Shogo Inoue

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.

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.

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.