Guillaume Neveux

3-D Aspect in the Five-Port Technique for Zero-IF Receivers and a New Blind Calibration Method

The five- or six-port circuit uses one or two additional outputs in comparison with classical homodyne demodulators. This paper demonstrates that the five- or six-port technique can take advantage of this particularity. The geometrical approach allows us to represent the 3-D aspect of the five-port technique. This study in space demonstrates the natural rejection of the even-order signal at the output of the direct receiver five-port circuit. Another benefit of this geometrical approach is a new blind calibration method. Many calibration methods have been proposed for the five-port circuit used as a homodyne receiver. Most of these methods were hard to be embedded and updated. This paper presents a new blind calibration method without any constraint on the system or the signal and with less algorithm computation cost.

Time-domain envelope measurements for characterization and behavioral modeling of nonlinear devices with memory

This paper presents a calibrated four-channel measurement system for the characterization of nonlinear RF devices such as power amplifiers. The main goal of this study is to perform the characterization of the bandpass response of a nonlinear device-under-test (DUT) driven by modulated carriers. The proposed setup enables the generation of L- or S-band (1-4 GHz) carriers with a modulation bandwidth up to 100 MHz. The carrier harmonics generated by the nonlinear DUT are ignored and considered to be sufficiently filtered. This characterization setup enables calibrated time-domain measurements of the complex envelopes of both incoming and outgoing RF waves at the input and output of the DUT. This means that the fundamental and harmonic frequencies of the envelope are measured and processed. A large set of modulation formats can be generated by using a computer-controlled arbitrary waveform generator. Complex envelopes are measured by using a four-channel sampling scope. The proposed calibrated setup can be used to study or to validate linearization techniques of power amplifiers. This characterization tool is also well suited for the extraction and validation of behavioral bilateral models of nonlinear RF analog equipment exhibiting memory effects

High-Current–High-Speed Dynamic Bias Control System Applied to a 100-W Wideband Push–Pull Amplifier

This paper presents a dynamic bias control system applied to a high power wideband amplifier. The amplifier used is based on a push-pull topology with LDMOS transistors and works in the 50-500 MHz frequency bandwidth. It delivers a nominal 100 W output power with 60% power-added efficiency (PAE) when it is fed with continuous signals. When it is driven by a 16QAM modulated signal, 6 dB input power back-off is necessary to keep an error vector measurement below 5%. This usual back-off technique results in lower PAE (43% in our case). By implementing the proposed bias control system, both 55% PAE and 5% EVM have been reached for 75 W average output power. The drain bias control circuit handles high currents and high voltages (7 A-28 V). The proposed implementation makes use of a class S modulator driven by a SigmaDelta modulator. Up to 1 Mbit/s envelope bit rate can be efficiently and accurately processed by using here dedicated circuits running at 20 MHz clock frequency.

Time-domain envelope measurements and simulations of pulse-to-pulse stability in microwave power amplifiers

This paper presents a new measurement system based on heterodyne receiver to characterize the impact of irregular pulsed signals on the pulse-to-pulse (P2P) stability of microwave power amplifiers. The aim of this work is to provide a way of identifying the key design parameters and specifications of power amplifiers, such as thermal management, which have a critical impact on P2P stability. This paper is focused on the impact of thermal effects by applying a worst-case radar waveform that integrates a long silence (i.e. off-time) between each sequence of periodic bursts of pulses. Time-domain envelope measurements and simulations of P2P stability are compared for a 10W S-band GaN HEMT amplifier, with particular regard to thermal time constants of the nonlinear electro-thermal model.

Implementation of dual gate and drain dynamic voltage biasing to mitigate load modulation effects of supply modulators in envelope tracking power amplifiers

This paper presents a combination of dynamic gate and drain biasing techniques applied to a S-Band - 10 W GaN power amplifier. A GaN-based drain supply modulator (DSM) and an integrated gate biasing circuit have been built and connected to a GaN RF power amplifier (RFPA). The complete circuit architecture is then implemented in a test bench for the study of the envelope tracking power amplifier (ETPA). The work reported here focuses on the nonlinear coupling between the drain supply modulator and the RF power amplifier and proposes a solution to mitigate the load modulation effect of the supply modulator that is prejudicial for the overall efficiency and linearity performances. It consists in implementing an appropriate dynamic gate bias control of the RF power amplifier. The experimental validation of the study is demonstrated here for a QAM-16 (2 MSymb/s) modulated carrier at 2.5 GHz. At 38 dBm output power, dynamic load variations of the drain supply modulator (in the 30-500Ω range) versus instantaneous input power level variations have been drastically reduced and maintained to a 40Ω average value. The measurement of the signal constellation diagram at the ETPA output was found to be a well suited way to optimize the tuning of bias trajectories. A measured minimal error vector magnitude (EVM) of 2% and a power added efficiency (PAE) of 40% are obtained when optimal tuning is reached.

4-Channel, time-domain measurement system using track and hold amplifier for the characterization and linearization of high-power amplifiers

We propose in this paper a 4-channel time-domain test bench for the characterization and linearity enhancement of microwave power amplifiers (PAs). The proposed time-domain measurement system utilizes four track and hold amplifiers (THAs) for direct subsampling of radiofrequency (RF) signals. The use of wideband THAs to replace samplers or mixers enables reducing analog IF circuit complexity. It permits direct digitization of RF signals like CW, two-tone and pulsed modulated signals, bringing more flexibility in the receivers performance by enhancing the dynamic range and bandwidth. This test bench is capable of completely extracting the phase, amplitude, and transfer characteristics of non-linear devices excited with CW or modulated RF signals. In this work, two-tone transfer characteristics of a 50 W GaN HEMT Nitronex PA were extracted and processed for applying digital pre-distortion linearization to enhance linearity performance. Time-domain envelope and carrier waveforms (voltage and current) along with third-order inter-modulation distortion (IMD) products with and without digital pre-distortion scheme are also presented.

High Efficiency and Linear Power Amplification for OFDM Signal by Combining Dynamic Bias and Digital Baseband Predistortion

This paper presents a technique that enables both efficiency and linearity enhancements for power amplifiers (PA) used in communication systems. It is here applied to a 100 W wide-band LDMOS push-pull amplifier (50-500 MHz) driven by OFDM signals. When the amplifier is driven by a CW signal and operates at a constant 28 V drain bias voltage, it exhibits 100 W output power with 60% power added efficiency (PAE). When it is driven by an OFDM signal, a 10 dB output power back-off is necessary to have a -25 dBc ACPR and PAE decreases down to 10%. By properly implementing an envelope tracking bias system 40 W output power along with 38% PAE and -27 dBc ACPR have been reached. Applying baseband digital predistortion provides additive improvements at high PAE (for only 1 point PAE lost the ACPR increases Pof 5 dB).

Performance measurements of Modified LINC transmitter for wireless applications

The LINC (Linear amplification with Nonlinear Components) transmitter efficiency is not degraded only by the power combiner, but also by the SCS (Signal Component Separator) architecture. In this article, we propose a Predistorted Modified SCS (PM-SCS) architecture and we present the measurement platform dedicated to the LINC system study. Measurement results show an efficiency improvement from 39.60% for regular LINC to 63.80% for PM-LINC.