Theme 2: Analog Front-Ends

Introduction

The analog domain is one of the key challenges for reconfigurable front-ends, as reconfiguration in this domain traditionally encounters most problems. The (electronic) analog front-end is defined as all analog functionality which is located in-between the signal to-be-processed or -transmitted and the digital processing core. As such, it includes receivers, and transmitters, but also the antenna sub-system. The so-called mixed-signal parts, that contain both digital and analog aspects, are considered part of the theme Analog Front-Ends, as the design issues are usually dominated by analog aspects. Within the STARS research theme “Analog Front-Ends”, the following Research Task Clusters (RTCs) have been identified:

RTC2.1: Analog Architectures

Similar to the importance of the architecture to the system is the importance of the Front-End architecture to the Front-End. If this architecture is chosen improperly, the reconfigurability of the entire system is at stake. It is hence worthwhile to subject these aspects to a thorough analysis. Major issues that are relevant in this sub-theme concern changing the RF spectrum and band of operation, reconfigurability over different modulation schemes (including efficient operation at different power levels, with possibilities for back-off and saturated operation). In particular, small and reconfigurable systems allow for only a minimum number of components to guarantee a really portable device. These components must together satisfy the needs for a large number of functions, to ensure that the number of applications to be carried out does not explode. In these devices, the architecture is of crucial importance to the results obtained. The research can be divided in three parts:

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Functional reconfigurability.

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Analog compatibility.

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(IC) Implementation of reconfigurability.

RTC2.2: Reconfigurable Antennas

For electromagnetic sensors and communication systems, antennas are crucial. They are the interface between the system and the air and their specifications, such as frequency of operation, pattern and gain form the basis for the system performance. Antennas are usually designed and carefully optimized for a specific single task. Reconfigurable (array) antennas (if such will be developed) would offer an enormous additional flexibility in antenna beam pattern characteristics, the operating frequency band, as well as realization of new functions such as input protection and polarization diversity of the transmitted and received fields. Reconfigurability allows to adapt the antenna systems to different functional modes (such as, e.g., communication, initial detection and ranging, tracking, classification) that would normally require different antenna aperture sizes (and obviously also different electronic components), for instance by ‘switching’ from a radar pencil beam tracking antenna to a volume search multiple beam antenna using a larger aperture, and by transmitting linear polarized radar waves at e.g. 3 GHz at one moment in time, followed by a circular polarized communication waveform at lower frequencies at the next moment. The research can be divided in two parts:

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Reconfiguration at the antenna (sub-)system level.

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Reconfiguration at the antenna element level.

RTC2.3: Reconfigurable Receivers

In reconfigurable systems all elements should support the required functionality.

This also applies to the receiver part. Existing receiver technologies do not support this system requirement sufficiently. In all electromagnetic sensors and communication systems, there is a receiver part. The receiver will filter and amplify the wanted RF signals out of the whole spectrum of signals received by the antenna. The signal is processed (demodulated and/or decoded) to get access to the information contained in the signal. The unwanted signals, which can be a million times stronger than the wanted signal, have to be filtered out and the wanted signal has to be amplified and clearly processed without distortion. Up to now receiver equipment is designed in a dedicated way and is fully tuned to the application. Current and future innovations in the field of high-speed ADC’s, wideband linearization techniques and digital processing will bring new, more universal receiver building blocks paving the way for reconfigurable receiver blocks serving all kind of functions.

In the cluster reconfigurable receivers, the following research topics are identified:

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Analog receiver sub-systems

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Mixed-signal integration

This work will lay the foundation for innovative reconfigurable receivers, which will be able to address the need for requirements such as higher and switchable bandwidth, strong selectivity requirements, etc.

RTC2.4: Reconfigurable Transmitters

In reconfigurable systems all elements should support the required functionality. This also applies to the transmitter part. Existing transmitter technologies do not support this system requirement sufficiently. In all electromagnetic sensors and communication systems, there is a transmitter part. A transmitter typically consists of a number of electronic functions that translate the digital information from the baseband processor into an analog high-frequency signal with a certain power that fits the requirements. Since these requirements may vary over time, for instance because the desired output power or the characteristics of the signal may vary, one has two choices. Either the transmitter is designed such that it is independent of these changes, so designed for the worst combination of requirements and otherwise over-designed, or it is designed such that it can be adapted or reconfigured depending on the requirements. In practice the art lies in finding the most efficient balance between these two extremes. So, an optimal amount of reconfiguration ability is required in a transmitter to be able to transmit efficiently under varying circumstances.

In the cluster reconfigurable transmitters, the following research topics are identified:

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Reconfigurable power amplifiers (PA’s).

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Distributed transmitters.

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Reconfigurable transmitter integration.