DE2549920C3 - Device for processing an electrical signal using elastic surface waves - Google Patents

Description

characterized by reading devices (2, 3; 5, 6; 7, 8) which are designed such that they excite at least one elastic or electromagnetic surface wave, which is a third signal represents and which interacts with the areas to produce a resulting elastic or surface electromagnetic wave, which is the convolution or correlation function of the signal represented by the areas with the third signa; represents.

2. Apparatus according to claim I _1, characterized in that the wave corresponding to the third signal is an elastic surface wave whose angular frequency is equal to the angular frequency which corresponds to the spatial period of the regions, the resulting wave being an electromagnetic surface wave generated by means of the devices (2,3) is obtained for exciting an electromagnetic wave.

3. Device according to claim I, characterized in that that the wave corresponding to the third signal is a surface electromagnetic wave, whose angular frequency is equal to the angular frequency that corresponds to the spatial period of the areas, wherein the resulting wave is an elastic surface wave generated either by means of the Initial signal transmitter (5, 6) or by means of the devices (2, 3) for exciting an electromagnetic Wave is won.

4. Device according to one of claims 1 to 3, characterized in that the second and third Signals have the same angular frequency as the initial signal.

5. Device according to one of claims I to 4, characterized in that the third signal is pulsed.

6. Apparatus according to claim I, characterized in that the reading devices (5, 6; 7, 8) two elastic surface wave !! excite whose angular frequencies are different from that of the initial signal and the second signal are different, with the resulting surface wave being one of those forming them Waves have different angular frequencies and an amplitude, which is the integral over the Interaction zone of the product of the amplitudes of the signal represented by the areas and the both sent by the reading devices

Represents signals

7. Device according to one of claims 1 to 3, characterized in that the second and third Signals are conjugated.

8. Apparatus according to claim 7, 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 start signal.

9. Device according to one of claims 1 to 8, characterized in that the devices for Exciting a surface electromagnetic wave a first electrode (3), which is located in the vicinity of the Surface or on the surface of the substrate (1) attached without contact with the transducer (5; 6) is, and a second electrode (2) included on a side of the substrate (1) opposite the first Electrode (3) is arranged, the second signal being applied to these electrodes (2,3).

10. Device according to one of claims 1 to 9, characterized in that the devices for Excitation of an electromagnetic surface wave, two interdigitally arranged metallic Contain combs (20,30) which are applied to the surface of the substrate (1) and between them the surface electromagnetic wave is generated by applying the second signal.

The invention relates to a device of the type specified in the preamble of claim 1 for processing an electrical signal using elastic surface waves.

Various devices have been proposed in which the interactions between elastic waves, d. ii. between pressure or shear vibration movements of different frequencies for the purpose of amplitude and frequency analysis of images without memory effect or further Interactions between elastic waves and electromagnetic waves used for storage will. The following can be mentioned as examples:

Devices in which a series of unit cells is used, each consisting of a capacitor and a solid-state diode, which are arranged in series and the insulator of the capacitor is provided with piezoelectricity; these devices form, for example, the subject of German patent application P 24 59 671.2;
Devices in which the distribution of the originating piezoelectric potential is stored, which appears during the non-linear interaction between elastic wave and electromagnetic wave, this storage either in the piezoelectric material itself or in additional layers, as is, for example, in the German patent application P 25 49 848.0-53 is proposed.

The object of the invention is to provide a device of the type specified in the preamble of claim 1 to train them to process various electrical signals supplied to them accordingly their type, duration and form are permitted.

This object is achieved according to the invention by the features indicated in the characterizing part of claim 1 Features solved

The device according to the invention enables electrical signals to be processed by correlation or convolution. This processing takes place by means of a previous storage of an intermediate signal, carried out according to any known method, which results from the nonlinear interaction between an initial signal converted into an elastic surface wave and an electromagnetic or elastic surface wave Interaction between the stored intermediate signal and an electromagnetic or an elastic surface wave takes place

Several embodiments of the invention are described below with reference to the drawings described in more detail. It shows

F i g. 1 shows an embodiment of the device according to of the invention that

Fig. 2, 3 and 5 curves showing the shape of the Device according to the invention show applied electrical signals,

4 shows an embodiment of the function of storing information representing "areas",

6 schematically shows a further embodiment the device according to the invention, and

F i g. 7 schematically shows yet another embodiment of the device from FIG. 1.

In these various figures , on the one hand, the same reference numerals relate to the same parts and, on the other hand, for better clarity of the drawings, the device and the signals have been shown on an arbitrary and overall enlarged scale.

In Fig. 1 are shown:

A piezoelectric substrate 1, for example in the form of a plate, which consists for example of lithium niobate LJNbO3 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, applied to the substrate 1 at the outer ends of the wafer and emitting or receiving elastic waves propagating on the surface of the substrate;

- Signal storage devices which are shown in FIG. 1 are symbolically represented by a layer 4, which is applied to the substrate 1 between the transducers S and 6 and has a double function: on the one hand it serves to isolate and on the other hand to hold the "areas", and one embodiment of which is below is specified;

Devices for transmitting and receiving an electromagnetic wave, which consist of two electrodes 2, 3, of which the electrode 2 is arranged on the side of the substrate 1 facing away from the transducers and the electrode 3 is arranged on the layer 4

With regard to the mode of operation of the device, a distinction is made between a storage phase (i.e. the Writing) and a phase of reading the signals.

The storage takes place in this structure and as an example that is not to be understood as a limitation

55 the statements in the above-mentioned German patent application P 25 49 848.0-53. During this storage phase, one of the transducers arranged on the substrate 1, for example the transducer 5, is excited by an electrical signal and delivers an elastic surface wave of the following form:

S = Au - j cos (f ȣ - kx) ,

where A is the amplitude of the signal, ω is its angular frequency, Ar 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 ο is assumed to be in the center of the interaction zone, which is one length L hat An example of such a signal is shown in FIG. 2 specified.

After the entire signal 5 has been converted into an elastic surface wave ν, -.- rden, a pulse T, which compared to the duration of the signal 5 has a short duration and the same angular frequency ω and in Fig. 3 is applied to electrodes 2 and 3

This pulse generated on the entire surface of the piezoelectric substrate 2, which is below the Electrode 3 is an electromagnetic surface wave of the following form:

T = B (I) · cos ("t,

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

AU- -λ ■ BU) ■ cos \ _ ", t ± (" .t - kx) '].

In principle, this interaction induces elastic surface waves, which are characterized by the value pairs (angular frequency, wave vector) which result from the sum and the difference of the value pairs that characterize the interacting waves . Here, however, we consider the expression of the phase term in its purest form, which corresponds to the difference: that is the only term that is suitable for storage, since it is independent of the time t during the duration of the interaction and is solely a function of the abscissa χ .

Since the electromagnetic surface wave T is not necessarily of short duration in the present case, the interaction between the two waves Sund T is not very short and, if the substrate 1 responds with such a time constant that the momentary interactions are integrated, one obtains χ at an abscissa point the result of the following integral:

60 ft (A) =

· Df

cos kx

where (-) is the total interaction time, or:

-V cos / ix

where C is the correlation function of the signals Sund and λ 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. Throughout the zone of interaction gives the values of the correlation functions between

and are spatially modulated by the factor cos kx.

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

As an example, FIG. FIG. 4 shows an embodiment of the layer 4 for retaining the areas which the Present information.

F i g. 4 again shows the substrate 1, which is covered by the electrodes 2 and 3. where the electrode 3 from the substrate through a thin layer of air 40 and one with the reference number 4 in its entirety designated arrangement of layers is separated.

The substrate 1 consists of a piezoelectric material such as lithium niobate or LiNbOj Lead zirconate titanate PZT. The intermediate space 40 has the task of closing the layers 4 away from the substrate 1 separate so that the elastic waves can freely propagate on the surface of the substrate.

The layer arrangement 4 sequentially and outwardly consists of: a silicon oxide layer 41; a layer 42 of silicon or of an amorphous semiconductor; a metallic electrode 43, which via a connection 45 with a bias potential! (not shown) is connected; and an insulating layer 44.

When the silicon layer 42 is N-conductive, it is used to store the regions. the electrode 43 brought to a positive potential; majority carrier depletion is then created in silicon layer 42 . There is a certain threshold potential difference between the two sides of the dielectric 41, above which minority charge carriers (in this example positive majority charge carriers) in the silicon layer 42 collect at the interface 41-42 . This phenomenon is exploited to store the areas in that the electrode 43 is (positively) biased in such a way that when the surface of the substrate 1 is at a uniform potential, it is brought just below the threshold potential. If the distribution of the potential on the surface of the substrate 1 represents a positive region, 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. In contrast, in the face of a negative area, the potential difference between the two sides of the layer 41 becomes greater than the threshold value and there is an accumulation of (positive) minority charge carriers at the interface 41-42 , the (negative) potential of the area concerned and, more generally , the distribution of the potential; ίο fixed on the surface of the substrate 1, which persists in this way after the termination of the non-linear interaction which produced it.

According to a modification of the device, whereby the storage phase is still considered, can at the same time as the converter 5 through there? Signal S of the transducer 6 can be excited by a signal U , which then generates an elastic surface wave fnlcrpnripr form:

U = Dft + * YcOS (m / f kx).

The stored signal will then be:

■ cos 2 kx ,

ι ο

that is, the correlation
C.

of the two signals 5 and U, which are still spatially modulated by the factor cos 2 kx but are compressed by a factor of 2 in relation to the previous case η.

In both cases the following is achieved:

The correlation of two signals, for example of a known signal (T or U) with an unknown signal S; ⁴ "- the storage not only of the start signal 5

for example, the Fourier transform of the initial signal can be 5 if the signal T is a linear frequency modulated signal such as that in FIG. 5: it is a signal whose frequency increases linearly from a minimum f _m at a point in time 4> to a maximum fa at a point in time fi, the amplitude being modulated by the signal B.

For the reading phase, either an elastic or an electromagnetic surface wave is excited, which interacts with the stored signal Q to form another electromagnetic or elastic wave

ί Form 5 surface wave that can be read.

According to a first variant, with the aid of one of the transducers 5 or 6, an elastic surface wave is generated which has the same angular frequency as that of the spatial modulation of the stored signal

bo corresponds to If the stored signal is the signal Q , the elastic surface wave used for reading has the following form:

-K)

1 · cos {mt ± kx)

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

The non-linear interaction of the signals / ι and H results in the following signal L \:

L ₂ =

COS 2 rnt

i ^; i? «m that is retained for the phase element which, according to the converter for emitting the signal /, corresponds to either the difference or the sum.

The signal / _ .. which is available at the terminals of the F.lektroclen 2 and 3 represents - modulated by the term cos (/) f - either a correlation or a convolution of the signals C and R , according to the sign of the signal R.

When the stored signal is the signal

is. the elastic surface wave used for reading has the following form:

• cos (2 ο / i 2Aa).

The non-linear interaction of the signals J ₂ and C: results in the following signal L ₂ :

L ₁

A "" Y "

■ COS eif

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

According to a second variant, an electromagnetic surface wave which has the angular frequency that corresponds to the spatial modulation of the stored signal Q is generated by means of the electrodes 2 and 3. In an analogous manner, one thus has a surface electromagnetic wave ATi for reading. When the stored signal is the signal

O, = c ( ^X \ - cos Av
V ϊ J

is. is applicable:

K \ = P (t) ■ coswf.

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

When the stored signal is the signal

Qi =

a surface electromagnetic wave is generated for reading

K ₂ = P (t) ■ cos2ü) f,

whose non-linear interaction with the signal Q _{2 generates} a signal M ₂ in

cos (2 eof ± 2kx)

results that is available at one of the transducers 6 or 5 and is analogous to the signal M \ , except for the compression factor.

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

It can be seen from the expressions obtained for the output signal that the device is different

Processing is allowed according to the type, duration and form of the signals 5, Γ or U, and / which are fed to it.

In particular if the signal / ι (t) is the conjugate signal of the signal 7 "(± /, list, that is, if the signal T is the impulse response of the filter matched to the signal / i, so that writing can be carried out

the restoration of the signal .9 is achieved with a high degree of efficiency, since the processing involves integrating the entire interaction zone. In the second case, when J ₂ (t) is the conjugate signal of the signal i / time compressed by a factor of two, that is

J ₁ (O = U (± 2 0

ι_- · ι, _ _t _ _i "_" _ IU - - n —-j: ~ ._ _ J: _ Mf 1 ..

iinait man until ut-iist-itn, ii ut.uiii ^ uiigt.11 uit. TTii.ut_i production of the signal S. The signals /, T and t / can, for example, be linear frequency-modulated pulses.

In a third variant of the reading phase, two surface waves (elastic or electromagnetic) are generated whose angular frequencies are different from that corresponding to the spatial modulation of the stored signal Q , which enables an output signal to be obtained whose carrier frequency is different from that of the signals used for writing is. For this purpose, the structure shown in FIG. 6 is used, which differs from that of FIG. 1 differs only by the addition of two electromechanical transducers 7 and 8 at the outer ends of the substrate I next to the transducers 5 and 6, respectively. These transducers 7 and 8 thus have a pitch which is different from that of the transducers 5 and 6.

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

They have the following form:

N ₁ = D, (t - ^Λ V cos | e "/ - Α ·, χ)

N ₂ = D ₂ (t ± ^X Y cosie ^ f ± A- ₂ A).

If the angular frequencies wi and ω ₂ satisfy the equality of the wave numbers, that is:

Ai ± Ar ₂ = ± k or ± 2 Ar,

the interaction delivers a signal of the following form:

■ COS ((«

which can be removed from electrodes 2 and 3. Various processings are achieved according to the kind, duration and shape of the signals Ni 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 as amplitude

If the two signals Ni and N _{2 have} constant amplitudes D \ and D ₂ , the following is obtained

Output signal

result in the

d.v.

Finally, if the amplitude Di is constant and the amplitude Eh is the conjugate amplitude of the amplitude ß of the write signal Γ, the restoration of the amplitude A of the initial signal 5. ίο is obtained at the output

Fig. 7 illustrates another embodiment of electrodes 2 and 3 of Fig. I, for example, a change in frequency between the input signal .S 'and the output signal or enables a filtering process, r,

F i g. 7 again shows the substrate I and the transducers 5 and 6 at the ends of the substrate. The function of electrodes 2 and 3 of FIG. 1 is implemented here by two combs 2ö and 3ö, which are arranged interdigitally, have a pitch ρ and are arranged in the middle of the substrate> n t parallel to the transducers 5 and 6, the combs 20 and 30 being connected to the generator 9 are. The combs 20 and 30 can be arranged directly on the substrate I in this embodiment. > -,

As before, the interaction of the elastic surface wave (ω, k), which is transmitted, for example, by the transducer 5 and represents the signal ^, with the electromagnetic surface wave, which represents the signal T m applied to the combs 20 and 30 and is characterized by a wave number which is no longer negligible compared to k.

but equal to "^, where ρ is the pitch of the ridges 20

and 30 denotes. The interaction has the η Generation of a time-independent potential area

marked and stored on the substrate,

A second interaction is provided between this area and an elastic surface wave (ίοι, k \) of the angular frequency ωι and the wave number Ατι. whereby

gill and where ν is the speed of propagation of the elastic waves on the surface of the substrate. This second interaction has the creation of an elastic surface wave of the shape

result, which is only progressive if for the wavenumber

K = k _t Ik t ² " ^{7 the} following applies: K = '"'.
P>'

in which case a signal is obtained at one of the transducers, the angular frequency of which has been modified and has become equal to the angular frequency W _{1 of} the elastic read wave.

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

llicr / u 3 IShilt drawing

Claims (1)

Patent claims: 1. Apparatus for processing an electrical signal (initial signal) using of elastic surface waves, consisting of: - a piezoelectric substrate; - at least one electromechanical converter, which receives the initial signal and propagates along the substrate elastic Emits surface waves; - Means for exciting elastic or electromagnetic surface waves, which a represent the second signal and the elastic surface waves mentioned in Interact to form spatially different and periodic areas, which represent the correlation function of the initial signal and the second signal; - Devices for holding the areas: