| 1. |
- Mashad Nemati, Hossein, 1980, et al.
(author)
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Varactor-Based Dynamic Load Modulation of RF PAs
- 2011
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In: European Microwave Conference, Manchester, Workshop "RF PA Efficiency Enhancement Techniques".
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Conference paper (other academic/artistic)
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| 2. |
- Prasad, Ankur, 1987, et al.
(author)
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Symmetrical modeling of GaN HEMTS
- 2014
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In: Technical Digest - IEEE Compound Semiconductor Integrated Circuit Symposium, CSIC. - 1550-8781. - 9781479936229
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Conference paper (peer-reviewed)abstract
- This paper presents a symmetrical small signal model for GaN HEMTs valid for both positive and negative Vds. The model takes advantage of the intrinsic symmetry of the devices typically used for switches. The parameters of the model are extracted using a new symmetrical optimization based extraction method, optimizing simultaneously for both positive and negative drain-source bias points. This ensures a symmetrical small signal model with lower modeling error. The small signal model can be further used to simplify the development of a large-signal model. The small signal model is validated with measured S- parameters of a commercial GaN HEMT.
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| 3. |
- ÖZEN, MUSTAFA, 1984, et al.
(author)
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High efficiency RF pulse width modulation with tunable load network class-E PA
- 2011
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In: 2011 IEEE 12th Annual Wireless and Microwave Technology Conference, WAMICON 2011. - 9781612840819
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Conference paper (peer-reviewed)abstract
- In this paper, a 10 W peak power 2 GHz highly efficient RF pulse width modulation (RF-PWM) based transmitter is presented. RF-PWM signals are generated with a dedicated 65 nm CMOS modulator and subsequently amplified with a GaN Class-E power amplifier (PA). The modulator use extended drain MOS (EDMOS) high voltage transistors to provide the required voltage swing to drive the GaN used as a switch. The imaginary load impedance of the Class-E is electronically tunable and is implemented with in-house high breakdown voltage SiC varactors. The tunable imaginary load impedance enables optimization of the Class-E versus the duty cycle (pulse width). The peak efficiency is therefore preserved over a wide range of output power levels. The measured drain efficiency of the Class-E output stage is above 70% over a 6.5 dB output power dynamic range. The overall transmitter efficiency is above 60% for the same dynamic range.
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| 4. |
- Andersson, Christer, 1982, et al.
(author)
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A packaged 86 W GaN transmitter with SiC varactor-based dynamic load modulation
- 2013
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In: 43rd European Microwave Conference, EuMC 2013 - Held as Part of the 16th European Microwave Week, EuMW 2013, Nuremberg, Germany, 7-10 October 2013. - 9782874870316 ; , s. 283-286
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Conference paper (peer-reviewed)abstract
- Output power scaling based on class-J dynamic load modulation (DLM) theory is used to design an unprecedentedly high power microwave transmitter with varactor-based DLM functionality. Matching networks are realized on high dielectric constant substrates in order to reduce the form factor. The fully matched DLM PA incorporates a 24-mm GaN HEMT powerbar and a stack of four SiC varactors, all fit into a CuW package (40 mm × 20 mm). Peak output power is reconfigurable by changing the drain voltage, while retaining the DLMeffect. Under pulsed conditions at 40 V the PA delivers a peak power of 86 W at 2.14 GHz. Efficiency enhancement by DLM is 10-15 percentage-units at 6 dB output power back-off (OPBO). Employing digital predistortion (DPD) with a vector switched generalized memory polynomial (VS-GMP) the ACLR is -46 dBc at an average output power of 17 W and a drain efficiency of 34%. These results prove the potential for high output power levels in varactor-based DLM transmitters.
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| 5. |
- Andersson, Christer, 1982, et al.
(author)
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A SiC Varactor With Large Effective Tuning Range for Microwave Power Applications
- 2011
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In: IEEE Electron Device Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 0741-3106 .- 1558-0563. ; 32:6, s. 788-790
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Journal article (peer-reviewed)abstract
- SiC Schottky diode varactors have been fabricated for use in microwave power applications, specifically the dynamic load modulation of power amplifiers. A custom doping profile has been employed to spread the C(V) over a large bias voltage range, thereby increasing the effective tuning range under large voltage swing conditions. The small-signal tuning range is approximately six, and punch through is reached at a bias voltage of -60 V, while the breakdown voltage is on the order of -160 V. An interdigitated layout is utilized together with a self-aligned Schottky anode etch process to improve the Q-factor at 2 GHz, which is 20 at zero bias and approximately 160 at punch through.
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| 6. |
- Andersson, Christer, 1982, et al.
(author)
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Nonlinear Characterization of Varactors for Tunable Networks by Active Source-Pull and Load-Pull
- 2011
-
In: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 59:7, s. 1753-1760
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Journal article (peer-reviewed)abstract
- Varactors are key components in the realization of tunable networks, for instance, in high-efficiency power-amplifier architectures. This paper presents a method to measure the varactor quality factor (Q-factor) in the presence of nonlinear distortion. The importance of correctly choosing the loading condition at the second harmonic is illustrated by multiharmonic active source- and load-pull measurements. Furthermore, the method also allows for accurate extraction of the bias-dependent series resistance without the need of area consuming resonant structures. The proposed method is applied to characterize a silicon-carbide (SiC) Schottky diode varactor at 3 GHz. The measured results reemphasize that varactors are not linear tunable, but inherently nonlinear components that require proper consideration of the higher order harmonics.
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| 7. |
- Andersson, Christer, 1982, et al.
(author)
-
Theory and Design of Class-J Power Amplifiers With Dynamic Load Modulation
- 2012
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In: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 60:12, s. 3778-3786
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Journal article (peer-reviewed)abstract
- A theory for class-J microwave amplifier operation as a function of drive level and fundamental load impedance is derived. Calculations show that, under appropriate operating conditions, it is sufficient to modulate the transistor load reactance to enable high-efficiency operation (>70%) over a large output power dynamic range (>10 dB) with high transistor power utilization. Such dynamic load modulation (DLM) networks are an ideal application of continuously tunable varactor technologies. Multiharmonic load–pull measurements are performed on a GaN HEMT and experimentally verify the theory of operation. A demonstrator amplifier using an SiC varactor technology is then designed and characterized by static measurements. The amplifier has a peak power of 38 dBm at 2.08 GHz and maintains efficiencies above 45% over 8 dB of power dynamic range. An analysis of the load network losses is performed to show the potential of the class-J DLM transmitter concept.
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| 8. |
- Prasad, Ankur, 1987, et al.
(author)
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Symmetrical Large-Signal Modeling of Microwave Switch FETs
- 2014
-
In: IEEE Transactions on Microwave Theory and Techniques. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9480 .- 1557-9670. ; 62:8, s. 1590-1598
-
Journal article (peer-reviewed)abstract
- This paper presents a new symmetrical field-effect transistor (FET) model suitable for microwave switches. The model takes advantage of the inherent symmetry of typical switch devices, justifying a new small-signal model where all intrinsic model parameters can be mirrored between the positive and negative drain-source bias regions. This small-signal model is utilized in a new and simplified approach to large-signal modeling of these type of devices. It is shown that the proposed large-signal model only needs a single charge expression to model all intrinsic capacitances. For validation of the proposed model, small-signal measurements from 100 MHz to 50 GHz and large-signal measurements at 600 MHz and 16 GHz, are carried out on a GaAs pHEMT. Good agreement between the model and the measurements is observed under both small-and large-signal conditions with particularly accurate prediction of higher harmonic content. The reduced measurement requirements and complexity of the symmetrical model demonstrates its advantages. Further, supporting operation in the negative drain-source voltage region, the model is robust and applicable to a variety of circuits, e. g., switches, resistive mixers, oscillators, etc.
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| 9. |
- Andersson, Christer, 1982, et al.
(author)
-
A 1-3-GHz Digitally Controlled Dual-RF Input Power-Amplifier Design Based on a Doherty-Outphasing Continuum Analysis
- 2013
-
In: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 61:10, s. 3743-3752
-
Journal article (peer-reviewed)abstract
- This paper presents a linear multi-harmonic analysis method to evaluate the performance of digitally controlled dual RF-input power amplifiers (PAs). The method enables, due to its low computational cost, optimization of PA efficiency and bandwidth in a complex design space involving two independent inputs. Under the idealized assumption of short-circuited higher harmonics, the analysis is used to prove the existence of a Doherty-outphasing continuum, featuring high average efficiency over 100% fractional bandwidth. With this result as a foundation, a combiner incorporating microwave transistor parasitics is analyzed without assuming short-circuited higher harmonics, showing that high average efficiencies are also achievable under more realistic conditions. A PA is straightforwardly designed from these calculation results using two 15-W GaN HEMTs. The simulated layout-ready (large-signal transistor model) PA average drain efficiency exceeds 50% over 1.1-3.7 GHz for a 6.7-dB peak-to-average power-ratio WCDMA signal. The measured PA has a maximum output power of 44 +/- 0.9 dBm and a 6-dB output power back-off (OPBO) power-added efficiency (PAE) of 45% over 1-3 GHz. After applying digital pre-distortion, excellent linearity is demonstrated when transmitting the WCDMA signal, resulting in an adjacent channel leakage power ratio lower than -57 dBc with corresponding average PAE of 50% and 40% at 1.2 and 2.3 GHz, respectively. This is, to the authors' knowledge, the most wideband OPBO efficiency enhanced PA reported to date, proving the effectiveness of employing linear multi-harmonic analysis in dual-input PA design.
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| 10. |
- Andersson, Christer, 1982, et al.
(author)
-
Decade bandwidth high efficiency GaN HEMT power amplifier designed with resistive harmonic loading
- 2012
-
In: IEEE MTT-S International Microwave Symposium Digest. - 0149-645X. - 9781467310871
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Conference paper (peer-reviewed)abstract
- The use of resistive loading at higher harmonics in wideband power amplifier design is proposed. Although the theoretical efficiency of such operation is lower than other classes the significantly simplified load network design potentially allows for multi-octave realizations. A decade bandwidth (0.4-4.1 GHz) GaN HEMT power amplifier was thereby designed, delivering more than 40 dBm output power with 10-15 dB gain and 40-62% drain efficiency. Linearized modulated signal amplification was then successfully demonstrated at multiple frequencies (0.9 to 3.5 GHz), using various downlink signals (LTE, WCDMA, WiMAX), with resulting ACLR lower than 46 dBc.
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