Junya Ago

Very small IF resonator filters using reflection of shear horizontal wave at free edges of substrate

A conventional surface acoustic wave (SAW) resonator filter requires reflectors consisting of numerous grating fingers on both sides of interdigital transducers (IDTs). On the contrary, it is considered that small-sized and low loss resonator filters without reflectors consisting of grating fingers can be realized by exploiting this characteristic of the shear horizontal (SH) wave or the Bleustein-Gulyaev-Shimizu (BGS) wave. There are two types of resonator filters: transversely coupled and longitudinally coupled. No transversely coupled filters (neither conventional nor edge-reflection) using the SH wave on a single-crystal substrate have been realized until now, because two transverse modes (symmetrical and asymmetrical modes) are not easily coupled. However, the authors have realized small low loss transversely coupled resonator filters in the range of 25 to 52 MHz using edge reflections of the BGS wave on piezoelectric ceramic (PZT: Pb(Zr,Ti)O/sub 3/) substrates for the first time by developing methods by which the two transverse modes could be coupled. Also the authors have realized small low loss longitudinally coupled resonator filters in the range of 40 to 190 MHz using edge reflection of BGS or SH waves on PZT or 36/spl deg/-rotated-Y X-propagation LiTaO/sub 3/ substrates for the first time. Despite being IF filters, their package (3/spl times/3/spl times/1.03 mm/sup 3/) sizes are as small as those of RF SAW filters.

Longitudinally Coupled Resonator Filter Using Edge Reflection of Bleustein-Gulyaev-Shimizu and Shear Horizontal Waves with Various Bandwidths Realized by Selecting Substrates

A conventional surface acoustic wave (SAW) resonator filter requires reflectors with many grating fingers at both sides of the interdigital transducers (IDTs). On the other hand, a small-sized low-loss resonator filter without grating fingers can be realized by utilizing the reflection of a Bleustein-Gulyaev-Shimizu (BGS) wave or a shear horizontal (SH) wave at the edge of a substrate. As a result, the authors have developed longitudinally coupled resonator filters using the reflection of BGS and SH waves at the edges of a substrate. Longitudinally coupled resonator filters on piezoelectric ceramic substrates for the first intermediate frequency (IF) stage have been realized to be low-loss, small-sized and extremely wide bandwidth (fractional bandwidth of 15%) filters as compared to the ordinary resonator filters, and they can have various kinds of bandwidths (2 to 15%) by employing ceramic substrates with various electromechanical coupling factors. On the other hand, the edge-reflection-type resonator filters on LiTaO3 single crystal for various first IF stages have also been realized to be low-loss and small-sized filters. In spite of being a wire-bonding type of IF filter, the package size of this filter is the same as that of the radio frequency (RF) SAW filter.

Transversely Coupled Resonator Filters Utilizing Reflection of Bleustein-Gulyaev-Shimizu Wave at Free Edges of Substrate

Smaller-sized and lower insertion loss surface acoustic wave (SAW) filters are urgently required for mobile telecommunications. We describe here that miniature, low-loss transversely coupled resonator filters without reflector electrodes could be realized and commercialized by utilizing the edge reflection of a Bleustein-Gulyaev-Shimizu (BGS) wave for the first time. The transversely coupled resonator filter has a narrower bandwidth than a longitudinally coupled one. A small, low-loss resonator filter for a first intermediate-frequency stage (first IF) of a spread spectrum (SS) codeless telephone system could be realized using a piezoelectric ceramic substrate with a coupling factor (k) of 0.20 and the transversely coupled resonator filter consisting of single finger electrodes. A filter for the first IF of the global system for mobile communication (GSM) requires a narrower bandwidth than SS codeless telephone, but a suitable substrate with a small coupling factor is not available. However, we could realize the small transversely coupled filter for GSM using split finger electrodes.

A Bleustein-Gulyaev-Shimizu Wave Resonator with 2 or 3 Resonances for Double Traps in TV and VCR (VTR)

A Bleustein-Gulyaev-Shimizu (BGS) wave with only a shear-horizontal (SH) displacement has the property of complete reflection at the free edge of a piezoelectric ceramic substrate. A BGS wave resonator utilizing this property is super-miniature and wide band, has a small capacitance ratio, and does not require frequency tuning. At present, two kinds of BGS resonators have been used as the additional traps at f ap and f as in TV-VCR VIF circuits. In this work, utilizing the responses generated due to the frequency characteristic of weighted IDT and even mode reflections at free edges of the substrate, we propose a new type of BGS resonator device which has two or three resonant frequencies for both f ap and f as . By applying this resonator in a VIF circuit, we have confirmed that it produces sufficient attenuations for practical use at both f ap and f as .