• The Journal of the Acoustical Society of Korea
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• v.43 no.2
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• pp.253-259
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• 2024

This paper proposes a new speech enhancement model based on a complex nested U-Net with a dual-branch decoder. The proposed model consists of a complex nested U-Net to simultaneously estimate the magnitude and phase components of the speech signal, and the decoder has a dual-branch decoder structure that performs spectral mapping and time-frequency masking in each branch. At this time, compared to the single-branch decoder structure, the dual-branch decoder structure allows noise to be effectively removed while minimizing the loss of speech information. The experiment was conducted on the VoiceBank + DEMAND database, commonly used for speech enhancement model training, and was evaluated through various objective evaluation metrics. As a result of the experiment, the complex nested U-Net-based speech enhancement model using a dual-branch decoder increased the Perceptual Evaluation of Speech Quality (PESQ) score by about 0.13 compared to the baseline, and showed a higher objective evaluation score than recently proposed speech enhancement models.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.42 no.4
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• pp.864-870
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• 2017

This paper describes a Dual Buck Converter with mode control using variable Frequency to Voltage for portable devices requiring wide load current. The inherent problems of PLL compensation and efficiency degradation in light load current that the conventional hysteretic buck converter has faced have been resolved by using the proposed Dual buck converter which include improved PFM Mode not to require compensation. The proposed mode controller can also improve the difficulty of detecting the load change of the mode controller, which is the main circuit of the conventional dual mode buck converter, and the slow mode switching speed. the proposed mode controller has mode switching time of at least 1.5us. The proposed DC-DC buck converter was implemented by using $0.18{\mu}m$ CMOS process and die size was $1.38mm{\times}1.37mm$. The post simulation results with inductor and capacitor including parasitic elements showed that the proposed circuit received the input of 2.7~3.3V and generated output of 1.2V with the output ripple voltage had the PFM mode of 65mV and 16mV at the fixed switching frequency of 2MHz in hysteretic mode under load currents of 1~500mA. The maximum efficiency of the proposed dual-mode buck converter is 95% at 80mA and is more than 85% efficient under load currents of 1~500mA.

• Proceedings of the IEEK Conference
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• 2004.06a
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• pp.217-220
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• 2004

This paper presents design simulation, implementation, and measurement of a miniaturized GPS/K-PCS dual-band LTCC chip antenna for mobile communication handsets. The dimension of LTCC chip antenna is $9mm{\times}15mm{\times}1.2mm$. The lower meander type antenna is to be tuned to the lower frequency (GPS) band and the upper meander antenna with via hole connection is to contribute the higher frequency (K-PCS) band. In order to lowering the resonant frequency for GPS band, two printed modified meander antenna with gap stub is used to integrate with PCS band operation. The measured resonant frequency at GPS band shifts to lower frequency about 100MHz. The measured impedance bandwidth(VSWR $\leq$ 2) are 55MHz and 120MHz at the resonant frequency. respectively.

• JSTS:Journal of Semiconductor Technology and Science
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• v.11 no.4
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• pp.329-335
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• 2011

In this paper, a dual-band integer-N frequency divider is proposed for 2.4/5.2 GHz multi-standard wireless local area networks. It consists of a multi-modulus imbalance phase switching prescaler and two all-stage programmable counters. It is able to provide dual-band operation with high resolution while maintaining a low power consumption. This frequency divider is integrated with a 5 GHz VCO for multi-standard applications. Measurement results show that the VCO with frequency divider can work at 5.2 GHz with a total power consumption of 22 mW.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.25 no.11
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• pp.1588-1595
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• 2021

Android-based smartphones receive the global navigation satellite system (GNSS) signals to determine their location and provide the GNSS raw measurement to users. The available GNSS signals on the current Android devices are GPS, GLONASS, Galileo, BeiDou, QZSS. This research has analyzed the performance of multi-GNSS position accuracy based on the pseudorange of the smartphone for maritime users. Smartphones capable of receiving dual-frequency are installed on a ship, and multi-GNSS raw information in maritime environment was measured to present the results of comparing the GNSS pseudorange-based dual-frequency positioning performance for each smarphone. Furthermore, we analyzed whether the results of the positioning performance can meet the HEA requirement of IMO for maritime navigation users. As the results of maritime experiment, it was confirmed that in the case of the smartphones supporting the dual-frequency, the position accuracy within 6 meters (95%) could be obtained, and the HEA position accuracy performance within 10 meters (95%) required by IMO could be achieved.

• Journal of electromagnetic engineering and science
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• v.16 no.3
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• pp.159-163
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• 2016

In this paper, a frequency tunable double band-stop resonator (BSR) with voltage control by varactor diodes is suggested. It makes use of a half-wavelength shunt stub as its conventional basic structure, which is replaced by the distributed LC block. Taking advantage of the nonlinear relationship between the frequency and electrical length of the distributed LC block, a dual-band device can be designed easily. With two varactor diodes, the stop-band of the resonator can be easily tuned by controlling the electrical length of the resonator structure. The measurement results show the tuning ranges of the two operating frequencies to be 1.82 GHz to 2.03 GHz and 2.81 GHz to 3.03 GHz, respectively. The entire size of the resonator is $10mm{\times}11mm$, which is very compact.

• Journal of the Optical Society of Korea
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• v.20 no.2
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• pp.300-304
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• 2016

A dual loop optoelectronic oscillator (OEO) based on an acousto-optic modulator (AOM) for single mode operation with an acousto-optic delay line is demonstrated in this paper. When the OEO operates, the free spectral range is a function of the total loop length of the OEO, which is mainly dependent on the propagation time of the acoustic wave in the AOM. Due to the huge difference in the magnitude between the speed of light and the acoustic velocity in the AOM, the effective loop length converted to light-propagation length of the OEO increases to 3.8 km. With 150 MHz oscillation frequency, phase noise of -118 dBc/Hz at 10 kHz frequency offset, and -140 dBc/Hz at 200 kHz frequency offset, is achieved.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.6 no.8
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• pp.1139-1145
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• 2002

Wavelet transformed data can filter signal with each frequency band, because it includes detail information about original signal. Therefore, in this paper, important two noises were removed by wavelet. About AWGN environment UDWT(undecimated discrete wavelet transform), applying hard-threshold, was used and about impulse noise environment, it can be possible to recognize edge of original signal as well as superior denoising effect by using two methods, denoising by threshold and slope of signal by wavelet. SNR was used as a judgemental criterion of a denoising effect and Blocks and DTMF(dual tone multi frequency) were used as a test signal.

• ETRI Journal
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• v.31 no.1
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• pp.77-79
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• 2009

The wave concept iterative procedure (WCIP) is used to analyze a quasi-square open metallic ring frequency selective surface (FSS). The quasi-square open metallic ring FSS is dual-polarized. When the incident plane wave is polarized in a direction parallel to the FSS' coupled parallel strips, it shows two rejecting bands. Moreover, another rejecting band can be obtained if the source plane wave is perpendicularly polarized with respect to the FSS' coupled parallel strips. The three resonant frequencies are inversely proportional to the length of the FSS' coupled strips to provide an easy fine tuning of the FSS structure. The simulated results obtained using WCIP are compared to the measured results, and a good agreement is reported.

• Journal of the Korean Society for Precision Engineering
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• v.32 no.6
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• pp.563-570
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• 2015

In this paper, Finite Element Analysis (FEA) for gear heat treatment using simultaneous dual frequency (SDF) induction heating is conducted. To do this, thermal-electromagnetic coupled FE model is built. A two dimensional FE model of gear and heater is introduced to reduce computation time. For more time-efficient analysis, harmonic analysis for electromagnetic model is adopted and transient analysis model, for heat transfer model. Through the coupled analysis, it can be found that the proposed FE model can solve for SDF induction heating of gear and heat treatment parameters can also be determined.