class-F Operation Research Articles

A Compact and Low Phase Noise Square-Geometry Quad-Core Class-F VCO Using Parallel Inductor-Sharing Technique

This article introduces a compact and low phase noise (PN) 19-GHz quad-core class-F voltage-controlled oscillator (VCO) based on a square-geometry transformer tank using the inductor-sharing technique. The proposed square-geometry transformer tank is inherently more compact than the prevalent topologies such as star geometry, dual-row geometry, and circular geometry. The inductor-sharing technique is introduced to merge neighboring inductors into smaller ones, which further reduces the chip area. Moreover, the proposed quad-core topology supports impedance boosting at harmonic frequencies without extra chip area consumption and class-F operation is adopted to achieve better PN performance. The quad-core VCO prototype is designed and fabricated in a 65-nm CMOS process. Measured performances are 17.6 to 19.4 GHz frequency range with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula> 137.2 dBc/Hz minimum PN at 10 MHz offset from 19 GHz carrier with 46 mW power consumption and 0.9-V supply, resulting a figure of merit (FoM) of 186.1 dBc/Hz. Thanks to the proposed square-geometry and inductor sharing technique, the proposed VCO is the smallest in quad-core VCOs with a similar operating frequency with a core chip area of 0.3 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> 0.3 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{2}$</tex-math> </inline-formula> and the corresponding FoM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathrm{A}}$</tex-math> </inline-formula> is 196.5 dBc/Hz.

A High-Power Capacity Transistor-Based Rectifier With Wide Input Power Range

This letter proposes a methodology for realizing the rectifier with a wide radio frequency (RF) input power range for large power capacity applications. The comprehensive analysis is given in this letter under the condition of class-F operation mode. The optimum conduction angle of the transistor corresponding to the maximum input power dynamic range is determined. Theoretical rectification efficiency of over 60% can be obtained in a 30 dB in-depth input power level. For validation, an RF-dc rectifier operating at 2.45 GHz is designed based on the GaN transistor. Measurements demonstrate that the rectification efficiency of between 60.4% and 82.1% is realized with a fixed dc load of 115 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $</tex-math> </inline-formula> when the RF input power is from 18 to 43 dBm. To the best of the authors’ knowledge, it is the first realization of a transistor-based RF-dc rectifier with a large input dynamic range of over 25 dB. The proposed rectifier shows great potential to be used in future high-power wireless power transfer (WPT) applications.

A 5.15–6.425 GHz Stagger-Tuning Neutralized Power Amplifier Using a Continuous-Mode Harmonically Tuned Network

This letter presents a 5.15–6.425-GHz GaAs HBT power amplifier (PA) for emerging Wi-Fi 6E applications. As a wider range of the operating frequency is specified, a stagger-tuning neutralized differential PA architecture is proposed to extend the bandwidth. In addition, both the linearity and efficiency of the PA are improved using a continuous-mode harmonically tuned network for Class-F operation. The average gain of the proposed PA reaches 33 dB at 4.9–6.7 GHz. With the 80-MHz MCS11 802.11ax signal, the output power meeting error vector magnitude (EVM) of −40 dB reaches 18–20 dBm with maximum power-added efficiency (PAE) of 9.3% at 5.15–6.425 GHz.

A Reconfigurable Class-AB/F Power Amplifier for 0.1–4.2 GHz Multistandard Applications

In this paper, a reconfigurable multi-mode Class-AB/F power amplifier (PA) is proposed for 0.1–4.2 GHz multistandard applications. The PA operates in linear mode (class-AB) for variable-envelope modulated signals and switching mode (class-F) for constant-envelope modulated signals. The proposed linear mode PA design is suitable for multi-band LTE, IOT, WSN and multi-standard RF transmitter, while switching mode PA design can be used in multi-band IOT-LPWA and BLE (Bluetooth Low Energy) RF transmitter. The proposed PA has a reconfigurable off-chip inter-stage and output matching networks over the specified frequency band, while the input stage is Complementary Current-Reuse common-gate with active shunt feedback configuration to achieve Ultra-Wideband (UWB) input matching. The proposed multi-mode PA is designed using a 130 nm CMOS process. Class-AB PA has a saturated output power of 23.5 dBm ± 1 dB over 0.1–4.2 GHz, a power-added efficiency (PAE) of 41%, a third-order intercept point (OIP3) of 17 dBm, and adjacent channel power ratio (ACPR) of − 29.3 dBc for LTE 15 MHz channel bandwidth. The maximum PAE of 62.1% under the class-F operation is achieved at output power of 24.5 dBm. The PA occupies 0.64 mm2 of chip area, while the estimated off-chip area is 13.3 mm2. The proposed PA consumes 164 mW, and 16 mW in class-AB and class-F, respectively.

Input-Harmonic-Controlled Broadband Continuous Class-F Power Amplifiers for Sub-6-GHz 5G Applications

A comprehensive analysis is presented for investigating the effects of input nonlinearity on performance and broadband design of continuous-mode class-F power amplifiers (PAs). New time-domain waveforms are derived considering input and output harmonic terminations for continuous-mode class-F operation. The derived design equations show that the typical fundamental load design space of a continuous class-F PA must be reengineered in the presence of second-harmonic input nonlinearity to new design space in order to achieve optimum class-F PA performance versus varying second-harmonic load impedance. For the practical validation, the impacts of input nonlinearity on the performance of continuous-mode class-F PAs are first confirmed with pulsed vector load–pull (VLP) measurements on a low-power GaN 2-mm device. Second, a broadband high-power GaN 24-mm part is designed following the proposed theory with in-package input second-harmonic terminations targeting 1.75–2.3-GHz frequency band for the sub-6 GHz 5G high-power applications. Efficiency higher than 65% with peak power more than 53.2 dBm was maintained over the target frequency band, with excellent flatness. Third, a Doherty PA is implemented based on the designed GaN 24-mm part to evaluate the broadband performance with modulated stimuli. Using a multicarrier signal having an instantaneous bandwidth of 395 MHz, the average drain efficiency of the Doherty PA at 8-dB output back-off is higher than 44%, and the linearized adjacent channel power ratio (ACPR) is better than −52 dBc.

A Highly Efficient X-Band Inverse Class-F SiGe HBT Cascode Power Amplifier With Harmonic-Tuned Wilkinson Power Combiner

A highly efficient sub-Watt X-band inverse class-F SiGe heterojunction bipolar transistor (HBT) cascode power amplifier (PA) is presented. With a multi-harmonic resonance filter and a low loss lumped-element Wilkinson power combiner as an output matching network, the inverse class-F operation is realized successfully and high output power and power added efficiency (PAE) are obtained simultaneously. A cascode configuration with a low base impedance termination and reduced voltage–current waveform overlap extends ${V} _{\rm{CE}}$ swing of the upper SiGe HBT in the cascode beyond BVCBO, leading to improvement in output power and PAE. As proof of concept, the proposed PA was implemented in a 0.13- ${{\mu }}\text{m}$ SiGe BiCMOS technology platform. Measured results shows 53.4% peak PAE with 26.1 dBm output power at 10 GHz, when operated on a 3.0-V supply. No performance degradation is observed after 24-h continuous mode operation. To the author’s best knowledge, this brief has the highest PAE among any Si-based X-band PAs with comparable output power, which demonstrates that the proposed harmonic-tuned Wilkinson power combiner approach is an appropriate solution for efficient PA design at X-band.

A Low-Flicker-Noise 30-GHz Class-F23 Oscillator in 28-nm CMOS Using Implicit Resonance and Explicit Common-Mode Return Path

This paper presents a millimeter-wave (mmW) frequency generation stage aimed at minimizing phase noise (PN) via waveform shaping and harmonic extraction while suppressing flicker noise upconversion via proper harmonic terminations. A 2nd-harmonic resonance is assisted by a proposed embedded decoupling capacitor inside a transformer for explicit common-mode current return path. Class-F operation with 3rd-harmonic boosting and extraction techniques allow maintaining high quality factor of a 10-GHz tank at the 30-GHz frequency generation. We further propose a comprehensive quantitative analysis method of flicker noise upconversion mechanism exploiting latest insights into the flicker noise mechanisms in nanoscale short-channel transistors, and it is numerically verified against foundry models. The proposed 27.3- to 31.2-GHz oscillator is implemented in TSMC 28-nm CMOS. It achieves PN of −106 dBc/Hz at 1-MHz offset and figure-of-merit (FoM) of −184 dBc/Hz at 27.3 GHz. Its flicker phase-noise ( $1/f^{3}$ ) corner of 120 kHz is an order-of-magnitude better than currently achievable at mmW.

Optimal Definition of Class F for Realistic Transistor Models

An optimal three-harmonic definition of class F at the intrinsic level is presented for realistic transistor models exhibiting IV characteristics with a nonzero knee voltage. This updated class-F definition is needed for use with the recently reported embedding device model , which predicts in a single harmonic balance simulation the voltage and current waveforms required at the package reference planes to sustain an intrinsic mode of operation. Optimal class-F operation is obtained by setting to infinite the third-harmonic output impedance of the transistor IV characteristics instead of using an open load for the third-harmonic termination. This is achieved by fine tuning the class-F quasi-rectangular drain voltage waveform. The required third-harmonic component of the drain voltage in the optimal class F is then found to be generated by the lossless inductive termination of the third-harmonic component of the drain displacement current arising from the nonlinear drain-to-source capacitance. The proposed class-F definition is verified for a gallium nitride (GaN) high electron mobility transistor using third-harmonic load–pull simulations with a realistic GaN transistor model. The optimal third-harmonic load termination predicted using the class-F definition is found to be in full agreement with the one obtained from the drain efficiency contour plots. A close agreement is also obtained for the predicted and measured optimal third-harmonic load termination, bringing experimental support for the proposed class-F definition.

Highly efficient wideband X‐band MMIC class‐F power amplifier with cascode FP GaN HEMT

Wideband high-power single-chip X-band class-F power amplifier with excellent output performances is reported. In order to achieve high-power class-F operation under minimised output capacitance impact at the frequency, high-voltage operation with minimised device size is pursued and its voltage swing becomes maximised by adopting high breakdown field-plate (FP) GaN high-electron-mobility transistor (HEMT) devices with cascode configuration. For the fabrication, 0.14 µm FP AlGaN/GaN HEMT technology with 58 GHz fT and ∼100 V breakdown is used. Based on on-wafer test at 44 V Vdd, the fabricated class-F power amplifier delivers maximum 61.1% power added efficiency (PAE) with 9.2 W at 10.2 GHz. With the help of high-voltage operating cascode devices of minimised size, it also delivers excellent bandwidth of 1.6 GHz at the point of 50% PAE and high-power density of 4.42 W/mm is demonstrated.

Split Slant-End Stubs for the Design of Broadband Efficient Power Amplifiers

This paper suggests a class-F power amplifier with split open-end stubs to provide a broadband high-efficiency operation. These stubs are designed to have wide bandwidth by splitting wide open-end stubs into narrower stubs connected in shunt in an output matching network for class-F operation. In contrast to conventional wideband class-F designs, which theoretically need a large number of matching lines, this method requires fewer transmission lines, resulting in a compact circuit implementation. In addition, the open-end stubs are designed with slant ends to achieve additional wide bandwidth. To verify the suggested design, a 10-W class-F power amplifier operating at 1.7 GHz was implemented using a commercial GaN transistor. The measurement results showed a peak drain efficiency of 82.1% and 750 MHz of bandwidth for an efficiency higher than 63%. Additionally, the maximum output power was 14.45 W at 1.7 GHz.

High-Efficiency Doherty Power Amplifiers: Historical Aspect and Modern Trends

In modern wireless communication systems, it is very important to realize simultaneously high-efficiency and linear operation of power amplifiers. This paper-overview describes the historical aspect of the Doherty approach to the power-amplifier design introduced in 1936 and modern trends in Doherty amplifier (DA) design techniques using multistage and asymmetric multiway architectures. To increase efficiency over the power backoff range, the switchmode class-E, conventional class-F, or inverse class-F operation mode by controlling the second and third harmonics can be used in the load network. The DA with a series-connected load, and inverted, push–pull, balanced, and parallel Doherty architectures are also described and discussed. Finally, examples of the lumped DA implemented in monolithic microwave integrated circuits, digitally driven Doherty technique, and broadband capability of the two-stage DA are given.

A Miniaturized WiMAX Band 4-W Class-F GaN HEMT Power Amplifier Module

In this paper, the design and fabrication of a miniaturized 4-W power amplifier for the WiMAX frequency band (2.3-2.7 GHz) is presented. The selected active device is a commercially available GaN HEMT chip from TriQuint Semiconducotr Inc., Hillsboro, OR. The optimum input and output impedances of the GaN HEMT at fundamental frequency are extracted using a custom designed tuning jig. A novel output matching network for class-F operation is proposed and designed using the measured impedances. For integration in a small package, the input and output matching networks are implemented using spiral inductors and interdigital capacitors, and their dimensions were determined using electromagnetic simulation. The fabricated power amplifier is 4.4 × 4.4 mm2 and has an efficiency above 50% and harmonic suppression above 40 dBc for second and third harmonics at an output power of 36 dBm.

A compact class-F/class-C Doherty amplifier

A Doherty amplifier is described in which odd harmonics from the class-C peaking amplifier flow to the main amplifier to achieve class-F operation, without the need for complicated space consuming harmonic control circuits. The measured efficiency exceeded 50% above the 6 dB back-off. The measured second and third harmonic levels were below −19 dBc. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26035

Design of Dualband Class-F PAs for Cellular and WLAN Applications

In this paper, highly efficient class-F power amplifiers(PAs) with harmonic-controlling transmission lines(TLs) were built for cellular and WLAN applications at 840 MHz and 2.4 GHz each. Also, based on these single-band PAs, a dualband class-F PA was designed after a careful investigation into the harmonics of the two frequencies. The harmonic-controlling TL was designed for the class-F operation at dualband by switching the length of the shunt <TEX>$\lambda$</TEX>/4 TL part, while the series <TEX>$\lambda$</TEX>/4 TL is optimized for both frequencies. To verify the performance, two class-F PAs optimized at each frequency and a dualband class-F PA at the corresponding frequencies were built with the secondand the third-harmonic control circuits at each frequencies. As a result, the PA#1 at 840 MHz has a peak drain efficiency of 81.2 % with an output power of 24.4 dBm, while the PA#2 at 2.35 GHz shows a drain efficiency of 94.5 % with an output of 22.8 dBm. Finally, the dualband class-F PA#3 showed 60.5 % and 50.9 % drain efficiencies at 840 MHz and 2.4 GHz, with powers of 23.8 dBm and 19.62 dBm, respectively.

High-Efficiency Class-FE Tuned Power Amplifiers

The results of exact time domain analysis of the novel switched-mode tuned Class-FE power amplifiers with a parallel quarterwave transmission line are presented with analytical derivation of the optimum load network parameters. Effects of the quarterwave transmission line and collector capacitance on the current and voltage waveforms are discussed. A Class-FE power amplifier is based on the combination of a class-F operating mode with Class-E switching conditions, thus extending the Class-F operation to higher frequencies for driving signals with duty cycles D < 0.5. The ideal collector voltage and current waveforms demonstrate a possibility of 100% efficiency without overlapping between each other. A possibility of alternative load network implementation including a series quarterwave transmission line or lumped-element approximation is also considered. The switched-mode Class-FE power amplifiers with a quarterwave transmission line offer a new challenge for RF and microwave power amplification providing high-efficiency operation conditions.

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

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.

Study and Design Optimization of Multiharmonic Transmission-Line Load Networks for Class-E and Class-F $K$-Band MMIC Power Amplifiers

A design-oriented analysis of microwave transmission-line class-E and class-F amplifiers is presented in this paper. Multiharmonic transmission-line load networks are analyzed and compared in terms of harmonic suppression and their effects on output power and efficiency. Based on this study, a design of highly efficient monolithic-microwave integrated-circuit amplifiers has been carried out. To allow circuit optimization and to simplify the design process, analytic expressions were derived for the most practical multiharmonic transmission-line networks. Fabricated amplifiers achieve state-of-the-art efficiency of 56.2% and 59.0% for class-E and class-F operation at K-band for power levels of 19.1 and 20.0 dBm, respectively. Moreover, without the need for supplementary filtering sections, harmonic suppression for operation well into compression is better than -25 and -30 dBc for the transmission-line class-F and class-E amplifiers, respectively.

Voltage-Clamped Class-E Inverter With Harmonic Tuning Network for Magnetron Drive

A passive lossless snubber utilizing harmonic resonance is proposed for the voltage-driven class-E inverter. This snubber reduces the peak resonant voltage stress across the switch in class-E operation by adding the third-order harmonic current into the fundamental resonant part and can be extended to a higher-order network for further reduction. Though the principle is actually equivalent to the class-F operation in RF power amplifiers, it is first tried for the class-E inverter without a current source inductor. A series of analyses is performed to find component values that provide the optimum harmonic condition, and the experimental results from the inverter power supply for driving a magnetron are presented

BJT class-F power amplifier near transition frequency

This paper presents the analysis and the design rules of bipolar junction transistor (BJT) class-F power amplifier operating at a frequency comparable with the transition one. Since the impulse of collector current becomes stretched with operation frequency increasing, its spectral content is changed. Thus, the requirements for the amplifier's output network and bias conditions should be corrected compared with the classic low-frequency case in order to achieve high-efficiency class-F operation. Using the simple BJT model, these new requirements were obtained in this paper. The presented results of simulation and experimental verification show the advantages of proposed approach.

A second harmonic class-F power amplifier in standard CMOS technology

For personal communications systems, the highest possible integration on monolithic technology of all RF functions is desirable. The most difficult component to be monolithically integrated with all other functions is the output power amplifier. This paper describes the design and test of an integrated class-F power amplifier with 200-mW output power at 1.9 GHz and a 3 V power supply based on a 0.6 /spl mu/m CMOS standard technology. A theoretical study of class-F operation that highlights the influence of nonideal active devices and output network topology on the circuit behavior was performed to have guidelines for amplifier optimization.