Surface Acoustic Wave Convolver Research Articles

Efficient Monolithic SAW Convolver Using Poly(3-Hexylthiophene)

The demonstration of organic semiconductor based monolithic surface acoustic wave (SAW) convolver has been reported. The characteristic low availability of intrinsic free charge in organic semiconducting polymer favors depletion mode of operation, increasing the effective nonlinear interactions. Input signals at different combinations of frequencies were used and the observed convolved signals showed notably high efficiency without the need of an applied bias. The record high efficiency has been -13.2 dBm for 42 MHz input signals at optimum input power of -6 dBm. The experimental results and the convolution mechanism were verified via numerical analysis in MATLAB.

The influence of the parameters of acoustoelectronic convolvers on the reduction of the noise immunity of asynchronous radio reception of wideband signals

A method for comparing the noise immunity of asynchronous radio reception of wideband signals using a surface acoustic wave convolver is proposed. The convolver is developed according to the acoustoelectronic technology applied in Russia and has the noise immunity of a perfect correlation radio receiver. The method is demonstrated for the example of the estimating the reduction of the noise immunity of radio reception due to reflections of acoustic waves from interdigital transducers and irregularities of the acoustic line.

On the possibility of asynchronous connection establishment with the use of broadband wireless access to the infrastructure of the GRID computer network based on surface-acoustic-wave convolvers

For the first time, the possibilities of asynchronous control of access to a wireless virtual segment of the spatially distributed GRID computer network based on the use of surface-acoustic-wave (SAW) acoustoelectronic means. It is shown that the use of modern SAW convolvers makes it possible to provide asynchronous superfast access to the GRID-network infrastructure and satisfy the basic requirements of the IEEE 802.11 standard.

Experimental and computational procedure for statistical estimation of the effect of the SAW-convolver characteristics on the noise immunity of correlation signal processing

Specific features of correlation radio reception with the use of surface-acoustic-wave (SAW) correlators are considered. It is shown that the experimentally measured two-frequency transfer characteristic provides complete representation of the properties of actual SAW convolvers determining the noise immunity of the radio reception. For the example of experimentally investigated prototype waveguide convolvers, the critical imperfections in modern devices based on actual SAW technology are determined and modeled on the basis of the criterion of the noise immunity of correlation processing.

Design on semiconductor coupled SAW convolver.

This paper presents results of a design study on a semiconductor coupled surface acoustic wave (SAW) convolver in which bi-directionally propagating SAWs, on a piezoelectric substrate with a high coupling coefficient, couple with bonded semiconductor diodes through multistrips. To obtain convolution signals with a high efficiency, we adopted a diode-balanced bridge structure for the non-linear operation. We also found that the tapping pitches of the multi-strip electrodes have robustness against operation frequency variation and temperature-dependent variation on the delay of the SAW. We verified the effectiveness of the device in a circuit simulation and an experiment on a test circuit, which was fabricated by using an epitaxial lift-off film-bonding process.

Characteristics of surface acoustic wave convolver in the monolithic metal–zinc oxide–silicon nitride–silicon dioxide–silicon structure

The nonlinear analysis of the metal–insulator semiconductor shows that the ac currents charging the interface traps lead to large dc operating voltage and an inefficient operation of the monolithic convolvers. These interface traps are annihilated during a low temperature anneal, which utilizes hydrogen atoms implanted underneath the SiO2–Si interface. The overlay piezoelectric ZnO film in the metal–ZnO–Si3N4–SiO2–Sistructure is protected from the influx of hydrogen atoms by an interposed silicon nitride layer. Hydrogen implantation and rapid thermal annealing steps are integrated in the process sequence of realizing an efficient metal–ZnO–Si3N4–SiO2–Si monolithic surface acoustic wave convolver.

Simulation Study on Semiconductor Coupled Surface Acoustic Wave Convolver through a Multi-Strip Electrodes

This paper presents results of simulation study on a semiconductor coupled surface acoustic wave (SAW) convolver, in which the propagating SAW on a highly coupling coefficient piezoelectric substrate, couples with a bonded semiconductor diodes through multi-strip electrodes. We focus our study on a relatively wide band device which is the main feature of a highly efficiency device. By using a simple analysis and circuit simulator, based on the simulation program with integrated circuit emphasis (SPICE), we clarified the effect of device parameters, such as the shape of multi-strip tapping electrodes, characteristics of diode, impedance matching condition, kinds of transmission code and electro-mechanical coupling coefficient of SAW, on the device performances. We discussed the phenomenon, which cause the degradation, focusing on the frequency domain. We also clarified the essential problems of second order effect on the wide bandwidth device, which should be solved.

New SAW-convolver demodulation technique using Costas-loop synchronization for high-speed spread-spectrum signal

A new synchronous-demodulation method for a high-speed spread-spectrum (SS) signal, which combines a surface acoustic wave convolver with a Costas-loop circuit has been proposed. From the convolver, in-phase and quadrature-phase components of the correlated signal can be directly derived. A control voltage obtained by a Costas-loop circuit adjusts the frequency and phase of a local-oscillation (LO) signal to those of the SS signal. Thus, in the receiver, synchronization of the LO signal and the received signal can be carried out independently of the transmitter. A quadrature phase-shift keying SS signal with 9 Mb/s and 60 Mc/s has been successfully demodulated using this method.

On the noise behavior of a SAW convolver used as a matched filter

The noise behavior of a surface acoustic wave convolver used as an analog matched filter is investigated in this paper. In contrast to the existing literature, the influence of noise processes with squared amplitudes is not neglected. It is shown that these quadratic noise contributions have a significant influence on the output signal-to-noise ratio (SNR) of the convolver for values of input SNR lower than 10 dB. The calculation is done for on-off keying coded signals but the results are also valid for other modulation schemes, e.g., phase shift keying.

New high performance SAW convolvers used in high bit rate and wideband spread spectrum CDMA communications system

New surface acoustic wave (SAW) convolver structures with high conversion efficiency and self-temperature compensation characteristics have been developed. Strong piezoelectric substrates, regardless of temperature coefficients of delay (TCD), can be used in these convolvers. New demodulation techniques using the developed SAW convolver for high bit rate and wideband spread spectrum code division multiple access (CDMA) communications have also been developed. I- and Q-channel demodulation data can be derived directly from binary phase shift keying (BPSK) or quadri-phase shift keying (QPSK) CDMA signals. In an experiment using a 128 degrees YX-LiNbO(3) substrate, CDMA signals of 9 Mbps (megabits per second) with 60 Mcps (megachips per second) spread by 13-chip Barker code and 11 Mbps with 140 Mcps spread by 25-chip Shiba's code were clearly demodulated, demonstrating the effectiveness of these techniques for use in future CDMA communications.

A Surface Acoustic Wave Elastic Convolver using a KNbO3 Single Crystal Substrate

Elastic convolvers are very important in signal processing devices of spread spectrum communication (SSC) systems. Highly efficient convolvers are required in the application of the spread spectrum and next stage communication systems. A high value of the coupling coefficient is very important for wideband and high efficiency surface acoustic wave (SAW) devices, such as SAW convolvers. Potassium niobate (KNbO3) has large piezoelectric constants and a very large electromechanical coupling coefficient (K2) of 0.53 for surface acoustic waves, which is about 10 times higher than that of LiNbO3. Therefore, highly efficient elastic SAW convolvers using KNbO3 substrates are expected in the future. In this paper, the use of the rotated 60° Y-cut, X-propagating KNbO3 substrates in convolvers is demonstrated. The experimental results show that the efficiency of the convolver using 60° Y–X KNbO3 is 15 dB higher than that of the convolver using Y–Z LiNbO3.

Dependence on waveguide width of elastic convolver efficiency

An elastic convolver based on a nonlinear effect in surface acoustic wave (SAW) on a Y-Z⋅LiNbO3 is widely used as a functional device in the area of communication system. Therefore, the efficiency, which is an important parameter for the SAW convolver, is quite low. There have been many reports on electrode structures and convolver materials for improving the efficiency. In this work, theoretical and experimental results are reported for the optimum width of a (Δ=v/v) waveguide which has high convolver efficiency. The theoretical calculation was obtained by using the scalar potential approximation. The efficiency has a peak at a waveguide width of around 1λ. In order to increase the power density multistrip beam width compressors have been used. Performance of a device having a 4-μs waveguide length, a central frequency of 43 MHz and using 10:1 beam width compressors is described. The validity of the theory is proven experimentally, and, therefore, the optimum waveguide width for the convolver efficiency in a conventional elastic convolver is around one wavelength of the input SAW.

Measurement of radio channels using an elastic convolver and spread spectrum modulation. II. Results

A spread spectrum measurement system using a surface acoustic wave convolver has been used to measure radio wave propagation in steel works at 1.75 GHz with an echo delay resolution of /spl ap/20 ns. Due to the high metal content of the factory halls, path loss is found to be small and its exponent to range between 1.1 and 2.3 only. We observed a delay spread between 82 and 548 ns depending on the size of the steel mill, its construction and machinery. Characterizing the radio channel by a stochastic delay line model the echo amplitude probability distribution is found to fit a Rician or log-normal distribution rather than a Rayleigh distribution. The fit of the amplitude distributions is determined by a /spl chi//sup 2/ hypothesis test. From the channel impulse response the coherence bandwidth is deduced to range between 2.4 and 27.4 MHz. >

Measurement of radio channels using an elastic convolver and spread spectrum modulation. I. Implementation

Using spread spectrum signals a measurement system has been built in order to measure the radio channel in steel works. It transmits a 511-chip long maximum length sequence with a chip rate of 44 MHz: binary phase shift keying modulated onto a 1.75 GHz carrier. A surface acoustic wave convolver yields the channel's impulse response with a time resolution of about 20 ns. The periodic autocorrelation performed within a measurement window removes aperiodic correlation sidelobes which limit the dynamic range of a matched-filter implementation. Additionally, absolute time delay measurements of all echoes were obtained using a synchronization cable connecting receiver and transmitter. Compared to other spread spectrum correlation techniques, the convolver makes possible a much simpler real-time measurement setup.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Full duplex transmission operation of a 2.45-GHz asynchronous spread spectrum using a SAN convolver

An asynchronous spread spectrum (SS) modem in the 2.45-GHz band has been implemented using an efficient ZnO-SiO(2)-Si surface acoustic wave (SAW) convolver. The modem, which can operate under full duplex transmission is based on a direct-sequence/code-shift-keying (DS/CSK) method for the modulation. Pseudonoise (PN) codes are chosen from a preferred pair of m-sequences of period 127, and the code rate is 14 MHz. The demodulation is carried out asynchronously, utilizing the coherent correlation characteristics of the SAW convolver. The main interference caused by a transmitted signal in the modem itself is effectively reduced by an RF isolator and the SS process gain. Adequate self-jamming rejection capability has been confirmed; a bit error rate of 10(-6) is observed at -78.3 dB of a desired-to-undesired-signal ratio using an artificial transmission line.

Theoretical analysis of nonlinear effects in surface acoustic waves on waveguide

AbstractA structure with a ribbon‐shaped metal thin film on a highly coupled anisotropic piezoelectric substrate acts to concentrate the acoustic wave energy into the region with the thin film. A device making use of the nonlinear interaction of the surface acoustic waves propagating in opposite directions on this Δ v/v waveguide is the surface acoustic wave convolver. However, a theoretical analysis on its efficiency is not sufficient.In the present research, the guided wave characteristics of this Δ v/v waveguide are derived accurately so that the nonlinear components generated on the waveguide are computed. The generation efficiency of the surface acoustic wave at the second harmonic generated from this mechanism in the direction orthogonal to the waveguide is analyzed theoretically. The conversion efficiency of the split waveguide‐type convolver proposed previously by the authors can be derived quantitatively so that the evaluation of the surface acoustic wave nonlinear device becomes possible.

Semidigital multiplication by discrete convolution using surface acoustic wave (SAW) devices

The computation of the product of two digital numbers by discrete convolution by a surface acoustic wave (SAW) convolver is described. The principal limitations of the method are discussed as well as realistic performance numbers that can be achieved by using available SAW device technology. The multiplication is done by convolving the 2-b streams that represent two digital input operands in a SAW convolver at a rate of 100 MHz. The convolver output is the product in mixed binary representation. It consists of one analog value per digit with a resolution of 0.5%. These values are digitized at a rate of 200 MHz by an 8-b flash analog-to-digital converter and added up to form the digital result. It is shown that such a device has a very high computing power that can be adapted to special applications. One extreme is the multiplication of 256-b integer numbers, corresponding to a dynamic range of 1:10/sup 77/, at a rate of 0.2 MIPS. The other extreme is the computation of matrix products where computing speeds of 12000 MIPS can be achieved for 8-b operands, as required, for example, in image filtering applications.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Analysis of focused surface wave transducers

A new acoustic field analysis, based on the Huygens principles, is given for an elastic surface acoustic wave convolver, made by using a focused transducer on a YZ-LiNbO3 piezoelectric crystal. In the acoustic field analysis, a new slowness function approximation is suggested for the anisotropy of the medium, instead of the conventional parabolic slowness function. The acoustic field analysis obtained by using this function is compared to the other analysis techniques and the results are discussed.

Growth and characterization of ZnO films deposited on a monolithic Si3N4-SiO2-Si configuration

The growth parameters for ZnO films have been optimized for a new monolithic surface acoustic wave convolver configuration Si3N4-SiO2-Si which is potentially immune to radiation damage compared with the SiO2-Si structure. A detailed study of the microstructural properties of these films was carried out with X-ray diffraction, rocking curves, scanning electron microscopy, ellipsometry and absorption spectra in the UV range. A standard deviation of 3° for the angle of C axis normal orientation, an angle m of 0.2° and a typical grain size of 80 Å were obtained. The deposited films were optically clear with a bandgap of 3.3 eV and refractive index of 2.0. Lattice strains of 0.18% and 0.77% along the a and c axes respectively were observed in the deposited films. Information on homogeneity, defects and direction of polar axis was obtained by a novel thermal imaging technique. The relation between stoichiometry (O:Zn ratio) and LMM transition energy of zinc in the deposited films was also investigated from Auger electron spectroscopy data.

Surface Acoustic Wave Convolver Using Multi-Channel Waveguide

We have studied on a new type surface acoustic wave convolver consisting of multi channel waveguide, namely, in which the drawbacks inherent to an acoustoelectric convolver, and also to an elastic convolver are eliminated. We have adopted focussed interdigital transducers as the input to the new convolver, and improved its frequency characteristics and the time bandwidth product.