• 한국정보통신설비학회:학술대회논문집
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• 2008.08a
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• pp.570-572
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• 2008

The modulation quality of the I/Q modulator in a wireless transmitter usually affects system performance and it mostly depends on both a nonlinearity and a distortion, from the third order intermodulation($IM_3$) signal and the error components such as an input amplitude error and a local phase error, respectively. This paper focused on how much the Single Sideband Ratio(SSR), which indicates the signal distortion, changes according to the variation of the error components. Consequently, since a desired signal, side band signal at the I/Q modulator output are also represented with those power series coefficients and the error components, the effects of the error components on SSR to meet the EVM specification of the WPAN can be clearly analyzed.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.4
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• pp.823-828
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• 2011

We have systematically designed and experimentally demonstrated the opto-electrical predistortion optical transmitter using microwave circuit modelling for reducing the nonlinearity of the distributed-feedback laser diode (DFD-LD). The DFB-LD is analyzed using microwave circuits model based on rate equations. Through the system-level simulation for predistortion method, the optimized characteristics of the RF components in the system are confirmed. The simulated and experimental results show the reduced distortion products. These results are analyzed as the evaluation parameters for the miniaturization and optimization of the opto-electrical predistortion method in radio-over-fiber systems.

• Journal of Advanced Navigation Technology
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• v.15 no.5
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• pp.789-794
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• 2011

This paper has analyzed the AM-AM and AM-PM characteristics of 7.9 GHz~8.4 GHz X-band TWT used for satellite communication and improved its linearity and IMD performance by using linearizer. The TWT amplifier with the linearizer shows better AM-AM and AM-PM conversion, and has increased 1 dB compression point by 12.3 dB and $2.0^{\circ}/dB$ phase distortion point by 10 dB. The 3rd order intermodulation distortion, IMD3 is measured to be 37.0 dBc that is 16.2 dB improvement at the operating output. This paper also proposed the measurement method of IMD for high power amplifier, and that TWT amplifier can have better linearity and output power by compensating for the AM-PM characteristics.

• Journal of Advanced Navigation Technology
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• v.10 no.1
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• pp.41-47
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• 2006

In this paper, a predistortion linearizer using the in-phase modulator is proposed. The harmonic generator of the proposed predistorter extracts a second harmonic signals. These signals are divided in-phase and quadrature-phase signals, and then amplifying each signals using variable gain amplifier. An in-phase modulator, modulate fundamental signal with second harmonic signals, generates the predistortion intermodulation distortion (IM) signals and controls amplitude and phase of them with modulation factors. As a result, this predistorter is suppressed intermodulation distortion signals of power amplifier effectively. The proposed linearizer has been implemented to operate in Cellular-band. The test results show that the third order IM is cancelled more than 20dB in case of CW 2-tone signals with ${\Delta}f$=1MHz. Also, it's improved the adjacent channel power ratio (ACPR) more than 7dB for IS-95 CDMA 1FA signals.

• Journal of Navigation and Port Research
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• v.27 no.5
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• pp.505-511
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• 2003

In this paper, a driving amplifier stage with 1 Watt output has been designed and fabricated, which is operating at UHF band( 470 ∼ 806 MHz) for digital TV repeater. In the driving amplifier stage, preamplifier and 1 Watt unit amplifier are integrated by one electric substrate which is 2.53 in dielectric constant and 0.8 mm thickness. When the driving amplifier stage is flown by bias voltage of 28 V DC and current of 900 mA. it has the gain of more than 53.5 dB. the gain flatness of $\pm$0.5 dB and return loss of less than -15 dB in 470 ∼ 806 MHz. Also, when two signals at 2 MHz frequency interval are input port into the driving amplifier stage with 1 Watt output, it resulted in excellent characteristics to designed specification with showing intermodulation distortion characteristics of more than 48 dBc.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.9
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• pp.944-949
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• 2003

In this paper, the double balance mixer(DBM) for Ku-band LNB using InGaP/GaAs HBT process is suggested for the characteristics of low DC power consumption, low noise figure, low intermodulation distortion and wide dynamic range. The 5 dB conversion gain, 14 dB NF, bandwidth 17.9 GHz and 50.34 dBc IMD are obtained under RF input power of -23 dBm, with bias condition as 3 V and 16 mA. The linearity of InGaP/GaAs HBT, the broad band input matching scheme and the optimization of bias point result in the low IMD, the broad bandwidth and the low power consumption characteristics.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.5
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• pp.480-485
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• 2004

In this paper, a new predistortion linearizing method using frequency up-conversion operation of mixer is proposed. This linearizing method doesn't require any additional signal sources in spite of frequency up-conversion mixing operation. This method extracts the 2nd low frequency intermodulation distortion signal from input signals and uses the extracted 2nd low frequency intermodulation distortion signal as mixing signal source. To show validation of the proposed predistortion method, we made K-PCS power amplifier. On 2-tone signals amplification process, the (C/I) ratio of amplifier is improved 26 ㏈ (@Po=22 ㏈m/tone), where two tones are 1.8544 ㎓ and 1.8556 ㎓, respectively. And (C/I) ratio is improved more than to 20 ㏈ for 17 ㏈ output signal dynamic range. On IS-95A CDMA 1FA amplification process, the improvements of adjacent channel power ratio(ACPR) are 10.8 ㏈ and 6.4 ㏈ at ${\pm}$885 ㎑ and ${\pm}$1.25 ㎒ offset points, respectively.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.1 s.104
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• pp.45-51
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• 2006

In this paper, a new predistortion linearizer for controlling the amplitude of low frequency intermodulation distortion signals is proposed. The low frequency intermodulation distortion(IMD) components are generated by harmonic generator. A vector modulator, modulate fundamental signal with low frequency IMD signals, generates predistortion IMD signals and controls amplitude and phase of them with modulation factors. As a result, this predistorter is suppressed IMD signals of power amplifier effectively. The predistortion linearizer has been manufactured to operate in cellular base-station transmitting band($869{\sim}894\;MHz$). The experimental results show that IMD3 of power amplifier are improved more than 20 dB for CW two-tone signals. Also, it's improved the adjacent channel power ratio(ACPR) more than 10 dB for IS-95 CDMA IFA signals.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.7A
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• pp.545-551
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• 2012

In this paper, K-band multi-channel receiver was designed and fabricated for low noise amplification and down conversion to L-band. The fabricated multi-channel receiver incorporates GaAs-HEMT LNA(Low noise amplifier) which provides less than a 2 dB noise figure, IR(Image Rejection) Filter for rejection of image frequency, IR(Image rejection) mixer to reject a image frequency and improve an IMD(Intermodulation Distortion) characteristic. Test results of the fabricated multi-channel receiver show less than a 3.8 dB noise figure, conversion gain of more than 27dB, and IP1dB(Input 1dB Gain Compression Point) of -9.5 dB and over.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.7
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• pp.1086-1093
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• 2001

A new linearization technique for RF high-power amplifiers(HPAs) using n-th order error signal generator (ESGn) is proposed. The n-th order ESG generates an error signal based on the complex envelope transfer characteristics of the HPA, which is combined at the output of the HPA. Therefore, the higher-order nonlinearlities are not affected by the ESG$\_$n/ and the stability of the linearized system is guaranteed due to the inherent open-loop configuration. Moreover, the output delay loss can be avoided, because the error signal is generated with the input signal of the HPA. The IMD(intermodulation distortion) improvement obtained applying the ESG$\_$7/ to 5 W class A HPA in cellular band demonstrates the feasibility of the proposed postdistortion system.