Seiichi Mitobe

A low-loss and wide-band DMS filter using pitch-modulated IDT and reflector structures

This paper proposes the use of pitch-modulated IDTs and reflectors for the realization of low-loss and wideband longitudinally coupled double-mode SAW (DMS) filters. This technique offers drastic improvement of the device performance through the introduction of a sufficient number of DoF in the DMS filter design. Namely, the pass-band becomes wide and flat, and insertion loss can be reduced through the suppression of the bulk acoustic wave (BAW) scattering. First, it is shown how the BAW scattering loss can be reduced by the use of the pitch-modulated structure. The DMS filter with this structure is designed so that the frequency response becomes similar to that of the filter with the conventional un-modulated structure, and device performances are compared both theoretically and experimentally. Then it is demonstrated how the total device performances are improved by the use of this technology when the device is designed optimally for given specifications. Adding to the reduced bulk wave scattering loss, various distinctive features offer drastic improvement of total device performances.

Simulation modeling and correction method for balance performance of RF SAW filters

In mobile phone RF stages, the balanced SAW filter has assumed an important role. In order to suppress signal distortion, amplitude and phase imbalance are required to be reduced. This paper describes a new simulation modeling of balance performance. The developed 8-port F-matrices model includes the effect of coupling capacitances and the end effect of excitation intensity of SAW using a modified Smiths equivalent circuit model. The simulation results show good agreement with measured results for 3IDT type DMS filters. Moreover, a correction design using an optimization program with the developed simulator engine has been carried out, and less than half level imbalance characteristics have been successfully obtained for 5IDT type DCS-RX filters.

Low-Loss and Wide-Band Double-Mode Surface Acoustic Wave Filters Using Pitch-Modulated Interdigital Transducers and Reflectors

This paper proposes use of pitch-modulated interdigital transducers (IDTs) and reflectors for the realization of low-loss and wideband longitudinally coupled double-mode surface acoustic wave (DMS) filters. This technique offers drastic improvement of the device performances through the introduction of a sufficient number of degrees of freedom in the DMS filter design. Namely, the pass-band becomes wide and flat, and insertion loss can be reduced through the suppression of the bulk acoustic wave (BAW) scattering. First, it is shown how the BAW scattering loss can be reduced by the use of the pitch-modulated structure. The DMS filter with this structure is designed so that the frequency response becomes similar to that of the filter with the conventional unmodulated structure, and device performances are compared both theoretically and experimentally. It then is demonstrated how the total device performances are improved by the use of this technology when the device is designed optimally for given specifications. Adding to the reduced bulk wave scattering loss, various distinctive features offer drastic improvement of total device performances.

A triple-beat-free PCS SAW duplexer

In general, surface acoustic wave (SAW) duplexers have the lower 3rd order linearity compared to bulk acoustic wave (BAW) duplexers. Actually, the specification for the inband 3rd order nonlinear distortion, triple beat, required for 1.9 GHz Personal Communications Service (PCS) band in CDMA2000 can be satisfied only by BAW duplexers. The objective of this work is to propose the design methodology for extremely high-linear SAW duplexers and to develop the triplebeat-free PCS SAW duplexers. The nonlinear elastic model, which we have proposed last year for predicting the triple beat, is applied to design the highly linear PCS SAW duplexers. The developed SAW duplexer achieves the extremely high linearity of approximately -90 dBc in the triple beat test, which is 20 dB better than the conventional duplexer keeping the equivalent filter characteristics and same packaging size. To the best of our knowledge, this is the first PCS SAW duplexer which satisfies the triple beat specification required in CDMA2000.

A bulk suppressed low loss TDNM-IF filter using LBO substrate

This paper describes for bulk suppression of SPUDT filter on LBO substrate. To suppress the bulk response, new advanced dual track filter is developed. The main track and sub track are identical structure, but phase-inversion each other. To prevent canceling the SAW responses of main track and sub track, all over of the sub track are covered with the absorber that avoid excite the SAW. However, sub track generates bulk acoustic wave (BAW) that are phase inversion against main track. Consequently, the BAW responses are canceled out for dual track without degrading SAW response. The developed 157MHz TDMA-IF filter is installed 5/spl times/7mm sized ceramic package, and achieves low loss of 4.5dB. Regarding to the bulk spurious, it is improved about 10dB comparing with conventional one track type SPUDT using LBO substrate, and its out of band rejection level is better than 50dB in 185-500MHz frequency range.

Low-loss SAW filter on Li/sub 2/B/sub 4/O/sub 7/ using novel-shape apodized structure for 1 GHz RF-ID system

This paper describes the longitudinally-coupled double mode SAW (DMS) filter on 45 X-Z Li2B4O7 (LBO) substrate for the 1 GHz RF-ID system in Japan. Since LBO has a lower dielectric constant, the aperture of the IDT on LBO tends to be wider so that the input and output impedance correspond to 50 Ω. The higher order transverse modes existing in such a wide aperture cause ripple responses in the pass band. Generally, to suppress higher order transverse modes, IDTs are apodized. However, it appears that the conventional apodized structure generates a notch response in the pass band due to the longitudinal modes. We theoretically analyze this longitudinal modes response using the longitudinal mode separation technique and propose a novel-shape apodized structure, which we termed “wave-shape apodization.” This completely suppresses both the notch response due to the longitudinal modes and the higher order transverse modes. Applying this wave-shape apodization, we successfully develop a practical 953 MHz SAW filter for the RF-ID system.

High attenuation SAW IF filter for digital terrestrial TV

In digital terrestrial broadcasting system, adjacent high-level signals of coexistence analog system act as a spurious signal, which causes the generation of intermodulation and a bit error after digital demodulation. Therefore, a band pass filter with a large out-of-band rejection is required in IF stage in digital TV receiver set. Generally, for a high-rejection transversal SAW filter with apodized transducer, overlapped length of comb finger tends to be very narrow in side-lobe portion of apodized transducer. In spite of compensating diffraction effect, the high suppression level cannot be realized due to second order effects in such narrow overlapped region. The developed SAW filter has dual-track structure. It consists of a main track of conventional apodized IDT and a sub truck of just narrow overlapped IDT. The total aperture length increases only about 5% to conventional single-track structure. The sub track set inversion phase with main track. The developed filter achieves 50dB attenuation level with 31-lambda total aperture. The improved attenuation level is successfully realized with the same chip size.