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Publication numberUS3925653 A
Publication typeGrant
Publication dateDec 9, 1975
Filing dateJan 21, 1974
Priority dateJan 21, 1974
Publication numberUS 3925653 A, US 3925653A, US-A-3925653, US3925653 A, US3925653A
InventorsOtto Oberdan W
Original AssigneeUniv Leland Stanford Junior
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Apparatus for transforming electronics signals between the time and frequency domains utilizing acoustic waves
US 3925653 A
Abstract
Apparatus for transforming electronic signals between the time domain and frequency domain in real time which comprises means for mixing the signal to be transformed with a predetermined chirp (variable frequency signal) in an acoustic wave convolver.
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Description  (OCR text may contain errors)

United States Patent Otto [ Dec. 9, 1975 Inventor:

Assignee:

Filed:

Oberdan W. Otto, I908 Angeles, Calif.

Board of Trustees of-Leland Stanford Jr. University, Stanford, Calif.

Jan. 21, 1974 Appl. No.: 434,965

US. Cl 235/181; 235/193; 324/77 B;

333/30; 333/72; 343/100 CL Int. Cl. G06G 7/19; HOlL 41/00 Field of Search 235/181, 193; 310/8.1;

324/77 R, 77 B; 333/30, 72; 343/100 CL;

[56] References Cited UNITED STATES PATENTS 3,760,172 9/1973 Quote 235/181 3,770,949 11/1973 Whitehouse et al. 235/181 3,774,019 11/1973 Cook 235/181 3,816,753 6/1974 Kino 310/81 3,833,867 9/1974 Solie 235/181 Primary ExaminerFelix D. Gruber Attorney, Agent, or FirmPaul B. Fihe ABSTRACT Apparatus for transforming electronic signals between the time domain-and frequency domain in real time which comprises means for mixing the signal to be transformed with a predetermined chirp (van'able frequency signal) i n an acoustic wave convolver.

4 Claims, 1 Drawing figure INPUT SIGNAL MIXER OUTPUT FREQUENCY M'XER QUADRLPLER 12 zo R.F. CHIRP JL 4 TIME GENERATOR (at- H8) ,ao INVERTER twv 8) RF (WI) 1 MIXER \9 GENERATOR MIXER US. Patent Dec. 9, 1975 3,925,653

TEEL MIXER OUTPUT FREQUENCY M'XER QUADRUPLER 2.0 R.F. CHIRP A A TIME GENERATOR -E s) 3o INVERTER I (o- \-S') 19 RF. (owl) M'XER J 8) APPARATUS FOR TRANSFORMING ELECTRONICS SIGNALS BETWEEN THE TIME AND FREQUENCY DOMAINS UTILIZING ACOUSTIC WAVES FIELD OF THE INVENTION The present invention relates to the processing of electronic signals and more particularly to apparatus for transforming signals between the time and frequency domains through utilization of acoustic waves.

BACKGROUND OF THE INVENTION It has been observed that a Fresnel transformation takes the mathematical form of convolution and moreover that initial multiplication of a signal by a complex chirp, then a Fresnel transformation, (convolution) and finally multiplication by a complex chirp provides a Fourier transformation. For example, L. Mertz has discussed this transformation relationship in Transformations in Optics (Wiley 1965) at pages 83 and 94.

The operation of convolution (and correlation) has been carried out through the parametric interaction of acoustic waves as explained in US. Pat. No. 3,760,172 issued Sept. 18, 1973, to Calvin F. Quate, and a large number of additional acoustic convolvers have been developed such as described in the Otto article entitled Lithium-Niobate Silicon Surface Wave Convoluter in ELECTRONICS LETTERS, Volume 8, No. 24.

SUMMARY OF THE PRESENT INVENTION It is the general objective of the present invention to provide apparatus for transforming an electronic signal between the time and frequency domain (e.g. Fourier transform) through utilization of suitable signal mixing and acoustic wave convolution.

Such objective is achieved generally through the mixing of the signal to be transformed with a complex chirp, thus to correspond to the mathematical multiplication mentioned hereinabove. The mixing means can take the form of a conventional electronic signal mixer. The mixed signal can be applied through a suitable transducer to generate an acoustic signal in a piezoelectric medium arranged to provide a convolution operation equivalent to the mentioned Fresnel transformation. Finally, means to provide a final mixing of the convoluted output with a chirp produces the final multiplication operation and the ultimate completed transformation.

BRIEF DESCRIPTION OF THE DRAWING The stated objective of the invention and the manner in which it is achieved, as summarized hereinabove, will be more fully understood by reference to the following detailed description of the exemplary apparatus depicted in the accompanying drawing wherein the single FIGURE constitutes a diagrammatic showing of electro-acoustic apparatus for obtaining the Fourier Transform of an arbitrary electronic signal.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENT OF THE INVENTION As illustrated diagrammatically, the input modulated electronic signal to be transformed at a RF. frequency w, is delivered to a conventional radio frequency mixer 14.

2 A tunable radio frequency chirp generator 12 is arranged to generate a chirp signal at a frequency w-w +6 with a linear frequency ramp which may extend over a frequency range 8 of 18 MHZ and have an overall pulse length sufficient to encompass the length of the input signal, and the chirp signal is also delivered to the mixer 14 which performs the electronic analogue of the mentioned multiplication and the mixed signals are delivered at the sum frequency, (0+5, (e.g. 200 MHz) to an 0 electro-acoustic interdigital transducer 18 on the surface of a piezoelectric medium 16 so as to generate an acoustic wave whichtravels to the right as viewed in the FIGURE. Such form of transducer and acoustic wave generation are discussed in more detail in US. Pat. application, Ser. No. 190,342 now US. Pat. No. 3,8l6,753, entitled Parametric Acoustic Surface Wave Apparatus to which reference is made for such details.

The RF. chirp signal is also delivered to a time inverter 20 which essentially reverses the slope of its linear frequency ramp so that the chirp frequency is now droo -8. The'time inverter 20 may be an acoustic inverter as described in detail in the mentioned US. Pat.

- application Ser. No. 190,342. Alternatively, the time inverted chirp may be generated by the common technique of spectral inversion of the original chirp. The inverted chirp is applied to another mixer 19 together with a continuous radio frequency signal at (0 from a tunable generator 21, to develop a mixed output at a frequency, ctr-8. This mixed signal is then applied to the opposite end of the piezoelectric medium 16 through another interdigital transducer 22 so to generate an acoustic wave which travels to the left as viewed in the FIGURE and because of such opposite direction of travel, the RF. chirps from the left and right transducers will have equivalent configurations in the piezoelectric medium.

Frequency conservation and phase matching conditions between the two acoustic signals are attained within the piezoelectric medium 16 so that parametric interaction occurs as explained in some detail in the mentioned US. Pat. No. 3,760,l72 and the acoustic energy is extracted by an acoustic detector 24 in the form of plates on the upper and lower surfaces of the piezoelectric medium 16 to provide the convolution of the two signals, which, in turn, as previously mentioned, provides a Fresnel transformation. The convolution operation provides addition of the basic radio frequencies and because of the opposite signal propagation, quadruples the chirp slope, thus providing an output signal at 2w+45. The detector (plate) length is greater than the length occupied by the signal so that the entire signal will undergo the parametric interaction.

The final multiplication is provided by a mixer 28 that combines the convoluted output at frequency 2w+45 with another chirp which can, in the present instance, be readily obtained by quadrupling the frequency with a conventional frequency quadrupler 26 of the generated R.F. input chirp mixed in another mixer 30 with the continuous wave signal from the c.w. radio frequency generator 21 to provide a frequency 4111-1-48. The output of the mixer 28 is then the Fourier Transform of the input signal at a frequency 2m and it is to be particularly observed that such output is obtained in real time.

Various modifications can obviously be made in the structure as described to perform the necessary steps of 3 chirp multiplication, Fresnel transformation (convolution) and final chirp multiplication. For example, the illustrated device utilized acoustic surface waves and the operation can as well be carried out with bulk acoustic waves as described in the mentioned US. Pat. No. 3,760,172. Furthermore, any other form of acoustic convolver can be utilized. Consequently, the foregoing description is not to be considered as limiting and the actual scope of the invention is only to be indicated 1 4 2. Apparatus for transforming an electronic signal according to claim 1 wherein said mixing means constitutes an electronic mixer separate from said piezoelectric medium. 3. Apparatus for transforming an electronic signal according to claim 1 which comprises means for time-inverting said chirp signal, means for generating a c.w. radio frequency signal, means for mixing the time-inverted chirp signal with the c.w. signal, and wherein said transducer means includes a first transducer for applying the mixed electronic signal and said chirp signal to one end of said piezoelectric medium, and a second transducer for applying the mixed inverted chirp signal and c.w. signal to the opposite end of said piezoelectric medium so that the acoustic signals from said transducers propagate in opposite directions. 4. Apparatus for transforming an electronic signal according to claim 1 wherein said detector means constitutes a plate detector having a length greater than that occupied by the signal to be transformed in said piezoelectric medium.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US3760172 *Jun 15, 1970Sep 18, 1973Univ Leland Stanford JuniorMethod of and apparatus for signal processing
US3770949 *Apr 21, 1972Nov 6, 1973Us NavyAcoustic surface wave correlators and convolvers
US3774019 *Sep 20, 1971Nov 20, 1973Sperry Rand CorpCorrelation system with recirculating reference signal for increasing total correlation delay
US3816753 *Oct 18, 1971Jun 11, 1974Univ Leland Stanford JuniorParametric acoustic surface wave apparatus
US3833867 *Oct 23, 1973Sep 3, 1974Sperry Rand CorpAcoustic surface wave convolver with bidirectional amplification
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4005417 *Aug 14, 1975Jan 25, 1977Raytheon CompanyFrequency spectrum analyzer
US4021657 *May 7, 1976May 3, 1977Thomson-CsfSurface elastic wave memory correlator
US4042928 *Mar 31, 1976Aug 16, 1977Esl IncorporatedTechnique of characterizing the nature of a radiation path transfer function by a few constants
US4049958 *Mar 3, 1975Sep 20, 1977Texas Instruments IncorporatedProgramable filter using chirp-Z transform
US4071828 *May 18, 1976Jan 31, 1978The United States Of America As Represented By The Secretary Of The Air ForceSelf synchronizing convolver system
US4115865 *Apr 6, 1977Sep 19, 1978Thomson-CsfHigh-speed correlating device
US4247903 *Jan 8, 1979Jan 27, 1981United Technologies CorporationMonolithic isolated gate FET saw signal processor
US4254388 *Sep 12, 1979Mar 3, 1981Clarion Co., Ltd.Frequency selector apparatus
US4259726 *Nov 3, 1978Mar 31, 1981The United States Of America As Represented By The Secretary Of The NavyDiode array convolver
US4449193 *Apr 23, 1981May 15, 1984Thomson-CsfBidimensional correlation device
US4649392 *Jan 24, 1983Mar 10, 1987Sanders Associates, Inc.Two dimensional transform utilizing ultrasonic dispersive delay line
US5117231 *Sep 22, 1989May 26, 1992Westinghouse Electric Corp.Doppler spectrum synthesizer
DE2938354A1 *Sep 21, 1979Apr 3, 1980Clarion Co LtdFrequenzwaehlvorrichtung
Classifications
U.S. Classification708/821, 324/76.23, 333/154, 324/76.22, 333/193
International ClassificationG06G7/00, G06G7/195
Cooperative ClassificationG06G7/195
European ClassificationG06G7/195