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This paper presents a BAW-based transceiver targeting wireless networks for biomedical applications. The use of high-Q microelectromechanical-systems resonators brings interesting benefits to the fundamental building blocks of the frequency synthesis, receiver, and transmitter and allows achieving at the same time low-power consumption, improved phase noise, and high selectivity in the receiver and transmitter paths. In the baseband, the power consumption is minimized thanks to the use of a phase analog-to-digital converter (ADC) which directly quantizes the phase of the received signal instead of using two separate amplitude ADCs. A complete wireless node composed of the transceiver integrated circuit (IC) and a microprocessing IC, both integrated in a standard digital 0.18-μm complementary metal-oxide semiconductor technology are described and validated by measurement results. The RF carrier phase noise is -136.2 dBc/Hz at 1-MHz offset. The transmitter demonstrates 1-Mb/s Gaussian frequency-shift keying modulation at an output power of 5.4 dBm with an overall current of 35 mA, in compliance with Bluetooth and Bluetooth low energy output spectrum requirements. At the receiver, further investigations are needed to find the origins of an unexpected sensitivity of -75 dBm at 200 kb/s.

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Applications for low-power, low data rate and short range wireless communications such as sensor networks require radio circuits with high-integration level and very low power consumption. Hybrid circuits combining MEMS and ICs show promising results [1][2][3]. This work presents an RF front-end using BAW resonators providing combined selectivity and impedance matching to a classical heterodyne receiver operating in the 2.4GHz ISM band.Using high-Q filters with good selectivity and low insertion loss in front of a receiver relaxes the overall linearity requirements and thus, the power consumption. Moreover, heterodyne receivers need to filter out their image band in order to avoid signal degradation at the IF. Traditionally, off-chip SAW filters are used to this purpose. The feasibility of high-Q RF filters realized with BAW resonators has been demonstrated with comparable or even better results than SAW devices. An above-IC integration of a filter realized with thin film bulk acoustic wave resonators (FBAR) on top of a BiCMOS receiver front-end has been reported in [2], offering promising solutions for integration of a complete RF SoC.The same aluminum nitride (AlN) process described in [3] but applied to solidly mounted resonators (SMR) is used. The thickness of the Al/AlN/Pt structure layers determines the resonance frequency. An additional step allows lowering it by loading the top electrode with an inert layer. In this work, the SMR devices have been integrated on a separate substrate. Test resonators having a coupling factor k 2 eff of 5.6% and series resonance Q as high as 580 were measured.The block diagram of Fig. 17.7.1 describes the architecture of the heterodyne front-end. The BAW filter is placed in front of the LNA to eliminate out-of-band interferers and relax the linearity requirements. A Gilbert switching mixer follows the LNA and downconverts the RF signal to the 100MHz IF. For measurement purposes, the front-end is terminated by source-follower output buffers.RF filters need correct impedance terminations in order to perform as specified. Input impedance matching is therefore a critical part of the LNA design. Classical LNAs require several critical inductors [4] to provide a real input impedance (typically 50Ω). On-chip inductors require a large silicon area and only offer limited quality factor. The main novelty of this work is to codesign the LNA and the filter using BAW resonators. With this approach, the input impedance matching is inherently accounted for and the designer can take advantage of extra degrees of freedom in sizing the resonators. Moreover, the use of only high-Q passive components helps in achieving better gain and noise figure performance.The proposed selective LNA topology is shown in Fig. 17.7.2. Similar to lattice filters, the Y 1 and Y 2 resonators are appropriately detuned to achieve the widest bandwidth. These devices are mutually coupled through the network formed by the transistors and the cross-coupled capacitors. As shown in Fig. 17.7.3, the resulting gain of the ...

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