E.S. Nam

Hanbat National University, Daiden, Daejeon, South Korea

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Publications (11)0.84 Total impact

  • Eun Soo Nam · M.S. Oh · H.Y. Kim · Y.J. Chong
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    ABSTRACT: We have developed a high-resolution, direct detection imaging ladar using a microchip laser and the 32times32 two dimensional InGaAs/InP pin photodiode array. With microchip lasers and compact microelectronic arrays of detectors and timing circuitry, we can fabricate a imaging laser radar small enough to be portable. The microchip laser employed in this lidar utilizes 1.55 mum InGaAsP/InP high power laser diode. The 32 times 32 InGaAs/InP PIN diode array offers robust, solid-state, good sensitivity. In the near future, InGaAs/InP APD having a larger arrays of 128 times 128 pixels and lenslet array will be developed which allows for the capture of entire 3-D images on a single laser pulse at high frame rates. The effort for the development of these detector and laser technologies will lead to 3-D imaging systems with higher spatial resolution at longer ranges in compact packages.
    No preview · Conference Paper · Dec 2008
  • Eun Soo Nam · D.Y. Kim · M.S. Oh · H.Y. Kim · Y.J. Jung · H.C. Kim · H.K. Yu
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    ABSTRACT: An LTCC-based photonic millimeter-wave receiver using a waveguide photodiode was developed for the detection of the analogue millimeter-wave optical signal transmitted over optical fiber. An LTCC- based photonic millimeter-wave receiver processed 2.67 Gbps of the HDTV data which are frequency-up converted optical signal of 60 GHz . The total bandwidth assigned for the HDTV is 528 MHz which is occupied by 88 channels whose unit channel bandwidth is 6 MHz. The transferred RF signal format was based on single carrier in 60 GHz band with 64 QAM modulation. The low cost LTCC based 60 GHz millimeter- wave photo-receiver was successfully demonstrated for the gigabit-per- second wireless HDTV broadcasting systems.
    No preview · Conference Paper · Jan 2008
  • Y.W. Kim · E.S. Nam · S.E. Hong · B.W. Kim · H.D. Cheong
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    ABSTRACT: We have experimentally compared to different collector layer thickness and analyzed the dependence of the dc and the RF characteristics of the non self-aligned single heterojunction bipolar transistors (SHBTs) on the collector layer's thickness. For this comparative study, we fabricated InGaAs/InP SHBTs with collector layer thicknesses of 3500 Å (sample A) and 5000 Å (sample B). The emitter size of SHBT was set to be 1.2 × 6 μm 2. We investigated the dependence of the cut-off frequency (f T) and the maximum oscillation frequency (fmax) on the collector current for SHBTs with different collector thicknesses and the same doping density to clarify the transit time and the charging time for the InGaAs/InP SHBT. In the sample A, maximum fmax and fT were measured to be 176 GHz and 143 GHz, respectively at VCE = 1.5 V and Ic = 12 mA. In sample B, the maximum fmax and f T were measured to be 126 GHz and 127 GHz, respectively at V CE = 1.5 V and Ic = 12 mA. The dc current gain (β) and the breakdown voltage (BVceo) at IB = 1 mA were 25 and 6 V in sample A, respectively. For sample B, the dc current gain (β) and the breakdown voltage (BVceo) at IB = 1 mA were 26 and 8 V, respectively. The offset voltages, Vce off-set, were independent of the collector layer thickness, and were about 0.11 V for sample A and sample B. The experimental results manifest that it takes a shorter time for charging and transition of electrons in InGaAs/InP SHBTs with thinner collector layers.
    No preview · Article · Sep 2006 · Journal- Korean Physical Society
  • Eun Soo Nam · M.S. Oh · S.E. Hong · H S Kim
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    ABSTRACT: In the 2 dimensional InGaAs/InP photodiode arrays on semi-insulating InP the dark current is limited by the diffusion and generation- recombination. The static dark current of the InGaAs/InP PiN photodiode arrays is proportional to the number of the pixels in the array. In PiN InGaAs photodiode array structure, the diffusion currents of the each pixel due to the thermally generated minority carriers diffusing into the depletion region are accumulated to reach total leakage current. This phenomenon of pixel number dependent leakage current is due to the accumulation of the contributed diffusion current as much as ~0.02 pA/cm<sup>-2</sup> from the each pixel photodiode comprising the array.
    No preview · Conference Paper · Aug 2006
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    ABSTRACT: Two dimensional InGaAs/InP PIN photodiode array on semi-insulating InP has been developed for the image sensing of the eye safe laser radar in the 1.55 μm wavelength range of the spectrum with high bandwidth and large area. The fabrication and dark current characteristics are discussed. Dark current characteristic is limited by the diffusion and generation-recombination in the 2 dimensional InGaAs/InP photodiode arrays on semi-insulating InP. The static dark current of the InGaAs/InP PIN photodiode arrays increases as proportional to the number of the pixels in the array.
    No preview · Conference Paper · Jan 2006
  • Y.W. Kim · S.E. Hong · E.S. Nam · H.D. Cheong
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    ABSTRACT: Extensively comparative studies are carried out on the performance of on-chip CMOS transformers in the presence and absence of patterned ground shields (PGS) at temperatures of 253 K, 298 K, 333 K, and 373 K. These transformers were fabricated using 0.18 micron CMOS processes and designed to be interleaved and center-tapped interleaved geometries, respectively, but with the same inner dimension, metal track width, track spacing and substrate properties. Based on the two-port S-parameters measured at different temperatures, all performance indicators, such as maximum available gain Gmax, Q-factor of the primary or secondary coil, power loss, and minimum noise figure of these transformers are extracted and compared with each other.
    No preview · Conference Paper · Jan 2005
  • D.Y. Jung · S.E. Hong · E.S. Nam · H.S. Kim
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    ABSTRACT: An optoelectronic integrated circuit (OEIC) operating in the 1.55-μm wavelength range is realized on InP substrate. The HBT and PD devices grown on vertically stacked layers are used to fabricate an OEIC. The high performance of both PD and HBT devices is explored, and the DC and RF characteristics are investigated. The vertically stacked HBT has a cut-off frequency (fT) of 100 GHz and a maximum oscillation frequency (fmax) of 75 GHz. The characteristics of a waveguide PD are evaluated, and a broadband OEIC using vertically stacked InP/InGaAs HBTs is designed for 10-Gbps optical communication systems.
    No preview · Article · Sep 2004
  • D.Y. Jung · H.G. Ji · H.C. Kim · E.S. Nam · C.S. Park
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    ABSTRACT: This paper presents a trans-impedance amplifier (TIA) of a source follower topology for bandwidth extension. An analytical model for designing a TIA with a source follower stage has been derived. Based on this approach, we have designed two TIAs, which are a conventional common source TIA (CS-TIA) and a proposed source follower TIA (SF-TIA) for bandwidth extension. They were implemented for a 2.5-Gbps optical receiver using commercial 0.5 μm metal semiconductor field-effect transistor (MESFET) technologies. The trans-impedance gain (TIG) of the two fabricated amplifiers is the same, at 59 dBΩ. The measured bandwidth of the CS-TIA is 2.35 GHz, and that of the proposed SF-TIA is 4.05 GHz, enhanced by 1.7 GHz.
    No preview · Article · Sep 2004
  • E.S. Nam · D.Y. Jung · S.E. Hong · H.S. Kim
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    ABSTRACT: High speed and high sensitivity p-i-n/HBT photoreceivers were implemented using an optoelectronic integration technology, where the p-i-n InP/InGaAs waveguide photodiode and InP/InGaAs HBTs are made from vertically stacked epitaxial layers on a semi-insulating InP substrate. The parasitic effects of the photodiode on the microwave performance of HBT are investigated, these being encountered in optoelectronic integrated circuits where the photodiode layers are grown under the InP/InGaAs HBT layers. We estimated a HBT unit current gain cut-off frequency fΤ of 82 GHz and the maximum oscillation frequency fmax of 64 GHz in the OEIC wafer with HBT on the photodiode layers at an emitter-collector voltage Vce of 1 V and a collector current Ic of 20 mA. These values represent 20 %-degraded rf performance, due to the parasitic junction capacitance of the p-i-n photodiode layer placed at the bottom of the HBT, compared with the values, fΤ of 107 GHz and fmax of 88 GHz, of the OEIC wafer with the photodiode on HBT.
    No preview · Article · Sep 2004
  • S.E. Hong · J.M. Lim · S.I. Kim · E.S. Nam
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    ABSTRACT: We report a preamplifier with wide bandwidth using high-speed and reliable InGaP/GaAs HBT applicable for 10-Gbps photoreceiver modules. The three-stage preamplifier with a negative feedback resistor demonstrates an effective transimpedance gain of 43 dBΩ, a 3-dB bandwidth of 14 GHz corresponding to a very high transimpedance-bandwidth product of 2.52 THzΩ, and an output return loss of -18 dB up to -3-dB bandwidth. This compact circuit is fabricated with an area of 800 × 700 μm2. A photoreceiver module of surface-mountable package type, that is composed of preamplifier and photodiode of surface-illumination type, demonstrates an optical bandwidth of 7.5 GHz at λ = 1.55 μm and a 45-psec rise/fall time for 10-Gbps. The module shows higher sensitivity for a 10-Gbps optical transmission system.
    No preview · Article · Sep 2004 · Journal- Korean Physical Society
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    ABSTRACT: Transimpedance amplifier (TIA) for 10 Gbps applications has been fabricated with InGaP/GaAs heterojunction bipolar transistors (HBTs). From the input-referred equivalent noise current density, the sensitivity was calculated. Eye diagram showed wide opened eye; when the input current was 58.6 μ Ap-p the output voltage was 33m Vp-p and rising/falling times were 35 psec. The chip size of fabricated transimpedance amplifier was 0.7 × 0.8 mm2. The measurement result showed transimpedance gain of 50 dBΩ and a -3dB bandwidth of 8.2 GHz. The differences between simulation and measurement were analyzed with chip layout considerations.
    No preview · Article · Jan 2002