Showing papers by "Bumman Kim published in 2010"

Investigation of a Class-J Power Amplifier With a Nonlinear $C_{\rm out}$ for Optimized Operation

Abstract: This paper presents the operation principle of Class-J power amplifiers (PAs) with linear and nonlinear output capacitors (Couts). The efficiency of a Class-J amplifier is enhanced by the nonlinear capacitance because of the harmonic generation from the nonlinear Cout, especially the second-harmonic voltage component. This harmonic voltage allows the reduction of the phase difference between the fundamental voltage and current components from 45° to less than 45° while maintaining a half-sinusoidal shape. Therefore, a Class-J amplifier with the nonlinear Cout can deliver larger output power and higher efficiency than with a linear Cout. As a further optimized structure of the Class-J amplifier, the saturated PA, a recently-reported amplifier in our group, is presented. The phase difference of the proposed PA is zero. Like the Class-J amplifier, the PA uses a nonlinear Cout to shape the voltage waveform with a purely resistive fundamental load impedance at the current source, which enhances the output power and efficiency. The PA is favorably compared to the Class-J amplifier in terms of the waveform, load impedance, output power, and efficiency. These operations are described using both the ideal and real models of the transistor in Agilent Advanced Design System. A highly efficient amplifier based on the saturated PA is designed by using a Cree GaN HEMT CGH40010 device at 2.14 GHz. It provides a power-added efficiency of 77.3% at a saturated power of 40.6 dBm (11.5 W).

A Multimode/Multiband Power Amplifier With a Boosted Supply Modulator

Abstract: A multimode/multiband power amplifier (PA) with a boosted supply modulator is developed for handset applications. A linear broadband class-F amplifier is designed to have a constant fundamental impedance across 1.7-2 GHz and its second and third harmonic impedances are located at the high-efficiency area. To reduce the circuit size for handset application, the harmonic control circuits are merged into the broadband output matching circuit for the fundamental frequency. An envelope-tracking operation delivers high efficiency for the overall power. The linearity is improved by envelope tracking (ET) through intermodulation-distortion sweet-spot tracking at the maximum output power level. The efficiency and bandwidth (BW) are enhanced by a boosted supply modulator. Multimode operation is achieved by an ET technique with a programmable hysteresis control and automatic switching current adaptation of the hybrid supply modulator. For demonstration purpose, the PA and supply modulator are implemented using an InGaP/GaAs heterojunction bipolar transistor and a 65-nm CMOS process. For a long-term evolution signal, the envelope-tracking (ET) PA delivers a power-added efficiency (PAE) and an error vector magnitude of 33.3%-39% and 2.5%-3.5%, respectively, at an average power of 27.8 dBm across 1.7-2 GHz. For a wideband code-division multiple-access signal across 1.7-2 GHz, the ET PA performs a PAE, an ACLR1, and an ACLR2 of 40%-46.3%, from -39 to -42.5ndBc, and -51 to -58ndBc, respectively, at an average output power of 30.1 dBm. The ET PA with an EDGE signal delivers a PAE, an ACPR1, and an ACPR2 of 37%-42%, from -56.5 to -59.3ndBc, and -63.5 to -69.5ndBc, respectively, at an average power of 28 dBm across the 300-MHz BW. These results show that the proposed design achieves highly efficient and linear power amplification for multimode/multiband wireless communication applications.

High efficiency and wideband envelope tracking power amplifier with sweet spot tracking

Abstract: This paper describes the implementation of a high efficiency and wideband envelope tracking power amplifier with sweet spot tracking. By modulating supply voltage of power amplifier (PA), efficiency can be increased significantly. And linearity is improved by envelope shaping and sweet spot tracking. The supply modulator has a combined structure of a switching amplifier and a linear amplifier to achieve high efficiency as well as wide bandwidth. The measurement results show efficiencies of 36.4/34.1 % for 10/20 MHz long term evolution (LTE) signals with peak to average power ratio (PAPR) of 7.5/7.42 dB.

Optimized Design of a Highly Efficient Three-Stage Doherty PA Using Gate Adaptation

Abstract: We demonstrate an optimized design of a highly efficient three-stage Doherty power amplifier (PA) for the 802.16e mobile world interoperability for microwave access (WiMAX) application at 2.655 GHz. The “three-stage” Doherty PA is the most efficient architecture among the various Doherty PAs for achieving a high peak to average power ratio (PAPR) signal. However, it has a problem in that the carrier PA has to maintain a saturated state with constant output power when the other peaking PAs are turned on. We solved the problem using a gate envelope tracking (ET) technique. For the proper load modulation, the gate biases of the peaking PAs were adaptively controlled, and the peak power and maximum efficiency characteristics along the backed-off output power region were successfully achieved. Using Agilent's Advanced Design System and Matlab simulations, the overall behavior of the three-stage Doherty PA with the ET technique employed was fully analyzed, and the optimum design procedure is suggested. For the WiMAX signal with a 7.8-dB PAPR, the measured drain efficiency of the proposed three-stage Doherty PA is 55.4% at an average output power of 42.54 dBm, which is an 8-dB backed-off output power. Digital predistortion was used to linearize the proposed PA. After linearization, a -33.15 dB relative constellation error performance was achieved, satisfying the system specifications. This is the best performance of any 2.655-GHz WiMAX application ever reported, and it clearly shows that the proposed three-stage Doherty PA is suitable as a highly efficient and linear transmitter.

Advanced Doherty Architecture

Abstract: For modulated signals with a high peak-to-average power ratio (PAPR), the transmitter has to be operated with its average output power backed off for an acceptable linearity at the expense of low efficiency. To achieve high efficiency and high linearity at the same time, both an efficiency enhancement technique and a linearization technique should be utilized. A powerful and reliable linearization technique, digital predistortion (DPD), is currently the most favored method for the linearization of base-station amplifiers [1]-[3]. Possible efficiency enhancement techniques are the hybrid envelope elimination and restoration/envelope tracking technique (H-EER/ET) and the Do-herty technique.

Design of Doherty Power Amplifiers for Handset Applications

Abstract: In this paper, we analyze the power drive of a Doherty power amplifier (PA), and introduce a technique for proper input dividing without a coupler. For the proper Doherty operation, we place a phase compensation circuit at the input of the carrier amplifier. We also propose an output matching of Doherty PA to reduce the number of matching components, and to match the output impedances to enhance efficiency and linearity in consideration of the uneven input drive. The PA circuit is fabricated using a 2-μm InGaP/GaAs heterojunction bipolar transistor process and combined for Doherty operation using merged lumped components. For the IEEE 802.16e m-WiMAX signal, which has a 9.54-dB crest factor and 8.75-MHz bandwidth, the PA has an error vector magnitude of 3% and a power-added efficiency of 40.2% at an output power of 26 dBm.

Broadband HBT Doherty Power Amplifiers for Handset Applications

Abstract: A Doherty power amplifier for IEEE 802.16e mobile worldwide interoperability for microwave access (m-WiMAX) is fully integrated on a 1.2 × 1.2 × mm2 die using a 2-μm InGaP/GaAs hetero-junction bipolar transistor (HBT) process. The direct input power dividing technique is employed on the chip. Broadband input and output matching techniques are used for broadband Doherty operation, and their effects are analyzed. A peaking amplifier 1.5 times larger than a carrier amplifier delivers high efficiency for m-WiMAX signal with a 9.6-dB crest factor and an 8.75-MHz bandwidth (BW). The PA with a supply voltage of 3.4 V has an EVM of 2.3% and a PAE of 31.5% at an output power of 24.75 dBm as well as an operating frequency of 2.6 GHz. A PAE over 30.3% and an output power of greater than 24.6 dBm with an EVM less than 3.15% and a gain variation of 0.2 dB are achieved across 2.5-2.7 GHz without any assisting linearization technique. After compensating AM-AM and AM-PM nonlinearity using a digital feedback predistortion algorithm, the PA exhibits a PAE of over 27% and an output power of over 23.6 dBm across 2.2-2.8 GHz while maintaining an EVM below 2.7%.

Analysis of Adaptive Digital Feedback Linearization Techniques

Abstract: A new lookup-table linearization technique is developed based on the digital feedback and digital feedback/predistortion (DFBPD) concepts. The linearization characteristics are investigated through system simulation of a real power-amplifier model with 90-W peak envelope power. The DFB suppresses forward-path nonlinear distortion as a gain reduction due to the FB effect, and this technique enhances the system tolerance without any bandwidth limitation. As the PD network is added to the FB loop, the linearization performance and system tolerance are further improved because of more accurate PD signal extraction. In addition, the gain is purely determined by the FB path, so the gain fluctuation in the forward path, including amplifier aging and temperature effects, is suppressed. The analysis and simulation allow experimental evaluation of the linearization mechanism and performance of the DFBPD technique for an 802.16 e mobile Worldwide Interoperability for microwave access signal.

Doherty amplifier with envelope tracking for high efficiency

Abstract: A Doherty amplifier assisted by a supply modulator is presented using 2.14 GHz GaN HEMT saturated power amplifier (PA). A novel envelope shaping method is applied for high power-added efficiency (PAE) over a broad output power range. Experimental comparison with the Doherty and saturated PAs with the supply modulator is carried out. For the 8 dB crest factor WCDMA 1FA signal, the Doherty PA supported by the modulator presents the improved PAE over the broad output power region compared to the standalone Doherty PA. In addition, it achieves better PAE than the saturated PA with the supply modulator due to the lower crest factor envelope signal applied to the Doherty PA. At the maximum average output power, back-off by 8 dB from the peak power, the Doherty amplifier employing bias adaptation shows the PAE of 50.9%, while the comparable saturated PA with supply modulator and standalone saturated Doherty amplifier and saturated PA provide the PAEs of 42.3%, 49.7%, and 35.0%, respectively.

A Saturated Doherty Power Amplifier Based On Saturated Amplifier

Abstract: A saturated Doherty power amplifier (PA) based on the saturated PA tuned by the self-generated harmonic currents is presented. When driven with mobile WiMAX 1FA signal, this Doherty PA demonstrates high efficiency performance (average 57%) over the WiMAX band from 2.5 GHz to 2.7 GHz. Simulated and experimental results allow the evaluation for the load modulation behavior of the saturated PA and bandwidth correlation between the Doherty and saturated unit PAs. The linearity requirement of the WiMAX signal is met using the digital feedback predistortion linearization technique.

Wideband LNA Using a Negative gm Cell for Improvement of Linearity and Noise Figure

Abstract: A differential common gate low noise amplifier (LNA) has been widely used for a wideband LNA. However, it has poor linearity due to a nonlinear transconductance in a MOSFET and poor noise performances from the common gate configuration. We propose a differential common gate LNA with a negative g m cell for the improvement of the linearity and noise figure. The cell comprises cross coupled transistors instead of a current source. The negative g m cell creates the opposite phased harmonic, canceling the distortion. The noise figure is improved by canceling the noise from the common gate transistors through the negative g m cell. The LNA is fabricated in 0.13 μm RF CMOS. The LNA has the bandwidth of 0.7 ∼ 3.5 GHz frequency and has provided the expected characteristics for linearity and noise figure.

Envelope tracking power amplifier robust to battery depletion

Abstract: A wideband envelope tracking power amplifier, which is robust to battery depletion, is introduced. An integrated boost converter keeps a stable operation of the PA supply modulator. Even at the battery depletion from 4.2V to 2.8V, there is no significant degradation of output power and linearity in the power amplifier. Moreover, the efficiency degradation by the additional regulator is minimized for the novel supply modulator architecture proposed in this work. The fabricated 2.535GHz envelope tracking power amplifier presents max/min power-added efficiencies of 32.3/26.2% for 10MHz BW 3GPP LTE standard along the battery voltage from 4.2V to 2.8V.

A 2.655 GHz 3-stage Doherty power amplifier using envelope tracking technique

Abstract: We demonstrates an optimized design of a highly efficient 3-stage Doherty PA for the 802.16e Mobile world interoperability for microwave access(WiMAX) application at 2.655-GHz. The ‘3-stage’ Doherty PA is the most efficient architecture among the various Doherty PAs for a high peak to average power ratio(PAPR) signal. However, due to the low quiescent bias point of the peaking PA, it has an improper load modulation problem, which causes over saturated operation of the carrier PA and insufficient peak power. We have solved the problem using a gate envelope tracking(ET) technique. Using the ADS and Matlab simulations, the behavior of the 3-stage Doherty PA employing the ET technique is presented. For the WiMAX signal with a 7.8 ∼ 8.5 dB PAPR and 20-MHz instantaneous bandwidth, the measured efficiency of the proposed 3-stage Doherty PA has been maintained 56.7 % at an average output power of 43.3 dBm, a 7.2 dB backed-off output power from peak output power level. These experimental results clearly show that the 3-stage Doherty with ET technique has a superior efficiency with high peak power. The PAs accompanied with the DPD are very good candidates for the highly efficient and linear base-station transmitter.

30.3% PAE HBT Doherty power amplifier for 2.5∼2.7 GHz mobile WiMAX

Abstract: The Doherty power amplifier for mobile WiMAX application is fully integrated in 1.2 mm × 1.2 mm using a 2-um InGaP/GaAs HBT process. The direct input power dividing technique is employed on a chip. Broadband input and output matching techniques are used for broadband Doherty operation. A 1.5 times larger peaking amplifier than carrier amplifier is used to have high efficiency for IEEE 802.16e m-WiMAX signal, which has 9.6 dB crest factor and 8.75 MHz bandwidth. The PA with a supply voltage of 3.4V has an EVM of 2.3% and a PAE of 31.5% at an output power of 24.75 dBm and an operating frequency of 2.6 GHz. The PAE of over 30.3% and the output power of over 24.6 dBm with the EVM of lower than 3.15% and the gain variation of 0.2 dB are achieved across 2.5∼2.7 GHz without any assistant technique for linearization.

LTE Power Amplifier for envelope tracking polar transmitters

Abstract: The capacitance between the base and collector terminals of hetero-junction bipolar transistors (HBT) varies with an RF input signal, and degrades linearity and efficiency. A second harmonic control circuit and a feedback inductor between the base and collector terminals are employed to prevent the distortion of the signal, and improve the efficiency and the linearity. The PA circuit is realized in a 1.2 mm by 1.2 mm die using a 2 µm InGaP/GaAs HBT process. For a long term evolution (LTE) signal at a frequency of 2.535 GHz with a 7.42 dB crest factor, 16 QAM, and a 20 MHz bandwidth, the PA with a supply voltage of 4.5 V has an EVM of 2.78% and a PAE of 32.6% at an average output power of 26.9 dBm. The PA is operated in an envelope-tracking mode with a boosted supply modulator from 3.4 V to 4.5 V, and delivers a PAE of 34.2% at an average output power of 26.4 dBm, while meets the LTE spectrum mask.

Doherty power amplifier design employing direct input power dividing for base station applications

Abstract: For base station applications, −3 dB hybrid coupler has been used for input power dividing stage of Doherty power amplifier (PA). The input direct dividing technique has only been applied for handset applications, because the coupler occupies a large size on a chip. However, this technique provides advantages on power gain and efficiency for base station applications, also. In this paper, we have proposed a design procedure of Doherty PA applying the input direct dividing technique. Implemented Doherty PA using two Cree CGH40045 GaN HEMT achieves excellent drain efficiency of 51.2% at 41 dBm output power for long term evolution (LTE) 1FA signal at 2.14-GHz. Moreover, the Doherty PA could be linearized to −45 dBc using the digital feedback predistortion technique.

A multi-mode envelope tracking power amplifier for software defined radio transmitters

Abstract: A multi-mode envelope tracking power amplifier is presented for software defined and cognitive radio solutions. A new 0.13um CMOS hysteretic-controlled hybrid switching supply modulator is developed for the mode dependent operation of the power supply modulator. Combined with 1.88GHz HBT class-AB/F PA operating with novel envelope shaping method, the proposed envelope tracking power amplifier shows high efficiency and linearity over broad output power range. It achieves the PAE of 45/46/34.3% at the average output power of 27.8/29/23.9dBm for EDGE/WCDMA/Mobile-WiMax, respectively, while satisfying the linearity specification without any digital pre-distortion technique. There are about 7% and 3% improvements of the overall PAE for EDGE and WCDMA, respectively, through the adaptive multi-mode operation.

Wideband digital feedback predistortion employing segmented memory compensation for linearization of Doherty amplifier

Abstract: A novel wideband digital feedback predistortion (WDFBPD) technique employing segmented memory compensation method is proposed for linearization of Doherty amplifier. Its memory effect modeling and linearization capabilities are demonstrated. Starting with an investigation of an abnormal memory effect of the Doherty amplifier, an appropriate dynamic system in the WDFBPD is deduced. The model has two segmented memory compensation elements for carrier PA correction at a low power and peaking PA correction at a high power. The validation of the proposed model in predicting a dynamic nonlinear behavior is carried out by comparing the output spectra, dynamic AM/AM and AM/PM characteristics, and the normalized mean square error. The superiority of the linearization performance is verified using the Doherty amplifier with 90 W Si LDMOSFETs. For a 2.14 GHz forward-link WCDMA 4FA signal, the adjacent channel leakage ratio at 5 MHz offset frequency is −51.5 dBc, which is an improvement of 5 dB compared to the conventional WDFBPD, at an average output power of 44 dBm.

Highly efficient Envelope Tracking transmitter at 3.5-GHz

Abstract: Envelope Tracking (ET) transmitter is introduced at a high frequecny, 3.5-GHz. As the frequency goes up, ET system has merits because the supply modulator is frequency independent circuit. For the optimum ET operation, the Power Amplifier (PA) has been designed as an average PA to have a maximum Power Add Efficiency (PAE) at the average V ds region. An improved supply modulator without sensing resistor is designed to mitigate the power dissipation. The supply modulator is optimized to average load impedance for higher efficiency and a proper ET shaping function is applied. The proposed supply modulator shows efficiency of 83.0% near the average load impedance of 14.7 Ω. In the interlock experiment, the ET transmitter delivers an excellent PAE performance, of 35.5% at an average output power of 40 dBm. Using digital feedback predistortion (DFBPD) technique, the Relative Constellation Error (RCE) has been successfully satisfied the specification with −32.7 dB. To the best of our knowledge, the PAE of 35.5% is the state-of-the-art for 3.5-GHz transmitter.

A wideband linear CMOS power amplifier design for 2.3-GHz and 2.6-GHz m-WiMAX system

Abstract: In this work, a fully-integrated linear CMOS power amplifier (PA) is implemented in a 0.18-μm 1P6M RF CMOS process for 2.3-GHz and 2.6-GHz m-WiMAX system application. A wideband twisted figure-8-shaped transformer is utilized as both the power combining and matching, which is operated across 1 GHz bandwidth. The PA operates at Class AB mode and can deliver 29.1 dBm with a 26.5% PAE at 1-dB compression point and offer 22 dB gain. EVM is lower than 5% at 19 dBm average power under the 16 QAM m-WiMAX modulation signal test. Digital feedback pre-distortion (DFDPD) technique is employed to improve spectrum linearity by 7 dB at 19 dBm average power level.

Doherty power amplifiers for handset applications

Abstract: The efficiency and linearity are enhanced by a direct input dividing and an uneven power drive. An optimized envelope tracking (ET) operation of Doherty power amplifier (PA) is presented. The PA and the supply modulator are realized using a 2 μm InGaP/GaAs HBT and 0.13 μm CMOS processes, respectively. For WiMAX application, it shows a PAE of 38.6% and an EVM of 3.64% at an output power of 24.22 dBm with a gain of 24.62 dB.

Digitally enhanced linear power amplifiers

Abstract: Signals for the next generation communication system have a large PAPR and wideband to handle large data using a spectrum efficient modulation scheme. The PAs should amplify the signal without any significant distortion, but still with high efficiency. Also, flexible transmitters with multimode and multiband capability are inevitable to handle the evolving various wireless communication systems. To meet the stringent requirements, digitally enhanced linear power amplifier receives a lot of attention because of the digital flexibility and capability. In this talk, we will introduce the key architectures in this area, sigma-delta digitized polar transmitter, ET technique for multimode operation, and Class-S Power Amplifier for digitized signal amplification. It will cover the basic concepts of the architectures and current research status.

An optimum design of high‐power amplifier with high efficiency using a realizable harmonic loading circuit

Abstract: An optimum design approach for a highly efficient power amplifier (PA) using a packaged high-power device is described.Large fundamental load impedance assisted by a simple second harmonic manipulation is explored to improve the efficiency when maintaining the power density. For demonstration of the performance, the PA is implemented using GaN HEMT device at 2.655 GHz. In the experiment, the fabricated PA achieves power-added efficiency (PAE) of 64.3% at the saturated output power of 49.2 dBm. For 802.16e mobile worldwide interoperability for microwave access signal, the PA delivers the PAE of ∼31% and ACLR of −49 dBc at the 10 dB backed-off power of 40 dBm after the digital feedback predistortion linearization. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:818–822, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25032