Pierre Dufilie

A new concept in SPUDT design: the RSPUDT (resonant SPUDT)

Presents new concepts in SPUDT design, leading to a new low loss transducer structure called Resonant SPUDT (RSPUDT). Resonant acoustic cavities are created inside the transducer while keeping a global unidirectionality required for low loss. As a result, some areas of the transducer are locally backward directional. SAW filters utilizing the RSPUDT exhibit improved filter characteristics (e.g. passband ripple, shape factor) and result in more compact filters. Two kinds of RSPUDT elementary cells were developed. The first one is the generalization of classical EWC cells to RSPUDT concept while the second improves the reflectivity per wavelength by 50% with the same critical dimensions. Measurements on both 200 MHz and 110 MHz lowloss filters on 38° Y rotated quartz are presented to illustrate the interest in these new SPUDT structures. The 200 MHz filter exhibits a 2 dB bandwidth of 0.30 MHz and a 40 dB bandwidth of 1.01 MHz while the 110 h MHz filter combines a 40 dB bandwidth 912.25 MHz and a 0.5 dB bandwidth of 0.9 MHz

Synthesis of SPUDT filters with simultaneous reflection and transduction optimization

The general design problem for the single-phase unidirectional transducer (SPUDT) is solved, resulting in a new nonlinear algorithm which computes quasi-optimum transduction and reflection functions for a given template. Load impedance effects are taken into account allowing the placing of constraints on the amplitude and phase of the transducer function as well as on the triple transit level. Several filters are presented showing how SPUDT can be used to design very linear and low triple transit levels or very compact filters for mobile radio applications.<<ETX>>

A low loss high performance filter structure

An improved structure for low loss, sharp cutoff, high-rejection filters has been developed. Center frequencies as high as 1500 MHz can be realized with standard optical processing techniques. Relative bandwidths of up to 0.67 K/sup 2/ are achievable. Data are presented for 900-MHz filters on 128 degrees YX-LiNbOI/sub 3/ and 950-MHz filters on 36 degrees YX-LiTaO/sub 3/ each having 3% and 1.6% relative bandwidths. 50-dB out-of-band rejection, and <6-dB insertion loss. By simple scaling of the designs to a 0.65- mu m minimum linewidth, a center frequency of 1.4 GHz can be achieved on LiNbO/sub 3/ and 1.5 GHz on LiTaO/sub 3/.<<ETX>>

Design and performance of 1 GHz range image impedance connected low loss SAW filters

An improved design technique of image impedance connected low-loss filters is presented. The technique makes it possible to control the fractional bandwidth in the range 0.7-3% on 36 degrees -rotated Y-cut LiTaO/sub 3/ (36-LTO). An accurate and simple method is used for characterization of propagation on 36-LTO above 1 GHz. The mass-loading coefficient was derived from experimental data and the attenuation coefficient was found to be 10/sup -2/ dB/ lambda /GHz, which is a much higher value than for LiNbO/sub 3/ but still compatible with low-loss filter manufacturing. Four high-performance low-loss SAW (surface acoustic wave) filters were manufactured on 36-LTO with various fractional bandwidths from 0.65 to 3%. Insertion losses as low as 6.5 dB at 800 MHz and 8.5 dB at 1400 MHz were obtained and out-of-band rejections as high as 50 dB were achieved, even with devices mounted in chip carriers.<<ETX>>

Low Cost SAW Convolver with High Spurious Suppression

Techniques have been developed for producing low cost monolithic SAW convolvers with excellent spurious suppression characteristics. Devices have been fabricated with 30 MHz bandwidth and processing times of 4 us and 15.8 vs which have exhibited 40 dB suppression of unwanted spurious responses. These convolvers have been incorporated in electrical circuits to produce correlators for PN coded waveforms with intended application in low cost spread spectrum comnunication systems. Performance data will be presented along with the potential range of performance for this class of SAW convolver.

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.

A simple design procedure for triple transit suppression in an apodized - Withdrawal weighted transducer filter structure

High performance SAW filters are characterized by their linear phase, low shape factor, small passband ripple, and high rejection. Classical filter design structures can achieve these performances, however the level of triple transit time spurious for these structures is typically twice the insertion loss + 6dB. The triple transit level can be reduced by adding low loss cell structures (such as Hanma-Hunsinger, EWC) to the transducers, however the filter analysis becomes inaccurate with the introduction of mechanical reflections (problems analyzing diffraction effects). The objective of this work is to develop a synthesis technique for high performance SAW filters with triple transit suppression.

Optimized STW devices with buried electrodes based on a mixed FEM/BEM numerical model

STW resonators on quartz are preferred over SAW due to their superior acceleration sensitivity, power handling, improved aging behavior, and 60% higher velocity. The achieved resonator Q at high frequencies using a metallic grating is lower than expected, mainly due to bulk mode scattering losses. The purpose of this study is to find the grating geometry which can reduce the propagation attenuation of the STW. STW propagation on Y+α°, X+90° propagation quartz cut (Euler angles 0,90-α,90) has been examined using a mixed FEM/BEM numerical model developed for buried electrodes for SAW propagation. It was found that by adjusting the a/p of the metal strips and by partially burying the electrodes one obtains SAW-like propagation properties with low propagation attenuation. For practical device design it is also necessary to be able to predict the turn-over temperature. To this end, simplified assumptions have been made to model the electrode and the piezoelectric substrate dilatations with temperature, and incorporated in the mixed FEM/BEM numerical model PerIDT presented at last years Ultrasonics Symposium. The optimized partially buried strip structure is used to obtain STW resonators with increased Q with predicted turnover temperature. Comparison with experiments will be shown. Partially buried electrode STW resonators with improved Q have been developed with the aid of the mixed FEM/BEM numerical model PerIDT.

Innovative SPUDT based structures for mobile radio applications

The IF filter is a key component in modern mobile radio receivers. Depending on the system design, the filter requirements goes from a very smooth prefiltering to a complete channel filtering. SPUDTs based structures are well suited for fractional bandwidths typically between 0.1% and 0.5%. Due to the reflectors presence inside the transducers, SPUDTs allows many different filters structures mostly using its reflective characteristic, its transduction characteristics or both. For base station applications, rejections in the 80 dB range are required. The first way to obtain as high a rejection is to use a cascade of 2 filters. We present a cascade of 2 filters at 201 MHz. The first is a classical SPUDT while the second is a new double track structure. A simple means to obtain as high a rejection in a single filter is to use a reflective array structure. We present a 71 MHz filter using this technique. The rejection is more than 75 dB for a 170 kHz 3 dB bandwidth and a 470 kHz 50 dB bandwidth. The simplest SPUDT structure consists of two SPUDTs on a single track. Due to its lack of symmetry, this structure is not well suited for balanced drive. A symmetric SPUDT structure was developed to fix this problem. Two balanced drive SPUDT filters are shown. The first is a 71 MHz GSM prefilter while the second is 85.4 MHz filter for CDMA. This filter exhibits a 0.85 MHz ±0.2 dB bandwidth, a 1.7 MHz 40 dB bandwidth for a 14 dB insertion loss

Analysis of SAW transducer having aperiodic multi-electrode cells using a coupled FEM/BIE numerical model

Low loss SAW filters sometimes require a structure with a complex geometry in order to improve the electro acoustical response (coupling coefficient, reflection coefficient, and static capacitance). Most of the coupling of mode models and P matrix models use parameters obtained from a single electrode periodic transducer analysis. In the case of complex electro acoustical cells (like HanmaHunsinger cells), it is sometimes necessary to obtain the COM parameters from the analysis of the entire electro acoustical cell, which means assuming that the filter contains an infinite array of identical electro acoustical cells the elementary cell of which is made of several electrodes. At the 2011 IEEE Ultrasonics Symposium, an original coupled Finite Element Model/Boundary Integral Equation (FEM/BIE) was presented in order to simulate an infinite array of single metallic electrodes [1]. In this paper, a generalization of this model to elementary cells more complex than one electrode will be presented. Like in the 2011 publication, the Finite Element Method is used for the finite part of geometry (the electrodes, part of the dielectric, and part of the piezoelectric substrate), while the semi infinite part of the geometry (piezoelectric part, and dielectric part) are taken into account using a Boundary Integral Equation. The theoretical and the numerical parts of the model will be presented, as well as Coupling of Modes or P matrix parameters determination for Hanma-Hunsinger low loss cells with various substrate materials and orientations. Using the results of the FEM/BIE analysis, a simulation of a filter containing modified Hanma-Hunsinger electro acoustical cells is made and is compared with measurements.