Stéphane Chamaly

An accurate design and modeling tool for the design of RF SAW filters

The main work for the SAW RF designer is to improve the filter performances and especially the insertion loss which has to be very low in the entire bandwidth, meaning that the control of the passband shape has to be very precise, Due to the proximity of SSBW when using LSAW, it is well known that standard P-matrix or COM models do not accurately predict the performance. The other difficulty is the 3D effects that could have a major impact on performances, especially when using ladder type filters. The third effect is the impact of electrical stray elements which can no longer be neglected. Our model can be separated in different parts. The acoustical model is used to analyze resonators or transducers. For this purpose, one possibility is to characterize test devices. We prefer to base our design directly on theoretical results. One way is to use the periodic FEM/BEM model to extract physical parameters describing the propagation of the wave and to use these parameters in a phenomenological model similar to COM or P matrix. This approach is well suited to periodic or almost periodic structures, as for example the resonators inside a ladder filter.

A new generalized two track RSPUDT structure for SAW filter size reduction: design and performance

High volume communication receivers continue to add features such as multimode operation, voice recognition, and Internet access with shrinking size. These evolutions reduce the available space for the RF and IF filtering functions. For systems such as CDMA and PCS the SAW IF filter is one of the largest components. This trend has lead to the development of DART filters, followed by the RSPUDT and recently by the two track RSPUDT. For the CDMA IF SAW filter the length of the SAW die has shrunk from 22 mm for a classical filter to 7/spl times/5 mm/sup 2/ for a two track RSPUDT design with simultaneous filter performance improvements. This paper will discuss the more common two track architectures with parallel and series connected transducer connections and basic principles of operation using the concept of symmetric and antisymmetric modes. We will then present a new generalized two track structure using the RSPUDT. This new structure works by designing each track to be in phase in the passband and out of phase in the rejection bands. This approach leads to steeper transitions and smaller die size. Implementation on the mask of the connections of the two different tracks will then be discussed. Experimental results will be included for both a CDMA (21/spl times/ 8 mm/sup 2/=>9/spl times/5 mm/sup 2/ package) and PCS (13/spl times/6.5 mm/sup 2/=>5/spl times/5 mm/sup 2/ package) filter.

Very low amplitude ripple SAW filter for infrastructure systems using 41°Y-X lithium niobate: Full FEM/BEM design approach

High data rate communication devices demand high relative bandwidth and therefore wide band filters are necessary. In infrastructure systems like base stations and microwave radio-links, such filtering function was carried out by ceramic filter technology. They were preferred for their low in-band ripple and VSWR necessary for low EVM and amplifier linearity. We have developed a design technique allowing SAW devices to advantageously replace ceramic filters in many systems .One important parameter that determines the performance of a piezoelectric device is the electromechanical coupling coefficient. RF filters designed on widely used 42?Y-X LiTaO3 are not meeting the stringent specification requested by infrastructure systems. To increase the width of the bandwidth and reduce the in-band ripple, a material with high electromechanical coupling coefficient is needed. This paper describes the search for the optimal working point using a full FEM/BEM approach and proposes a new design technique on 41?Y-X LiTaO3. This technique is applied to high reliability RF filters. On 41?Y-X LiTaO3, bandwidths larger than 8% at 3 dB attenuation are achieved leading to very low amplitude ripple. A GSM Rx filter for base station at 1747.5 MHz is demonstrated. Filter bandwidth is 140 MHz leading to ripple in the frequency band 1710 MHz to 1785 MHz being lower than 0.2 dB nominal and 1 dB over temperature and total 6 sigma manufacturing. Insertion loss is 2.5 dB while image rejection is better than 45 dB. Size is 3 ? 3 mm2 in a high reliability ceramic cavity package. The close correspondence between simulation and measurement demonstrates the ability of our methodology to design SAW devices rapidly and accurately on virtually any material. The filters designed by this technique on 41?Y-X LiTaO3 are demonstrating a wide band and very low in-band ripple perfectly matching the infrastructure systems requirement.

Ab-initio mesh-less modelling of three dimensional massloading effects in SAW and BAW devices

Brute force three dimensional simulation of Surface Acoustic Wave (SAW) and Bulk Acoustic Wave (BAW) devices with massive metallic electrodes of finite-aperture, massive busbars and massive protective closure structures is a prohibitively difficult task. This paper presents conceptually new ideas and implementation tools based on a mesh-less analysis of the problem, to tackle the daunting task of modelling 3D massloading effect with high accuracy. A sophisticated combination of spectral theory, weak Galerkin method and Greens function theory has been employed. A proof of concept has been provided.

Miniaturized SAW designs using high aspect ratio electrodes

The aim of this work is to miniaturize SAW filters using massive high aspect ratio metallic electrodes. These structures are capable of slowing down the surface wave and reduce the wave-length by 10 times. It is therefore expected that the size of devices using such high metal thickness is reduced by a significant amount. In this work, the relationship of the SAW propagation properties to substrate orientation and metallization thickness is studied theoretically using FEM-BIM approach and experimentally in order to achieve designs of a filter demonstrating a size miniaturization by a factor of 2 and a very low loss 20% bandwidth filters both at 40MHz range. This technique is very promising to miniaturize SAW filter at both low and radio frequency.