Werner Ruile

SAW devices for consumer communication applications

An overview of surface acoustic wave (SAW) filter techniques available for different applications is given. Techniques for TV IF applications are outlined, and typical structures are presented. This is followed by a discussion of applications for SAW resonators. Low-loss devices for mobile communication systems and pager applications are examined. Tapped delay lines (matched filters) and convolvers for code-division multiaccess (CDMA) systems are also covered. Although simulation procedures are not considered, for many devices the theoretical frequency response is presented along with the measurement curve.<<ETX>>

Review of models for low-loss filter design and applications

The most frequently used models for surface acoustic wave (SAW) devices are the impulse model, the equivalent circuit models, the Coupling-of-Modes model, and the matrix models. While the impulse-model is only a first order model the other models include second order effects, e.g. reflections, dispersion, and charge distribution effects. The influence of diffraction and refraction on the transfer function of a SAW filter can be described by the angular spectrum of straight-crested waves model. A survey of these different models will be given. The simulation of low-loss filters requires flexible analysis tools, which can cope with different geometries and substrates. Operating with a parameter set, which depends only on the substrate crystal and not on the specific geometry of the SAW filter, is advantageous. Due to the high insertion attenuation of conventional transversal filters the requirements on the accuracy of the analysis are focused on S21, whereas for low-loss filters all elements of the S-matrix are important. The comparison of simulations with a P-matrix model, which fulfills the above mentioned prerequisites, and measurements of different types of low-loss filters, e.g. SPUDT, DMS, and transverse-mode coupled resonator filters are presented

NONLINEAR ACOUSTOELECTRIC INTERACTIONS IN GAAS/LINBO3 STRUCTURES

Surface acoustic waves accompanied by very large piezoelectric fields can be created in a semiconductor/piezoelectric hybrid system. Such intense waves interact with the mobile carries in semiconductor quantum well structures in a manner being strongly governed by nonlinear effects. At high sound intensities, a formerly homogeneous two-dimensional electron system breaks up into well confined stripes surfing the wave. As a result, we observe a strong reduction of electronic sound attenuation. On the other hand, large momentum transfer between the electron system and the wave results in nonlinear acoustoelectric effects and acoustoelectric amplification. We describe our experimental findings in terms of a generalized theory of the acoustoelectric effect and discuss the importance for possible device applications.

FEM analysis of the reflection coefficient of SAWs in an infinite periodic array

A finite element tool for the analysis of infinite gratings of interdigital transducers in surface acoustic wave (SAW) devices has been developed. The computation of one period of the infinite structure together with the application of periodical boundary conditions makes the analysis of the total geometry possible. The eigenfrequencies of such a structure in the sagittal plane are calculated, and parameters (velocity, reflection) for the simulation programs of complete SAW devices are derived from them. The dependence of these parameters on the electrode shape has been analyzed and is presented.<<ETX>>

Efficient analysis tool for coupled-SAW-resonator filters

The advantages of the coupled-mode (COM) formalism and the transmission-matrix approach are combined in order to create exact and computationally efficient analysis and synthesis tools for the design of coupled surface acoustic wave resonator filters. The models for the filter components, in particular gratings, interdigital transducers (IDTs) and multistrip couplers (MSCs), are based on the COM approach that delivers closed-form expressions. To determine the pertinent COM parameters, the COM differential equations are solved and the solution is compared with analytically derived expressions from the transmission-matrix approach and the Greens function method. The most important second-order effects, such as energy storage, propagation loss, and mechanical and electrical loading, are fully taken into account. As an example, a two-pole, acoustically coupled resonator filter at 914.5 MHz on AT quartz is investigated. Excellent agreement between theory and measurement is found.<<ETX>>

GIANT ACOUSTOELECTRIC EFFECT IN GAAS/LINBO3 HYBRIDS

The acoustoelectric effect in a hybrid of a strong piezoelectric material and a semiconductor layer containing a two-dimensional electron system is investigated. Caused by the very strong interaction between a surface acoustic wave and the mobile carriers in the semiconductor, the acoustoelectric effect is very large as compared to other materials, which might be interesting for device applications. Moreover, the tunability of the sheet conductivity of the electron system enables us to tune the magnitude of the acoustoelectric effect over a wide range. We present experimental results for a GaAs/LiNbO3 layered hybrid system at room temperature and describe our experimental findings quantitatively using a recently developed model calculation.

Z-path IF-filters for mobile telephones

IF-filters for channel selection in mobile phone systems must offer narrow bandwidths together with very steep skirts and excellent stopband rejection. Surface acoustic wave (SAW) filters fulfill these requirements. But if conventional transversal design techniques are used chip sizes become too large. The propagation path of the SAW was folded in order to make better use of the total chip length. The use of two slightly inclined reflectors results in a Z-shaped filter which conserves the temperature stability of quartz substrate. At a center frequency of 45 MHz, filters were developed on small chips with good passband characteristics and an insertion loss better than 10 dB. A filter with signal suppression of 20 dB and an ultimate relative stopband rejection of 60 dB is shown.<<ETX>>

High performance low-loss SAW filters for mobile radio with improved stopband rejection

A low-loss surface acoustic wave (SAWs) filter configuration is presented that uses a dual-track configuration with a transducer coupling between the tracks. This filter was developed to obtain a high stopband rejection, small passband ripple, and small size, which is needed in mobile communication systems. A partial finger-splitting and an optimized binary withdrawal weighting were also incorporated into the design together with a nonresonant unidirectional configuration. Filters at 450 MHz were fabricated on 36 degrees rotYX-LiTaO/sub 3/ using a simple single-layer technology. An insertion loss of 3 to 4 dB was achieved over a bandwidth of 6.5 MHz with a passband ripple of less than +or-0.5 dB. The stopband rejection is better than 50 dB.<<ETX>>

Rayleigh-Mode Saw-Filters on Quartz for Timing Recovery at Frequencies Above 1 GHz

Different types of SAW-fiLters on quartz for timing recovery at frequencies up to 2 GHz have been designed and fabricated. Because of the good compromise between Low insertion Loss and smaLL temperature coefficient the RayLeigh-wave has been used. The fiLters have been produced with a standard photoLithographic process with projection printing and Liftoff technique. To achieve center frequencies above 1 GHz the filters have to operate at higher harmonics. Methods for the synthesis and the anaLysis of these fiLters have been developed. The fabricated fiLters are characterized by periodic structures and good suppression of reflection at the center frequency. The reproducibiLity of the center frequencies is comparabLe to that of fiLters operating beLow 1 GHz.

New resonator filter with high sidelobe suppression

A new resonator filter for IF applications which is superior to conventional approaches is reported. The design places acoustically coupled resonator cascades between two weighted single-phase unidirectional transducers (SPUDTs). This allows narrow bandwidth and small chip size, high sidelobe suppression, moderate group delay ripple and low loss at the same time. For full custom design sophisticated CAD tools are necessary. A filter was built at 225.0 MHz with a chip size smaller than 10 mm in a surface mounted device (SMD) package. The fractional bandwidth is 0.14%, sidelobes are suppressed more than 40 dB, the group delay ripple is smaller than 0.5 mu s, and the insertion loss is 4.5 dB.<<ETX>>