Jun Tsutsumi

High-frequency SAW duplexer with low-loss and steep cut-off characteristics

In CDMA (code division multiple access), analog, and partly TDMA (time division multiple access) cellular phone systems, transmitting and receiving are carried out simultaneously. Thus, an antenna duplexer is needed. An antenna duplexer using ladder-type SAW filters was first applied in an AMPS (Advanced Mobile Phone System)-CDMA system in 1998. The package size was 9.5 /spl times/ 7.5 /spl times/ 2 mm. The development of SAW antenna duplexers will require SAW filter designs that enable lower loss and a sharper cut-off, electrode materials that provide higher power durability, and package designs that enable lower loss and a smaller size. The miniaturization of this duplexer has been achieved by improving the filter chip and reducing the package size to 5 mm square. However, SAW duplexer with low-loss and steep cut-off characteristics is needed for high frequency applications. Through improved SAW filter characteristics, a duplexer for a 1.9 GHz PCS (personal communication services)-CDMA system has been realized. This paper describes these advanced technologies.

1.9 GHz range ultra-low-loss and steep cut-off double mode SAW filter for the Rx band in the PCS antenna duplexer

This paper describes the DMS (double mode SAW) filter design techniques to achieve the ultra-low-loss and steep cut-off characteristics required for the Rx filter in the PCS (personal communications service) duplexer. It is the first attempt to employ DMS filters for antenna duplexers in mobile phones. It is demonstrated that the common ground inductance L/sub g/ and the coupling capacitance C/sub c/ between the input and output terminals of the DMS filters dramatically enhances the skirt steepness and the attenuation for the lower frequency side of the pass band. Based on this result, we propose a novel DMS filter structure that easily controls the L/sub g/ and C/sub c/ values. Moreover, we propose a compact DMS filter structure connected in parallel, which reduces the insertion loss. Applying these technologies to the Rx filter, we develop a DMS-employing PCS antenna duplexer.

A miniaturized 3 /spl times/ 3-mm SAW antenna duplexer for the US-PCS band with temperature-compensated LiTaO/sub 3//sapphire substrate

This paper describes a temperature-stable and miniaturized SAW antenna duplexer for the 1.9 GHz US-PCS band that uses a temperature-compensated 42/spl deg/ Y-X:LiTaO/sub 3//sapphire bonded substrate. In this duplexer, the temperature coefficient of frequency is reduced to half or two-thirds of that of a conventional LiTaO/sub 3/ substrate. Also, it is shown that our new duplexer has a smaller insertion loss and offers sufficient power durability. These improvements are mainly due to the characteristics of sapphire, such as its larger thermal conductivity and smaller dielectric constant. Furthermore, the performance of our SAW duplexer is compared with that of two kinds of BAW duplexers, which are competitive technologies. As a result, it is shown that our newly developed SAW duplexer offers equal or better performance in a smaller package. This implies that our SAW duplexer is the best and the smallest PCS duplexer.

Extremely low-loss SAW filter and its application to antenna duplexer for the 1.9 GHz PCS full-band

An antenna duplexer for the 1.9 GHz PCS-band handsets is realized by developing extremely low-loss and ultra-steep cut-off SAW filters. In this paper, design techniques to achieve the characteristics that satisfy all severe specifications required for the PCS-band duplexer is presented. Developed SAW duplexers have the insertion loss of -2.0 dB and -3.2 dB in the Tx and Rx band, respectively. Also, the attenuation levels are -53 dB and -45 dB. The device size is as small as 5/spl times/5/spl times/1.5 mm/sup 3/. These performances are sufficient for the PCS duplexer to be practical.

Ultra-miniaturized and high performance PCS SAW duplexer with steep cut-off filters

This paper describes PCS SAW duplexer using unique design methods in order to realize steep cut-off performance, which are based on ladder and DMS design for Tx and Rx, respectively. It is found that SAW resonator having narrow electrode fingers makes transverse leakage of SAW energy suppress around resonant frequency, so that band edge and skirt performance of Tx filter is much improved. For Rx part, new DMS (Double Mode SAW) is proposed which uses inductors and capacitors in the device effectively to realize higher rejection and better cut-off performance. We have succeeded to realize ultra-miniaturized PCS SAW duplexers for the US and Korean market using these technologies.

Transversely coupled resonator filters with 0.1% fractional bandwidth in quartz

This paper describes the realization of transversely coupled resonator filters (TCF) with 0.1% fractional passband width in quartz substrate. The coupling of modes analysis in the transverse direction is applied to the TCF design for the investigation of the passband width determination. As a result, it is found that the passband width can be widened by making the surface acoustic wave (SAW) velocity difference between the interdigital transducer (IDT) region and the resonator gap region smaller. We propose to apply the grating structure to the common ground bar to reduce the SAW velocity difference, instead of uniform metal. We fabricate TCFs using the grating type common ground bar in quartz for specific applications.

Surface acoustic wave device with a thicker partial bus bar area and optimal bus bar to electrode tip gap

Efficient transverse energy confinement, and provision of a surface acoustic wave filter having preferable characteristics of both insertion loss and shape factor are obtained. In the surface acoustic wave filter, electrode fingers of one comb electrode are laid in a state of being inserted to the electrode fingers of the other comb electrode, and a thick film thicker than each plurality of electrode fingers is produced in a partial area of the bus bar, and a tip gap is provided between the top of each plurality of electrode fingers and the end face of the opposed bus bar, with a distance therebetween set not greater than 0.2λ (where, λ is one period of the comb electrode).

Ultra-Steep Cut-Off Double Mode SAW Filter and Its Application to a PCS Duplexer

This paper describes the double mode surface acoustic wave (DMS) filter design techniques for achieving the ultra-steep cut-off characteristics and low insertion loss required for the Rx filter in the personal communications services (PCS) duplexer. Simulations demonstrate that the optimal combination of the additional common ground inductance Lg and the coupling capacitance Cc between the input and output terminals of the DMS filters drastically enhances the skirt steepness and attenuation for the lower frequency side of the passband. Based on this result, we propose a novel DMS filter structure that utilizes the parasitic reactance generated in bonding wires and interdigital transducer (IDT) busbars as Lg and Cc, respectively. Because the proposed structure does not need any additional reactance component, the filter size can be small. Moreover, we propose a compact multiple-connection configuration for low insertion loss. Applying these technologies to the Rx filter, we successfully develop a PCS SAW duplexer.

Passband widening of transversely coupled resonator filters using the fundamental symmetric and antisymmetric modes

This paper describes a method for widening the passband of transversely coupled resonator filters (TCF) using only the fundamental symmetric and antisymmetric modes. The coupling of modes analysis in the transverse direction is applied to the TCF design to investigate the passband width. As a result, it is found that the passband width can be increased by making the surface acoustic wave (SAW) velocity difference between the interdigital transducer (IDT) region and the resonator gap region smaller. It is proposed that a grating structure be applied to the common ground bar, instead of the uniform metal, to reduce the SAW velocity difference. Using the grating-type common ground bar, filters are fabricated on ST-quartz substrate. The passband of a single filter with a center frequency of 248 MHz is widened up to 410 kHz without any increase of the insertion loss. The effect of the impedance mismatch at the junction of two cascaded devices is investigated. It is shown that the filter performance is improved by reduction of the small parasitic capacitance existing at the cascade point. Experimentally, the capacitance formed between the bus bar of the IDT and the bottom surface of the ceramic package is reduced. The insertion loss is reduced by 0.0 dB, and 3 dB passband is widened by 8 kHz for a filter with a center frequency of 248 MHz. On the basis of these two improvements, cascaded TCFs are fabricated. For a filter with a center frequency of 248 MHz, an insertion loss of 5.5 dB and a 3-dB passband width of 270 kHz are obtained.

A novel reflector-filter using a SAW waveguide directional coupler

The SAW waveguide technique was used to form a novel reflector-filter for the realization of compact IF filters in CDMA handsets. The reflector-filter design is an attractive technique to obtain characteristics with steep skirts in a short device length, because the SAW propagation path is folded and the frequency response is synthesized by utilizing both IDT and reflector responses. In this paper, we propose a new reflector-filter structure using a SAW waveguide directional coupler. For the implementation of the proposed reflector-filter, the key technology is the design of SAW waveguides. We have formed SAW waveguides using Al gratings loaded on the surface of the substrate. The pitch of the Al gratings has been chosen unequal to half the acoustical wavelength to avoid the occurrence of the gratings stopband at the filters passband position. Using the proposed reflector-filter structure, PCS-CDMA IF filters were fabricated on quartz substrates. The filter exhibited an insertion loss of 8.5 dB, a 5 dB bandwidth of 1.45 MHz, and a rejection of more than 33 dB at the center frequency +/-1.25 MHz with the package size of 4.8/spl times/9.1 mm/sup 2/. i.e., half the size of a conventional transversal filter was achieved using the proposed reflector-filter technique.