Hugo Gomes

Receiver Front-End Architectures – Analysis and Evaluation

In todays world, the exponential growth from communications between people/companies in different places (at same time), the increasing requirement to measure and control all processes, the analysis in real time, the mandatory requirement to provide of information and entertainment data to electronic devices that must be increasingly smaller and more complex, requires a continuous and nonstop searching for new technologies with greater capacity, lower cost, reduced size and improved reliability. The communications systems based on radio-frequency (RF) transmission are one of the greatest examples of this challenging demand. These systems, present in almost all equipment used in daily life as mobile phones, notebooks, wireless sensors, among other, require an increasing versatility and ability to storage of data, huge transmission rates of information and size reduction. All this need for more sophisticated equipment, along with a greater number of services available in a single equipment (preferably portable), besides the drastic size reductions from the electronic components, requires a constant search for new architectures and new materials in order to maximize the features offered. One of the most important parts from a RF system device is this receiver architecture. In receivers, the entry block has a key role in performance and reliability of the system. Any unresolved issue caused by this block, generates enormous problems in the following blocks of the receiver’s architecture. For this reason, considering the constant increase of services available for the same frequency bands, associated with the growing number of users for each service, the entry receiver architecture must be capable to resolve issues such as blocking problems, peak-to-average power ratio (PAPR) problems, among others. In other hand, must be capable to offer good selectivity, sensitivity, lower energy consumption for a small price. This chapter is organized in the following way. Firstly, a general review about the most common receiving architectures is done, emphasizing its main advantages and drawbacks. Moreover, some enhancements to these architectures are also presented and its principal benefits are explained, such as Hartley and Weaver configurations. This section ends with 25

Diode Power Probe Measurements of Wireless Signals

In this paper, we conduct a thorough analysis of the nonlinear behavior of diode power probes and demonstrate how memory effects can alter power measurements of signals with wide modulation bandwidths and high values of peak-to-average power ratio. We show analytically, by simulations, and with measurements, that commonly used single-tone calibration procedures for diode power probes can provide erroneous values when measuring modulated signals used in many new wireless standards. We show that high values of peak-to-average-power ratio can degrade the calibration results due to the low-frequency response imposed by the power probes baseband circuit impedance. This effect is first theoretically demonstrated by use of a Volterra series, and then validated by simulations and measurements with a diode power probe circuit. This study provides engineers with guidelines for techniques for correction of diode power probe measurements.

The use of intermodulation distortion for the design of passive RFID

This paper proposes a radio frequency identification (RFID) system based on the distortion mechanism of a nonlinear device for implementing the complete transceiver architecture. The TAG is intended to be used in location scenarios, where the time of arrival approach will be implemented to measure the distance of the TAG to the reader.

The impact of long-term memory effects on diode power probes

This paper presents an analysis of long term-memory effects on power measurements with diode power probes. We show that a power probe calibrated with a single-tone sinusoidal excitation can provide erroneous values when used with modulated signals. This fact is ascribed to the low-frequency response imposed by the power probe baseband circuit. This hypothesis is first theoretically demonstrated by use of a Volterra series, and then validated by simulations and measurements using a diode power probe.

Interference cancellation: New configuration technique for cancellation of strong interferences from adjacent frequency bands.

This paper presents a study on existing techniques on cancellation of strong interference in frequency bands adjacent to the radio receivers. It also proposed a new configuration for cancellation of this strong interference, merging techniques known with a new model developed. The idea is to build an end cancellation/attenuation interference of affordable sub-system, that is universal and adjustable to the technology of radio frequency used by the receiver (compensating the intermodulation distortion created in LNA).

Dating and Raman spectroscopy of rock art paintings in Ebo, Angola

ABSTRACT The Ndalambiri rock shelter in the Ebo region of Angola is a key site for assessing human occupation there given its potential association between stratigraphic contexts and rock art panels. Focusing on the Iron Age and European contact periods, this study characterised the site’s rock paintings using Raman spectroscopy, while also obtaining AMS radiocarbon dates from paint residues and charcoal collected in stratigraphic context during a trial excavation below one of the painted panels. Raman spectroscopy results revealed the use of a carbon-based pigment (charcoal?), haematite and calcite to prepare black, red and white paints respectively. AMS dating of a black paint sample showed that it was produced between the seventeenth and the twentieth centuries, corresponding to the last known phase of rock art production in the area, as further indicated by its stratigraphic position and the depiction of firearms at the site. Earlier occupation of the site associated with metallurgical activity was dated to the mid-first millennium AD and may suggest that the oldest rock art at Ndalambiri corresponds to the arrival of metal-using populations in the region.