Surface Acoustic Wave Transversal Filter Research Articles

High Quality

Ken Laker advanced surface acoustic wave (SAW) filter and resonator technology with significant decreases in the size, weight, and cost of oscillators, fast frequency-measuring filter banks, and compact fast-frequency- hopping synthesizers. His compact SAW resonator chip at 780 MHz had a Q factor of almost 5,000, five times that of larger electromagnetic equivalents. His technique of designing withdrawal-weighted SAW transversal filters increased out-of-band rejection from 30 dB to more than 60 dB.

Fabrication of a Slotted SiO2 Film/Embedded Grating Electrodes/128° YX-LiNbO3 Structure

In this paper, we describe the fabrication of Al grating electrodes embedded in a slotted SiO2 film on a 128° YX-LiNbO3 substrate in order to control both reflection characteristics and the temperature coefficient of frequency (TCF) of surface acoustic wave (SAW) devices. First, the fabrication process is discussed. It is shown that the combined usage of ion milling and reactive ion etching enables independent control of the thicknesses of the slotted SiO2 film and grating electrodes to be embedded in the slots. Next, the process is applied to the fabrication of an SAW transversal filter, showing the possibility of controlling the reflection characteristics and TCF independently.

Design of withdrawal-weighted SAW filters.

This paper presents a new design algorithm for a withdrawal-weighted surface acoustic wave (SAW) transversal filter. The proposed algorithm is based on the effective transmission loss theory and a delta function model of a SAW transversal filter. The design process consists of three steps, which eventually determine eight geometrical design parameters for the filter in order to satisfy given performance specifications. First, the number of fingers in the input and output interdigital transducers (IDTs), plus their geometrical sizes is determined using the insertion loss specification. Second, the number and positions of the polarity reverses in the output IDT are determined using the bandwidth and ripple specifications. Third, the number and position for withdrawing and switching specific fingers in the output IDT and attached electrode area are determined to achieve the desired sidelobe level. The efficiency of the technique is illustrated using a sample design of an IF filter consisting of a uniform input IDT and withdrawal-weighted output IDT. The proposed algorithm is distinct from conventional techniques in that it can optimize the structural geometry of a withdrawal-weighted SAW filter in a direct manner by considering all the performance specifications simultaneously.

Low-Loss Surface Acoustic Wave Filter on Natural-Single Phase Unidirectional Transducter Orientations of a Li 2B 4O 7 Substrate

Natural-single phase unidirectional transducers (NSPUDT) have attracted much attention for the implementation of low-loss surface acoustic wave (SAW) devices. In this paper, we describe a low-loss SAW filter using NSPUDT orientations of a Li2B4O7 substrate previously reported by the authors. Since the unidirectionality of NSPUDT is inherent to the substrate orientation, it is necessary to make the receiving transducer unidirectional in the opposite direction in order to obtain a low-loss filter using two transducers with reverse directivity. A new transducer configuration to reverse the directivity of an NSPUDT substrate is proposed, which utilizes reflector banks within the ladder transducer. The configuration has the advantage that it can be fabricated through a single level and a single metallization with minimum electrode width of λ/4. The principle of the operation of a reversal of directivity transducer is described. A 200-MHz-band low-loss SAW transversal filter with minimum insertion loss below 3 dB and low passband ripple are demonstrated with a theoretical filter response using coupling-of-modes theory.

Noise and dynamic range optimization of SAW transversal filters

A model for surface acoustic wave (SAW) transversal filters with special attention to the system and circuit designer's point of view is summarized. In the ideal situation the SAW transversal filter is driven with a voltage and the short-circuit current is sensed, which results in a minimization of the triple transit echo distortion. The aperture (width) of the SAW device is the only parameter that is not determined by the frequency dependence of the transfer and therefore it can be used to optimize the SAW device in relation to the electronic circuitry. Noise and dynamic range calculations on an amplifier-filter-amplifier configuration, are performed. It is shown that for a low noise floor at the input of the SAW device, the aperture of this device should be chosen large. However, the dynamic range of the amplifier-filter-amplifier configuration can be maximized by choosing a small aperture.

Timing Recovery with SAW Transversal Filters in the Regenerators of Undersea Long-Haul Fiber Transmission Systems

Surface-acoustic-wave (SAW) filters have been generally accepted as the best available choice for timing recovery in repeatered transoceanic fiber transmission systems operating in the range of 300 Mbit/s as well as in other digital transmission systems operating from approximately 0.1 to 1 or 2 Gbit/s. The SAW technology is ready and reliable, filter size is consistent with the severe space limitations of undersea repeater housings, and cost is reasonable, especially for the transversal (tapped-delay-line) filter type. This paper updates the relationship between system performance and the characteristics of transversal SAW filters, which have a finite impulse response and non-minimum-phase behavior. New results relate to passband ripple (typical in these filters), thermal characteristics, and the impact of the-delay-line structure on filter ringing time.

Timing recovery with SAW transversal filters in the regenerators of undersea long-haul fiber transmission systems

Surface-acoustic-wave (SAW) filters have been generally accepted as the best available choice for timing recovery in repeatered transoceanic fiber transmission systems operating in the range of 300 Mbit/s as well as in other digital transmission systems operating from approximately 0.1 to 1 or 2 Gbit/s. The SAW technology is ready and reliable, filter size is consistent with the severe space limitations of undersea repeater housings, and cost is reasonable, especially for the transversal (tapped-delay-line) filter type. This paper updates the relationship between system performance and the characteristics of transversal SAW filters, which have a finite impulse response and non-minimum-phase behavior. New results relate to passband ripple (typical in these filters), thermal characteristics, and the impact of the delay-line structure on filter "ringing" time.

Suppression of bulk modes in SAW transversal filters by gold transducers

Unwanted bulk modes in surface-acoustic-wave (SAW) transversal filters are demonstrated to be dependent on the transducer metallisation. Experimental results are presented that compare Au with the more conventional Al metallisation and show that bulk modes can be suppressed by > 20 dB.

Novel programmable high-speed analog transversal filter

A totally monolithic surface acoustic wave transversal filter has been demonstrated which utilizes an integrated multiplexed FET array to program the desired filter function. The device is based on ZnO on Si SAW technology with the FET array being fabricated using a standard NMOS processing schedule. Experimental results are presented which show the analog correlation of RF modulated waveforms (f o = 100 MHz) with various preprogrammed filter functions.