Jurgen Machui

SAW devices in cellular and cordless phones

Cordless and cellular phone systems are one of the most rapidly growing areas of telecommunication and have become part of modern life. In addition personal communication with global access and wireless data networks will emerge. Handheld phones provoked a continuously increasing demand on miniaturized high performance components and led to the establishment of SAW filters in their radio circuits. Inversely the specific performance of SAW components influences the architecture of the receiver circuit. Radio quality could be increased, weight, size and total circuit cost were reduced. The present paper reviews specific requirements of filtering tasks in cellular and cordless phones. It shows benefits of SAW devices and explains challenges SAW designers face today. A number of representative filter solutions are sketched giving a brief outline of todays state of the art.

Design, fabrication, and application of GHz SAW devices

To meet the increasing demand of high performance filters in GHz radio communication systems, we have improved design techniques and fabrication processes. Different types of filters in the range of 1 to 3 GHz, a 2.45 GHz resonator with 18 dB insertion attenuation and a quality factor of 1500, wideband delay lines at 2.45 GHz, with 400 MHz and 600 MHz bandwidth, identification tags at 2.45 GHz, and ladder type bandpass filters for PCS and WLAN applications at 1.9 GHz and 2.45 GHz, were developed and manufactured. It will be shown, that these devices with submicron linewidth transducers down to 0.3 /spl mu/m can be manufactured with tight process tolerances.

A new low loss SAW filter structure with extremely wide bandwidth for mobile communication systems

The authors present a low-loss surface-acoustic-wave (SAW) filter with a dual-track configuration which is characterized by a novel arrangement of interdigital transducers (IDTs) and reflectors in each acoustic track as well as a special electrical connection of the IDTs. Broadband filter characteristics can easily be achieved by using chirped components. The inherently good stopband rejection of the new structure has been further improved by applying proper weighting techniques to the IDTs and reflectors. A filter with a relative bandwidth of 10% and a center frequency of 200 MHz has been designed by means of a novel synthesis method. The filter has been fabricated on 128 degrees Y-X LiNbO/sub 3/. A minimum insertion loss of 4 dB, a small passband ripple of about 1 dB, and a stopband rejection of better than 35 dB were measured. Excellent agreement between simulation and measurement has been found.<<ETX>>

Two-track-reflector-filters for CDMA mobile telephones

IF-filters for channel selection in mobile phones based on a CDMA system must offer very steep skirts as well as excellent phase linearity and small amplitude ripple within the passband. To fulfill all these requirements a conventional transversal surface acoustic wave (SAW) filter needs a large chip size. In order to reduce the total chip length we folded the propagation path of the SAW taking advantage of the reflector filter technique. Therefore, the usable time window for weighting becomes almost twice as large. We employed weighted reflectors not only to reflect the SAW but also to shape the filter frequency response. Thus we have more flexibility to design the transducers. We can make them shorter but still have lower impedances on quartz than with an unweighted reflector design. With this technique, we built filters at a center frequency of 110 MHz with an insertion attenuation of less than 15 dB, a 5 dB bandwidth of 1.26 MHz and an attenuation of more than 30 dB outside of a 1.80 MHz band. The chip is mounted in a 15.6/spl times/6.8 mm/sup 2/ SMD package. The reflector filter fulfills the frequency response specification required for CDMA mobile telephones on a chip length reduced by about 4 mm compared with the transversal or SPUDT design technique.

Design of a low loss SAW reflector filter with extremely wide bandwidth for mobile communication systems

The design and performance of a low-loss surface acoustic wave (SAW) reflector filter are presented. The structure is a dual-track configuration incorporating two interdigital transducers (IDTs) and reflectors in each track. Extremely wide bandwidth can be obtained if chirped IDTs and reflectors are used. From the theoretical conditions for low-loss operation of the reflector filter, a design rule for the distances between the chirped components and for their lengths is derived. Because the transfer function of the filter is predominantly determined by the reflectors, a new synthesis method for chirped reflectors has been developed. For the design of the reflectors, phase-weighting and finger-width-weighting techniques were used to reduce passband distortions and improve the shape factor and stopband rejection. The filter has been fabricated on 128 degrees YX-LiNbO/sub 3/. The center frequency and fractional bandwidth are 200 MHz and 100%, respectively, the minimum insertion loss is 4 dB, a passband ripple is about 1 dB, and the stopband rejection is better than 35 dB. >

2D simulation of diffraction and reflection improves Z-path SAW filters for mobile communications

Z-path SAW filters are used to reduce the chip size of channel selection filters in mobile telephones. For these devices the conventional ID simulation methods are inappropriate as the SAW partly travels at an angle to the principal device axis due to the Z-shaped folding of the propagation path. We therefore use an approach which allows for the simultaneous analysis of diffraction, refraction and multiple reflections within the device. We demonstrate that the full 2D simulation is able to predict the insertion loss, the shape of the pass-band skirts, the stop-band level and the occurrence of spurious acoustic signals by comparing our results with the measured response of a Z-path device. Excellent agreement between measurement and simulation is obtained.

A novel SAW filter for IF-filtering in DECT systems

We have developed an improved SAW filter for IF-filtering in DECT systems. The filter is a two track reflector filter using EWC-SPUDTs as in- and output-IDTs and reflectors in the center of each track The propagation path of the SAW is folded in order to make better use of the total chip length. A similar configuration with identical reflectors in the tracks is known in literature, however, we used different reflectors in the tracks and this way we could improve the filter performance and especially the stop band attenuation considerably. The SPUDTs are withdrawal weighted, for the reflector design we used an electrode width weighting technique. The filter fits into a very small QCC10 package (9.1/spl times/7.1/spl times/1.8 mm/sup 3/) and has high performance so that it can be used in a DECT base-station, too. The substrate is LiTaO/sub 3/, X112.2Y, the center frequency is 110.59 MHz, the minimum IL is 8 dB typically, the 3-dB-bandwidth is 1.1 MHz and the stopband attenuation is better than 40 dB.

New system applications of modern RF SAW filters

Modern mobile communication systems have a radio frequency between 800 MHz and 2.0 GHz. Wireless communication systems are one of the most rapidly growing areas of telecommunication. The cellular phone and the cordless phone are already established in todays life. Additional systems like personal communication systems with global access and wireless data networks will become part of tomorrows communication. The development of such systems is focused on both technological evolution and functional features. The continuously increasing demand for miniaturised components has led to an establishment of SAW components in the circuit of advanced radio devices especially. Furthermore, the specific performance of RF SAW components has an influence on the receiver circuit already. The radio quality is increased, weight, size and total circuit cost are reduced.

Determination of Parameters for the Simulation of Surface Acoustic Wave Devices with Finite Elements

Surface acoustic wave (SAW) filters are widely used in the frequency range between 30 MHz up to 3 GHz due to their outstanding filter characteristics and their reproducible production at low costs. This frequency range and thus also SAW filters will become even more important with the growth of new communication techniques in the near future.