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Evolution of the SAW Transducer for Communication Systems

Evolution of the SAW Transducer for Communication Systems. Donald C. Malocha Electrical & Computer Engineering Dept. University of Central Florida Orlando, Fl. 32816-2450 dcm@ece.engr.ucf.edu

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Evolution of the SAW Transducer for Communication Systems

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  1. Evolution of the SAW Transducer for Communication Systems Donald C. Malocha Electrical & Computer Engineering Dept. University of Central Florida Orlando, Fl. 32816-2450 dcm@ece.engr.ucf.edu Special thanks to the UFFC_S and contributing members who initiated, built and maintain the UFFC_S Digital Archive.

  2. Presentation Approach • In recognition of the 50th Anniversary of the UFFC_S, the presentation will focus on the SAW transducer evolution through the UFFC_S publications. • The presentation highlights the development through the “eyes” of the UFFC, not necessarily crediting or citing the first publication, inventor, etc. • There is a large body of contributions in other publications, patents, worldwide symposiums, non_English journals, etc., which makes it virtually impossible to site the first disclosure of ideas. • Every significant SAW transducer embodiment has eventually graced the pages of UFFC publications. • Disclaimer:The materialpresented doesnotrepresent the views of the society fdhfdthftghffdhsdtewratseafowieejfcoiswejvcoiswejefoisiwifvnwomopskefoiwejkfoiwemfoimcwvwejfiowejriofjweoivmoiwejfiwjfiowejifojweiojfg9wer0iwekpvoewpo. If there are errors or inaccuracies in the presentation, please email me the correct citation(s). Your input is appreciated. dcm@ece.engr.ucf.edu

  3. Any sufficiently advance technology is indistinguishable from magic. Arthur C. Clarke

  4. SAW Transducer’s Degrees of Freedom • Transducer Parameter Degrees of Freedom • Amplitude • Phase • Delay • Frequency • Device Infrastructure Degrees of Freedom • Material Choice • Thin Films on the Substrate • Spatial Diversity on the Substrate • Electrical Networks and Interface

  5. Introduction • _ Transduction • _ Reflection • _ Re-Generation • _ Non-Linearity's • This presentation addresses the first three properties applicable to SAW transducers

  6. Transducer Embodiment Fundamentals –basic bag of tricks • Fundamental concepts used in all transducers • Electrodes • Sampling • Apodization

  7. Multi- Electrode Transducers Note: Floating Electrode • Split electrode transducer used to eliminate reflections • Minimizes triple transit and self-resonance • 3rd Harmonic Operation “Reflection of a Surface Wave from Three Types of ID Transducer”, A. De Vries, R. Miller and T. Wojcik, 1972 IUS, pp. 353-358 “Applications of Double Electrodes in SAW Device Design”, T. Bristol, et.al., 1972 IUS, pp. 377-380

  8. Transducer Sampling- Harmonics Note: Floating Electrode “Surface Acoustic Wave Multielectrode Transducers”, H. Engan, UFFC_T, 1975, pp. 395-401

  9. First Reference to a Balanced SAW Transducer (Dual Track) First introduced with regards to sampling “Design of Interdigital Arrays for Acoustic Surface Wave Filters, C. Atzani and L. Masotti, 1972 IUS, pp. 242-252

  10. Space Harmonic Control • Changing electrode a/p can control harmonics “Space-Harmonic Response of Surface Wave Transducers”, R.D. Weglein and G.R. Nudd, 1972 IUS, pp. 346-352.

  11. Interdigitated IDT (IIDT) Interleaved I/O transducers Low loss structure No weighting “SAW Filters Employing Interdigitated Interdigital Transducers, M. Lewis, 1982 IUS, pp.12-17.

  12. Low Loss IIDT Antenna Duplexer Weighted transducer structure “Low Loss SAW Filter for Antenna Duplexer”, M. Hikita, T. Tabushi, H. Kojima, A. Nakagoshi and Y. Kinoshita, IUS 1983, pp 77-82.

  13. Q: How do we build arbitrary filter responses? A: Use sampling theory and weight the electrodes. Tap Weighting and Delay • Apodization maps ideal tap weights into the spatial profile of the transducer. • Idealized attenuated tap weights and electrodes provide delay. Variable spatial profile, uniform amplitude Uniform spatial profile, variable amplitude “Acoustic Surface Wave Filters”, R. Tancrell, 1969 IUS, pp. 48-64

  14. FIR Filter to Apodized SAW Transducer Relations between transversal filter, impulse response and SAW transducer. The transducer is a spatial mapping of the time domain response. “Acoustic Surface Wave Filters”, R. Tancrell, 1969 IUS, pp. 48-64.

  15. SAW Transducer Sampling A SAW transducer can use an arbitrary sampling frequency regardless of center frequency, with a uniform sampling rate, subject to the Nyquist criteria. Not required to use an integer number of electrodes per wavelength to obtain a filter response. “SAW Filter Sampling Technique”, Hunsinger & Kansy, UFFC_T, 1975, pp. 270_273

  16. Dual Passband Filters “Multipassband Low Loss SAW Filters”, B. Potter & T. Shoquist, 1977 IUS, pp., 736_739.

  17. Apodized SAW Filter RF @t=0 Main SAW TTE

  18. SAW Apodization Analysis Arbitrary SAW Apodization Profile SAW Conductance SAW Apodization Loss

  19. SAW Amplitude Beam Profile as a Function of Frequency Amplitude profile vs beam position @ 4 different frequencies - Conductance vs frequency -Transfer function assumes a uniform integrating transducer

  20. Slanted transducers 2 wavelength gaps; in-line; dummy electrodes; split electrode design Slant Centered Apodized IDT “Low Shape Factor Design Considerations”,P. Meyer, 1975 IUS, pp. 334_335 SAW transducer schematic; dummy electrodes removed for clarity

  21. Acoustic Conductance vs Apodization Technique Each transducer has the exact same impulse response, but the apodization pattern affects the electrical parameters and can be a problem, yielding a poor filter response due to electrical circuit interactions.

  22. Example Low Shape FactorSlant-Apodized Transducer Filter

  23. Phase Weighting Approach a uniform beam profile “Phase Weighting for Low Loss Filters”, M. Hikita, Y. Kinoshita, and T. Tabuchi, 1980 IUS, pp. 308-312.

  24. Distance Weighting • Each track is approximately a rect fcn. • Uniform magnitude of beam profile • Each track is uniform but differing bandwidth/group delay • Sum of sampling functions • Vary bandwidth by apodization profile • Group delay varies with track • Structure shown yields linear phase due to symmetry “ Acoustic Surface Wave Filters Using New Distance Weighting Technique”, K. Yamanouchi and T. Meguro, IUS 1980, pp. 313-316.

  25. Weighting Techniques • Q: How do we weight both transducers to obtain better filter performance? • A: Apply tap weighting to the transducer without using apodization • Better filter shape factor • Smaller device

  26. Phase Weighting _ SAW Coded Transducer “Evaluation of Digitally Coded Acoustic Surface Wave Matched Filters”, W. Jones, C.S. Hartmann, and L. Claiborne, UFFC-T, 1971, pp.21-27 Example of matched filter response

  27. Block Weighting to a Desired Response Phase, block, or a modified withdrawal weighting concept. No apodization but weighted IR. Hamming Function Approximation “Synthesis of Periodic Unapodized Surface Wave Transducers”, T. Bristol, IUS 1972, pp. 377-380

  28. Withdrawal Weighting • “Weighting IDT SAW Transducers by Selective Withdrawal Weighting of Electrodes” C.S. Hartmann, 1973, IUS, pp 423-426 • Approximates apodization pattern • Works well for small fractional bandwidths • Allows weighting of in-line transducers • Actually removed electrodes

  29. Series Weighted IDT Amplitude Weighted - yields nearly uniform spatial beam profile Uses a voltage divider across the aperture “Series Weighting of SAW Transducers”, H. Engan, 1974 IUS, pp. 422-424

  30. Combining Series-Withdrawal Weighting “Combining Series Section Weighting with Withdrawal Weighting in Surface Acoustic Wave Transducers”, F. Sandy, UFFC_T, Vol. 26, No. 4, 1979, pp. 308-312

  31. Tap Weight Enhancement Analog tap weight control rather than just unity taps weights “Tap Weight Enhancement for Broadband Filters” D.C. Malocha, S. Datta, and B.J. Hunsinger, UFFC-T, 1978, pp. 51-54.

  32. Capacitive Tap Weighted Network • Uses thin film capacitors fabricated in a multi-level process • a) a balance structure • b) an unbalanced structure • Generates an analog amplitude weighted SAW-uniform spatial beam profile “CTW SAW Transducers”, Malocha & Hunsinger, 1975, IUS, pp. 411-413.

  33. Apodized, linear dispersive, and slanted transducers. ( Chirp first discussed by R. Tancrell, 1969,1971) Spatial Diversity “Acoustic Radiation Measurements and Calculations for Three Surface Wave Filter Designs”, M. Daniel and J. de Klerk, 1973 IUS, pp.449-455.

  34. Non-Linear Phase Filter Using Dispersive Transducers Single dispersive transducer filter In-line doubly dispersive transducer filter Slanted doubly dispersive filter

  35. SAW Slanted Dispersive Transducer Slant provides frequency/spatial diversity and eliminated Fresnel ripple in passband “ Surface Acoustic Wave Slanted Correlators for Linear Pulse Compressors”, B. Potter and C.S. Hartmann, IUS 1977, pp. 607-610.

  36. Linear Phase Filter using Dispersive Transducers To 1st order, flat passband and linear phase.

  37. Linear Phase Slanted Transducer • Transition band is determined by impulse response length. • Each strip is a relatively narrowband response but the summation is a wideband response. • Each strip’s group delay determines whether it is a linear or non-linear phase filter. “Wide-Band Linear Phase SAW Filter Design Using Slanted Transducer Fingers” , C.K. Campbell, Y. Ye and J. Sferrazza Pappa, UFFC-T, 1982, pp. 224-228.

  38. Band-edge frequency Mid-band frequency Band-edge frequency Center frequency • Bandwidth is determined by the upper and lower strip band edge frequencies. Center of transducer beam Slanted Transducer Energy Distribution vs Frequency vs Beam Position Filter response is visualized as the sum of multiple individual narrowband frequency responses which are spatially separated across the transducer aperture.

  39. Example Slanted Transducer Frequency Response

  40. Slanted Transducer Weighting Across Passband “Tapered Transducers- Design and Applications”, L. Solie, 1998 IEEE IUS, pp.27-37.

  41. Slanted Transducer Weighting Technique • Sidelobes are dependent on weighting of electrodes. Block weighting is a form of capacitive weighting but allows only discrete amplitude steps. “Tapered Transducers- Design and Applications”, L. Solie, 1998 IEEE IUS, pp.27-37.

  42. Multi-Phase Unidirectional SAW Transducers • Q: How do we eliminate bi-directional loss? • A: Change 3-port device into 2 port device over bandwidth of interest • UDT requires some non-symmetry in transducer/electrical network • Theoretically can have 0 dB loss • TTE can be zero at center frequency • Phasing network determines directivity • Matching network determines electrical reflection

  43. Three Phase UDT • Requires multi-level crossovers. • Requires a 1 or 2 element 60o degree phaseshift network between ports. • Requires 1 or 2 element matching network. • Unidirectional fractional bandwidth up to approximately 20%. “Wideband Unidirectional Interdigital Surface Wave Transducers”, C.S. Hartmann, W. S. Jones and H. Vollers, UFFC-T, 1972, pp378-381

  44. 3 Phase UDT Operation • Analyzed as 3 collinear transducers. • Unit cell is 1 wavelength; no subharmonics. 1/3 wavelength electrode period; strong 2nd harmonic

  45. Simulation of forward and reverse responses 3 Phase UDT – Fo Vector Analysis

  46. Quadrature 3-Phase Forward response Reverse response “Quadrature 3 Phase Unidirectional Transducer”, D.C. Malocha, UFFC-T, Vol.26, no. 4, 1979, pp.

  47. Apodized 3Phase UDT

  48. Three Phase UDT Low Loss Filter Results Wide Band Filter Response Narrowband Filter Response

  49. Group-Type UDT (GUDT) • Single level fabrication • Electrical phase shift network of 45o (1 or 2 elements) and matching network (often 1 element) is used with the spatial offset such that a SAW is launched in one direction over a determined bandwidth. • Phasing always yields real input impedance; proper beam width choice eliminates separate matching network. “Low Insertion Loss Acoustic Surface Wave Filter Using Group-Type Unidirectional Interdigital Filter Transducer”, IUS, 1975, K. Yamanouchi, F. Nyffeler and K. Shibayama, pp. 317-321

  50. + + + + I-Inphase + + I-Inphase + + Joining of transducers eliminates a wavelength within each unit cell composed of an I and Q port. Q-Quadrature Q-Quadrature Group-Type UDT • GUDT uses interleaved transducers which are spatially offset from synchronism by an integer number plus one quarter wavelength. • Single level metallization – no crossovers.

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