A SiGe:C BiCMOS WCDMA zero-IF RF front-end using an above-IC BAW filter

Abstract

The design and integration of an RF front-end for WCDMA applications using an above-IC BAW band-pass filter is reported in this paper. SoC integration will become easier to achieve using the proposed above-IC approach. The use of a BAW filter between the LNA and the mixer permits also to relax linearity constraints and thus, power consumption for the down-conversion mixers. This first experimental chip is designed and fabricated in a 0.25µm SiGe:C BiCMOS process enhanced with above-IC capabilities. The BAW filter is fabricated by CEA-LETI and CSEM. The above-IC BAW process is plugged over the BiCMOS final passivation layer, and the electrical contact with the rest of the circuit is realized at the last IC metal layer. This circuit uses film bulk acoustic resonators (FBAR). The piezoelectric efficiency of the AlN layer is confirmed by RF characterization of stand-alone resonators, presenting a coupling coefficient k t 2 of 6.3% and a Qfactor around 900 [1].One of the major issues of FDD x-CDMA standards is the fullduplex mode operation of the receive and transmit sections. This leads to very stringent requirements on the receiver in order to meet the desired sensitivity (-107dBm) while coping with the strong out-of-band -23dBm TX leakage [2]. In terms of system specifications, the noise factor, the conversion gain and also the out-of-band 2 nd -and 3 rd -order linearity are the major parameters to be taken into account for a thriving WCDMA receiver.Up-to-date SiGe:C BiCMOS processes offer active and passive devices to meet all linearity and noise specifications of 3G at low power consumption. Within this technology frame, the zero-IF architecture is a system implementation that permits to fulfill the WCDMA standard with a very high level of integration. The proposed circuit is a simplified implementation of a zero-IF frontend to evaluate all the major features ( Fig. 21.3.1). From the system point of view, the input LNA has to be a single-ended circuit, connected directly to the single RX path of a duplexer. It is followed by an on-chip balun, with medium insertion losses, allowing a high level of integration. In order to cope with the large unwanted Tx signal and to relax the down-conversion mixer 2 nd order non-linearity constraints, system specifications impose the use of a narrow-band RF band-pass filter at 2.14GHz. The filter mask is depicted in Fig. 21.3.2. Simulations of such RF band-pass filters implemented with BAW resonators predict better out-ofband rejection than the existent data on SAW filters. This leads to a mixer specification with reduced linearity performance with respect to a classical zero-IF RX path, thus, lowering its power consumption. Moreover, the SoC approach avoids parasitics from ESD diodes and magnetic coupling from wire-bonding, thus, lowering the total noise factor. In addition, this also allows a large choice of matching impedances.The single-ended LNA is based on a cascode topology with degeneration emitter inductor in order to get the best trade-off between 50Ω matching and noise...

Single‐Chip Scanning Probe Microscopes

“…Gold has also been used for RFswitch applications and is being studied as a structural material for applications requiring low loss at high frequencies [78]. Piezoelectric materials have been integrated on top of the CMOS stack for RF applications such as surface acoustic wave (SAW) mechanical filters, thin-film bulk acoustic resonators (FBARs) or bulk acoustic wave (BAW) resonators [95], [96]. Zinc-oxide piezoelectric films have been shown to be compatible with CMOS processing, as demonstrated in an early multisensor chip [97].…”

Techniques for Tuning BAW-SMR Resonators for the 4th Generation of Mobile Communications

“…The resonance condition is established when the acoustical path (in thickness direction) corresponds to odd integer multiples of the half acoustic wavelength. The bulk acoustic wave resonator is basically constituted by a piezoelectric layer sandwiched between two electrodes ( Fig.1) [2,3].…”

“…Two configurations are proposed: the membrane suspended structure (FBAR -Film Bulk Acoustic wave Resonator) [3], where the resonator is suspended by an air-bridge (Fig.1a); and the solidlymounted structure (SMR -Solidly Mounted Resonator), where the resonator is mounted over a stack of alternating materials (Fig.1b). This stack is built on a Bragg reflector basis and it has an acoustic mirror behavior [2][3]. Both, air and acoustic mirror, present an optimum discontinuity for reflecting the acoustic waves at the interface with the bottom electrode, confining waves into the main resonant structure.…”

Ladder-lattice bulk acoustic wave filters: Concepts, design, and implementation

“…Two configurations are proposed: the membrane suspended structure [2], where the resonator is suspended by an air-bridge (Fig. 2a); and the solidlymounted structure, where the resonator is mounted over a stack of alternating materials (Fig.…”

“…Indeed, recent results show low losses, temperature stability, large power handling capability, and reduced dimensions [1]. Moreover, having a manufacturing process compatible with silicon technologies, BAW filters can be directly integrated above active circuits, making possible the design of fully integrated RF front-ends [2]. Nonetheless, classical BAW filter topologies (ladder and lattice) cannot combine high selectivity and high isolation.…”