DE2549920A1 - SYSTEM FOR PROCESSING ELECTRICAL SIGNALS USING ELASTIC SURFACE WAVES - Google Patents

Description

75008 PARIS / France

Our reference: T 1882

System for processing electrical signals using elastic surface waves

The invention relates to a system for processing electrical signals using the non-linear Interactions between elastic surface waves or between elastic waves and electromagnetic waves Waves.

In particular, it implements the processing of signals by means of correlation or, above all, by means of convolution a storage of these signals and by means of their interactions.

Various devices have already been proposed in which the interactions between elastic Waves, i.e. between pressure or shear vibration movements of different frequencies for the purpose of Amplitude and frequency analysis of images without storage

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ORIGINAL INSPECTED

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effect or further interactions between elastic Waves and electromagnetic waves are used for storage. The following can be mentioned as examples:

- the devices in which a series of elementary cells is used, each consisting of a capacitor and consist of a solid state diode which are arranged in series and wherein the insulator of the capacitor is equipped with piezoelectricity. These devices are, for example, the subject of German patent application P 24 59 671.2;

- the devices in which the distribution of the piezoelectric potential of origin is stored which occurs during the nonlinear interaction between elastic wave and electromagnetic wave appears, with this storage either in the piezoelectric material itself or in additional Layers takes place, as proposed, for example, in the German patent application "Information storage device", which claims the priority of French patent application No. 74.37078 was filed at the same time.

The invention provides a system for processing a Signal through correlation or, above all, convolution. This processing takes place by means of a corresponding one any known method carried out previous storage of an intermediate signal, which results from the non-linear interaction between an initial signal converted into an elastic surface wave and a electromagnetic or elastic wave results. An output signal is obtained by a second non-linear interaction between the stored intermediate signal and an electromagnetic wave or an elastic surface wave takes place.

Several embodiments of the invention are shown in FIGS

^609822/0657 ORlGtNAL! NSPECTEO

Drawings shown and are described in more detail below. Show it:

Fig. 1 shows an embodiment of the system according to

the invention,

Figs. 2, 3

and 5 curves showing the shape of the system

according to the invention · supplied electrical Signals show

Fig. 4 shows an embodiment of the function of

Storage of "areas" representing information,

6 schematically shows a further embodiment

form of the system according to the invention, and

Fig. 7 shows schematically yet another Aus

implementation of the system of FIG. 1.

In these various figures, on the one hand, the same reference numerals relate to the same parts and, on the other hand are, for the sake of clarity of the drawings, the system and the signals in an arbitrary and overall manner enlarged scale has been shown.

In Fig. 1 are shown:

a piezoelectric substrate 1, for example in the form of a plate, which _{consists for example of lithium niobate LiNbO 3} and on the surface of which elastic waves can propagate;

- two electromechanical transducers 5 and 6, for example of the type with interdigitally arranged combs, which are applied to the substrate 1 at the outer ends of the plate and are located on the surface de3

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Transmit or receive elastic waves propagating on the substrate;

- Signal storage devices, which are symbolically represented in Fig. 1 by a layer 4, which is based on the Substrate 1 is applied between the transducers 5 and 6 and has a double function: on the one hand it serves they for isolation and on the other hand for holding the "areas", and one embodiment of which continues is given below;

- Devices for transmitting and receiving an electromagnetic Wave consisting of two electrodes 2, 3, of which electrode 2 is on top of that of the transducers remote side of the substrate 1 and the electrode 3 is arranged on the layer 4.

Regarding the mode of operation of the system, a distinction is made between a phase of storage (i.e. writing) and a phase of reading the signals.

The storage takes place in this structure and as not Example to be understood as a restriction according to the explanations in the above-mentioned German patent application "Information Storage Device".

It is thus remembered that during this ■ storage phase one of the transducers arranged on the substrate 1, for example the transducer 5, by an electrical one Signal is excited and delivers an elastic wave of the following form:

S = A (t - |). cos (cot - kx)

where A is the amplitude of the signal, ω is its angular frequency, k is its wave number, ν is the speed of propagation of the elastic waves on the surface of the substrate 1 and Ox is the direction of propagation of these waves and where the origin 0 is assumed in the center of the interaction zone which has a length L. An example for "

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such a signal is indicated in FIG.

After the entire signal S is converted into an elastic wave, a pulse T becomes the opposite the duration of the signal S has a short duration and the same angular frequency ω and is shown in FIG. 3 the electrodes 2 and 3 applied.

This pulse is generated on the entire surface of the piezoelectric substrate 1, which is below the electrode is an electromagnetic wave of the following form:

T = B (t) .cos ut

which interacts in a non-linear manner with the field created by the piezoelectric effect from the grid of mechanical stresses due to the elastic wave S. The result of this Momentary interaction at a point χ is proportional to:

A (t - ~). B (t). cos [(jt - (cot - kx)]

In principle, this interaction induces elastic surface waves, which are generated by the value pairs (angular frequency, Wave vector), which result from the sum and the difference of the value pairs that identify the interacting waves. However, one only considers the expression of the phase element here, that corresponds to the difference: that is the only link that can be used for storage suitable, since it is independently and solely a function of the abscissa during the duration of the interaction of the time t χ is.

Since the electromagnetic wave T is not necessarily of short duration in the present case, the Interaction between the two waves S and T does not

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very briefly and when the substrate 1 responds with such a time constant that an integration of the momentary interactions takes place, the result of the following integral is obtained at an abscissa point χ:

Q ₁ (x) = I / A (t - |). B (t). German J. cos kx

where θ is the total interaction time, or: Q ₁ (x) = α. C (-). cos kx

where C is the correlation function of the signals S and T and α is a proportionality factor.

To simplify writing, this factor is set equal to one in the following.

At the end of the non-linear interaction, there is thus a potential state at an abscissa point χ which is proportional to the value of the correlation function. The values of the correlation functions which lie between C (- -TjT-) and C {-j-) and are spatially modulated by the factor cos kx are obtained in the entire .. interaction zone.

This potential state, which represents the correlation function C, is represented on the substrate 1 by the layer 4 stored, of which it has been said above that symbolically all known devices for fixing the Represents the surface potential state of the substrate 1 » These facilities are specified, for example, in the above-mentioned German patent applications and can from modifying either the surface charge or the number of trapped electrons one homogeneous semiconductors or the stored charges in pn-transitions and associated capacitors. The layer 4 is in reality either integrated into the substrate 1 or consists of additional layers, which generally from the substrate 1 by a

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2 B 4 9 9? O

a thin layer of air are separated.

As an example, Fig. 4 shows an embodiment of the layer 4 to record the areas that represent the information,

Fig. 4 again shows the substrate 1, which by the Electrodes 2 and 3 is covered, the electrode 3 being separated from the substrate by a thin layer of air 40 and an arrangement of layers designated in its entirety by the reference number 4.

The substrate 1 consists of a piezoelectric material such as lithium niobate LiNbO-, or lead-zirconate-titanate PZT. The intermediate space 40 has the task of separating the layers 4 from the substrate 1 so that the elastic waves can propagate freely on the surface of the substrate.

The layer arrangement 4 consists successively and outwardly of: a silicon oxide layer 41; one layer made of silicon or an amorphous semiconductor; a metallic electrode 43, which has a connection 45 with a bias potential (not shown) is connected; and an insulating layer 44.

To store the regions, if the silicon layer 42 is N-conductive, the electrode 43 is at a positive potential brought; a depletion of the majority charge η is then generated in the silicon layer 42. It there is a certain threshold potential difference between the two sides of the dielectric 41, above which minority charge carriers (in this example positive minority charge carriers) in the silicon layer 42 accumulate at the interface 41-42. This phenomenon is used to save the areas by using the

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Electrode 43 is biased (positive) such that if the surface of the substrate 1 is at a uniform potential, it is just below the threshold potential is brought. If the distribution of the potential on the surface of the substrate 1 represents a positive area, the potential difference between the two sides of the layer 41 remains below the threshold value and there is no change in occupation of the charge carriers. Against this, in the face of a negative area the potential difference between the two sides of the layer 41 is greater than the threshold value and it finds an accumulation of (positive) minority charge carriers takes place at the interface 41-42, which represents the (negative) potential of the area concerned and, more generally, the distribution of the potential on the surface of the substrate 1 fixed that this way after the termination of the nonlinear interaction from which it is generated has been, persists.

According to a modification of the system, where-always nor the storage phase is considered, can be excited at the same time as the converter 5 by the signal S of the converter 6 by a signal U, which then a generated elastic wave of the following form:

U = D (t + ^) ♦ cos (Ut + kx)

The stored signal will then be;

Q ₂ (x) = I / A (t - ^). D (t + ^). German J. cos 2 kx

2x

that is, the correlation C (-) of the two signals S and U, which is still spatially modulated by the factor cos 2 kx, but by a factor of 2 in relation to the previous one Case are compressed.

In both cases the following is achieved:

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the correlation of two signals, for example a known signal (T or U) with an unknown one Signal S;

- The storage not only of the initial signal S, but also of a coded signal Q, which for example can be the Fourier transform of the initial signal S if the signal T is a linear frequency modulated signal is, such as the signal shown in Fig. 5: it is a signal whose frequency is linear from

a minimum f at a point in time t up to a maxim ^ o

mum f increases at a point in time t * , the amplitude being modulated by the signal B.

Either an elastic or an electromagnetic phase is used for the reading phase Excited wave that interacts with the stored signal Q to form another electromagnetic wave or to form elastic wave that can be read.

According to a first variant, with the aid of one of the transducers 5 or 6, an elastic wave is generated which has the same angular frequency as that which corresponds to the spatial modulation of the stored signal. If the stored signal is the signal Q ₁ , the elastic wave used for reading has the following form:

J ₁ = R (t - ^). cos («t - kx)

and, depending on whether the signal is fed to converter 6 or 5, the sign plus or the sign is obtained Minus.

The non-linear interaction of the signals J ₁ and Q ₁ results in the following signal L ₁ :

₁ = [ f C φ. R (t £ S). dx j .-

COS

by maintaining that for the phase element that corresponds to the converter for emitting the signal J,

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? B 4 9 9 2 O

equals neither the difference nor the sum.

The signal L ₁ , which is available at the terminals of the electrodes 2 and 3, is - modulated by the term cos cot - either a correlation or a convolution of the signals C and R, according to the sign of the signal R.

2x

If the stored signal has the signal Q ₂ (x) = C (--—). cos 2kx

the elastic wave used for reading has the following form:

J ₂ = R (t - ~). cos (2 «t-2kx).

The non-linear interaction of the signals J ~ and Q "results in the following signal L ₃ :

L ₂ = Γ J C (- ^ f). R (t - - ^). dx J. cos 2 wt

which is analogous to the signal L ₁ , except for the compression by a factor of 2.

According to a second variant, the electrodes 2 and 3 generate an electromagnetic wave which has the angular frequency that corresponds to the spatial modulation of the stored signal Q. In an analogous manner, one thus has an electromagnetic wave K ₁ for reading. When the stored signal is the signal
Q ₁ = C (-). cos kx, the following applies:

K ₁ = P (t). cos ω t

The interaction of these signals results in a signal M ₁ in cos (cot - kx), which is available at one of the transducers 5 or 6.

When the stored signal is the signal

2x
Q ₂ - C (tt ~) · cos 2 kx, an electromagnetic wave K ₂ = P (t) is generated for reading. cos 2 ctft, whose

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Nonlinear interaction with the signal Q ₀ results in a signal M ₂ in cos (2 ω t − 2kx), which is available at one of the transducers 6 or 5 and _{is analogous to the signal M 1} , except for the compression factor.

It should be noted that in these two variants the signals obtained for a given stored signal Q. L or M are identical.

Look at the expressions obtained for the output signal that the device perform various processings according to the type, duration and shape of the signals S, T or U, and J allowed to be fed to it.

In particular, if the signal J ₁ (t) is the conjugate signal of the signal T (- t), that is, if the signal T is the impulse response of the _{filter matched to the signal J 1} , so that J ₁ (t) = can be written T (+ t), the restoration of the signal S is achieved with good efficiency, since the processing is carried out on the entire interaction zone, in the second case when J ₂ (t) is the conjugate signal of the If the signal U is compressed by a factor of two, _{i.e. J 2} (t) = U (-2t), the restoration of the signal S is obtained under the same conditions. The signals J, T and U can be, for example, linearly frequency-modulated pulses.

In a third variant of the reading phase, two waves (elastic or electromagnetic) are generated, their circular frequencies are different from that corresponding to the spatial modulation of the stored signal Q, what allows an output signal to be obtained whose carrier frequency differs from that of the signals used for writing is. For this purpose, one uses the one shown in FIG. 6

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The structure shown differs from that of FIG. 1 only by the addition of two electromechanical transducers 7 and 8 at the outer ends of the substrate 1 next to the transducers 5 and 6, respectively. This converter 7 and 8 thus have a pitch that is different from that of transducers 5 and 6.

For example, two elastic waves are used for the Read sent either from transducers 5 and 6 or from transducers 7 and 5 in the same direction.

They have the following form:

^{= D} 1 (t - v ") . COS (ι ^W 1 ^fc - ^k 1 χ) = ^D 2 (t . COS ( ω- t + k ₂ X)

If the angular frequencies OJ., And (^ satisfy the equality of the wave numbers, that is:

- k ₂ = - k or -2k,

so the interaction delivers a signal of the following form:

/ c φ. D ₁ (t - £). D ₂ (t - ^) dx I. cos (O ₁ -. «

which can be removed from electrodes 2 and 3. Various processing is achieved according to the type, duration and shape of the signals N ₁ and N _2. In particular, if the amplitude D- is constant and if the amplitude D _{2 is} a short rectangular pulse, the output signal has the correlation function C (-) as the amplitude. If the two signals N ₁ and N _{9 have} constant amplitudes D ₁ and D2, the following output signal is obtained

C (?). dx

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Finally, if the amplitude D _{1 is} constant and the amplitude D _{2 is} the conjugate amplitude of the amplitude B of the write signal T, the restoration of the amplitude A of the initial signal S is obtained at the output.

FIG. 7 illustrates another embodiment of the electrodes 2 and 3 of FIG. 1, for example, a Changing the frequency between the input signal S and the output signal or a filtering process makes possible.

Fig. 7 again shows the substrate 1 and the transducers 5 and 6 at the ends of the substrate. The function of the electrodes 2 and 3 of FIG. 1 is realized here by two combs 20 and 30 which are arranged interdigitally, one Have pitch ρ and are arranged in the center of the substrate 1 parallel to the transducers 5 and 6, the combs 20 and 30 are connected to the generator 9. The combs 20 and 30 can in this embodiment directly be arranged on the substrate 1.

As before, the interaction of the signals emitted, for example, by the transducer 5 and representing the signal S is ensured elastic surface wave (to, k) with the electromagnetic wave that is transmitted to the combs 20 and 30 represents the applied signal T and is characterized by a wave number which is no longer negligible compared to k is, but is equal to -, where ρ denotes the pitch of the ridges 20 and 30. The interaction has the generation of a time-independent potential

+ 2tt

area, which is marked by (o, k - - ^) and which is stored on the substrate.

A second interaction is provided between this area and an elastic surface wave (CO ₁ , k ₁ ) of the angular frequency co- and the wave number k-, where k- = —— and where ν is the speed of propagation

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of elastic waves on the surface of the substrate. This second interaction has the creation of a elastic wave of the form (<*? .., k., - k - --— result,

ι ι ρ

which is only progressive if for the wave number K = k ₁ ί k - ^ - applies: K = -, in which case one receives a signal at one of the transducers whose angular frequency is modified and equal to the angular frequency CO .. the elastic Has become a wave of readings.

The system according to the invention can be used in particular in the manufacture of computers in which the Operations are carried out by processing elastic waves.

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Claims (12)

Claims t (JT) System for processing an electrical signal using elastic surface waves, with: - a piezoelectric substrate; - At least one electromechanical transducer that receives the initial signal and on the surface of the substrate emits elastic waves; - Devices for exciting an elastic or electromagnetic Wave which corresponds to a second signal and which interacts with the elastic waves occurs to form spatially distinct and periodic zones or "areas" which the correlation function represent the initial signal and the second signal; - Devices for holding the areas; characterized by reading devices which at least excite an elastic or electromagnetic wave that corresponds to a third signal and that corresponds to the areas interacts to form a resulting elastic or electromagnetic wave, which is the convolution or correlation function of the signal represented by the areas with the third Signal represents. 2. System according to claim 1, characterized in that the second signal corresponding to a wave electromagnetic wave is. 3. System according to claim 1, characterized in that the second signal corresponding to a wave is elastic surface wave. 4. System according to claim 2 or 3, characterized in that the wave corresponding to the third signal is an elastic surface wave whose circular fre- 609822/0657 frequency is equal to the angular frequency, that of the spatial Period of the ranges corresponds to the resulting wave being an electromagnetic wave which is obtained by means of the means for exciting an electromagnetic wave. 5. System according to claim 2 or 3, characterized in that that the wave corresponding to the third signal is an electromagnetic wave whose angular frequency is equal to the angular frequency that the corresponds to the spatial period of the areas, where if the read wave is an elastic surface wave is, the resulting wave is a surface elastic wave generated either by means of the initial signal transducer or is obtained by means of the devices for exciting an elastic wave. 6. System according to any one of claims 1 to 5, characterized characterized in that the second and third signals have the same angular frequency as the initial signal. 7. System according to one of claims 1 to 6, characterized in that the third signal is pulse-shaped is. 8. System according to claim 2 or 3, characterized in that that the reading devices excite two elastic surface waves whose circular frequencies of the of the initial signal and the second signal are different, the resulting wave being one of the previous ones has different angular frequency and an amplitude, which is the integral over the interaction zone the product of the amplitudes of the signal represented by the regions and that by the readers represents the two signals sent out. 6 09822/0657 9. System according to any one of claims 1 to 5, characterized in that the second and third signals are conjugated. 10. System according to claim 9, characterized in that the second signal is a linearly frequency-modulated Signal and that the signal represented by the areas is the Fourier transform of the initial signal is. 11. System according to one of claims 1 to 10, characterized in that the devices for exciting an electromagnetic wave a first electrode that is near the surface or on the surface of the substrate is attached without contact with the transducer, and contain a second electrode, the is arranged on one side of the substrate opposite the first electrode, with electrodes on this the second signal is applied. 12. System according to one of claims 1 to 11, characterized characterized in that the means for exciting an electromagnetic wave are two interdigitally arranged contain metallic combs that are applied to the surface of the substrate and between which the electromagnetic wave is generated by applying the second signal. 609822/0657 Blank page