 06/2015; 25(6):1-1. DOI:10.1109/LMWC.2015.2421351 · 2.24 Impact Factor
  • Girdhari Chaudhary, Yongchae Jeong
    [Show abstract] [Hide abstract]
    ABSTRACT: In this letter, the design of power divider with negative group delay (NGD) characteristics is presented. From an analysis, the NGD associated with different transmission paths is found to be identical and obtained by loading resistor connected short-circuited coupled lines with an open-circuited isolation port. The proposed structure is validated by constructing a two-way microstrip line power divider with equal power division ratio, which is centered at 2.14 GHz. The measured results show excellent agreement with simulations and theoretically predicated results. From the measurement, the group delays and magnitudes of -parameters between the different transmission paths are determined as , , , and . The measured input/output return losses and isolation at center frequency are higher than 28.92 dB, 26.76 dB, and 42.2 dB.
    IEEE Microwave and Wireless Components Letters 06/2015; 25(6):1-1. DOI:10.1109/LMWC.2015.2421280 · 2.24 Impact Factor
  • Phirun Kim, Girdhari Chaudhary, Yongchae Jeong
    [Show abstract] [Hide abstract]
    ABSTRACT: This article presents a design of wideband balun with high isolation using a branch-line structure. Theoretical analysis of the proposed balun shows that the reflection coefficient characteristics with two transmission poles can be obtained by controlling the characteristic impedances of transmission lines (Zt, Z1, and Z2). The high isolation can be obtained by adding a shunt coupled-line short stub and resistor (R) between the output ports. The proposed balun was designed at the center frequency (f0) of 2.6 GHz for a current-mode class-S amplifier application. The measured results were in good agreement with the simulations, showing that power division ratios were 3.09 dB and 3.14 dB, whereas the return loss was 21.39 dB at the f0 and higher than 20 dB over a bandwidth of 0.98 GHz (1.98–2.96 GHz). The isolation between output ports was higher than 18 dB for the bandwidth of 0.75 GHz (2.21–2.96 GHz). The measured phase difference between the output ports was 180° ± 9° over a frequency range of 2.2–2.98 GHz. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1228–1234, 2015
    Microwave and Optical Technology Letters 05/2015; 57(5). DOI:10.1002/mop.29065 · 0.62 Impact Factor
  • 04/2015; 15(2):76-81. DOI:10.5515/JKIEES.2015.15.2.76
  • 04/2015; 13(4). DOI:10.14801/jkiit.2015.13.4.45
  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper presents the design of an impedance transformer with high selectivity and wide out-of-band suppression characteristics. There are two poles in the passband provide a sharp characteristic. For validation, a 50-to-20 Ω impedance transformer has been implemented at a center frequency (f0) of 2.6 GHz. From the measurement, a return loss higher than 20 dB over a passband bandwidth of 0.8 GHz (2.2-3 GHz) and the insertion loss less than 0.4 dB over the same bandwidth. The out-of-band suppression higher than 17 dB from DC to 1.85 GHz and higher that 11 dB from 3.5 GHz to 7.2 GHz are obtained.
    IEEE Radio & Wireless Week 2015, San Diego, CA; 01/2015
  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper demonstrates a design and analysis of a dual-band negative group delay (NGD) network using defected microstrip structure (DMS). The group delays (GD) and signal attenuation (SA) of each band can be controlled independently by resistors connected across U-shaped DMS slots. For the experimental validation, the NGD network is designed and fabricated. For enhancement of the NGD bandwidth, two-stage NGD networks with slightly different center frequencies are connected in cascade. From the measurement, the GDs of -3.86±0.94 ns and -3.26±1.07 ns are obtained at 3.32-3.44 GHz and 4.63-4.76 GHz, respectively.
    IEEE Radio & Wireless Week 2015, San Diego, CA; 01/2015
  • Girdhari Chaudhary, Yongchae Jeong, Jaejoong Im
    [Show abstract] [Hide abstract]
    ABSTRACT: In this letter, we present the novel design and implementation of a microstirp line reconfigurable negative group delay circuit (NGDC) using a branch-line. Theoretical analysis shows that reconfigurable characteristics in the proposed circuit can be obtained by properly choosing the characteristic impedances of the branch-line and tuning only the termination resistance. Therefore, the proposed reconfigurable NGDC does not require any extra resonators. For experimental validation, the proposed circuit was designed and fabricated for a wideband code division multiple access downlink frequency operating at a center frequency ( ${f_0}$) of 2.14 GHz. Measurement results show the group delays variation of $ - 2~hbox{ns}$ to $ - 10~hbox{ns}$ with signal attenuation variation of $ - 25~hbox{dB}$ to $ - 36.6~hbox{dB}$ at ${f_0}$. For enhancement of the negative group delay bandwidth, two NGDCs operating at slightly different center frequencies are cascaded and measured.
    IEEE Antennas and Wireless Propagation Letters 01/2015; 14:883-886. DOI:10.1109/LAWP.2014.2383393 · 1.95 Impact Factor
  • Yongchae Jeong, Girdhari Chaudhary
    [Show abstract] [Hide abstract]
    ABSTRACT: This study presents a novel approach to the design and implementation of transmission-type negative group delay (NGD) networks based on a coupled line doublet structure. To improve the reflection coefficients, a quarter-wavelength transmission line is connected between the input and through ports of a coupled line section. For the doublet structure, two coupled line sections are arranged in a symmetrical manner by connecting them back-to-back with the help of the quarter- wavelength through line. For the experimental demonstration, two planar NGD networks (unmatched and matched doublet NGD networks) are designed, simulated and measured at a centre frequency of 2.14 GHz. From the measurement, a group delay (GD) of −5.66 ns and signal attenuation (SA) of 18.78 dB were obtained in the case of an unmatched NGD network. Similarly, for the matched NGD case, a GD of −6.33 ns, SA of 20.69 dB and input/output return losses >29 dB were obtained at the centre frequency.
    IET Microwaves Antennas & Propagation 01/2015; 9(8). DOI:10.1049/iet-map.2014.0351 · 0.97 Impact Factor
  • Phirun Kim, Girdhari Chaudhary, Yongchae Jeong
    [Show abstract] [Hide abstract]
    ABSTRACT: An impedance transformer (IT) with a ultra-high impedance transforming ratio (UHITR) is presented in this letter. The UHITR is obtained by controlling coupling coefficients of cascaded open-circuited coupled lines. Two transmission poles have appeared in the passband for an under-matched region. For the validation, the IT with impedance transforming ratio of 10 was designed at a center frequency $(f_{0})$ of 2.6 GHz. From the experiment, insertion and return losses at $f_{0}$ were determined as 0.55 dB and 21.47 dB, respectively. Within the operating band from 2.515 to 2.73 GHz, the insertion and return losses were better than 0.8 dB and 18 dB, respectively. The out-of-band suppression characteristics are higher than 20 dB from dc to 1.92 GHz and better than 18 dB from 3.28 to 7.2 GHz.
    IEEE Microwave and Wireless Components Letters 01/2015; DOI:10.1109/LMWC.2015.2429075 · 2.24 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this letter, a linearity degradation according to the time mismatching between RF and envelope paths in the hybrid envelope tracking (ET) power amplifier (PA) has been mathematically analyzed. From analysis, an asymmetric IM3 level of ET PA can be found due to the time mismatching between RF and envelope paths and AM-to-PM distortion of PA. For the experimental demonstration, the hybrid ET PA was designed for a wideband code division multiple access downlink band operating at a center frequency of 2.14 GHz. For the accurate time matching, the group delay time adjustor (GDTA) with 5 ns variation was employed in front of the RF PA. In the experiment, 4.78 dB improvement of ACPR for 4-FAs (frequency allocations) WCMDA signal of 20 MHz channel bandwidth was obtained by the optimum group delay tuning of the GDTA.
    IEEE Microwave and Wireless Components Letters 01/2015; DOI:10.1109/LMWC.2015.2440661 · 2.24 Impact Factor
  • Girdhari Chaudhary, Yongchae Jeong
    [Show abstract] [Hide abstract]
    ABSTRACT: This article presents a novel approach to the design of a compact wideband negative group delay (NGD) network using cross coupling between open stubs. The NGD time can be controlled by external series resistors, whereas the NGD bandwidth can be controlled by the coupling coefficient between open stubs. To verify the design concept, the NGD network operating at center frequency of 1.96 GHz was designed and fabricated. From the measurement results, a maximum achievable NGD time of −1.1 ± 0.2 ns was obtained over a 410 MHz BW with a maximum signal attenuation of 29.23 dB. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2495–2497, 2014
    Microwave and Optical Technology Letters 11/2014; 56(11). DOI:10.1002/mop.28627 · 0.62 Impact Factor
  • Phirun Kim, Girdhari Chaudhary, Yongchae Jeong
    [Show abstract] [Hide abstract]
    ABSTRACT: This article presents the design of a wideband impedance transformer with out-of-band suppression characteristics. The out-of-band suppression characteristics are obtained by loading several transmission zeros at both the lower and upper stop-bands. For experimental validation, a 50-to-25 Ω transformer has been implemented at a center frequency (f0) of 2.6 GHz. The measured results were in good agreement with simulations, showing a return loss better than 20 dB over 0.92 GHz (2.1–3.02 GHz) and an out-of-band suppression better than 18 dB over DC to 1.42 and 3.8 to 6.65 GHz. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2612–2616, 2014
    Microwave and Optical Technology Letters 11/2014; 56(11). DOI:10.1002/mop.28664 · 0.62 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper presents a novel design of negative group delay circuit (NGDC) with very low signal attenuation (SA) and multiple-poles in group delay (GD) characteristics. The very low SA is obtained due to high characteristics of coupled lines. Theoretical analysis shows that the multiple-poles in GD characteristics can provide wider negative GD bandwidth and be obtained by connecting coupled lines resonators with slightly different center frequencies separated by quarter-wavelength transmission lines. For experimental validation, the NGDCs with 2-poles and 3-poles in GD characteristics are designed, simulated, and measured. The measurement results have a good agreement with theoretical predictions
    European Microwave Conference, Rome, Italy, 2014; 10/2014
  • Girdhari Chaudhary, Yongchae Jeong
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper presents the design and analysis of novel topologies of reflective-type negative-group-delay (NGD) networks with very small signal attenuation (SA). The proposed topologies are based on short-circuited coupled lines. Theoretical analysis shows that predefined group-delay (GD) time with very small SA can be obtained due to the high characteristic impedance of a coupled line and the small coupling coefficient. Due to the very low SA characteristics of the proposed networks, the burden of compensating general-purpose gain amplifiers can be reduced and provide stable operations while integrated to RF systems. This paper also analyses performance degradation of the GD time and SA of the proposed NGD networks according to the temperature-dependent resistance variation. For an experimental validation of the proposed topologies, distributed microstrip line NGD networks (type-I and type-II) are designed, simulated, and measured for a wideband code division multiple access (WCDMA) downlink frequency operating at a center frequency of 2.14 GHz. These results show a GD time of $-{hbox {7.27 ns}}$ with an SA of 7.43 dB for the type-I NGD network, and $-{hbox{6.3}}$ and 9.23 dB for the type II- NGD network at the center frequency, and agree closely with the simulations. To enhance the NGD bandwidth, two NGD networks with slightly different center frequencies are connected in parallel, which provides wider bandwidth than the single stage case and shows practical applicability.
    IEEE Transactions on Microwave Theory and Techniques 10/2014; 62(10):2316-2324. DOI:10.1109/TMTT.2014.2345352 · 2.94 Impact Factor
  • Girdhari Chaudhary, Yongchae Jeong, Jongsik Lim
    [Show abstract] [Hide abstract]
    ABSTRACT: In this letter, a design for a dual-band negative group delay circuit (NGDC) using dual-plane U-shaped defected structures is presented. The center frequency and group delay (GD) time of each band are separately controlled by a defected microstrip structure (DMS) and a defected ground structure (DGS) with resistors connected across the DMS and DGS slots. To verify the design concept, the NGDC is designed, fabricated, and compared with the circuit simulation. To get a wideband bandwidth, two NGDCs with different center frequencies are connected in a cascade design. From the measurements, the GD times of $-4.54 pm 0.6~{rm ns}$ and $-4.20 pm 0.5~{rm ns}$ are obtained at 3.46–3.58 GHz and 5.10–5.20 GHz, respectively.
    IEEE Microwave and Wireless Components Letters 08/2014; 24(8):521-523. DOI:10.1109/LMWC.2014.2322445 · 2.24 Impact Factor
  • Namsik Ryu, Seunghyun Jang, K.C. Lee, Yongchae Jeong
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper presents a novel CMOS Doherty power amplifier (PA) with an impedance inverter using a variable balun transformer (VBT) and adaptive bias control of an auxiliary amplifier. Unlike a conventional quarter-wavelength $(lambda /4)$ transmission line impedance inverter of a Doherty PA, the proposed VBT impedance inverter can achieve load modulation without any phase delay circuit. As a result, a $lambda /4$ phase compensation circuit at the input path of the auxiliary amplifier can be removed, and the total size of the Doherty PA can be reduced. Additionally, an enhancement of the power efficiency at backed-off power levels can successfully be achieved with an adaptive gate bias in a common gate stage of the auxiliary amplifier. The PA, fabricated with 0.13-µm CMOS technology, achieved a 1-dB compression point (P1 dB) of 31.9 dBm and a power-added efficiency (PAE) at P1 dB of 51%. When the PA is tested with 802.11g WLAN orthogonal frequency division multiplexing (OFDM) signal of 54 Mb/s, a 25-dB error vector magnitude (EVM) compliant output power of 22.8 dBm and a PAE of 30.1% are obtained, respectively.
    IEEE Journal of Solid-State Circuits 06/2014; 49(6):1356-1365. DOI:10.1109/JSSC.2014.2313561 · 3.11 Impact Factor
  • Girdhari Chaudhary, Yongchae Jeong, Jongsik Lim
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper presents a novel approach to the design and implementation of a distributed transmission line negative group delay filter (NGDF) with a predefined negative group delay (NGD) time. The newly proposed filter is based on a simple frequency transformation from a low-pass filter to a bandstop filter. The NGD time can be purely controlled by the resistors inserted into the resonators. The performance degradation of the NGD time and signal attenuation (SA) of the proposed NGDF according to the temperature dependent resistance variation is also analyzed. From this analysis, it is shown that the NGD time and SA variations are less sensitive to the resistance variation compared to those of the conventional NGD circuit. For an experimental validation of the proposed NGDF, a two-stage distributed microstrip line NGDF is designed, simulated, and measured at an operating center frequency of 1.962 GHz. These results show a group delay time of $-{hbox {7.3 ns}}$ with an SA of 22.65 dB at the center frequency and have good agreement with the simulations. The cascaded response of two NGDFs operating at different center frequencies is also presented in order to obtain broader NGD bandwidth. NGDFs with good reflection characteristics at the operating frequencies are also designed and experimentally verified.
    IEEE Transactions on Microwave Theory and Techniques 02/2014; 62(2):234-243. DOI:10.1109/TMTT.2013.2295555 · 2.94 Impact Factor
  • Girdhari Chaudhary, Yongchae Jeong
    [Show abstract] [Hide abstract]
    ABSTRACT: This letter presents a novel design and implementation of a transmission-line negative group delay (NGD) network with improved signal attenuation (SA). Theoretical analysis shows that the NGD time can be controlled by characteristic impedance of the coupled line, coupling coefficients, and resistor, respectively. The low SA characteristic in the proposed structure is obtained due to high characteristic impedance of the coupled line. To validate the proposed structure, the transmission-line NGD networks are fabricated and measured at 2.14 GHz. From the experiment, the differential-phase group delay (GD) time and SA for a single stage are ${-}$ 6.16 ns and 8.65 dB over bandwidth of 15 MHz, respectively. For bandwidth enhancement, two-stage NGD networks with slightly different center frequencies are designed and fabricated, where GD of ${-}7.48 pm 0.84~$ns and SA of 17.45 dB were obtained over a bandwidth of 28 MHz.
    IEEE Antennas and Wireless Propagation Letters 01/2014; 13:1039-1042. DOI:10.1109/LAWP.2014.2327098 · 1.95 Impact Factor

Publication Stats

211 Citations
73.98 Total Impact Points

Institutions

  • 2008–2015
    • Chonbuk National University
      • Department of Electronic Engineering
      Tsiuentcheou, Jeollabuk-do, South Korea
    • Georgia Institute of Technology
      • School of Electrical & Computer Engineering
      Atlanta, Georgia, United States
  • 2007–2011
    • Soonchunhyang University
      • Department of Electrical and Communication Engineering
      Onyang, Chungcheongnam-do, South Korea