Showing papers by "Bumman Kim published in 2008"

Analysis of a Fully Matched Saturated Doherty Amplifier With Excellent Efficiency

Abstract: A saturated Doherty amplifier based on class-F amplifiers is analyzed in terms of its load modulation behavior, efficiency, and linearity. Simulations included the amplitude ratio and phase difference between the fundamental and third harmonic voltages, the current/voltage waveforms, load lines, and the third-order intermodulation amplitudes/phases of the carrier and peaking amplifiers. The saturated doherty power amplifier was implemented using two Eudyna EGN010MK GaN HEMTs with a 10-W peak envelope power. For a 2.14-GHz forward-fink wideband code-division multiple-access signal, the doherty amplifier delivers an excellent efficiency of 52.4% with an acceptable linearity of -28.3 dBc at an average output power of 36 dBm. Moreover, the amplifier can provide the high linearity performance of -50 dBc using the digital feedback predistortion technique.

High-Efficiency Hybrid EER Transmitter Using Optimized Power Amplifier

Abstract: This paper describes a new design approach for a power amplifier (PA) of the highly efficient hybrid envelope elimination and restoration (H-EER) transmitter. Since the PA operates mostly at the average power region of the modulation signal, power-added efficiency (PAE) of the PA at the average drain voltage is very important for the overall transmitter PAE. Accordingly, the PA is designed to have a maximum PAE in that region. The performances of the proposed PA and a conventional PA under H-EER operation are evaluated via ADS and MatLab simulations using a behavioral large-signal model of a silicon LDMOSFET, which verifies that the proposed PA has significant advantages for the H-EER transmitter in both PAE and output power. A saturated amplifier, inverse class F, has been implemented using a 5-W peak envelope power LDMOSFET for 3GPP forward-link single-carrier wideband code-division multiple-access at 1 GHz with a peak-to-average power ratio of 9.8 dB. An envelope amplifier is built that has an efficiency of above 68% and peak output voltage of 31 V for an interlock experiment. The overall PAE of the transmitter with a conventional PA is 35.5% at an output power of 29.2 dBm. On the other hand, the transmitter with the proposed PA delivers significantly improved performances: PAE increased by 4% and output power by 2.5 dB. The H-EER transmitter has been linearized by the digital feedback predistortion technique. The measured error vector magnitude is reduced to 1.47% from 6.4%. These results clearly show that the proposed architecture is a good candidate for efficient linear transmitters.

A New RF CMOS Gilbert Mixer With Improved Noise Figure and Linearity

Abstract: The noise figure of an RF CMOS mixer is strongly affected by flicker noise. The noise figure can be improved using pMOS switch circuits, which insert current at the on/off crossing instants of the local oscillator switch stage because the circuits reduce the flicker noise injection. When it is applied to a conventional Gilbert mixer, the injection efficiency and linearity are degraded by the nonlinear parasitic capacitances of the pMOS switch circuits and the leakage through the parasitic path. We propose the pMOS switch circuits with an inductor, which tunes out the parasitic components at 2fo and closes out the leakage path. The mixer fabricated in 0.13-mum CMOS at 2.4-GHz center frequency has provided improved characteristics for linearity and noise figure.

A Highly Efficient and Linear Class-AB/F Power Amplifier for Multimode Operation

Abstract: The class-AB/F power amplifier (PA), a multimode PA, which can operate at both class-AB and class-F modes, is analyzed and compared with the conventional class-F and class-AB PAs. The open-circuited third harmonic control circuit enhances the efficiency of the PA without deteriorating the linearity of class-AB mode of the PA. The voltage and current waveforms are simulated to evaluate the appropriate operation for the modes. To demonstrate the multimode PA, the PA is implemented using an InGaP/GaAs HBT process and it is tested with reverse-link IS-95A code division multiple access (CDMA) and PCS1900 global system for mobile communications signals in the personal communications service band. The class-AB operation for a CDMA signal delivers a power-added efficiency (PAE) of 38.9% and an adjacent channel power ratio of 49.5 and 56.5 dBc at the offset of 1.25 and 2.25 MHz, respectively, at the output power of 28 dBm. The maximum PAE of 64.7% under the class-F operation is measured at 32.5-dBm output power for a GSM signal. The class-AB/F PA is a good candidate for the multimode PA of next-generation wireless communication systems.

A New Wideband Adaptive Digital Predistortion Technique Employing Feedback Linearization

Abstract: We develop a new wideband digital feedback predistortion (WDFBPD) technique for modulated signals with wide bandwidths by combining digital feedback predistortion (DFBPD) linearization and memory-effect compensation techniques. For the experiments, a class-AB amplifier using an LDMOSFET with 90-W peak envelope power is employed. The proposed technique is compared with existing DFBPD and memory polynomial (MP) techniques for a 2.14-GHz forward-link WCDMA 2FA signal with 10-MHz carrier spacing. The experimental results show that the new WDFBPD technique has better linearization performance than conventional DFBPD and lower computational complexity than the MP technique.

A Wideband Envelope Tracking Doherty Amplifier for WiMAX Systems

Abstract: We have demonstrated a wideband envelope tracking Doherty amplifier. The amplifier is implemented using Eudyna 10-W GaN high electron mobility transistor. For world interoperability for microwave access (WiMAX) signals of the 802.16d and 802.16e, the Doherty amplifier covers the 90 MHz bandwidth (2.3-2.39 GHz) of the Korea's mobile WiMAX (WiBro). The performance of gain, power-added efficiency (PAE), and relative constellation error (RCE) are nearly uniform for the bandwidth. In order to improve the linearity, we have applied the envelope tracking technique to the gate of the Doherty amplifier. The envelope tracking amplifier delivers a significantly improved RCE performance of 35.3dB, which is an enhancement of about 4.3dB, maintaining the high PAE of about 30% for the 802.16 d signal at an average output power of 35 dBm.

Toward Integrated Circuit Size Reduction

Abstract: In this article, voltage-basis, current-basis, and normalized scattering matrices were introduced and it was shown that three different scattering matrices are the same only with equal termination impedances but only the normalized scattering matrix is correct with arbitrary termination impedances. The scattering matrices can be calculated from impedance, admittance, or ABCD matrices characterizing a network. However, if the network has more than three ports, the calculation process from the admittance or impedance matrices is not simple. For this, conversion formulas of the ABCD parameters into the normalized scattering parameters were presented for the impedance-transforming directional couplers. If one can have any choice of the termination impedances of the directional couplers as shown in this article, the total size of a microwave integrated circuit can be reduced.

A Sub-2 dB NF Dual-Band CMOS LNA for CDMA/WCDMA Applications

Abstract: This letter presents the design and experimental results of a 1.8/2.14 GHz dual-band CMOS low-noise amplifier (LNA), which is usable for code division multiple access and wideband code division multiple access applications. To achieve the narrow-band gain and impedance matching at both bands, an extra capacitor in parallel with the Cgs of the main transistor and a harmonic tuned load are switched. Except for the output blocking capacitor and series inductor, all components are integrated on a single-chip. The LNA is designed using a 0.13mum- CMOS process and employs a supply voltage of 1.5 V and dissipates a dc power of 7.5 mW. The measured performances are gains of 14.54 dB and 16.6 dB, and noise figures of 1.75 dB and 1.97 dB at the two frequency bands, respectively. The linearity parameters of and P1dBin are -16dBm and -5.8 dBm at the 1.8 GHz, -14.8 dBm and -5.3 dBm at the 2.14 GHz, respectively.

A Parallel Power Amplifier With a Novel Mode Switching Control

Abstract: Two parallel operating power amplifiers (PAs) are controlled by a novel mode switch for high efficiencies at both the back-off power region and high power region. The mode switch is realized by the base-collector (BC) junction diode which reuses the dc current of the low power mode amplifier. A 836 MHz CDMA PA has been demonstrated using InGaP/GaAs heterojunction bipolar transistor with fully integrated matching component for small package and low cost. It shows a 13 mA idle current, 15.4% power added efficiency (PAE), ACPR1 at 16 dBm of the low power mode operation and a 40.5% PAE, ACPR1 at 28 dBm of the high power mode operation.

Wide-band CMOS loop-through amplifier for Cable TV tuner

Abstract: A fully integrated loop-through amplifier (LTA) for cable TV tuner is presented in a 0.18 mum CMOS process. It covers the whole frequency band from 48 MHz to 860 MHz and allows a second TV and multiple tuners. This circuit employs a parallel connection of common-gate and common-source (CG-CS) amplifiers for broadband matching. The performances are enhanced by current amplification for high linearity and by noise canceling for low noise figure. There are global and local feedback circuits to achieve wide-band input matching and flat gain. We have achieved a gain of 5 dB, a noise figure (NF) of 8.2 dB, an IIP2 of 78 dBmV, an IIP3 of 59 dBmV and SR11 of -11 dB at 850MHz. The power consumption of the circuit is 92.4mW from a 3.3-V supply and the area of chip is 0.075mm2.

Class-AB/F Doherty Power Amplifiers

Abstract: The class-AB/F Doherty power amplifier (PA) adopts the concept of the class-AB/F PA to enhance efficiency while satisfying linearity. The third harmonic control circuits of the PA improve the efficiency without deteriorating the linearity, and the Doherty PA improves the linearity further by IM3 cancelation. The class-AB/F chips are fabricated by an InGaP/GaAs HBT process and combined on a PCB with a-quarter-wavelength transformer. The operation of the class-AB/F Doherty PA is demonstrated with a 54 Mbps/64 QAM OFDM signal having a 10.3 dB PAPR. The Doherty PA has EVM of 3% and the PAE of 31.5% at 24 dBm of average output power, 10.5 dB backed-off from P1dB of 34.5 dBm. The PA operates efficiently and linearly, suitable to the next generation of handset applications.

Envelope injection consideration of high power hybrid EER transmitter for IEEE 802.16e mobile WiMAX application

Abstract: We have implemented a Hybrid Envelope Elimination and Restoration transmitter for 2.655 GHz IEEE 802.16e WiMAX applications using 90 W (P 3dB ) GaN High Electron Mobility Transistor. When the tantalum capacitor is eliminated at the drain bias network of the high power amplifier (PA), bias signals at the drain and gate are seriously fluctuated due to the ‘f2-f1’ component. To suppress the fluctuation in the H-EER transmitter, we have proposed a modified bias circuit architecture using an emitter follower. For the interlock experiment, power-added efficiency (PAE) of the transmitter has been achieved 37.04 % at an output power of 41.18 dBm with drain efficiency (DE) of 39.1 %. By using digital predistortion technique, the Relative Constellation Error (RCE) has been satisfied the specification of −30.4 dB. These results clearly show that the proposed bias circuit architecture is very effective for bias modulation techniques such as EER or ET power amplifier.

Modified Small Asymmetric Impedance Transformers

Abstract: In this paper, modified small asymmetric impedance transformers are suggested The impedance transformers should transform a real impedance into another one For this purpose, design technique, being able to transform a complex impedance (admittance) into a real impedance (admittance) only with a transmission-line section, is required Using this, two types of modified ones are introduced and simulated at a design center frequency of 1 GHz Their simulation results show considerable bandwidths compared with their sizes

The fully‐integrated CMOS RF power amplifier using the semilumped transformer

Abstract: A semilumped output transformer for fully-integrated RF CMOS power amplifier is proposed in this paper. To demonstrate this transformer, a 2.5-GHz CMOS power amplifier is implemented with a 0.18-μm RF CMOS process used for WiMAX application. The power amplifier can achieve 39% PAE (power added efficiency) at P1dB (1 dB compression point) and output power of 30 dBm. The linearity can satisfy the spectrum mask of the WiMAX signal requirement basically. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2857–2860, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23811

Investigation on wideband digital feedback predistortion technique for mobile WiMAX multicarrier applications

Abstract: We have developed a new wideband digital feedback predistortion technique for wideband signals by combining digital feedback predistortion linearization and memory-effect compensation techniques, and investigated linearization performance for 802.16e mobile WiMAX 2FA signal. For this purpose, a 2.655-GHz class-AB amplifier with 170-W peak envelope power is fabricated. The proposed technique is compared with the digital feedback predistortion. We have experimentally demonstrated that the new wideband digital feedback predistortion technique is suitable to linearize amplifiers for mobile WiMAX multicarrier application. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 3048–3052, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23877

Branch-line hybrids with - 15 dB coupling power

Abstract: In this paper, -15 dB branch-line hybrid was realized. In the case of-15 dB coupling power, the characteristic impedances of transmission lines were 49.20 Omega and 276.689 Omega and it was discussed to realize the high characteristic impedance of 276.689 Omega using coupled transmission lines. Using the method suggested, the problem how to realize the high characteristic impedance of 90deg transmission lines will be solved.

Performance enhancement of linear power amplifier employing digital technique

Abstract: Current wireless communication systems require highly efficient and linear power amplifiers. However, there is a trade-off relationship between the efficiency and the linearity. To enhance the performance over the barrier limited by the trade-off, digital control and digital error correction for linearity of a power amplifier become hot research items. We will introduce the digital techniques to enhance performances. It includes the RF transmitter architecture controlled by digital circuit such as a delta-sigma modulator, and the digital feedback pre-distortion technique, which linearizes the highly efficient saturated power amplifiers.

Optimized design of wideband transformer for handset CMOS power amplifier application

Abstract: This paper analyzes the bandwidth characteristic of a transformer with a view point of the impedance matching and provides design rules. Based on the rules, two designs were demonstrated, the dual narrow path band transformer and the distributed active transformer (DAT) optimized for a wide bandwidth.

Compact and Wideband Coupled-Line 3-dB Ring Hybrids

Abstract: In this paper, two types of wideband 3-㏈ ring hybrids are compared and discussed to show the ring hybrid with a set of coupled-line sections better. However, the better one still has a realization problem that perfect matching can be achieved only with －3 ㏈ coupling power. To solve the problem, a set of coupled-line sections with two shorts is synthesized using one- and two-port equivalent circuits and design equations are derived to have perfect matching, regardless of the coupling power. Based on the design equations, a modified Π-type of transmission-line equivalent circuit is newly suggested. It consists of coupled-line sections with two shorts and two open stubs and can be used to reduce a transmission-line section, especially when its electrical length is greater than π. Therefore, the 3λ/4 transmission-line section of a conventional ring hybrid can be reduced to less than π/2. To verify the modified Π-type of transmission- line equivalent circuit, two kinds of simulations are carried out; one is fixing the electrical length of the coupled-line sections and the other fixing its coupling coefficient. The simulation results show that the bandwidths of resulting small transmission lines are strongly dependent on the coupling power. Using modified and conventional Π-types of transmission-line equivalent circuits, a small ring hybrid is built and named a compact wideband coupled-line ring hybrid, due to the fact that a set of coupled-line sections is included. One of compact ring hybrids is compared with a conventional ring hybrid and the compared results demonstrate that the bandwidth of a proposed compact ring hybrid is much wider, in spite of being more than three times smaller in size. To test the compact ring hybrids, a microstrip compact ring hybrid, whose total transmission-line length is 220°, is fabricated and measured. The measured power divisions(S₂₁, S₄₁, S₂₃ and S₄₃) are －2.78 ㏈, －3.34 ㏈, －2.8 ㏈ and －3.2 ㏈, respectively at a design center frequency of 2 ㎓, matching and isolation less than －20 ㏈ in more than 20 % fractional bandwidth.

Gate-Bias Control Technique for Envelope Tracking Doherty Power Amplifier

Abstract: The gate-biases of the Doherty power amplifier are controlled to improve the linearity performance. The linearity improvement mechanism of the Doherty amplifier is the harmonic cancellation of the carrier and peaking amplifier at the output power combining point. However, it is difficult to cancel the harmonic power for the broader power range because the condition for cancelling is varied by power. For the linearity improvement, we have explored the linearity characteristic of the Doherty amplifier according to the input power and gate biases of the carrier and peaking amplifier. To extend the region of harmonic power cancellation, we have injected the proper gate bias to the carrier and peaking amplifier according to the input power levels. To validate the linearity improvement, the Doherty amplifier is designed using Eudyna 10-W PEP GaN HEMT EGN010MKs at 2.345 ㎓ and optimized to achieve a high linearity and efficiency at an average output power of 33 ㏈m, backed off about 10 ㏈ from the P 1㏈ . In the experiments, the envelope tracking Doherty amplifier delivers a significantly improved adjacent channel leakage ratio performance of －37.4 ㏈c, which is an enhancement of about 2.8 ㏈, maintaining the high PAE of about 26 % for the WCDMA 1-FA signal at an average output power of 33 ㏈m. For the 802.16-2004 signal, the amplifier is also improved by about 2 ㏈, －35 ㏈.

Highly Efficient High Power Hybrid EER Transmitter for IEEE 802.16e Mobile WiMAX Application

Abstract: We have described a high power hybrid envelope elimination and restoration(H-EER) transmitter for IEEE 802.16e Mobile World Interoperability for Microwave Access(WiMAX) using an efficiency optimized power amplifier(PA). The PA has been designed to have maximum PAE at the important power generation , region using Nitronex 100-W PEP GaN HEMT. For the high power application, H-EER transmitter should be considered the regenerative oscillation problem due to the PA`s bias fluctuation effect and bias modulator stability issue. Therefore, the bias modulator for H-EER transmitter has been designed to suppress the regenerative oscillation. For the interlock experiment, the bias modulator has been built with the efficiency of 72% and peak output voltage of 30 V for the envelope signal with a PAPR of 8.5 dB. The H-EER transmitter for WiMAX application has been achieved a high PAE characteristic, 38.8 % at an output power of 41.25 dBm. By using digital predistortion(DPD) technique, the Relative Constellation Error (RCE) has been satisfied the specification of -34.5 dB. This is the first work at 2.655 GHz high power H-EER transmitter for WiMAX application.