Renato Negra

A Novel Architecture of Delta-Sigma Modulator Enabling All-Digital Multiband Multistandard RF Transmitters Design

This paper proposes a new architecture of delta-sigma (DS) modulator suitable for RF digital transmitter design. This novel architecture considerably reduces the speed requirements of the digital signal processing block. The novelty lies in the implementation of a specific fully digital up-conversion in combination with a low-pass DS modulator to produce high-frequency digital-like signals, which can be used to drive highly efficient switching-mode power amplifiers. The proposed architecture is suitable for reconfigurable all-digital, multistandard and multiband wireless transmitters. The novel transmitter architecture has been validated using simulation and implemented on a field-programmable gate array development board for two different signals, code division multiple access and orthogonal frequency division multiplex.

Concurrent Dual-Band Class-F Load Coupling Network for Applications at 1.7 and 2.14 GHz

Highly efficient multiband power amplifiers (PAs) are key elements for the development of future multistandard multiband communication terminals and cognitive radios. This paper reports the design of a multiharmonic dual-band Class-F power amplifier for applications at wireless communication frequencies based on a switchless multiharmonic multiband load coupling network topology. The proposed output network topology is able to precisely synthesize Class-F impedance conditions with up to three harmonics at two distinct nonharmonic frequencies without the need of switches or electronically tunable elements. The proposed topology was used to design a Class-F PA in hybrid technology for the frequency bands at 1.7 and 2.14 GHz. Optimum impedances for maximum efficiency of the used GaAs MESFET for the two bands were determined by multiharmonic load-pull measurements and synthesized by the proposed switchless dual-band Class-F network. With a dual-band input matching network, the fabricated PA achieves 44.0% and 61.3% drain efficiency for an output power of more than 32.8 dbm and 34.4 dbm at 1.7 and 2.14 GHz, respectively. To the best knowledge of the authors, this is the first concurrent multiharmonic dual-band PA reported in open literature.

Study and Design Optimization of Multiharmonic Transmission-Line Load Networks for Class-E and Class-F

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.

K

This paper presents a high efficiency class-E power amplifier (PA) suitable for wireless transmitters operating at 2 GHz. Compact impedance transformation network is designed, using micro-strip transmission lines, so that it simultaneously achieves fundamental load transformation and harmonic impedance control using only two open-circuit stubs (2fo, 3fo). The dimensions of the networks elements were determined in order to concurrently attain a high harmonic suppression, minimum loss and high power added efficiency. The measurement results of the PA prototype, which is designed using a 10 W gallium nitride (GaN) HEMT transistor, showed state-of-the-art drain and power added efficiency (PAE). The achieved PAE, power gain and output power, when the drain is biased at 50 V, were equal to 74%, 12.6 dB and 11.4 W respectively. In addition, a second and third harmonic suppression in excess of -40 dBc and -75 dBc, respectively, is achieved without extra circuit tuning or additional filtering.

-Band MMIC Power Amplifiers

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.

High-efficiency GaN class-E power amplifier with compact harmonic-suppression network

This paper proposes a new approach to reduce the sampling rate in delta-sigma (DeltaSigma) transmitters and, hence, to lower considerably the speed requirements of all critical digital circuit blocks. The proposed method relies on oversampling the signal by inserting zeros after the low-pass DeltaSigma-modulation and to use one of the harmonic outputs of the sampler instead of its fundamental. The optimum sampling frequency in terms of signal integrity and out-of-band performance is determined for this configuration through simulations. Using a sampling frequency of only 288 MHz, EVM and ACPR for a WiMAX signal with a bandwidth of 2 MHz around 2.45 GHz are 7 % and -55 dBc, respectively

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 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.

Digitally Optimized Delta-Sigma Modulator for WiMAX Transmitter Design

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.

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

This paper proposes a novel architecture to realise a highly-efficient and linear bandpass (BP) delta-sigma (DeltaSigma) transmitter. The novel transmitter topology takes advantage of the fact that nowadays digital signals are in-phase (/) and quadrature (Q) modulated. Instead of using the combined signal, the proposed architecture processes the RF I and Q signals in two separate branches and combines them only prior transmission over the antenna. Doing so has several benefits in regard to practical implementation since the signal bandwidths in the proposed system are narrower than in the conventional architecture. Simulations of such a transmitter using GaAs FETs highlights the potential of the novel RF I/Q BPDeltaSigma architecture as it features high-linearity as well as better signal-to-noise ratio than the conventional topology.