• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2002.11a
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• pp.182-185
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• 2002

A RE predistorted asymmetric Doherty amplifier for CDMA IS-95 signal has been fabricated using GaAs FETs. The Doherty amplifier used a Class AB main device and a Class C auxiliary device. At 6 ㏈ back-of from Pl ㏈ of 34 ㏈m, PAE of 27% was measured. This Doherty amplifier has higher PAE than Class AB for over 20 dB range of pout power. A RF predistortion linearizer is applied to the Doherty amplifier to improve the IMD cancellation performance. The 3rd order IMD cancellation of 12.2 ㏈ was achieved at output power of 18 ㏈m.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.2
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• pp.76-80
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• 2007

In this paper, the PAE (Power Added Efficiency) and the linearity of the Doherty amplifier has been improved using dual bias control and PBG (Photonic BandGap) structure. The PBG structure has used to implement on output matching circuit and dual bias control has applied to improve the PAE of the Doherty amplifier at a low input level by applying it to a carrier amplifier. The Doherty amplifier using the proposed structure has improved PAE by 8% and 5dBc of IMD3 (3rd Inter-Modulation Distortion) compared with those of the conventional class AB amplifier. In addition to, it has been evident that the designed the structure has showed more than a 30% increase in PAE for flatness over all input power level.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.9
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• pp.924-931
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• 2002

In this paper, a new λ/4 bias transmission line that is added dumbbell-shaped defected ground structure(DGS) on ground plane of the conventional λ/4 bias transmission line is proposed. This DGS λ/4 bias transmission line maintains high characteristic impedance, but physical width is wider and length is shorter than that of the conventional bias line. If the proposed bias line is attached on signal transmission line, this bias line can reduces the $3^{rd}$ harmonic signal as well as the$2^{nd}$ harmonic signal. With harmonic reduction characteristics, efficiency and linearity of amplifier are improved. The proposed bias line is adopted in power amplifier on IMT-2000 base-station transmitting band. This paper presents several simulations and experimental results of DGS to show validity of the proposed power amplifier using the new λ/4 bias transmission line. Experimental results represent that the $3^{rd}$ harmonic signal is reduced about 26.5 dB and efficiency is improved about 9.1 % and IMD3 is improved 4.5 dB than the conventional structure.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.5
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• pp.510-518
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• 2010

In this paper, the designed and implemented results of CFL linearization chip which can be used in mobile radio and TRS terminal of UHF band(380~910 MHz), using $0.6\;{\mu}m$ BiCMOS process based on Si, are shown. As gain control circuits for modifying transmit power are inserted not only in feedback path but also in forward path, the stability of CFL is maintained. And, DC-offset correction function of S/H structure, which is suitable for walkie-talkie PTT operation and is easily implemented, is realized. The performance test results of transmitter show that the regulation of FCC emission mask at PEP 3 W(34.8 dBm) is satisfied when the CQPSK modulated signal is fed and more than 30 dBc improvement of 3rd order IMD is achieved when two-tone signal is inputted.

• Proceedings of the IEEK Conference
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• 2000.11a
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• pp.341-344
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• 2000

Advanced FeedForward method use Predistortion method and FeedForward method simultaneously. This method better than original Feedforward method in linearity and supply smaller power to pre-power amplifier than different methods, and then it has higher power efficiency and better linearity than original Feedforward method. A linear power amplifier using Advanced feedforward method is designed and fabricated for IMT-2000 transmission system (2110㎒ -2170M㎓). This amplifier's power gain is about 40㏈ and it's 3-rd IMD(Intermodulation distortion) are smaller than about -55㏈c(@ 10MHz).

• 한국정보통신설비학회:학술대회논문집
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• 2006.08a
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• pp.15-18
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• 2006

We have proposed a broadband analog feedforward optical transmitter using a wideband $180^{\circ}$ hybrid coupler instead of conventional frequency-sensitive phase shifter with the narrow bandwidth property using a wideband $180^{\circ}$ hybrid coupler, the wide-band linearization technique enhances the linearity of the feedforward optical transmitter. In two-tone cases, the $3^{rd}-IMD$ products was enhanced more than 10 dB in 385 MHz range(1.375$\sim$l.76 GHz).

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.2 s.117
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• pp.183-190
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• 2007

This paper presents the design of 860 MHz band transmitter for improving power amplifier's linearity using Cartesian feedback method. For eliminating the effects of gain, phase mis-match, and DC offset, we estimate the property variations using ADS software. The implemented Cartesian feedback transmitter exhibits IMD3 of -54 dBc at an output power of 43 dBm and this result shows that the linearity is improved for 22.4 dB, compared with the test of the power amplifier without Cartesian feedback system. Thus, we verify that the proposed Cartesian feedback transmitter can be applied to narrow-band transmitter systems.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.9
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• pp.967-973
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• 2003

This paper presents a new predistortion method which injects the 2nd low-frequency intermodulation signal of RF signals into the input bias line of the amplifier. New 2nd intermodulation signal extraction circuit is also proposed. We have shown that this method can suppress the 3rd IM apparently and sometimes do the 5th IM, through mathematical analysis, then confirmed it with simulation and verified it on the desk test. When the input signal CDMA IS-95 lFA is applied, measured ACPR improvements are 25 dBc, 22.5 dBc, and 6 dBc at 0.885 MHz, l.25 MHz and 2.25 MHz offset respectively. Also, when applying the CDMA IS-95 3FA, the measured ACPR improvement is 20 dBc at 0.885 MHz offset.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.44 no.4
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• pp.1-9
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• 2007

Linearity is the one of the most important features for analog-optic transmission system. In our research, the available bandwidth for the feed-forward compensation circuit is enhanced by using a 180 hybrid coupler in the circuit. The bandwidth having the decreased 3rd-order intermodulation distortion(IMD3) over 10 dB is extended over 200 MHz with the center frequency of 1.6 GHz. We performed an efficient bandwith measurement for the feed-forward compensation system, which uses the network analyzer instead of the traditional measuring system that uses two RF signal generators and the spectrum analyzer. We identify the usefulness of this method from experimental results. In this study, we used cheap digital-purpose laser diodes for economical aspect, which proves the efficiency of the proposed analog system. The spurious-free dynamic range is improved about 6 dB/Hz.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.1
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• pp.68-72
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• 2012

In this paper, highly linear power amplifier using bandpass filter based on metamaterial and Composite Right- / Left-Handed (CRLH) structure is proposed. The proposed bandpass filter consist of the series capacitor, series microstrip line and the parallel inductor, parallel microstrip line. The insertion loss is minimized at operation frequency and the $2^{nd}$ harmonic is suppressed by the bandpass filter using the CRLH structure. And we improved the Adjacent Channel Leakage Ratio (ACLR) using the characteristic of the proposed bandpass filter. At 2.14 GHz, we have obtained the output power of 38.83 dBm, the $2^{nd}$ harmonic of .61.33 dBc, the $3^{rd}$ IMD of .54.67 dBc, and ACLR of .51.33 dBc at 5 MHz offset, -56.50 dBc at 10 MHz offset, respectively.