Pouya Aflaki

Accurate Power Efficiency Estimation of GHz Wireless Delta-Sigma Transmitters for Different Classes of Switching Mode Power Amplifiers

This paper proposes a new closed-form expression for computing the power efficiency of delta-sigma (DS) radio frequency (RF) transmitters. Due to the large bandwidth of the pulsewidth modulated (PWM) signal at the output of the DS modulator, the peak efficiency of the power amplifier (PA) when driven by a PWM signal is considerably different than its peak efficiency when the input signal is a continuous sine wave. A weight averaging of the efficiency over the frequency bandwidth of the PWM signal is considered for accurate estimation and prediction of the power efficiency of DS RF transmitters. It is shown that, for a low-pass DS transmitter, the overall average power efficiency of the DS transmitter can be accurately estimated by the product of the modulated peak efficiency of the PA and the coding efficiency of the modulator. For bandpass DS transmitters, an additional parameter that accounts for the duty cycle effect on the efficiency of switching-mode PAs has to be considered. To validate the new proposed expression, a DS transmitter for WiMAX, CDMA and EDGE standards is designed, prototyped and tested. The comparison of the simulated and measured efficiencies of the DS transmitter proves the validity and accuracy of the proposed expression.

Design and implementation of an inverse class-F power amplifier with 79 % efficiency by using a switch-based active device model

This paper presents the design and implementation of an inverse class-F power amplifier using a commercially available GaN 2 W power transistor. A switch-based model for this transistor was implemented in ADS and used to design this high efficiency amplifier. Simulation results with the developed model show drain efficiency of 79%, more than 19 dB of large-signal gain for an output power of greater than 5 W at 1 GHz. These values are confirmed by measurements, showing the usefulness of the switch-based active device model for this type of switching-mode power amplifiers.

Dedicated Large-Signal GaN HEMT Model for Switching-Mode Circuit Analysis and Design

A novel large-signal gallium nitride (GaN) high electron mobility transistor (HEMT) model that focuses on and improves analysis and design of switching-mode power amplifiers (PAs) is presented in this letter. The proposed model can be constructed using standard DC and AC characterization measurements and easily implemented in any computer-aided design (CAD) software to simulate and design switching-mode amplifiers. The model can predict the behavior of a switching-mode PA accurately at saturation and, due to the proposed approach, also well in the weak compression region. Using the developed model, an inverse class-F PA is designed and fabricated for validation purposes. The prototype developed using the proposed model achieved power-added efficiency (PAE) of 67% for an output power of 36.7 dBm at 2.35 GHz. Comparison between simulation and measured results of the manufactured PA proves the validity and accuracy of the proposed model.

Dual-band rat-race balun structure using transmission-lines and lumped component resonators

This paper presents a new dual-band rat-race balun structure for microwave circuit designs and applications. The proposed design methodology for the dual-band rat-race calls for conventionally designing a balun at the higher frequency, f1, by using distributed components. To achieve good performance also at the second lower frequency, f2, resonators connected to open-circuited stubs are added to the initial design. This leads to small physical dimensions of the entire circuit, especially if the two frequency bands are far apart, because the main body of the balun is dimensioned for the smaller wavelength. A dual-band rat-race balun has been designed and fabricated at 2.14 and 3.6 GHz. Measurement and 2.5D electromagnetic simulation results are found to be in good agreement.

Novel Compact Transmission-line Output Network Topology for Class-E Power Amplifiers

This paper presents a new low-complexity transmission-line load transformation network topology suitable to synthesis class-E impedance termination with a minimum of circuit elements. Only one additional stub, besides the quarter wavelength drain bias stub, is used to control simultaneously fundamental, second and third harmonic frequency impedance termination. In this way, loss in the load coupling network is minimised resulting in higher efficiency than by using other approaches. Design and performance of a highly efficient class-E power amplifier operating at 1 GHz based on the proposed transmission-line output network topology are presented. State-of-the-art power added efficiency of 80% at 1 GHz for an output power of 7 W is measured.

On the large-signal modeling of AlGaN/GaN HEMTs for RF switching-mode power amplifiers design

A large-signal model for GaN HEMT transistor suitable for designing switching-mode power amplifiers (SMPAs) is presented along with its parameters extraction procedure. This model is relatively easy to construct and implement in CAD software since it requires only DC and S-parameter measurements. The modeling procedure was applied to a 4-W packaged GaN-on-Si HEMT and the developed model is validated by comparing its small- and large-signal simulation to measured data. The model has been employed for designing a switching-mode inverse class-F power amplifier. Very good agreement between the amplifier simulation and measurement shows the validity of the model.

Compact Load-Coupling Network for Microwave Current Mode Class-D Power Amplifiers

This paper presents the design and implementation of a highly efficient current-mode class D (CMCD) power amplifier (PA) using a 2W GaN HEMT device. A switched-based model was developed in-house for the commercially available GaN power device and used extensively for the analysis and the design of the CMCD PA. The compact load coupling network, comprising a load transformation network, a higher harmonic impedance termination tank and a balun, used for the 1 GHz power amplifier measures only 37 mm times 76 mm while providing suitable means for tuning the performance of the amplifier. The fabricated CMCD PA achieves a drain efficiency of 65% for an output power of around 36 dBm with more than 7.4 dB of power gain at 1 GHz.

Large-signal modeling of AlGaN/GaN HEMTs based on DC IV and S-parameter measurements

In this paper, a large-signal model for GaN HEMT transistors for designing RF power amplifiers is presented. This model is relatively easy to construct and implement in CAD software since it requires only DC and S-parameter measurements. The modeling procedure is applied to a 4-W packaged GaN-on-Si HEMT and the developed model is validated by comparing its large-signal simulation to measured data under different classes of operation.

Diversity gain through synthesizing multiple polarizations

A novel technique for synthesizing an array of antenna elements with multiple polarization characteristics based on angular movements of a single antenna is developed. The diversity performance of the synthesized antenna array is then compared to that of a single static antenna through an extensive set of measurements based on capturing the CDMA 2000 signals (transmitted from nearby base stations) in an indoor multipath environment. The experimental evaluations which are shown to be in good agreement with theoretical predictions demonstrate significant improvement in signal detection. The measured diversity gain realized for some practical target detection requirements demonstrates the effectiveness of the proposed array synthesizing technique.

A new approach to design a frequency synthesizer using Direct Digital Synthesis technique

In this paper a new method to generate a high resolution Ka-band frequency synthesizer is presented. Using a DDS (direct digital synthesizer) as a central oscillator followed by a chain of precisely designed multipliers, a very high resolution and fast switching time Ka-band synthesizer with acceptable phase noise is achieved. The output power of Ka-band synthesizer is around -5 dBm all over 5 GHz bandwidth. To implement the design, a DDS having approximately 0.5 Hz resolution and proper phase noise around -145 dBc/Hz is used. The 330-400 MHz output frequency of the DDS is increased to the desired 24-29 GHz band.