• Korean Journal of Optics and Photonics
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• v.13 no.6
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• pp.543-547
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• 2002

We have constructed two extended-cavity diode lasers which are phase-locked with a 9.2 GHz frequency offset. We adopted a digital servo circuit for the phase-locking. The relative linewidth of the phase-locked lasers was less than 2 Hz. Using the measured beat spectrum, we found the carrier concentration to be about 93 %. We measured phase noise and relative frequency stability of the lasers. The Allan deviation at the gate time of 20 s was $2.7{\times}10^{-19}$.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.7
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• pp.635-645
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• 2016

In this paper, we showed the phase noise of voltage controlled oscillator(VCO) can be radically improved using FLL(Frequency Locked Loop). At first, a 5 GHz VCO is fabricated using a hair-pin resonator. The fabricated VCO shows a phase noise of -53.1 dBc/Hz at 1 kHz frequency offset. In order to improve the phase noise of the fabricated VCO, a FLL is constructed using the feedback loop that consists of the VCO, a frequency detector composed of 5 GHz resonator, loop-filter, and level shifter. The fabricated FLL is designed to oscillate at a frequency of 5 GHz, and its measured phase noise is about -120.6 dBc/Hz at 1 kHz offset frequency. As a result, the phase noise of VCO can be radically improved by about 67.5 dB applying FLL. In addition, the measured phase noise performance is close to that of crystal oscillator.

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.2
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• pp.157-164
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• 2011

This work is devoted to the technique application of lock-in infrared Thermography in the shipbuilding and ocean engineering industry. For this purpose, an exploratory study to find the optimized test conditions is carried out by the design of experiments. It has been confirmed to be useful method that the phase contrast images were quantified by a reference image and weighted by defect hole size. Illuminated optical intensity of lower or medium strength give a good result for getting a phase contrast image. In order to get a good phase contrast image, lock-in frequency factors should be high in proportion to the illuminated optical intensity. The integration time of infrared camera should have been inversely proportional to the optical intensity. The other hand, the difference of specimen materials gave a slightly biased results not being discriminative reasoning.

• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.4
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• pp.376-381
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• 2013

위상잠금 열화상에서는 일반적으로 변조된 주파수의 광램프를 쓰고 있다. 하지만 램프의 광도 분포는 입력신호가 평단(flat)특성임에 불구하고 심지어 불균일하여 검사 시편내에 측면 열유동을 만들어낸다. 이러한 열유동은 원치 않는 효과로서 측면의 분해능을 감소시키는 등과 같이 관심 결함구조의 영상에 부정적인 영향을 미친다. 본 고에서 검토되는 방식은 열원으로서 LCD 프로젝터와 같은 것을 이용하여 각 가진픽셀에 개별적으로 진동진폭, 광도 오프셋, 위상지연 등을 할당하는 방법에 대한 접근기술이다. 이러한 반복적인 자체학습 과정에 의한 조명 패턴을 통하여 측면 열유동이 제거되고 분해능이 향상되도록 제공하는 것이다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.11
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• pp.842-850
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• 2018

In this paper, the design and fabrication of a frequency-locked-loop(FLL) 5-GHz oscillator with a single resonator is presented. The proposed oscillator is the simplified version of the previous FLL oscillator with two separate resonators in the VCO and frequency detector. The resonator is commonly used in the VCO and frequency detector of the proposed oscillator configuration. The 5-GHz oscillator is implemented on the hetero-multilayer substrate composed of a Rogers' RO4350B laminate, which has excellent high-frequency performance, and the commercial FR4 three-layer substrate. The frequency locking occurs at approximately 5 GHz and has an output power of 3.8 dBm. The phase noise has a free-run VCO phase noise at frequencies above 1 kHz, and an FLL background noise at frequencies below 1 kHz. For this loop-filter, the phase noise showed an improvement of approximately 12 dB at the offset-frequency of 100 Hz.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.10
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• pp.773-782
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• 2018

A frequency-locked loop(FLL) is a negative-feedback system that uses a frequency detector to improve the phase noise of a voltage-controlled oscillator(VCO). In this work, a theoretical analysis of the phase noise of a VCO in an FLL is presented. The analysis shows that the phase noise of the VCO follows the phase noise determined by the frequency detector and the loop filter within the FLL loop bandwidth, while the phase noise of the VCO appears outside the loop bandwidth. Therefore, it is possible to design an FLL that minimizes the phase noise of the VCO based on the theoretical analysis results. The theoretical phase noise results were verified through experiments.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.7
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• pp.540-549
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• 2017

A phase frequency detector(PFD) composed of logic circuits is widely used in a phase locked loop(PLL) due to the easy implementation for integrated circuits. A frequency locked loop(FLL) removes the reference oscillator in the PLL, and the resonator serves as a reference oscillator. A frequency detector(FD) is indispensable for the FLL configuration, and a FD, which is usually composed of a mixer is used to build an FLL. In this paper, instead of FD using mixer, a FD is constructed by using 1.175 GHz resonator composed of microstrip and PFD taking the versatility of PFD into consideration. Using the designed FD, FLL oscillating at a frequency of 1.175 GHz is composed. As a result of comparison with the FLL composed of FD using mixer, it was confirmed that the proposed FLL has better phase noise performance than FLL using mixer FD with FLL bandwidth.

• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.1
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• pp.40-45
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• 2013

The purpose of this study was to detect the pin hole defect of dental composite restoration using lock-in thermography method. Amplitude and phase images of the composite resin specimens were analyzed according to the lock-in frequency and the diameter of defect area. Through the amplitude image analysis, at lock-in frequency of 0.05 Hz, defect diameters 2-5 mm exhibited the highest amplitude contrast value between defective area and sound area. The lock-in frequency range of 0.3-0.5 Hz provided good phase angle contrast for the defect area. At lock-in frequency range of 0.5 Hz, defect diameter of 5 mm exhibited the highest phase contrast value. It is concluded that the infrared lock-in thermography method verified the effectiveness for detecting the pin hole defect of dental composite restoration.

• Journal of the Korean Society for Nondestructive Testing
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• v.35 no.3
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• pp.200-205
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• 2015

An ultra-precise infrared microscope consisting of a high-resolution infrared objective lens and infrared sensors is utilized successfully to obtain location information on the plane and depth of local heat sources causing defects in a semiconductor device. In this study, multi-layer semiconductor chips are analyzed for the positional information of heat sources by using a lock-in infrared microscope. Optimal conditions such as focal position, integration time, current and lock-in frequency for measuring the accurate depth of the heat sources are studied by lock-in thermography. The location indicated by the results of the depth estimate, according to the change in distance between the infrared objective lens and the specimen is analyzed under these optimal conditions.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.9
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• pp.44-51
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• 2019

Three types of samples with defects were measured by lock-in med-IR (infrared) thermography with various lock-in frequencies for different materials. The lock-in method can be used to detect defects when an external energy source is applied to the object, the non-uniformity of the incident thermal energy distribution is eliminated, and the camera's measurement cycle is synchronized with the load cycle of the incident energy source. For inspecting samples with defects, results of thermal images are analyzed when three types of materials, i.e., SM45C, STS316L, and AL6061 are tested and three lock-in frequencies, i.e., 0.08, 0.1, and 0.12 Hz are applied. In this study, the optimal lock-in frequencies were determined by comparing the results of each material and lock-in frequency measured using the mid-IR camera.