Gamal M. Hegazi

Switch-based GaN HEMT model suitable for highly-efficient RF power amplifier design

A new approach to accurately model the transistor performance In radio frequency (RF) switching-mode operation is proposed. The purpose of the presented switch-based model is to facilitate and speed up considerably extraction and implementation of large-signal device models for computer added design (CAD). Only a small number of DC and low-frequency small-signal S-parameter measurements are required for the extraction of the complete set of element parameters of the model. Accuracy and efficacy of the nonlinear model in predicting the performance of a single-ended RF power amplifier (PA) is demonstrated by experimental results. For a PA based on a commercial GaN HEMT, measured output power and efficiency match with simulations over a broad frequency range. Moreover, robustness of the developed switch-based model is demonstrated by the design of a voltage-mode class-D PA.

Improved LINC power transmission using a quadrature outphasing technique

A new improved approach to LINC power transmission is presented based on a quadrature outphasing technique, which depends on the constant envelope decomposition of the in-phase and quadrature parts of the input signal. In this approach, the processing of the resultant constant envelope components requires a bandwidth far smaller than if a simple LINC transmission technique were used, resulting in reduced sensitivity to components mismatch, far less spectral regrowth and superior linearity than the simple LINC approach. Experimental results at HF band show that the new technique improves the spectral re-growth by more than 10 dB for an 8-ary DPSK signal compared to the regular LINC transmission.

High power RF switch MMICs development in GaN-on-Si HFET technology

The development of a high power RF SP4T MMIC switch using AlGaN/GaN HFETs on Si substrate is reported for applications up to 2 GHz. The off-state capacitance(Coff) of a single-gate GaN based HFET is 250 fF and the on-state resistance (Ron) is 4.1 Omega at a gate length of 0.7 mum and a width of 1 mm. The MMIC SP4T switch with a size of 1.2 x 1.6 mm2 is implemented for system applications of three transmit paths and a receiver, of which each was configured with a series-shunt self-biased configuration. The switch has achieved an insertion loss of -0.95 dB with power handling of P(-0.1dB)=45 dBm at 1 GHz at the transmitter paths and an optimized isolation of better than 28 dB at the receiver path of up to 2.5 GHz. In addition, a high voltage switch driver using the GaN power HFET technology was designed with an input control voltage of 0/2.3 V to provide an output voltage of 0/28 V. This development provides a baseline design for our first generation MMIC switches in GaN technology.

The Development of a High Power SP4T RF Switch in GaN HFET Technology

The development of a high power single-pole four throw (SP4T) hybrid switch using AlGaN/GaN heterostructure field effect transistors (HFETs) on Si substrate is reported for the first time for applications up to 1.5 GHz. The off-state capacitance of a single-gate GaN based HFET is 250 fF and the on-state resistance is 4.1 at a gate length of 0.7 m and a width of 1 mm. The hybrid SP4T switch with a size of 44 mm was implemented for system applications of three transmit paths and a receiver, of which each was configured with a series-shunt self-biased configuration. The switch has achieved an insertion loss of 1.4 dB with power handling of 43 dBm at the transmitter paths and an optimized isolation of better than 25 dB at the receiver path at 1.5 GHz. In addition, a high voltage switch driver using the GaN HFET technology was designed with an input control voltage of 0/4 V to provide an output voltage of 0/26 V. This development provides a baseline design for our next generation monolithic microwave integrated circuit switches in GaN technology.

Practical high-efficiency partial-Envelope Tracking power amplifier system with broadband applications

Spectrally-efficient high peak-to-average power ratio (PAPR) waveforms exhibit disadvantages compared to constant-envelope waveforms for frequency-agile systems when power-efficiency is paramount. EER and Envelope Tracking offer high efficiency but require precise adjustment and wide bandwidth power supplies/modulators. Frequency agility introduces implementation complexities when systems must tune wide frequency ranges or cover multiple channels. Combining advantages of Envelope Tracking and EER, a partial-envelope tracking power amplifier system demonstrates robust operation across multiple channels, requires no frequency dependent adjustments, and exhibits excellent spectral purity combined with high power-efficiency. Experimental UHF data shows 135 watts of output power with 55% efficiency using LDMOS devices, for uplink WCDMA (approximately 4dB PAPR).

X-band all-waveguide radial combiner for high power applications

The development of a 12-way X-band all-waveguide radial divider/combiner is presented. The radial combiner is comprised of three parts: a center feed, a radial line, and peripheral waveguide ports. The center feed is comprised of two sections: a rectangular waveguide section and a mode transducer section. The latter is a circular waveguide fed by four-way in-phase combiner to convert the rectangular waveguide TE10 mode to a TE10 circular waveguide mode for in-phase feeding of all peripheral ports. For design evaluation, the 12-way combiner was built and tested but also two back-to-back test fixtures, one for the mode transducer and the second for the radial combiner were fabricated and tested as well. The measured insertion loss and phase imbalance of the combiner over a 10% operating bandwidth are less than 0.35 dB and ±5°, respectively. The structure is suitable for high power and should handle few kilowatts.

Modeling and Implementation of a Novel Coaxial Line Multi-Octave High Power Combiners with Low Inter-Modulation Distortion

A novel wide band high power combiner has been developed. The design is optimized for minimal loss, high isolation, and minimal number of ferrite cores. An effective flux canceling circuitry has been implemented to significantly improve its inter-modulation distortion performance. Extensive analysis has been carried out using circuit and EM CAD tools to understand their performance. The combiner has been successfully fabricated, tested, and full performance evaluation will be given in this paper.

1 GHz instantaneous bandwidth digital pre-distortion for multi-concurrent channel wideband power amplifiers

This paper presents an extremely broadband digital predistortion linearization (DPD) technique that uses an adaptive Volterra-based model of the nonlinear distortion transfer function. The model is parameterized to accommodate higher order terms as necessary to accurately approximate the actual broadband nonlinear transfer function. The algorithm uses matrix and tensor factorizations to significantly simplify the complexity of the hardware implementation by identifying and removing mathematical redundancy and ignoring the components of the model that have negligible impact on the performance. This results in fewer multiplications and allows the addition of higher order terms to the model without the exponential growth in complexity. Polyphase filtering techniques are also used to run these operations in parallel which allows very broadband operation using signal processing operating at much lower data rate commensurate with the capabilities of off-the-shelf FPGAs. Measured results of the linearization technique are presented for multi-carrier concurrent waveforms into a 100 W GaN power amplifier showing an improvement in intermodulation products of more than 30 dB over an instantaneous bandwidth of 1 GHz. To our knowledge, this is far higher instantaneous bandwidth than other wideband DPD linearization techniques published in the literature.

Multi-octave high power recycling combiner using coaxial line to improve overall efficiency of outphasing power amplifier

A novel wide band high power recycling approach has been developed. The design is optimized for high efficiency, high isolation, and minimal number of ferrite cores. The combiner part includes an effective flux canceling circuitry to significantly improve its inter-modulation distortion performance, and the isolating resistors can be replaced by an efficient RF to DC conversion circuitry. The recycling combiner has been successfully fabricated, tested, and full performance evaluation have been carried out. This combiner allows portion of the wasted components of the signal to be reused by the power supply; thus the over all efficiency of the wide band outphasing power amplifier can be improved.