A Low-Power 2.4GHz CMOS Receiver Front-End Using BAW Resonators

Abstract

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 ...

A low power high reliability dual-path noise-cancelling LNA for WSN applications

“…The power consumption is similar to other low power LNAs [5][6][7][8], but noise figure and IIP 3 of the DPNC LNA is much better than others. Moreover, noise figure and IIP 3 of this work are comparable to [9][10][11], yet power consumption is much lower.…”

“…Thus, no headroom problem exists in this design due to no cascode devices, such that this DPNC architecture can be applied to any advance process with low supply voltage. Table I summaries the DPNC LNA and other similar LNA designs, including two subthreshold LNAs [5][6], two WSN LNAs [7][8], a highly linear LNA [9], a differential LNA with BAW filter [10] and an active-balun LNA with transformer using [11]. The power consumption is similar to other low power LNAs [5][6][7][8], but noise figure and IIP 3 of the DPNC LNA is much better than others.…”

Analysis of a novel BAW-based power amplifier

“…In particular, Bulk Acoustic Wave (BAW) resonators, with their high quality factors, enable sharp bandpass filtering together with low insertion losses [1]. These properties have already been exploited in local oscillators [2], [3] and in low-noise amplifiers [4], with designs that carefully study the interactions between circuit and MEMS, i.e. by co-designs.…”

A robust wireless sensor node for in-tire-pressure monitoring

“…Since the attenuation near the series resonance frequency of the BAW is very high, low side injection of the local oscillator (LO) signal leads to a high additional suppression of the image frequency, allowing for a low intermediate frequency (IF) of 10.7MHz. In contrast to [3], the presented receiver utilizes the narrow bandwidth of a single BAW resonator instead of a filter consisting of several resonators. The LNA is followed by an RC-polyphase network to generate the I-and Q-phases for the image-reject mixer.…”