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Session: Telemedicine - and Fetal ECG
Session starts: Friday 25 January, 13:00
Presentation starts: 13:15
Room: Lamoraalzaal

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Yao Liu (Delft University of Technology)
Wouter Serdijn (Delft University of Technology)

Abstract:
Radio frequency (RF) powered sensor devices have gained more and more interest in wireless in-body area network (IBAN) applications. In contrast to a device powered by a battery with limited lifetime, an RF powered device has “unlimited” lifetime since it extracts power from propagating radio waves. The RF powered sensor device is often used in applications such as implantable medical devices where battery replacement is impossible without surgery. Besides a data link, the RF powered sensor device also has a wireless energy link enabled by an RF energy harvester. Nowadays, the energy link [1] and data link [2] are mainly optimized separately. Only a few papers discuss their system level integration [3]. In these systems, the two links are effectively decoupled by employing two different frequency bands, but demanding two bulky antennas and associated external matching components, thereby limiting the size reduction of the whole sensor device. Sharing the same antenna between an energy link and a data link is necessary to reduce the size of the RF powered sensor device dramatically, but presents some design challenges at the interface of the antenna, energy harvester and the first stage of the receiver, i.e., low noise amplifier (LNA). The antenna interface of an energy harvester is usually optimized to increase the available input voltage by a voltage-boosting network [1]. However, an LNA interface is usually designed for a 50Ω resistive input impedance, which is not optimized for the voltage-boosting network and will reduce the passive gain of the network considerably. Moreover, a 50Ω impedance requirement adds an important constraint on the LNA design, thereby restricting the performance and power reduction of the LNA. Taking into account the extremely limited power budget, this limitation is more severe in RF powered IBAN devices. This paper presents an optimally mismatched antenna interface and an LNA based on this interface for the combination of the energy harvester and the LNA. The interface offers large passive voltage boosting to improve the voltage gain and NF of the LNA in a low power environment, and increases the sensitivity of the energy harvester as well. The interface and LNA have been designed at circuit level and verified with simulations in AMS 0.18µm IC technology. A comparison with another LNA design based on a standard 50Ω power matched interface shows the proposed LNA has 12.3dB higher voltage gain and 1.8dB lower NF at a power consumption of only 50µW.