Francisco Javier Ortega-González

Load–Pull Wideband Class-E Amplifier

A new technique to design wideband Class-E power amplifiers (PAs) based on the synthesis of specific load admittances at fundamental and harmonics is shown. This technique symplifies the design of wideband Class-E amplifiers by making it independent on any specific load network, implementation, and intrinsic transistor output capacitance COUT. Simulations and actual measurements on a 15-W VHF wideband Class-E PA prototype designed using this method show 35% fractional bandwidth with 80% drain efficiency

Low cost Ka band transmitter modules for LMDS equipment mass production

Two different Ka band medium power transmitters for LMDS (Local Multipoint Distribution System) applications have been designed proving successful performance while introducing low cost components and simple mounting techniques for industrial purposes. Commercially available BGA and LM packaged components are attached with epoxy dispensing procedures to a 0.254 mm height cost effective plastic substrate. The output power stages are die form MMIC amplifiers which are first mounted on separate carriers. A novel epoxy-on-bonding die attaching technique is used in order to prevent undesired bonding to plastic quality and performance. New active biasing networks are employed so that no later adjustment is necessary to control the overall transmitter behaviour. Active biasing also allows higher PAE than usual resistor dividers for gate biasing while preserving linearity and P1 dB output power. The transmitter modules work at 31.15 GHz and 25.7 GHz respectively. The measured P1 dB was 26.5 dBm and PAE at P1 dB was 16%.

The Design of a Multilevel Envelope Tracking Amplifier Based on a Multiphase Buck Converter

Envelope tracking (ET) and envelope elimination and restoration (EER) are techniques that have gained in importance in the last decade in order to obtain highly efficient radio frequency power amplifier that transmits signals with high peak-to-average power ratio. In this study, a multilevel multiphase buck converter is presented as a solution for the envelope amplifier used in ET and EER. The presented multiphase buck converter generates multilevel voltage using “node” duty cycles and nonlinear control. In this way, the multilevel is implemented using only one simple power stage. However, the complexity of the multilevel converter implementation has been shifted from complicated power topologies to complicated digital control. Detailed discussion regarding the influence of the design parameters (switching frequency, output filter, and time resolution of the digital control) on the performance of the proposed envelope amplifier is presented. The design of the output filter is conducted fulfilling the constraints of the envelope slew rate and minimum driver pulse that can be reproduced. In the cases when these two constraints cannot be fulfilled, they may be relieved by the modified control that is presented and experimentally validated. Finally, in order to validate the concept, a prototype has been designed and integrated with a nonlinear class F amplifier. Efficiency measurements showed that by employing EER, it is possible to save up to 15% of power losses, comparing to the case when it is supplied by a constant voltage. Additionally, adjacent channel power ratio has been measured. The obtained results showed the value higher than 30 dB for signals up to 5 MHz of bandwidth, without using a predistortion technique.

An adaptive phase alignment algorithm for cartesian feedback loops [Applications corner]

An adaptive algorithm to correct phase misalignments in Cartesian feedback linearization loops for power amplifiers has been presented. It yields an error smaller than 0.035 rad between forward and feedback loop signals once convergence is reached. Because this algorithm enables a feedback system to process forward and feedback samples belonging to almost the same algorithm iteration, it is suitable to improve the performance not only of power amplifiers but also any other digital feedback system for communications systems and circuits such as all digital phase locked loops. Synchronizing forward and feedback paths of Cartesian feedback loops takes a small period of time after the system starts up. The phase alignment algorithm needs to converge before the feedback Cartesian loop can start its ideal behavior. However, once the steady state is reached, both paths can be considered synchronized, and the Cartesian feedback loop will only depend on the loop parameters (open-loop gain, loop bandwidth, etc.). It means that the linearization process will also depend only on these parameters since the misalignment effect disappears. Therefore, this algorithm relieves the power amplifier linearizer circuit design of any task required for solving phase misalignment effects inherent to Cartesian feedback systems. Furthermore, when a feedback Cartesian loop has to be designed, the designer can consider that forward and feedback paths are synchronized, since the phase alignment algorithm will do this task. This will reduce the simulation complexity. Then, all efforts are applied to determining the suitable loop parameters that will make the linearization process more efficient.

Low Cost Millimeter Wave Transmitter Based on SMT Techniques

The aim of this paper is to present a millimeter wave transmitter (Ka band) designed to be manufactured using low cost, surface mountable millimeter wave components onto soft PTFE based substrates. The system employs recently developed millimeter wave monolithic integrated circuits (MMICs) packaged in surface mountable Ball Grid Arrays (BGA) for the low power subsystems and surface mountable Land Grid Arrays (LM packages) for the driving power stages, mainly the power amplifiers. Tailored active bias servos are also employed to improve efficiency and reliability and to reduce adjustments and manufacturing costs also. Output power compression point of P1dB = 26dBm and Power Added Efficiency PAE=18 % have been measured at 31 GHz.

Class-E amplifiers and applications at MF, HF, and VHF

Class E amplifiers have been used in a very broad frequency range. This paper expose a general review of the basic application of class E amplifiers for lower frequencies (MF, HF, VHF), including typical components, applications, and results.

Hybrid Envelope Elimination and Restoration Technique for Enhancing the Linearity of Switchmode Envelope Amplifiers

This letter shows a new technique for enhancing the linearity of switchmode envelope amplifiers used in Envelope Elimination and Restoration (EER) amplifiers. The proposed solution increases the linearity of EER amplifiers using switchmode converters as envelope amplifiers avoiding additional hardware for compensating their inherent distortion at low output voltage levels. This technique combines hybrid EER (H-EER) and drive modulation techniques applied to a radio frequency (RF) amplifier operating in mixed mode. It is illustrated by means of an L-Band suboptimum Class-E power amplifier using GaN HEMTs linearized by a multi-phase switchmode envelope amplifier.

Antennas' correlation influence on the GMD-assisted MIMO channels performance

The use of multiple antennas in MIMO (multiple-input multiple-output) systems at both the transmit and receive sides produces the effect known as antennas correlation which impact the overall channel performance, throughput and bit-error rate (BER). The geometric mean decomposition (GMD) is a signal processing technique which can be used to process transmit and receive signals in MIMO channels. The GMD pre- and post-procesing in conjunction with dirty-paper precoding shows some advantages over the popular singular value decomposition (SVD) technique which provides GMD-assisted MIMO systems a superior performance particularly when the channel is affected by antennas correlation. This paper analyses the impact of antennas correlation on the performance of GMD-assisted wireless MIMO channels highlighting the advantages over SVD-assisted ones.

Efficient adaptive compensation of I/Q imbalances using spectral coherence with monobit kernel

Abstract This paper shows a new algorithm to improve the performance of IQ demodulators and frequency converters exhibiting gain and phase imbalances between their branches. This algorithm does not require any input calibration signal and is independent of the input signal level. It exploits the spectral coherence (SC) concept using a monobit kernel to achieve optimization targets with minimum time to convergence, low computational load, and a wide range of input levels. Its effectiveness is shown through a low-IF receiver that improves its image rejection ratio (IRR) from 30 dB to 60 dB.