Christian Musolff

Linear and Efficient Doherty PA Revisited

Designing a simultaneously linear and efficient radio-frequency (RF) power amplifier (PA) is no simple task. The Microwave Theory and Techniques Technical Committee on The High Power Amplifier Components (MTT-5), aiming to promote this challenge at the student level, organized the ninth version of its annual high efficiency PA contest at the 2013 IEEE Microwave Theory and Techniques Society (MTT-S) International Microwave Symposium (IMS2013). Built upon our participation in 2012, the 3.5-GHz linear Doherty PA design was only slightly modified in response to a change in the gain requirement of this years competition rules.

Polyharmonic Distortion modeling of RF BAW components

For the first time the Polyharmonic Distortion (PHD) model has been used to characterize the nonlinearities of Bulk Acoustic Wave (BAW) components. For that purpose a measurement setup has been developed by extending a nonlinear vector network analyzer with required external components enabling X-parameter measurements at high power levels. By discussion of selected components of the BAW resonators PHD model and performing simulations in an RF design environment the importance of PHD model for improved BAW filter design has been demonstrated.

Measurement setup for X-Parameter characterization of bulk acoustic wave resonators

In this work a modern measurement method has been utilized in order to characterize nonlinear behavior of bulk acoustic wave (BAW) solidly mounted resonators (SMR). Unlike typical nonlinearity characterization methods, the method which was employed here not only records amplitudes, but also the phase of generated harmonics. Furthermore, the relations between the harmonics of different order are given. The modeling approach being used is the poly harmonic distortion (PHD) modeling approach, realized by the measurement of X-Parameters. For that purpose it was necessary to extend a nonlinear vector network analyzer (NVNA) by external components in order to enable high power measurements. Afterwards, several optimization steps were required to perform phase calibration. This difficulty arose due to the high power incident tones and steep resonator impedance curves on the one hand and the limited power provided by the phase calibration standard on the other hand.

Linear Doherty PA at 5 GHz

At the 2014 International Microwave Symposium (IMS2014) in Tampa, Florida, the power amplifier (PA) design competition celebrated its tenth anniversary. Back in 2004, it was the first student design competition that the IEEE Microwave Theory and Techniques Society (MTT-S) organized and, since then, the only one that has been held regularly every year. We started to participate in this competition in 2012, which also happened to be the year when a significant change in the competition rules was adopted. Starting in 2012, the power-added efficiency (PAE) in the figure of merit (FOM) that is used to evaluate the PAs, FOM = PAE/4?f, was measured at a power level at which the intermodulation distortion (IMD) that the PA produces from a two-tone excitation first exceeds 30 dBc. With that new rule, not only did linearity start to play a major role but also the test signal changed from continuous wave (CW) to a modulated signal with a peak to average ratio of 3 dB.

Hybrid recursive active filters for duplexing in RF transmitter front-ends

Duplex filters in modern base stations are designed as cavity filters, which are expensive and have big dimensions. Thanks to the emerging digital technology and fast digital converters, it is possible to transfer the efforts of designing analog duplex filters into digital numeric algorithms applied to feedback structures, operating on power amplifiers in transmitters. The design of a digital baseband feedback applied to the analog power RF amplifiers (hybrid filter) is presented and verified by measurements. The use of multiple digital feedback branches allows the closed loop system to show a periodic band-pass behavior at the output of the RF amplifier with a larger bandwidth up to 500 KHz. Moreover the band pass magnitude reaches up to 17 dB difference between maximum gain and attenuation.

X-Parameter Characterization of TC SAW Filters With Enhanced Dynamic Range

Increasing the integration of radio frequency frontend modules for mobile communication devices results in rising power densities within the components. Additionally, advanced communication techniques demand for more frequency bands to be supported. As a result, the probability of significant nonlinear emissions disturbing adjacent channels increases, and accurate modeling of the device’s response is required. The X-parameter-based modeling approach can be applied to this problem. In this paper, a measurement setup, which is based on a nonlinear vector network analyzer, is utilized in order to characterize a surface acoustic wave (SAW) filter. Due to the low power levels of the generated higher order harmonics and the demand for a power sweep, a high dynamic range (DR) is required. The application of frequency selective attenuators enables an increase of the effective DR by more than 40 dB. Based on this improved measurement setup, single-tone and two-tone X-parameter models of the SAW filter are created and evaluated for their ability to predict intermodulation distortion (IMD). Classic, scalar IMD measurements are used as a reference for the assessment of capabilities and limitations of both X-parameter approaches.

Physically Inspired Digital Predistortion for Dual Input Doherty Power Amplifiers and Automatic in-Situ Identification

A novel approach for the linearization of dual input Doherty power amplifier (DPA) is derived by taking inspiration from the operation of the device. A new point of view is evaluated and an automatic identification procedure is developed, reducing the complexity of the predistorter, improving linearity and efficiency at the same time and avoiding the usage of crest factor reduction (CFR). It is also emphasized the importance of a power dependent phase relationship between the inputs of the dual input DPA. A validation of the theory is performed by means of a MATLAB/ADS envelope co-simulation.

Hybrid recursive active filters for duplexing in RF transmitter front-ends: HYBRID RECURSIVE ACTIVE FILTERS

Duplex filters in modern base stations are designed as cavity filters, which are expensive and have big dimensions. Thanks to the emerging digital technology and fast digital converters, it is possible to transfer the efforts of designing analog duplex filters into digital numeric algorithms applied to feedback structures, operating on power amplifiers in transmitters. The design of a digital baseband feedback applied to the analog power RF amplifiers (hybrid filter) is presented and verified by measurements. The use of multiple digital feedback branches allows the closed loop system to show a periodic band-pass behavior at the output of the RF amplifier with a larger bandwidth up to 500 KHz. Moreover the band pass magnitude reaches up to 17 dB difference between maximum gain and attenuation.