A 915 MHz GaN HEMT-based class-E rectifier is proposed in this paper to be used for DC+AC wireless power recovery. Taking advantage of the time reversal (TR) duality principle, the rectifier was derived from a class-E inverter, whose output network was designed for high-efficiency operation over a wide range of resistive loads. The addition of an appropriate gateside termination allows the device to be turned-on without an additional RF source for gate driving. The rectifier reduced sensitivity to load variation, as well as its capability for efficiently and linearly recovering the envelope of an AM RF excitation, were then characterized. An average efficiency of 82% has been measured for the combined RF-to-DC and RF-to-AC power conversion of a 1.6 W modulated carrier. Frequency multiplexing and frequency modulation alternatives for high-level DC+AC wireless power transmission are finally presented.This work was supported by the Ministry of Economy and Competitiveness (MINECO) through TEC2014-58341-C4-1-R and TEC2014-58341-C4-2-R projects, co-funded with FEDER. The authors wish to thank Prof. Christian Brañas, University of Cantabria, by his assistance with the transformer characterization. David Vegas and José R. Pérez-Cisneros also thank the support provided by the pre-doctoral BES-2015-072203 and the pre-doctoral mobility EEBB-I-15-10447 grants, respectively

García García, José Ángel

Pérez Cisneros, José Ramón

Ruiz Lavín, María de las Nieves

Vegas Bayer, David

English

M. Nieves Ruiz

David Vegas

Jose R. Perez-Cisneros

Jose A. Garcia

Crossref

GaN HEMT class-E rectifier for DC+AC power recovery

UCrea

GaN HEMT Class-E Rectifier for DC+AC Power Recovery  M. Nieves Ruiz *, David Vegas *, José R. Pérez-Cisneros *† , José A. García * * Department of Communications Engineering, University of Cantabria, 39005 Santander, Spain †Aragon Institute of Engineering Research (I3A), University of Zaragoza, 50018 Zaragoza, Spain  Abstract— A 915 MHz GaN HEMT-based class-E rectifier is proposed in this paper to be used for DC+AC wireless power re-covery. Taking advantage of the time reversal (TR) duality prin-ciple, the rectifier was derived from a class-E inverter, whose out-put network was designed for high-efficiency operation over a wide range of resistive loads. The addition of an appropriate gate-side termination allows the device to be turned-on without an ad-ditional RF source for gate driving. The rectifier reduced sensitiv-ity to load variation, as well as its capability for efficiently and lin-early recovering the envelope of an AM RF excitation, were then characterized. An average efficiency of 82% has been measured for the combined RF-to-DC and RF-to-AC power conversion of a 1.6 W modulated carrier. Frequency multiplexing and frequency modulation alternatives for high-level DC+AC wireless power transmission are finally presented.   Index Terms— Class-E, GaN HEMT, rectifier, wireless power transmission.  I. INTRODUCTION  Far-field wireless power transmission (WPT) links are con-ceived for the remote recovery of DC power, mainly motivated by the increased interest on powering wireless sensors, RFID tags, or many other DC loads requiring low voltage and current levels. Although the grid and most common power-demanding loads operate with AC, the case for instance of induction mo-tors, implementing linear and efficient AC-to-RF and RF-to-AC power converters still remains as a challenging task [1]. Thus, intermediate conversions from AC-to-DC and from DC-to-AC, with more than mature implementations and good per-formance, are common at both sides of the link.  In [2], the integration of two class-E power amplifiers and a pair of identical class-E rectifiers, making use of center-tap transformers, allowed the simultaneous transmission of both semi-sinusoids in the utility waveform, based on well-known AM and polarization multiplexing concepts. However, the use of diode-based rectifiers in the receiving side imposes a rele-vant limitation for high power recovery. If considering that fast switching Schottky diodes with high voltage and current capa-bility are rarely available at the 915 MHz, 2.45 GHz or 5.8 GHz ISM frequency bands, those rectifiers could only deliver low levels to the DC and AC loads (a few tens of milliwatts accord-ing to the device and levels reported in [2]).  A GaN HEMT-based rectifier is proposed in this paper, as the choice for high power recovery. Considering the extreme sensitivity of class-E topologies to load variations [3] and that the transistor could be even destroyed under extreme loading conditions (not so uncommon in applications like fluorescent lamps, electric heating, etc.), a load-invariant topology has been selected. Additionally, a self-synchronous operation [4] has been forced to avoid the need for an auxiliary RF source to drive its gate terminal, not usually available at the remote position. Besides validating its capability for DC and AC power recovery at a few watts, alternatives to the AM/polarization multiplexing technique in [2] are also tested.  II. SELF-SYNCHRONOUS RECTIFIER Taking advantage of the time reversal duality principle [5], a rectifier with reduced sensitivity to load variation was derived from a class-E power amplifier (PA), designed for maximum efficiency under load modulating conditions. Considering the available nonlinear models for RF/microwave FET devices may fail when reproducing the third quadrant of their voltamperic characteristics, this could be the only way to pro-ceed unless an own dedicated model were extracted. A.   Drain Terminating Network and PA Design A CGH35030F GaN HEMT packaged device from Wolfspeed was selected for the designs. After adjusting the in-put power level to force a switch-type of operation, loadpull simulations at the fundamental, 915 MHz, were completed (see Fig. 1). A nearly infinite choke was used, with open circuit ter-minations forced at the higher order harmonics. As it could be expected from [6], a trajectory with maximum efficiency and variable output power exists. Under the theoretical assumptions RON=0 and ROFF=∞, this impedance path would result in zero voltage but variable slope voltage switching at turn on. A drain terminating network was then designed, able to ap-proximate the optimum path under varying load condition, RL. A modification to the inductive impedance inverter in [3] was employed, as presented in the inset of Fig. 1.   Fig. 1. Efficiency (-) and output power (--) load-pull contours from simu-lations, together with the simulated (--) and measured (-) Zin(f) evolution with RL. The drain-side network schematic has been included in the inset. 0 1.01.0-1.010.05.02.03.04.00.20.40.60.8Output power contours Efficiency contours Zd_simZd_meas44 dBm41 dBm38 dBm32 dBm35 dBm80%70%60%Ls CsLp CpDRLZinThe evolution with RL of its input impedance, simulated and measured for a 5-500 Ω range, is also plotted over the contours in Fig.1. The lumped-element parasitics have been taken into consideration. The class-E PA design was completed with the input match-ing and biasing networks. A peak efficiency of 83.2% was ob-tained at 75 Ω, staying above 70% along a resistive termination range from 20 to 200 Ω (over 8 dB of power backoff).  B. Self-synchronous Rectifier Derivation The circuit schematic for the designed class-E topology, once prepared for its use as rectifier, is shown in Fig. 2. In order to guarantee a self-synchronous operation, the gate-side circuit was slightly modified to synthesize the required inductive ter-mination, calculated according to [7]. Coils and capacitors are high Q parts from Coilcraft and ATC, respectively.  Fig. 2. Schematic and component values for the designed rectifier. C. Continuous Wave (CW) Characterization  Once the self-synchronous operation was accomplished, the rectifier was characterized with a 915 MHz CW excitation. A peak overall efficiency of 84.4% was measured for an 85 Ω load resistance, corresponding to a 21.5 V DC output voltage. As it can be appreciated from Fig. 3a, the recovered voltage linearly follows the amplitude of the RF input signal, with an efficiency value better than 80% for input power levels above 32 dBm (Vin > 24 V). This particular feature makes it attractive for be-ing used as high-level envelope detector. The sensitivity of the rectifier to a varying load may be ob-served from the results in Fig. 3b. Although a significant varia-tion of Vout is appreciated, the peak in the drain-to-source volt-age waveform (Vds_peak = 3.562⋅Vout for nominal operation) is kept below the device breakdown voltage (better than 120 V). The degradation in efficiency, when compared to its use as PA in section IIA, is due to the input mismatch. A class-E rec-tifier of this kind, designed for a load-independent high-effi-ciency performance, is expected to offer a resistive input im-pedance. Although not included in this work, the mismatching losses may be reduced with the use of a resistive compression network and a plurality of similar rectifiers [8].   Fig. 3. Measured profiles for the efficiency and the rectified voltage vs the amplitude of the 915 MHz excitation a) and the DC load resistance b).  III. RF-TO-DC+AC POWER CONVERSION In order to exploit the capability of the selected topology for linearly and efficiently working as envelope demodulator (Fig. 3a), two similar self-synchronous rectifiers were combined to recover a 50 Hz waveform, based on the low power approach in [2]. The implemented measurement setup is shown in Fig. 4, where two 915 MHz carriers, amplitude modulated with each of the semi-sinusoids, were conveniently amplified and em-ployed as excitations. The high-level demodulated waveforms were captured with an oscilloscope, while the total RF input power was measured with the aid of two power sensors.   Fig. 4. Measurement set-up for characterizing the RF-to-DC+AC power converter, resulting from combining two self-synchronous rectifiers.   The recovered semi-sinusoids were first captured with the rectifiers loaded by the optimum RL= 85Ω  value from Fig. 3b. Shown in Fig. 5, no significant distortion is appreciated with peak values around 21 V for an average input power of 32 dBm in each branch (peak levels 6 dB higher). Under this loading condition, the average output power per branch was as high as 1.32 W, for a global efficiency around 82%. 12.5 nH 1.8 pF2.5 nH 3.9 pF120 nH56 pFRLVout1.65 nH2.7 pF56 pF120 nHVGGRFin0 100 200 300 400 500 6000255075100Efficiency(%)RL (Ω)010203040V out(V)0 10 20 30 40 50 60 700255075100Vin (V)Efficiency(%)010203040V out(V)a)b)ÊÔÓÃÏÞÖÆÊÔÓÃÏÞÖÆÊÔÓÃÏÞÖÆÊÔÓÃÏÞÖÆÊÔÓÃÏÞÖÆÊÔÓÃÏÞÖÆ𝑉𝑜𝑢𝑡 𝑡𝑉𝑜𝑢𝑡 𝑡𝑉𝐺𝐺𝑉𝐺𝐺𝑅𝐹𝑖𝑛𝑅𝐹𝑖𝑛Σ∆𝑂𝑠𝑐𝑖𝑙𝑙𝑜𝑠𝑐𝑜𝑝𝑒𝑃𝑜𝑤𝑒𝑟 𝑠𝑒𝑛𝑠𝑜𝑟𝐺𝑒𝑛𝑒𝑟𝑎𝑡𝑜𝑟𝐺𝑒𝑛𝑒𝑟𝑎𝑡𝑜𝑟𝐷𝑟𝑖𝑣𝑒𝑟𝐷𝑟𝑖𝑣𝑒𝑟𝑡50𝐻𝑧 𝑉𝐶𝑠𝐶𝑠𝐶𝑝𝐶𝑝𝐶𝑏𝑅𝑎𝑐𝑃𝑜𝑤𝑒𝑟 𝑠𝑒𝑛𝑠𝑜𝑟𝑅𝐷𝐶1: 285Ω85ΩWith the aim of extracting the DC and AC components through mutually isolated output ports, a COTS center-tap transformer with a 2:1 ratio between the primary and secondary windings was added. Its connection in Fig 4 allows stepping-up the voltage. The winding magnetization inductances were measured at 50 Hz for appropriately selecting the required Cs and Cp resonating capacitors. A high-valued capacitor of 10000 µF was employed for bypassing the DC load (Cb). The wave-form at the AC port, captured with the oscilloscope, has been added to Fig. 5. Although not represented, a DC voltage value of 6.7 V was measured at the Σ (DC) output port.  Fig. 5. Demodulated semi-sinusoids under optimum resistive loading. The measured waveform at the ∆ port, when adding the transformer, is included.  IV. DC+AC WPT ALTERNATIVES  As alternatives to the use of AM modulation together with polarization multiplexing in [2], two classic analog communi-cation techniques were also tested for the receiving part of a WPT link, using the above described RF-to-DC+AC power converter: amplitude modulation combined with frequency multiplexing, and frequency modulation. Fig. 6 shows a photo-graph of the implemented measurement setup, common to both approaches. A 40 W cavity duplexer for 900 MHz E-GSM band operation constitutes the core element added to the diagram in Fig. 4.    Fig. 6. Photograph of the implement set-up, including details of the GaN HEMT rectifiers and the cavity duplexer.  A. AM with Frequency Multiplexing Considering the passbands of a GSM duplexer (880 - 915 MHz and 925 - 960 MHz), as well as the 26 MHz available band-width for the 915 MHz ISM band, two carriers at 902 and 928 MHz may be amplitude modulated with their respective semi-sinusoids. Notice that the bandwidth of an AM signal, 100% modulated by a semi-cycle of the 50 Hz waveform, is limited to a few hundreds of Hz. The generated AM RF components were combined and amplified to reproduce the conditions to be obtained at the antenna port in the receiving side of the link. A total average power of 41 dBm was applied to the duplexer in-put (RFin port detail in Fig. 6). The modulating semi-sinusoids were recovered without appreciable distortion by the rectifier circuits, with 72.2% and 68.5% of average efficiency values. The measured efficiency reduction, if compared to section III results, is due to duplexer insertion losses. B. FM approach The AC waveform may be also demodulated from a constant envelope FM signal. If using a carrier at 919.5 MHz with 8.5 MHz of frequency deviation, the same cavity duplexer may be employed as a frequency discriminator. Following an old and proven idea [9], the utility waveform or any other modulating signal could be extracted, with a trade-off between linearity and efficiency. With 6.3 W of RF input power, 1.9 and 2 W of av-erage output power were obtained at the outputs of the rectifi-ers, resulting in this case in a total efficiency for the DC+AC recovered power about 62%. V. CONCLUSION A GaN HEMT-based Class-E rectifier has been proposed for its use in high-level DC+AC wireless power recovery. The drain-side network has been designed for an efficient operation over a wide range of resistive loads, while an inductive gate side termination allows the desired self-synchronous switching. Its reduced sensitivity to load variation has been shown, as well as its capability for efficiently and linearly recovering the enve-lope of an AM RF excitation with an average efficiency of 82%. Frequency multiplexing the AM components or frequency modulating with the utility waveform, alternative high-level DC+AC WPT links may be configured. The proposed architec-tures, restricted to the receiving side, could be also employed for recovering a higher frequency waveform, the case of the hundreds of kHz or few MHz switching waveforms of inductive and resonant WPT systems. ACKNOWLEDGMENT  This work was supported by the Ministry of Economy and Competitiveness (MINECO) through TEC2014-58341-C4-1-R and TEC2014-58341-C4-2-R projects, co-funded with FEDER. The authors wish to thank Prof. Christian Brañas, University of Cantabria, by his assistance with the transformer characteriza-tion. David Vegas and José R. Pérez-Cisneros also thank the 051015202530Recoveredsemi-sinusoids(V)Time (ms)0 5 10 15 20-30-20-100102030AC waveform(V)DuplexerGaN HEMT Self-synchronousrectifiersRLRFinVout (t)Oscilloscope probessupport provided by the pre-doctoral BES-2015-072203 and the pre-doctoral mobility EEBB-I-15-10447 grants, respectively. REFERENCES [1] N. Shinohara, Wireless Power Transfer via Radiowaves, London: J. Wiley & Sons, 2014.  [2]   J.R. Pérez-Cisneros, M.N. Ruiz, M. Lobeira, C. Brañas, J. de Mingo, J.A. García “Class-E Power Converters for AC (50/60 Hz) Wireless Transmis-sion,” IEEE MTT-S International Microwave Symp., San Francisco, May 2016. [3] M. K. Kazimierczuk and Xung T. Bui, “Class E Amplifier with an Induc-tive Impedance Inverter,” IEEE Trans. Industrial Elect., vol. 37, no. 2, pp. 160-166, April 1990. [4] M. Roberg, T. Reveyrand, I. Ramos, E. A. Falkenstein and Z. Popovic, “High Efficiency Harmonically Terminated Diode and Transistor Recti-fiers,” IEEE Trans. Microwave Theory Tech., vol. 60, pp. 4043–4052, Dec. 2012. [5] D. C. Hamill, “Time Reversal Duality and the Synthesis of a Double Class E DC-DC Converter,” 21st Power Electron. Specialist Conf., PESC’90, pp. 512-521, 1990.  [6] M. Acar, A. J. Annema and B. Nauta, "Analytical Design Equations for Class-E Power Amplifiers," IEEE Trans. Circuits Syst. I: Regular Papers, vol. 54, pp. 2706-2717, Dec. 2007. [7] I. Ramos, M.N. Ruiz, J.A. García, D. Maksimovic, Z. Popovic, "GaN Mi-crowave DC–DC Converters," IEEE Trans. Microwave Theory and Tech-niques,  vol. 63, no.12, pp. 4473-4482, Dec. 2015. [8]    T. W. Barton, J. M. Gordonson and D. J. Perreault, "Transmission Line Resistance Compression Networks and Applications to Wireless Power Transfer," IEEE Journal Emerging Selected Topics Power Elect., vol. 3, pp. 252-260, March 2015. [9]    C. 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A 915 MHz GaN HEMT-based class-E rectifier is proposed in this paper to be used for DC+AC wireless power recovery. Taking advantage of the time reversal (TR) duality principle, the rectifier was derived from a class-E inverter, whose output network was designed for high-efficiency operation over a wide range of resistive loads. The addition of an appropriate gate-side termination allows the device to be turned-on without an additional RF source for gate driving. The rectifier reduced sensitivity to load variation, as well as its capability for efficiently and linearly recovering the envelope of an AM RF excitation, were then characterized. An average efficiency of 82% has been measured for the combined RF-to-DC and RF-to-AC power conversion of a 1.6 W modulated carrier. Frequency multiplexing and frequency modulation alternatives for high-level DC+AC wireless power transmission are finally presented

Ruiz, M.N.

Vegas, D.

Perez-Cisneros, J.R.

Garcia, J.A.

Repositorio Universidad de Zaragoza

GaN HEMT Class-E Rectifier for DC plus AC Power Recovery

https://repositorio.unican.es/xmlui/bitstream/10902/12382/1/GaNHEMTClassERectifier.pdf

GaN HEMT class-E rectifier for DC+AC power recovery

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