• 한국정보통신설비학회:학술대회논문집
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• 2007.08a
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• pp.19-21
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• 2007

디지털용 Uncooled DFB 레이저 다이오드를 이용하여 광대역 아날로그 피드포워드 광송신기를 제작하였다. 광송신기의 상호변조왜곡 성분 및 잡음성분을 제거하기 위해 광 피드포워드 보상기법을 사용하였으며, 다중서비스를 위해 $2.05{\sim}2.60$ GHz(550 MHz)에서 상호 변조왜곡 성분이 10 dB 이상 억제되었고, 상대강도잡음은 1.5 dB 이상 억제되었다. 2.3 GHz 에서 3 차 상호변조왜곡성분이 21.3 dB, SFDR 이 7.11 dB 향상된 결과를 얻었다. 또한 단일 모드 광섬유 전송 실험을 통해 전송길이에 따른 3 차 상호변호 왜곡성분의 크기 변화를 확인하였다.

• Journal of Satellite, Information and Communications
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• v.12 no.4
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• pp.115-119
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• 2017

Intermodulation distortion degrades the S/N(signal-to-noise) of the original signal and also affects the adjacent channels. Intermodulation distortion is mainly caused by the nonlinear characteristics of the power amplifier. If the power amplifier with nonlinear characteristics has a memory effect, the intermodulation distortions occurred in the power amplifier are generated in various and complex forms. The predistorter is used as a way to improve intermodulation distortions. In order to efficiently utilize the performance of the predistorter, the memory effect of the power amplifier must be reduced. In this paper, we describe the design method of bias circuit to reduce the memory effect in power amplifiers. To reduce the memory effect, the bias circuit must have a high impedance for the signal and a low impedance for the envelope(modulating signal) and the second harmonic component of the signal. To verify the performance of the bias circuit designed considering the memory effect, a power amplifier operating at 170 ~ 220MHz was designed and implemented. The designed bias circuit has a large impedance in the operating frequency band and low impedance in the envelope signal and the second harmonic of the signal. As a result of the performance measurement, it was found that the asymmetric intermodulation distortion component is improved by 3.7dB.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.45 no.5
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• pp.33-39
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• 2008

We have experimentally demonstrated the transmission performance of a feedforward optical transmitter using an external light injection technique. The feedforward compensation method shows 31 dB intermodulation distortion suppression and 2.2 dB noise reduction. A high side-mode suppression ratio exceeding 35 dB of the wavelength of the locked Fabry-Perot laser diode was obtained over 12 nm ranges. The suppression characteristics of the intermodulation distortion for various wavelength differences and transmission lengths were measured and analyzed as the evaluation criteria for the system performance in WDM/SCM based radio-over-fiber systems.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.43 no.5 s.347
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• pp.17-24
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• 2006

The optical feedforward is known as a complicated technique in spite of its superior linearization. Here we optimized the feedforward circuit parameters using a systematic approach for optimum efficiency. A systematic approach was verified by transmission experiments of 2.14 GHz two tones. The compared third order IMD was enhanced by 38 dB for two-tone case. The experimental results for transmission of W-CDMA signals were described. The ACPR was enhanced by 20 dB for 1 W-CDMA carrier and by 16 dB for 3 W-CDMA carriers. Also, noise level was reduced by 7 dB.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2003.05a
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• pp.92-96
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• 2003

In this paper, 30 W power Amplifier for IMT-2000 repeater was developed gain flatness and the third IMD (Intermodulation distortion) by Microwave absorber. The absorption ability of the absorber is measured up to -10 ㏈ and -4 ㏈ at 3.6 ㎓, 2.3 ㎓ band respectively. Non using absorber power amplifier has the gain over 57 ㏈, the gain flatness of ${\pm}$0.33 ㏈ and the third IMD of 27 ㏈c at 33.3 W output. Otherwise, using absorber power amplifier has the gain over 58㏈, the gain flatness of less than ${\pm}$0.9, the third IMD over 29 ㏈c at the same output power. As a result, the characteristic of the different type show improvement of 1 ㏈ in gain, 0.3 ㏈ in Gain flatness and 1.77 ㏈c in IMD.

• 한국정보통신설비학회:학술대회논문집
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• 2008.08a
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• pp.296-299
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• 2008

최근 통신시스템과 핸드폰, PDA등의 통신기기들의 발전에 따라 사용자들은 높은 데이터 전송률과 고속의 통신서비스를 요구하고 있다. 이러한 상황에서 유 무선 통합 시스템인 Radio-over-Fiber(RoF) 시스템은 그 대안으로 대두되고 있다. 본 논문에서는 광전자소자를 선 왜곡 방식에 적용하여 광 송신기의 선형성을 향상시키는 방법을 제안하였다. 선 왜곡 방식은 두 개의 루프로 구성되어 있으며, 광 부품인 레이저 다이오드와 포토 다이오드 그리고 RF 부품인 위상변위기, 감쇄기, RF 결합/분배기, RF 증폭기를 사용하였다. 메인 루프에서 주 레이저 다이오드의 비선형성에 의해 발생된 왜곡신호성분은 보조 루프에서 부 레이저 다이오드를 이용하여 추출된 선 왜곡신호에 의해서 제거된다. 제안된 선형화 기법을 적용하여 2.4 GHz에서 선형화 기법을 적용하기 전보다 3차 상호변조 왜곡성분이 약 30dB 향상된 결과를 얻었다.

• Proceedings of the IEEK Conference
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• 2007.07a
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• pp.159-160
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• 2007

Two analog predsitorters (PDs) using the mixing operation are proposed to compensate for the memory effects of the power amplifier and then significantly cancel IM3 components with the independent control of IM3 terms. In the first PD, IM3 terms are generated by using mixing operation of low frequency terms. In the second PD, the double mixing operation of the fundamental components is used. For a two-tone signal with 20-MHz tone spacing, the notable IM3 suppression is achieved over a whole output power range.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.10a
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• pp.53-56
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• 2003

A linear power amplifier is particularly emphasized on the CDMA system using a linear modulation scheme, because IMD which cause adjacent channel interference and co channel Interference is mostly generated in a nonlinear power amplifier. In this paper, a new type of linearization technique proposed. It is presented that balanced MESFET predistortion linearizer added. Experimental result are present for Korea PCS frequency band. The implemented linearizer is applied to a 30dBm class. A power amplifier for simulation performance. Two-tone signals at 1850 MHz and 1851.23 MHz are injected into the main power amplifier. The main power amplifier with a 12.1dB gain and a P1dB of 30 dBm(two-tone) was utlized. The reduction of IMD is around 22dB.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.7
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• pp.1369-1373
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• 2003

A linear power amplifier is particularly emphasized on the CDMA system using a linear modulation scheme, because IMD which cause adjacent channel interference and co channel interference is mostly generated in a nonlinear power amplifier. In this paper, a new type of linearization technique proposed. It is presented that balanced MESFET Predistortion linearizer added. Experimental result are present for Korea PCS frequency band. The implemented linearizer is applied to a 30㏈m class A power amplifier for simulation performance. Two-tone signals at 1850 MHz and 1851.23 MHz are injected into the main power amplifier. The main power amplifier with a 12.1㏈ gain and a P1㏈ of 30 ㏈m(two-tone) was utilized. The reduction of IMD is around 22㏈.

• Journal of Navigation and Port Research
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• v.27 no.4
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• pp.437-441
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• 2003

In this paper, the 30 W power amplifier for an IMT-2000 repeater was developed a gain flatness and the third IMD (Intermodulation distortion) by microwave absorber. The absorption ability of the absorber is shown up to -10 dB and -4 dB at 3.6 GHz, 2.3 GHz band, respectively. The power amplifier without absorber has the gain over 57 dB, the gain flatness of $\pm$0.33 dB and the third IMD of 27 dBc at 33.3 W output. Otherwise, the power amplifier with absorber has the gain over 58 dB, the gain flatness of less than $\pm$0.9, the third IMD over 29 dBc at the same output power. As a result, the characteristic of the different type shows improvement of 1 dB in gain, 0.3 dB in gain flatness and 1.77 dBc in IMD.