Pierre Medrel

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.

Characterization and nonlinear modeling of MASMOS® transistor in order to design power amplifiers for LTE applications

This paper reports on the first experimental characterizations and modeling process of a MASMOS® transistor with a classical model, largely used for the modeling of other transistors. From DC IV and S-parameters measurements a large signal model (LSM) has been carried out. The great interest of this model is to allow a simulation time reduced by a factor of 100 compared to foundry model, like BSIM3 model, in classical one-tone HB simulation and to perform multi-tones simulation which is not possible with the foundry model due to prohibitive simulation times. The LSM has been validated through extensive multi-tones and load pull measurements. A good agreement between LSM simulation results and measurements fully validates the proposed modeling methodology. This LSM will serve to design a power amplifier (PA) for LTE applications.

A new design approach of high efficiency S-band 25 W mixerless power modulator based on high voltage 50V GaN-HEMT technology

In this paper, a novel concept for efficient and wideband, S band - 25W power modulator designed by taking the advantages of high voltage (50V) GaN HEMT technology is reported. The main objective of this study is to demonstrate the interest of merging both amplitude modulation and power amplification functions without the use of mixer in order to get high efficiency performances (>45%). To fully validate this principle, a two-stage power modulator circuit has been fabricated and tested. It delivers an output modulated (AM) power wave to a 50 Ω load and is based on a variable gain control principle with switched saturated states operating always at maximum Power Added Efficiency (PAE). PAE of around 45 % over 400 MHz RF bandwidth is achieved. With a fixed input power (CW) of 19 dBm, >10 dB output power range is obtained corresponding to 15V to 45V drain bias control, with 2.5 W and 25 W RF output powers respectively.

High speed and highly efficient S-band 20 W mixerless vector power modulator

This paper presents a performance evaluation of an original highly efficient and linear GaN-HEMT Vector Power Modulator (VPM) based on the design of a two-stage saturated variable gain (SVG) amplifier and a multi-level discrete supply modulator (SM). The proposed novel architecture for transforming a digital baseband data stream into an RF Vector modulated power waveform (RF Power DAC) is validated using a specific laboratory test bench. The main objective of this study is to merge signal modulation and DC to RF energy conversion functions into a single and compact GaN based mixer-less circuit. Using high-voltage 50 V GaN technology, a 20 W S-band vector power modulator having overall average PAE of around 40 % is reported. The concept demonstrator is experimentally validated up to 100 Msymbols/sec 16-QAM modulation scheme. Functional time alignment with phase and amplitude compensation procedure focusing on measured constellation at 40 Msymbols/sec enables to reach excellent EVM performances of around 3.2 %.

Cross-correlation method measurement of error vector magnitude and application to power amplifier non-linearity performances

Error Vector Magnitude (EVM) is used by communication systems designers as one way to express distortions in digital communications. These distortions may come from initial modulator amplitude and phase imbalances, from linear distortions or non-linear distortions in the transmission chain. It is a good indicator of power amplifiers non-linearity. We propose to use a closed form method based on cross-correlation between input and output signal of the power amplifier as a way to measure either EVM or Noise Power Ratio (NPR). We show the small differences that exist between both measurements. We show also that it can be applied to the measurement of signal EVM at the output of a signal generator or transmission chain.