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Oh, Sangyeol,Jeong, Jichai,Lee, Jaehoon IET 2015 Electronics letters Vol.51 No.25
<P>A common noise suppression filter in a differential pair using the coupled microstrip line (CML) to edge-coupled coplanar waveguide (ECCPW) transition is proposed. The filter consists of CMLs, ECCPWs, and shorting via holes that connect the CMLs and ECCPWs, and provides wideband common noise signal suppression using an even-mode impedance mismatching technique between the CMLs and ECCPWs and wideband differential signal propagation for high-speed circuit systems. A bandgap effect is realised in even mode, based on the CML to ECCPW transition without a multilayer. This method was verified using the three-dimensional full-wave high-frequency structure simulator and experimental measurements.</P>
Investigation of the Lower Bound of Outage Threshold in Indoor Power-Line Networks
Jaeyoung Shin,Jichai Jeong Institute of Electrical and Electronics Engineers 2016 IEEE Transactions on Power Delivery Vol. No.
<P>We theoretically investigate lower bound of the outage threshold based on channel capacity degradation in indoor power-line networks and its practical applicability to a realistic indoor power-line network existing in practice. We estimate the channel capacity degradations of arbitrary channels in networks with uniformly distributed branches with regular length. The channel capacity degradations are estimated under various network configurations, such as network size, branch characteristics (including the number and length), and loading conditions (including the number, type, impedance, and location). Based on the channel capacity degradation, the lower bounds of the outage threshold of arbitrary channels, which can evaluate the quality of the channels, are given. To evaluate the practical applicability of the simulated results, we compare the lower bounds of the outage threshold between a realistic network and simple networks. It is shown that the Pearson's correlation coefficients between the realistic network and the simple networks are predominantly greater than 0.85 (-value 0.01) in almost all cases, which shows a strong correlation in terms of the outage behavior. Therefore, our investigation enables estimating the outage behavior of a realistic network, without sufficient prior information of the network configuration using a simple network with a similar network configuration.</P>
A Low Power and Wide Variable Gain RF Receiver Front-end for 5.25-㎓ Band
Youngbin Ahn,Jichai Jeong 대한전자공학회 2010 ICEIC:International Conference on Electronics, Inf Vol.1 No.1
A CMOS front-end with wide variable gain and low power consumption for 5.25 ㎓ band has been designed and simulated with the TSMC 0.18 ㎛ CMOS technology. To obtain wide variable gain range, a p-MOSFET is connected in a shunt configuration for the low noise amplifier (LNA) section. For a mixer, a single balanced and folded structure is employed for the low power consumption. The bias currents of the transconductance and switching stages in the mixer area can be separated without using a current bleeding path. The proposed front-end has a maximum gain of 33 ㏈ with a variable gain range of 25 ㏈. The noise figure and third-order input intercept point (IIP3) are 5.2 ㏈ and -8.5 ㏈m, respectively. For the operating condition, the proposed front-end consumes 7.1 ㎽ at a high gain mode, and 2.6 ㎽ at a low gain mode.
Shin, Jaeyoung,Jeong, Jichai SOCIETY OF PHOTO-OPTICAL INSTRUMENTATION ENGINEERS 2014 JOURNAL OF BIOMEDICAL OPTICS Vol.19 No.6
<P>We improved the performance of a functional near-infrared spectroscopy (fNIRS)-based brain-computer interface based on relatively short task duration and multiclass classification. A custom-built eight-channel fNIRS system was used over the motor cortex areas in both hemispheres to measure the hemodynamic responses evoked by four different motor tasks (overt execution of arm lifting and knee extension for both sides) instead of finger tapping. The hemodynamic responses were classified using the naive Bayes classifier. Among the mean, max, slope, variance, and median of the signal amplitude and the time lag of the signal, several signal features are chosen to obtain highest classification accuracy. Ten runs of threefold cross-validation were conducted, which yielded classification accuracies of 87.1%2.4% to 95.5%2.4%, 77.5%1.9% to 92.4%3.2%, and 73.8%3.5% to 91.5%1.4% for the binary, ternary, and quaternary classifications, respectively. Eight seconds of task duration for obtaining sufficient quaternary classification accuracy was suggested. The bit transfer rate per minute (BPM) based on the quaternary classification accuracy was investigated. A BPM can be achieved from 2.81 to 5.40 bits/min.</P>
Dong, Sunghee,Jeong, Jichai IOP 2018 Journal of neural engineering Vol.15 No.1
<P> <I>Objective</I>. Memory is formed by the interaction of various brain functions at the item and task level. Revealing individual and combined effects of item- and task-related processes on retrieving episodic memory is an unsolved problem because of limitations in existing neuroimaging techniques. To investigate these issues, we analyze fast and slow optical signals measured from a custom-built continuous wave functional near-infrared spectroscopy (CW-fNIRS) system. <I>Approach</I>. In our work, we visually encode the words to the subjects and let them recall the words after a short rest. The hemodynamic responses evoked by the episodic memory are compared with those evoked by the semantic memory in retrieval blocks. In the fast optical signal, we compare the effects of old and new items (previously seen and not seen) to investigate the item-related process in episodic memory. The Kalman filter is simultaneously applied to slow and fast optical signals in different time windows. <I>Main results</I>. A significant task-related HbR decrease was observed in the episodic memory retrieval blocks. Mean amplitude and peak latency of a fast optical signal are dependent upon item types and reaction time, respectively. Moreover, task-related hemodynamic and item-related fast optical responses are correlated in the right prefrontal cortex. <I>Significance</I>. We demonstrate that episodic memory is retrieved from the right frontal area by a functional connectivity between the maintained mental state through retrieval and item-related transient activity. To the best of our knowledge, this demonstration of functional NIRS research is the first to examine the relationship between item- and task-related memory processes in the prefrontal area using single modality.</P>