Wan-Jong Kim

Simon Fraser University, Burnaby, British Columbia, Canada

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Publications (10)5.55 Total impact

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    ABSTRACT: This paper presents a novel 3-way distributed Doherty power amplifier with an extended efficiency range for WCDMA repeater or base-station applications. This distributed Doherty amplifier consists of one main amplifier and two peaking amplifiers. In order to get high efficiency at a high back-off power, the peaking amplifier structure is based on the dual-fed distributed amplifier form. The 2140 MHz measured results of the 3-way distributed Doherty amplifier yielded 11 dB power gain, with 39.5 % power added efficiency (PAE) at 9.5 dB backoff power. High linearity performance of -54 dBc ACPR is achieved after using memory compensated digital predistortion.
    Microwave Symposium, 2007. IEEE/MTT-S International; 07/2007
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    ABSTRACT: This paper describes a new efficient crest factor reduction technique for wideband applications. The technique is based on using peak cancellation to reduce the peak-to-average power ratio (PAPR) of the input signal. Conventional iterative peak cancellation requires several iterations so as to converge into the targeted PAPR, since filtering causes peak re-growth. The proposed algorithm is able to eliminate several iterations, which subsequently saves hardware resources. In numerical simulations using four WCDMA carriers, it achieves a PAPR of 5.7dB with a fixed EVM of 10%. A 240W PEP Class AB power amplifier was utilized to verify the performance of the proposed technique and demonstrate the efficiency gains. The measured results demonstrate that this algorithm can enhance the efficiency of our PA by up to 6.6%, when compared to the efficiency without the PAPR technique.
    Analog Integrated Circuits and Signal Processing 03/2007; 51(1):19-26. DOI:10.1007/s10470-007-9038-8 · 0.47 Impact Factor
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    ABSTRACT: This paper describes a predistorter (PD) based on piecewise pre-equalizers for use in multichannel wideband applications. The predistortion linearizer consists of piecewise pre-equalizers along with a look-up-table-based digital PD that together compensate for nonlinearities, as well as memory effects of power amplifiers (PAs). It takes advantage of multiple finite-impulse-response filters that significantly reduce the complexity when compared to memory polynomial methods. The proposed method was also compared with the conventional Hammerstein structure. A 300-W peak envelope power Doherty PA was first modeled by measured time-based samples in order to verify the adjacent channel power ratio (ACPR) performance in simulation using a multitone and single wideband code-division multiple-access (W-CDMA) carrier. Furthermore, the experimental results applying two W-CDMA carriers verify that the proposed method provided similar improvement to that of the memory polynomial approach. The experimental results verified the complexity reduction and superior ACPR performance over the conventional Hammerstein structure
    IEEE Transactions on Microwave Theory and Techniques 10/2006; 54(9-54):3469 - 3478. DOI:10.1109/TMTT.2006.880639 · 2.24 Impact Factor
  • Kyoung-Joon Cho · Wan-Jong Kim · Jong-Heon Kim · S.P. Stapleton ·
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    ABSTRACT: This paper presents a 40 W gallium-nitride microwave Doherty power amplifier for WCDMA repeater applications. The main and peaking amplifier are implemented using two 20 W PEP GaN HEMTs. Its performance is evaluated for broadband gain, power efficiency and adjacent-channel-power-ratio (ACPR). The experimental results of the GaN Doherty amplifier yielded a power gain over 11 dB from 1.8 GHz to 2.5 GHz, 65 % power added efficiency at 40 W peak power. Good linearity performance of -55 dBc ACPR is obtained after using a baseband digital pre-distortion technique
    Microwave Symposium Digest, 2006. IEEE MTT-S International; 07/2006
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    Kyoung-Joon Cho · Wan-Jong Kim · Jong-Heon Kim · S.P. Stapleton ·
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    ABSTRACT: The linearity of a 30-W high-power Doherty amplifier is optimized using post-distortion compensation. A balanced high-power Doherty amplifier using two push-pull laterally-diffused metal-oxide semiconductor (LDMOS) field-effect transistors (FETs) is linearized by optimum adjustment of the peaking compensation line, shunt capacitors, and gate biases. The measured results of an optimized Doherty amplifier for a four-carrier wideband code division multiple access (W-CDMA) signal, achieved -43 dBc adjacent channel leakage ratio (ACLR) at a ±5 MHz offset frequency. This is an ACLR improvement of 12.2dB and 6.5dB in comparison to the Doherty amplifier before optimization and a ClassAB amplifier, respectively.
    IEEE Microwave and Wireless Components Letters 12/2005; 15(11-15):748 - 750. DOI:10.1109/LMWC.2005.858985 · 1.70 Impact Factor
  • Wan-Jong Kim · S.P. Stapleton · Jong Heon Kim · C. Edelman ·
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    ABSTRACT: When compared to other linearization methods, adaptive DP provides sufficient linearization with less complex RF hardware by depending primarily upon DSP rather than analog manipulation. The adaptive DP system may be implemented in EDA software along with interconnected test equipment (arbitrary RF signal source and vector signal analyzer). Through the use of a training signal, a simple adaptive algorithm may be employed to update the LUT coefficients until an optimum setting is achieved and used to predistort the input to the amplifier. This "connected solution" approach can provide key information to design engineers for optimizing the DSP architecture of a PA. For future work, other issues are taken into account, such as temperature and electrical memory effects.
    IEEE Microwave Magazine 10/2005; 6(3-6):54 - 61. DOI:10.1109/MMW.2005.1511914 · 1.13 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The linearity of a 30 W high power Doherty amplifier is optimized using post-distortion compensation. A balanced high power Doherty amplifier using two push-pull LDMOS FETs is linearized by optimum adjustment of the peaking compensation line, shunt capacitors and gate biases. The optimized Doherty amplifier measured results for a 4-carrier W-CDMA signal, achieved -43 dBc ACLR at a ±5 MHz offset frequency. This is an ACLR improvement of 12.2 dB and 6.5 dB in comparison to the Doherty amplifier before optimization and a class AB amplifier, respectively.
    Microwave Symposium Digest, 2005 IEEE MTT-S International; 07/2005
  • Wan-Jong Kim · S.P. Stapleton · Kyoung Joon Cho · Jong Heon Kim ·
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    ABSTRACT: Digital predistortion has been shown to effectively address the growing demand for highly linear and more power efficient amplifiers in base stations. Doherty amplifiers have demonstrated greater efficiency than traditional amplifiers but with a high adjacent channel power ratio. This paper describes a digital predistortion implementation within the ADS Ptolemy environment and a connected solution consisting of an electronic signal generator (ESG), power amplifier (PA), and vector signal analyzer (VSA). The connected solution enables the evaluation of a PA's performance with the addition of digital predistortion. A 30 W Doherty amplifier with a weak memory was evaluated within the connected solution. Two WCDMA carriers were applied to our system, and the results show 15 dB reduction at 5 MHz offset and 12 dB reduction at -5 MHz offset.
    Vehicular Technology Conference, 2004. VTC2004-Fall. 2004 IEEE 60th; 10/2004
  • Kyoung-Joon Cho · Wan-Jong Kim · Jong-Heon Kim ·
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    ABSTRACT: This paper presents a linearizer using the feedforward loop without delay lines which can be applied to personal communication system (PCS) base-station applications. This linearizer uses an IM amplifier and an auxiliary amplifier in order to remove the delay lines used in the feedforward technique. The delay line in the error loop is changed by the main power amplifier (PA) and the error amplifier is utilized to amplify the error signal which is combined with the output of the main amplifier. Two-tone signals at 1.85 GHz and 1.85125 GHz with -17 dBm/tone from synthesizers are injected into the linearizer. The main PA in the linearizer with a gain of 50 dB and an average power of 10 W was fabricated. The reduction of intermodulation distortion (IMD) is around 19 dB
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    ABSTRACT: T his article presents a method for power amplifier lineariza-tion known as baseband adaptive digital predis-tortion. Using an EDA software package with both DSP (Digital Signal Processing) and RF capabilities, connected to a vector signal generator and a signal analyz-er, this hardware/software connected system allows an actual hardware power amplifier to be optimally linearized for a specific wireless transmission standard.