Daniel Rönnow

A comparative analysis of behavioral models for RF power amplifiers

A comparative study of nonlinear behavioral models with memory for radio-frequency power amplifier (PAs) is presented. The models are static polynomial, parallel Hammerstein (PH), Volterra, and radial basis-function neural network (RBFNN). Two PAs were investigated: one was designed for the third-generation (3G) mobile telecommunication systems and one was designed for the second-generation (2G). The RBFNN reduced the total model error slightly more than the PH, but the error out of band was significantly lower for the PH. The Volterra was found to give a lower model error than did a PH of the same nonlinear order and memory depth. The PH could give a lower model error than the best Volterra, since the former could be identified with a higher nonlinear order and memory depth. The qualitative conclusions are the same for the 2G and 3G PAs, but the model errors are smaller for the latter. For the 3G PA, a static polynomial gave a low model error as low as the best PH and lower than the RBFNN for the hardest cross validation. The models with memory, PH, and RBFNN, showed better cross-validation performance, in terms of lower model errors, than a static polynomial for the hardest cross validation of the 2G PA

Recent advances in electrochromics for smart windows applications

Electrochromic smart windows are able to vary their throughput of radiant energy by low-voltage electrical pulses. This function is caused by reversible shuttling of electrons and charge balancing ions between an electrochromic thin film and a transparent counter electrode. The ion transport takes place via a solid electrolyte. Charge transport is evoked by a voltage applied between transparent electrical conductors surrounding the electrochromic film/electrolyte/counter electrode stack. This review summarizes recent progress concerning: (i) calculated optical properties of crystalline WO3, (ii) electrochromic properties of heavily disordered W oxide and oxyfluoride films produced by reactive magnetron bias sputtering, (iii) novel transparent reactively sputter-deposited Zr–Ce oxide counter electrodes and (iv) a new proton-conducting antimonic-acid-based polymer electrolyte. Special in depth presentations are given on elastic light scattering from W-oxide-based films and of electronic band structure effects affecting opto–chronopotentiometry data in Zr–Ce oxide. The review also contains some new device data for an electrochromic smart window capable of very high optical transmittance.

Wide-band dynamic modeling of power amplifiers using radial-basis function neural networks

A radial-basis function neural network (RBFNN) has been used for modeling the dynamic nonlinear behavior of an RF power amplifier for third generation. In the model, the signals envelope is used. The model requires less training than a model using IQ data. Sampled input and output signals were used for identification and validation. Noise-like signals with bandwidths of 4 and 20 MHz were used. The RBFNN is compared to a parallel Hammerstein (PH) model. The two model types have similar performance when no memory is used. For the 4-MHz signal, the RBFNN has better in-band performance, whereas the PH is better out-of-band, when memory is used. For the 20-MHz signal, the models have similar performance in- and out-of-band. Used as a digital-predistortion algorithm, the best RBFNN with memory suppressed the lower (upper) adjacent channel power 7 dB (4 dB) compared to a memoryless nonlinear predistorter and 11 dB (13 dB) compared to the case of no predistortion for the same output power for a 4-MHz-wide signal.

Towards the smart window : progress in electrochromics

Electrochromic devices have the ability to produce reversible and persistent changes of their optical properties. The phenomenon is associated with joint ion and electron transport into/out of an electrochromic thin film, in most cases being a transition metal oxide. This paper outlines the various applications of such devices in smart windows suitable for energy-conscious architecture, in variable-reflectance mirrors, and in display devices. Critical materials issues and design concepts are discussed. The paper also covers two specific research topics: computed electronic structure of crystalline WO3 incorporating ionic species, showing how reflectance modulation emerges from a first-principles calculation; and Li+ dynamics in heavily disordered Ti oxide, illustrating how diffusion constants derived from impedance spectroscopy can be reconciled with the Anderson—Stuart model.

Single-beam integrating sphere spectrophotometer for reflectance and transmittance measurements versus angle of incidence in the solar wavelength range on diffuse and specular samples

A multipurpose instrument for the measurement of reflectance and transmittance versus angle of incidence for both specular and diffuse samples in the solar wavelength range has been constructed and evaluated. The instrument operates in the single-beam mode and uses a common light source for three experimental setups. Two integrating spheres, 20 cm in diameter, are used for diffuse transmittance and reflectance measurements. The transmittance sphere can be turned around an axis through the sample to vary the angle of incidence. The reflectance sphere uses a center mounted sample and a special feature is the position of the detector, which is mounted on the sample holder at the center of the sphere. This way the detector always sees the same part of the sphere wall and no light can reach the detector directly from the sample. The third setup is an absolute instrument for specular samples. It uses a small averaging sphere as a detector. The detector is mounted on an arm which rotates around the center of the sample, and it can thus pick up both the reflected and transmitted beams including all multiply reflected components. The averaging sphere detector is insensitive to small side shifts of the detected beams and no multiple reflections between detector and optical system occur. In this report a number of calibration procedures are presented for the three experimental setups and models for the calculation of correct transmittance and reflectance values from measured data are presented. It is shown that for integrating sphere measurements, the geometry of the sphere and the diffusivity of the sample as well as the sphere wall reflectance and port losses are important factors that influence the result. For the center mounted configuration these factors are particularly important and special emphasis is given to the evaluation of the reflectance sphere model. All three instrument setups are calibrated using certified reference materials and nonscattering mirrors and substrates. The results are also compared to the results of a double-beam Beckman integrating sphere for near normal angles of incidence and Fresnel calculations. The results in this article show that good agreement is obtained between results from the different instruments if, and only if, proper evaluation procedures are applied to the measured signals.

A Technique to Extend the Bandwidth of an RF Power Amplifier Test Bed

In this paper, a method for increasing the bandwidth of a test bed for dynamic characterization of power amplifiers (PAs) is described. The technique is readily implemented using commercially available instruments, which makes it suitable for, e.g., production testing. The bandwidth extension technique is combined with coherent averaging of the measurements in order to simultaneously increase the bandwidth and dynamic range of the test bed. The errors in the obtained wideband signal are also estimated. The method is evaluated experimentally on a base station PA for the third-generation wideband code division multiple access system and on a Doherty amplifier. A tenfold increase in bandwidth to a total of 144 MHz and a more than 10-dB increase in dynamic range to 78 dB were obtained in practice. In addition, the obtained wideband signal is used for behavioral amplifier modeling.

Measuring Volterra kernels of analog to digital converters using a stepped three-tone scan

The Volterra theory can be used to mathematically model nonlinear dynamic components such as analog-to-digital converters (ADCs). This paper describes how frequency-domain Volterra kernels of an ADC are determined from measurements. The elements of the Volterra theory are given, and practical issues are considered, such as methods for signal conditioning and finding the appropriate test signals scenario and suitable sampling frequency. The results show that, for the used pipeline ADC, the frequency dependence is significantly stronger for second-order difference products than for sum products and the linear frequency dependence was not as pronounced as that of the second-order Volterra kernel. It is suggested that the Volterra kernels have the symmetry properties of a specific box model, namely, the parallel Hammerstein system.

Design review of an instrument for spectroscopic total integrated light scattering measurements in the visible wavelength region

A spectroscopic total integrated scattering instrument, which uses a focusing sphere and a broadband light source, has been constructed. It records total reflectance and transmittance spectroscopically, in the wavelength region 400–1000 nm. Diffuse reflectance and transmittance values below 10−4 can be registered. These measurements require low scattering optical components and low noise electronics. Design details are given about the detection system, particularly the low noise preamplifier. The purpose of the instrument is to measure diffuse reflectance and transmittance spectra of interference coatings. Such spectra can give information about the amplitude of the roughness of the interfaces and reveal if the interfaces are topographically correlated or uncorrelated. Examples of spectra in both reflectance and transmittance mode are given.

A Kautz-Volterra Behavioral Model for RF Power Amplifiers

A new type of behavioral power amplifier (PA) model, a discrete-time Kautz-Volterra (KV) model, is presented. In the model a priori knowledge of the system properties in terms of different poles for different nonlinear orders is used, which is needed for modeling nonlinear and linear memory effects in PAs. An accurate model can thus be achieved with a small number of parameters. Simulated results of parallel Hammerstein and Wiener structures and from modeling the behavior of a PA are presented

Characterization of Memory Effects in Power Amplifiers Using Digital Two-Tone Measurements

In this paper, a novel method to measure the amplitude and phase of two-tone third-order intermodulation products generated in a high-power amplifier is presented. The method is based on the sampled input and output signals of the amplifier. The presented measurement setup and the associated algorithms for the calculation of the amplitudes and phases are considerably faster and simpler than the current methods. By making use of the sampled input and output signals of the amplifier and the signal processing techniques, the need for a nonlinear reference, a tunable attenuator, and a phase shifter in the existing measurement setups is eliminated, which makes it simple and easy to use. Hence, this is a substantial simplification of the measurement setup compared to what has been reported earlier. The proposed measurement setup is also suitable for fast automated measurements, which is of interest for many applications that are both laboratory and production oriented. In addition, a method to increase the bandwidth of the measured signal is used to overcome the bandwidth limitation set by the Nyquist criteria for sampled systems. Measurements are done on two base-station high-power amplifiers and are found to be in agreement with theory and reference measurements.