• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.11 s.114
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• pp.1050-1057
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• 2006

This paper proposes a new predistortion linearizer with amplitude modulator and PFG(Polar Function Generator) using second order harmonic signals. This linearizer consists of PFG that combine with in-phase and quadrature-phase of second harmonic signals and amplitude modulator in main path. The predistorted third order intermodulation distortion(IMD3) signals that are generated by amplitude modulator with fundamental and PFG signals, improve a amplifier nonlinear characteristics. The proposed linearizer and amplifier have been manufactured and tested to operate in cellular base-station transmitting band$(869\sim894MHz)$. The test results show that IMD3 can be removed by more than 22.5 dB in case of CW 2-tone signals ${\Delta}f=1$ MHz, and the adjacent channel power ratio(ACPR) also can be improved by more than 8.4 dB for CDMA IS-95 1FA signals.

• Proceedings of the IEEK Conference
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• 2000.11a
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• pp.349-352
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• 2000

In this paper, predistorter for PCS has been designed and fabricated. In predistorter system IMD signal generator was very important element. In this LPA IMD signal generator was fabricated using main signal cancellation and error signal cancellation of feedforward method and two amplifier that had same IMD characteristics. This LPA showed IMD characteristics of 52㏈c operation in 48㏈m(60W) and made 12㏈ IMD characteristic improvement when it was excited by two tone. In this LPA, to make more IMD characteristic improvement the IMD characteristic resemblance between main amplifier and predistortion amplifier is very important.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 2006.07a
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• pp.317-317
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• 2006

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.6 s.97
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• pp.644-651
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• 2005

In this paper, a new predistortion method to reduce nonlinearity or a traveling wave tube amplifiers(IWTAs) is proposed. Nonlinear transfer characteristics of TWTA are analyzed using carrier complex power series. Inverse carrier complex power series or a predistortion linearizer to linearizer TWTA are also proposed. The inverse nonlinear distortion characteristics of predistorter can be realized with reflective structure that is composed of Schottky diode and resistive-terminated transmission line. The AM-to-AM and the AM-to-PM characteristics for TWTA by proposed predistortive linearizer on K-band were improved from -5.825 dB and -37.321^{\circ} to 0.786 dB and 6.742^{\circ}, respectively.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.5 s.108
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• pp.408-415
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• 2006

This paper suggests an improved system-level model of RF power amplifiers(PAs) including memory effects, and validates the suggested model by analyzing the power spectral density of the output signal with a predistortion linearizer. The original three-box(Wiener-Hammerstein) model uses input and output filters to capture RF frequency response of PAs. The adjacent spectral regrowth that occurs in three-box model can be perfectly removed by Hammerstein structure predistorter. However, the predistorter based on Hammerstein structure achieves limited performance in real PA applications due to other memory effects except RF frequency response. The spectrum of the output signal can be predicted accurately using the suggested model that changes a memoryless block in a three-box model with a memory polynomial. The proposed model accurately predicts the output spectrum density of PA with Hammerstein structure predistorter with less than 2 dB errors over ${\pm}30$ MHz adjacent channel ranges for IEEE 802.11 g WLAN signal.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.3
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• pp.499-508
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• 2017

A new digital pre-distortion technique to linearize power amplifier (PA) is proposed for concurrent dual-band transmitters. In the conventional dual-band DPD techniques, two independent dual-feedback paths are required to compensate nonlinear cross-products between different bands as well as the nonlinear self-products of each band's own signal. However, it increases hardware complexity and expense. In this paper, we propose a new DPD method requiring only a single feedback path. In this new structure, the proposed technique first estimates the dual-band PA characteristics using the single feedback path. The DPD parameters are then extracted from the estimated PA characteristics. The DPD performance of the proposed method is validated through computer simulation. According to the results, the proposed technique can achieve comparable performance to the conventional two feedback DPD with significantly reduced hardware complexity.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.12 s.103
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• pp.1239-1245
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• 2005

In this paper, a new predistortion linearizer using second harmonic components feedforwarding is proposed. The harmonic generator of the proposed predistorter that consists of a small signal amplifier extracts second harmonic signals. A vector modulator that modulate fundamental signal with second harmonic signals, generates the inverse third order intermodulation distortion signals and controls amplitude/phase of them with modulation factors. As a result, this linearizer is suppressed IMD3 signals of power amplifier effectively. The test results show that the third order IMD of power amplifier is suppressed more than 20 dB for CW two-tone signals. Also, it's improved the adjacent channel power ratio(ACPR) more than 5 dB for CDMA(IS-95) 4FA signals.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.4C
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• pp.403-413
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• 2009

We compare three predistortion methods to prevent signal distortion and spectral re-growth due to the high PAPR (peak-to-average ratio) of OFDM signal and the non-linearity of high-power amplifiers. The three predistortion methods are pth order inverse, indirect learning architecture and look up table. The pth order inverse and indirect learning architecture methods requires less memory and has a fast convergence because these methods use a polynomial model that has a small number of coefficients. Nevertheless the convergence is fast due to the small number of coefficients and the simple computation that excludes manipulation of complex numbers by separate compensation for the magnitude and phase. The look up table method is easy to implement due to simple computation but has the disadvantage that large memory is required. Computer simulation result reveals that indirect learning architecture shows the best performance though the gain is less than 1 dB at $BER\;=\;10^{-4}$ for 64-QAM. The three predistorters are adaptive to the amplifier aging and environmental changes, and can be selected to the requirements for implementation.

• Journal of the Korean Institute of Telematics and Electronics C
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• v.35C no.9
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• pp.64-72
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• 1998

In this paper, the design of a current integrator for low-voltage, low-power, and high frequency applications using complementary high swing cascode current-mirror is presented. The proposed integrator decreases output current errors due to non-zero input resistance and non-infinite output resistance of the simple current integrator. As a design example, the 3rd order Butterworth lowpass filter is designed by a leapfrog method. Also, we apply the predistortion design method to reduce the magnitude distortion which occurs at a cutoff frequency by the undesirable phase shift of a lossless current integrator. The designed current-mode filter is simulated and examined by SPICE using 0.8$\mu\textrm{m}$ CMOS n-well process parameters. The simulation results show 20MHz cutoff frequency and 615㎼ power dissipation with a 2V power supply. And the cutoff frequency of the filters can be easily changed by the DC bias current.

• Journal of Advanced Navigation Technology
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• v.10 no.3
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• pp.256-262
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• 2006

This paper proposes a new predistortion linearizer to compensate for AM/AM and AM/PM in the nonlinear characteristics of amplifier. This consists of common-emitter amplifier and schottky diode that is connected between emitter and ground. When effective resistance of the schottky diode with bias condition varies, common-emitter amplifier with series feedback has a increase of amplitude and expansion of phase. This makes a amplifier nonlinear characteristics are to be improved. The proposed linearizer and amplifier has been manufactured and tested to operate in cellular base station frequency (869~894MHz). The test results show that third order intermodulation distortion (IMD3) cab be removed by more than 10.4dB in case of CW 2-tone signals ${\Delta}f$=1MHz, and the adjacent channel power ratio (ACPR) also can be improved by more than 9.6dB for CDMA IS-95 1FA signals.