• Journal of Advanced Marine Engineering and Technology
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• v.32 no.1
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• pp.147-152
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• 2008

This paper has been fabricated the two different type of variable attenuators using a characteristics of a 3 dB directional coupler and pin diodes. One was not analyzed using the conventional even-odd modes but used simple two-port techniques. The resulting scattering parameters described operation characteristics for the general case where the terminating impedances are equal and unequal. After analyzing resistor role of the ${\pi}$ type fixed attenuator. this paper used a pin diode instead of a resistor. The variable attenuators were fabricated using pin diodes for current-controlled attenuation on the coupled ports of a 3 dB branch-line coupler and ${\pi}$ type fixed attenuator. The realized variable attenuators have more than 33 dB attenuation ranges at 2.1 GHz. and the input and output reflection coefficients are less than -13 dB. These results could be applied to mobile communication systems. It can be varied gain of the power amplifier according to change a outdoor environmental temperature and improved linearity.

• Research in Mathematical Education
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• v.26 no.3
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• pp.235-252
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• 2023

We investigated the classification of learner groups for students' mathematical modeling competency and analyzed the characteristics in each profile group for each country and variable using PISA 2012 data from six countries. With a perspective on measuring sub-competency, we applied the latent profile analysis method to student achievement for mathematical modeling variables - Formulate, Employ, Interpret. The findings showed the presence of 4-6 profile groups, with the variables exhibiting high and low achievement within each profile group varying by country, and a hierarchical structure was observed in the profile group distribution in all countries, interestingly, the Formulate variable showed the largest difference between high-achieving and low-achieving profile groups. These results have significant implications. Comparison by country, variable, and profile group can provide valuable insights into understanding the various characteristics of students' mathematical modeling competency. The Formulate variable could serve as the most suitable predictor of a student's profile group and the score range of other variables. We suggest further studies to gain more detailed insights into mathematical modeling competency with different cultural contexts.

• Journal of Fisheries and Marine Sciences Education
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• v.29 no.3
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• pp.778-784
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• 2017

This paper proposes a sensorless speed control of a permanent magnet synchronous motor (PMSM) based on an adaptive sliding mode observer (SMO) for electric propulsion system of small ships. An adaptive observer gain is proposed based on the Lyapunov's stability criterion to reduce the chattering problem at any speed operation instead of the constant gain observer. Furthermore, a cascade low-pass filter with variable cut-off frequency is suggested to strengthen the filtering capability of the observer. The experimental results from a 1.5 kW PMSM drive are provided to verify the effectiveness of the proposed adaptive SMO. The result shows that the proposed method gives good speed control performances even when the PMSM operates at 0.5% from its rated speed value.

• Journal of international Conference on Electrical Machines and Systems
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• v.3 no.4
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• pp.367-373
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• 2014

The most common current controller for the Switched Reluctance Motor (SRM) is the hysteresis controller. This method, however, suffers from such drawbacks as variable switching frequency, consequent audible noise and high current ripple. These disadvantages make this controlling method undesirable for many applications. The alternative solution is the PI controller. Since the fixed gain PI current controller can only be optimized for one operating point, and on the other hand, SR motor is highly nonlinear, PI controller gain should be adjusted according to incremental inductance. This paper presents a novel method for PI current controller gain adaptation which is simple and yields a good performance. The proposed controller has been implemented on a test bench using a eZdsp F28335 board. The performance of the current controller has been investigated in both simulation and experimental tests using a four-phase 8/6 4KW SRM drive system.

• JSTS:Journal of Semiconductor Technology and Science
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• v.10 no.4
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• pp.309-315
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• 2010

A fully-differential low-voltage low-power electrocardiogram (ECG) amplifier by using the nonfeedback PMOS pseudo-resistors is proposed. It consists of two operational-transconductance amplifiers (OTA) in series (a preamplifier and a variable-gain amplifier). To make it insensitive to the gate leakage current of the OTA input transistor, the feedback pseudo-resistor of the conventional ECG amplifier is moved to input branch between the OP amp summing node and the DC reference voltage. Also, an OTA circuit with a Gm boosting block without reducing the output resistance (Ro) is proposed to maximize the OTA DC gain. The measurements shows the frequency bandwidth from 7 Hz to 480 Hz, the midband gain programmable from 48.7 dB to 59.5 dB, the total harmonic distortion (THD) less than 1.21% with a full voltage swing, and the power consumption of 233 nW in a 0.13 ${\mu}m$ CMOS process at the supply voltage of 0.7 V.

• Journal of Mechanical Science and Technology
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• v.18 no.4
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• pp.630-639
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• 2004

The Stewart platform manipulator is a closed-kinematics chain robot manipulator that is capable of providing high structural rigidity and positional accuracy. However, this is a complex and nonlinear system, so the control performance of the system is not so good. In this paper, a new robust motion control algorithm is proposed. The algorithm uses partial state feedback for a class of nonlinear systems with modeling uncertainties and external disturbances. The major contribution is the design of a robust observer for the state and the perturbation of the Stewart platform, which is combined with a variable structure controller (VSC). The combination of controller and observer provides the robust routine called sliding mode control with sliding perturbation observe. (SMCSPO). The optimal gains of SMCSPO, which is determined by nominal eigenvalues, are easily obtained by genetic algorithm. The proposed fitness function that evaluates the gain optimization is to put sliding function. The control performance of the proposed algorithm is evaluated by the simulation and experiment to apply to the Stewart platform. The results showed high accuracy and good performance.

• Proceedings of the KIEE Conference
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• 1999.07f
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• pp.2610-2612
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• 1999

In controlling vector of induction motor, PID controller is required much time as the expert should control manually a gain of controller according to plant or a change of circumstances. Accordingly, this paper has gotten a gain of PID controller used neural network by self-funning method in order to settle above problem. The neural network can describe an input/output features in spite of non-linear system which is hard to get mathematical model by controlling the strength of connection by learning. It has a strong character against a distortion and noise of input information, and is suitable modeling of diver-variable system which is composed of several input/output. This paper has represented the self-tunning method for gain of PID controller used neural network when using PID controller to control speed of induction motor, and has checked strong characters against distortion and noise of input information through simulation.

• Proceedings of the KIEE Conference
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• 2006.07b
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• pp.719-720
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• 2006

In the mechanical system, optimization of motion control is very essential in the aspect of automation technique progress. In the servo system, the function of controller is very important but most of the controllers have played only the role of pulse generator because the controller with main function is very expensive. In this thesis, the system was composed of PC, commonly used driver AC servo motor and a produced control board. The PC transmit a gain, a locus data to a driver and controller. At the same time, it converts imformation from the controller and convert them into data and offer an output with graph. The role of a controller is to trasmit a locus data to a driver and counting the pulse on the phase of an encoder to the PC. We have performed the experiment in order to confirm with variable PID parameter capable of the optimization of gain tuning with the counting of feedback control sensor signal with regard to the external interface into the system, such as torque. Based on the experiment result, we have confirmed as follows: First, it was confirmed that we could easily input control factors P.I Gain, constant $K_P,\;K_I$ into PC. Second, not only pulse generator function was possible, but with this pulse it was also possible to count using software with PIC chip. And third, using the multi-purpose PIC micro chip, simple operation and the formation of small size AC Servo Controller was possible.

• JSTS:Journal of Semiconductor Technology and Science
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• v.9 no.1
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• pp.22-28
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• 2009

This paper presents a fast received signal strength indicator (RSSI) circuit for wireless communication application. The proposed circuit is developed using power detectors and an analog-to-digital converter to achieve a fast settling time. The power detector is consisted of a novel logarithmic variable gain amplifier (VGA), a peak detector, and a comparator in a closed loop. The VGA achieved a wide logarithmic gain range in a closed loop form for stable operation. For the peak detector, a fast settling time and small ripple are obtained using the orthogonal characteristics of quadrature signals. In $0.18-{\mu}m$ CMOS process, the RSSI value settles down in $20{\mu}s$ with power consumption of 20 mW, and the maximum ripple of the RSSI is 30 mV. The proposed RSSI circuit is fabricated with a personal handy-phone system transceiver. The active area is $0.8{\times}0.2\;mm^2$.

• ETRI Journal
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• v.30 no.4
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• pp.526-534
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• 2008

This paper presents a fully integrated 0.13 ${\mu}m$ CMOS MB-OFDM UWB transmitter chain (mode 1). The proposed transmitter consists of a low-pass filter, a variable gain amplifier, a voltage-to-current converter, an I/Q up-mixer, a differential-to-single-ended converter, a driver amplifier, and a transmit/receive (T/R) switch. The proposed T/R switch shows an insertion loss of less than 1.5 dB and a Tx/Rx port isolation of more than 27 dB over a 3 GHz to 5 GHz frequency range. All RF/analog circuits have been designed to achieve high linearity and wide bandwidth. The proposed transmitter is implemented using IBM 0.13 ${\mu}m$ CMOS technology. The fabricated transmitter shows a -3 dB bandwidth of 550 MHz at each sub-band center frequency with gain flatness less than 1.5 dB. It also shows a power gain of 0.5 dB, a maximum output power level of 0 dBm, and output IP3 of +9.3 dBm. It consumes a total of 54 mA from a 1.5 V supply.