Andrew J. Slobodnik

Saw oscillator with digital compensation for temperature related frequency changes

The inherent temperature instability of surface acoustic wave (SAW) clock oscillators is improved by the use of a thermometer oscillator circuit that senses temperature changes in the SAW substrate. The thermometer oscillator is used in combination with a calibrated programmable read only memory and a logic circuit and provides frequency corrections to the clock oscillator. The basic device is an oscillator clock circuit using a SAW substrate having a delay path orientation with good temperature stability. A second oscillator, the thermometer oscillator circuit, and the electronic compensation scheme are added in order to produce minimum temperature coefficient of delay over all temperatures in the range of interest. The thermometer oscillator delay path utilizes a high temperature coefficient of delay orientation of the same SAW substrate and at an appropriate angle to the clock oscillator delay path orientation. Its frequency of oscillation is used as a highly accurate thermometer in order to control a correction signal applied to a variable phase shifter in the clock oscillator loop.

Switchable SAW Filter Banks at UHF

The design and testing of two high-performance 9channel switchable SAW fiiter banks are described. Bank #l covers 360-468 MHz in 12-MHz steps (no Titer at 420 MHz) with each channel consist- ing of a length apodized and a withdrawal weighted transducer. Input multiplexing is achieved by the parallel interconnection of three induc- tively tuned sets of three series connected transducers. This scheme re- sults in both low and uniform insertion loss between channels. A mean value of 25.8 dB with a standard deviation of 0.75 dB was achieved. The highest spurious signals in the frequency domain are approximately 57 dB down and are due to electromagnetic feedthrough. The individ- ual high-frequency SAW fiiters themselves are capable of 63-65dB spurious suppression with approximately 19dB insertion loss. If needed, low-loss narrow-band matching techniques can be used and are de- scribed. Bank #2 covers 321-345 MHz in 3-MHz steps with a mean channel insertion loss of 19.8 dB. This includes l .S dB of output switch (a 9 X 1 switch used to select the desired frequency channel) insertion loss and can be compared to an individual Titer value of 14 dB. Sub- stantial improvement over power division is achieved. For this bank the strongest frequency spurious was approximately 61 dB.

Lithium tantalate SAW substrate minimal diffraction cuts

A simple physical theory is presented for thed escription of surface acoustic wave (SAW) orientations on anisotropic crystalline substrates having minimal diffraction spreading. The resultant conditions for thee xistence of these minimal diffraction cuts( MW) agree with those derived from formal diffraction theory. These techniques are illustrated by the theoretical and experimendtaisl covery of two new MDC orientations on LiTaO3, having diffraction retarded by approximately a factor of 20 over isotropic materials. Euler angies for the cut having superior spurious mode suppression are λ = 0, γ = 167.1 167.1±0.4, θ = 90°.

Acoustic Surface Wave Diffraction and Beam Steering.

Abstract : The report contains a detailed description of diffraction in acoustic surface wave devices. This source of loss is highly important in the design and realization of bandpass filters, long time delay lines and other devices for electronic sensors and communications systems. A complete review of acoustic surface wave diffraction on anisotropic substrates is presented. Full experimental verification of theory is provided. Complete computer program listings and descriptions are provided. The limits of applicability of the parabolic velocity surface theory are quantitatively delineated. Universal diffraction loss design curves are given for all parabolic materials. A limitation in the use of the exact angular spectrum of waves theory occurs for materials having a power flow angle slope approximately - 1 unless the velocity surfaces are very accurately known. Both YZ LiNbO3 and 16-1/2 degree double rotated LiNbO3 fall in this category. Approximate diffraction loss design curves are given for YZ LiNbO3. A complete tabular summary of all important material properties affecting acoustic surface wave device design is included. (Author)

SAW Butterworth Contiguous Filters at UHF

Abstruct-The design, fabrication, and testing of a set of 16 dualchannel contiguous surface acoustic wave (SAW) Butterworth filters is described. Each filter has a narrow-band (10.15 MHz) and wide-band (20.3 MHz) channel, and center frequencies vary from 248.8 MHz to 401.2 MHz. Theory for determination of finger overlap functions yielding Butterworth frequency responses is given. The SAW substrate used is the minimal diffraction cut of LiTa03 which has excellent bandpass filter properties. In addition to having diffraction suppressed by a factor of 20 over isotropic materials, these properties include superior spurious mode rejection when compared to other popular SAW substrates, and a coupling constant or kZ of 0.0154. An accurate transducer circuit model including parasitic elements is determined to allow optimum choice of matching elements for addressing insertion loss, VSWR, and triple transit suppression design goals. Direct optical projection onto the SAW substrate from 1OX negative masters in combination with the photoresist stripping technique was used for fabrication. Agreement between theory and experiment is good and double detection frequency measurement using SAW Butterworth filters is demonstrated.

A 2.2 GHz SAW Delay Line Fabricated by Direct Optical Projection

A new type of unidirectional transducer is presented which has three phases and requires a 90” electrical phase shift network. Experimental results of a broadband transducer are presented. The device exhibits an excellent third harmonic response and offers t o increase the usable frequency range of unidirectional transducers for a given line width resolution. I . INTRODUCTION Unidirectional transducers (UDT) are a necessity for filters requiring low loss (< 10 dB) and good triple transit suppression. The two most popular structures are the 3 phase UDT [ l ] , and the group type UDT [ 21. The three phase UDT uses three samples per wavelength, which comprise the unit cell, and a 60° phase shift network [ 31. The group type UDT uses four samples per period, of which two periods comprise the unit cell, and a 90° phase shift network. The group type unidirectional has a good fundamental and third harmonic response. However, the structure gives rise to unwanted subharmonics which can lead to filter distortion. A new type of UDT which has three phases and requires a 90’ electrical phase shift network is presented. The structure of the quadrature three phase UDT consists of four wavelength samples per period, one period comprising a unit cell, with two of the samples grounded as shown in Fig. 1. The Manuscript received August 30, 1978;revised January 1, 1979. The author is with Texas Instruments Incorporated, Dallas, TX 75222. 0018-9537/79/0700-0313SO0.75

A SAW Multiplexer Using Flat Exponential Filters

R. C. Williamson, “Reflection grating filters,” in Surface Wave Filters-Design, Construction and Use, H. Mattews, Ed. New York: Wiley, 1977, ch. 9, pp. 381-442. R. C. M. Li and J . Melngailis, “The influence of stored energy at step discontinuities on the behavior of surface-wave grating,” IEEE Trans. Sonics Ultrason., vol. SU-22, pp. 189-198, May 1975. W. S. Goruk and G. I. Stegeman, “Surface acoustic waves at a free-metallized interface,” Phys. Le??. ,vol. 53A, pp. 63-64, May 1975. E. L. Cambiaggio and F. C. Cuozzo, “SAW reflection from conducting strips on LiNbOj,” IEEE Trans. Sonics Ultrason., vol. SU-26, pp. 340-344, Sept. 1979. K. Shibayama, K . Yamanouchi, H. Sato, and T. Meguro, “Optimum cut for rotated Y-cut Limo3 crystal used as the substrate of acoustic-surface-wave filters,”Proc. IEEE, vol. 64, pp. 595597, May 1976. J . Temmyo, I . Kotaka, T. Inamura, and S. Yoshikawa, “Precise measurement of SAW propagation velocity on LiNbO3,” IEEE Trans. Sonics Ultrason., vol. SU-27, pp. 218-219, July 1980. H. McSkimin, “Pulse superposition method for measuring ultrasonic wave velocities in solids,” J. Acous. Soc. Amer., vol. 33, pp. 12-16, Jan. 1961. pp. 195-205, Apr. 1973.

SAW Filters at 1 GHz Fabricated by Direct Step on the Wafer

Narrow bandwidth low sidelobe SAW filters operating at center frequencies up to 1 GHz are described. Direct step on the wafer lox reduction fabrication techniques were used to achieve the necessary O.52-pm linewidths on ST quartz. Three-halves electrodes (sixthwave) effectively reduce reflection distortion without requiring eighthwave photolithographic resolution.

Design of Optimum Acoustic Surface Wave Delay Lines at Microwave Frequencies (Short Papers)

Optimum procedures for designing microwave acoustic surface wave delay lines are given. Combined beam steering fraction loss curves are provided as a function of the basic material parameter, the slope of the power flow angle, to allow optimum choice of material for a given application. Methods for designing uniform periodic interdigital transducers including finger ohmic loss, lossy tuning elements, and parasitic capacitance have been extended to account for beam steering and diffraction.