An improved wide-band model of CRF Filters using two different approaches

In this paper, we present an acoustic band pass filter “CRF” (Coupled Resonator Filter); a combination of three BAW resonators for WCDMA applications. These filters are used in mobile telephony and provide high quality factors and miniaturization. We first, introduce the structure of CRF and its functioning, and then we describe their electro-acoustical model in wide-band. Filter characterizations show coupling effects in the filter out band response, thus to explain this behavior two different hypotheses are made. The first one discusses the transverse effect in the top piezoelectric layer of the CRF and the second one considers the RF pads effect. Simulations are done with ADS (Advanced Design System) from Agilent. Finally, simulations are compared to measurements for both propositions to find the principal cause of the coupling effect.