CA1089083A - Acoustic surface wave devices - Google Patents
Acoustic surface wave devicesInfo
- Publication number
- CA1089083A CA1089083A CA258,899A CA258899A CA1089083A CA 1089083 A CA1089083 A CA 1089083A CA 258899 A CA258899 A CA 258899A CA 1089083 A CA1089083 A CA 1089083A
- Authority
- CA
- Canada
- Prior art keywords
- transducer
- electrodes
- acoustic surface
- surface wave
- envelope
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
- H03H9/46—Filters
- H03H9/64—Filters using surface acoustic waves
- H03H9/6489—Compensation of undesirable effects
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
- H03H9/02—Details
- H03H9/02535—Details of surface acoustic wave devices
- H03H9/02818—Means for compensation or elimination of undesirable effects
- H03H9/02858—Means for compensation or elimination of undesirable effects of wave front distortion
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
- H03H9/02—Details
- H03H9/125—Driving means, e.g. electrodes, coils
- H03H9/145—Driving means, e.g. electrodes, coils for networks using surface acoustic waves
- H03H9/14517—Means for weighting
- H03H9/1452—Means for weighting by finger overlap length, apodisation
Landscapes
- Physics & Mathematics (AREA)
- Acoustics & Sound (AREA)
- Surface Acoustic Wave Elements And Circuit Networks Thereof (AREA)
Abstract
ABSTRACT:
A length-weighted interdigital trans-ducer has bus bar shaped to follow the overlap envelope. Conductive areas are provided outside the envelope and within the aperture to compen-sate for wavefront distortion.
A length-weighted interdigital trans-ducer has bus bar shaped to follow the overlap envelope. Conductive areas are provided outside the envelope and within the aperture to compen-sate for wavefront distortion.
Description
lV~9~3 PHB 32,514 This invention relates to acoustic surface-wave ;
devices.
The use of acoustic surface waves has enabled -devices, such as frequency selective filters, to be manu-factured which are small, compact and are moreover compa-tible with integrated circuit manufacturing techniques. ~;
Such devices enable difficulties such as bulk and manufact-uring cost associated with the provision of inductors to be avoided.
An acoustic surface-wave filter is commonly formed `~ by a thin wafer of piezoelectric material on one surface of -~
which a launching and a receiving transducer are arranged respectively to launch and to receive an acoustic surface '!'~ wave propagating over the surface. Each transducer normally - ~ 15 comprises an interdigital array of strip electrodes, the arrays being formed, for examplei by a photolighographic process from a layer of a suitable metal deposited on the~
surface of the wafer.~ ~
The frequency response of the filter is determined 20 ~ by the number, spacing and d~imensional configuration of the electrodes making up each transducer. For convenlence of computation, a mathematical model of the array is consider-.
ed~1n~which~each e~lectrode i~s regarded as representing anindividual~acoust~ic~wave~source~and;the results~ obtained -~25 ~ from this mode1 are found~ to~be generally satisfactory~in -~
.,-:
. : ~:
:, : . . . ~ -~LQ8~083 PHB 32514 ~ ~
'.':', '-' ' practice for design purposes. By employing techniques of Fourier synthetis and computer optimisat;on on this mathe-matical model, a suitable relative distribution of magni-tude and spacing of such sources in the launching and receiving transducer arrays can be determined which can prov~de a good approximation to a desired band-pass response. The spacing of the launching and receiving transducers along the line of propagation of the acoustic surface waves will introduce a delay in the signal path;
however, in many applications such a delay is not im-portant or can be allowed for. For example, in the case of an intermediate frequency filter for a television receiver, since the entire received signal receîves the same delay, this delay is simply equivalent to displacing the receiving aer;al further from the transmitter.
. ;
-o ~ ~ ~ Alternativel`y, this property of the -devi~ce~can be employed to provide a desired delay. ~ ~-Within an interdigltal array acoustic surface wave transducer, the electrodes partially reflect ~ acoustic surface waves and are also caused by the acoustic surface waves to generate an electrical signal and reradiate. These~reflections and re-radiations, which~can together~be~called "interactions" will be additive in a conventiona;l transducer having its 25 ~ ~ electrodes~at an~effectlve;spaclng of half a wavelength of acoustic~surface waves~at a frequency fo, so as to produce~ripples~ln the~ampl~itude-frequency and phase-requency response~of th;e transducer in the ~egion of that frequency fo.
, :
~1~89~83 An object of this invention is to provide an alternative acoustic surface wave device having a "length-weighted" transducer with low "interactions", compensation ; ~
for wavefront distortion and a good yield of devices in ~ :
manufacture.
According to the invention there is provided an :
acoustic surface wave device including a body of piezo-electric material on one surface of which is formed a launch-ing or receiving transducer including an interdigital array :
of two sets of electrodes, in which each set is connected to one of two opposite bus bars and each electrode has a part which overlaps a part of an adiacent electrode of the opposite set, in which the length of the overlapping electrode parts .. ~:
`~ varies along the line of acoustic surface wave propagation through the transducer, the~limits of the envelope o~ the 1 overlapping electrode parts normal to the propagation line. defining the acoustic aperture oF the transducer, in which the two bus bars are shaped to follow the overlap envelope so that the electrodes are connected to the bus bars immedla~ely out-side the envelope, and in:which at least one conductive area is provided outside the envelope and wlthin the aperture such : that the or:each conductive area compensates at least partly for wavefront distortion due to the varying length of the ~ -overlapping:parts:o~ some of the electrodes, the or each con-25 ~ ductive area extending over a:distance along the line of acoustic surface~wave propagation through the transducer sub-stantially~equal~to~the sum of~the widths of those electrodes for whose varying length it provides compensation. : -3 (a) ;:
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~08~3 The invention will now be descrlbed ;n more detail with reference to the drawing in which Fig. 1 shows a conventional acoustic surface wavefilter.
Figs. 2A and 2B show two alternative electrode geo~etrics and Fig. 3 a transducer having additional electrodes outside the overlap envelope.
Fig. 4 shows in plan view an acoustic surface wave device according to the invention, and Figs. 5 and 6 illustrate modifications of the arrangement -of the length-weighted transducer and compensating metallised area of the device shown in Figure 4.
Figure 1 of the accompanying drawing shows schematically in plan view a conventional acoustic surface wave filter which can be used as~an intermediate frequency filter for a television receiver. A body 1 in the form of a wafer of piezoelectric material has applied to its upper surface a launching transducer 2 and a receiving transducer - ~.
3. The transducers include interdigital arrays of electrodes ,~ 20 formed on the surface of the body 1, suitably by photo- -.. . .
lithography from a vapour-deposi~ed layer of metal.
The interdigital electrode array of the launching transducer 2 is adapted to direct acoustic surfac~ waves ~-. . . .
,, : :
', : : ' "
!~ 3 ~. .: : : : .:
, ~089~83 PHB 32,514 parallel to the line of acoustic surface wave propagation -~-4 through that transducer. The interdigital electrode array of the receiving transducer 3 is arranged in an acoustic surface waves path with the transducer 2 and is adapted to receive acoustic surface waves launched towards it by the transducer 2. Each interdigital array comprises two sets of strip electrodes 5, each set being connected to one of two opposite bus bars. The bus bars 6, 7 lead to respect-ive input terminals 8, 9 of the launching transducer 2, and 10 the bus bars 10, 11 lead to respective output terminals 12, 13 of the receiving transducer 3.
The frequency response of the filter is the combi-nation of the frequency responses of the two transducers.
~ .
The electrodes 5 are at an effective spacing of a half :
` 15 wavelength of acoustic surface waves at a frequency fo, ~;
which frequency may be the same or different for the two~
transducers. Each electrode 5~has a part which overlaps a - part of an adjacent electrode 5 connected to the opposite bus bar, and the shape of the envelope of the overlapping .
electrode parts of each transducer, shown in dotted outline, is designed to produce a required amplitude-frequency res-ponse~for each~transduce~r~. ~
The~limits of~the envelope of the overlapping ;., electrode parts normal to the propagation line 4 define ^~ 25~ the acoustic aperture A~of~each transducer. In figure l the transducer 2~ lS 'length-weighted' i.e. the length of the overlapping~parts of the~electrodes 5 varies along the ,~.: , :
~ 4 `: '~ ~ ' ' '~
: ,- -~08!!~0~33 PHB 32,514 propagation line 4 through that transducer, and the trans- -ducer 3 is a 'uniform' transducer i.e. the length of the ~ `
overlapping parts of the electrodes 5 does not vary along the propagation line 4 through that transducer.
The conventional acoustic surface wave filter described above with reference to Figure 1 is designed to - have a desired frequency response. However, it is subjectto various secondary effects which can produce unwanted perturbations in that frequency response and so degrade its performance. Two of these secondary effects, i.e. "inter-actions" and wavefront distortion, will now be discussed in turn.
Within an interdLgital array acoustic surface wave transducer, the electrodes partially reflect acoustic surface waves and are also caused by the acoustic surface waves to generate~an electrical signal and reradiate. These ~ reflections and re-radiations, which can together be called `~ ; "interactions" will be additive in a conventional trans-`` ; ducer having its electrodes at an effective spacing of half;a wavelength of acoustic surface waves at a frequency fo, so as to produce ripples in the amplitude-frequency and .
phase - frequency response of~ the transducer in the region of~that frequency~fo.
The above described problem of reflections is re- ;
~ cognised and a solution proposed ln~a paper entitled "Appli-cations of double electrodes in acoustic surface wave device , ~ ~ , ..
~ designi' by T.W.~ Bristol et al presented to the Proc. IEEE
,, ;: , : . :
.. , ~ :: : ' '. .. ' , ~ , . .
1089083 PHB 32, 514 Ultrasonics Symposium, October 1972, where it is said that by dividing each electrode into a split pair the reflections cancel at the centre frequency, since the periodicity of the discontinuities is doubled. It is also said that double electrodes couple to both the fundamental and third harmonic modes with essentially equal strength while retaining the inherent reflection suppression for both modes. Figures 2A
and 2B of the accompanying drawings show a conventional acoustic surface wave transducer geometry and a double elec-trode transducer geometry respectively as illustrated in theProc. IEEE paper.
We have found that there are two main disadvan-tages to the above-proposed double electrode transducer geometry. -The first disadvantage is that fabrication errors are more likely to result in breaks in the electrodes or shorts between them, and so the yield of good devices in manufacture is reduced. In particular, a break which severs ;
a major part of only one of the long electrodes in the 'length-weighted' transducer of the filter shown in Figure l mayi throw the filter out of the desired response speci-~ fication. ; ;~
-~ In an intermediate frequency television filter fabricated on a chip of bismuth silicon oxide, the width :
of the electrodes and the gaps~between~them are 10 /u using the conventional electrode geometry of Figure 2A, but are 5 /u using the double~electrode geometry of Figure 2B. In : :.
~ this casé the use of a double electrode geometry can result -~ ~ : '.'`.'"
: ~ : 6 ' . .
'.
108,.~83 PHB 32, 514 `:' in a significant reduction in the yield of good devices.
The second disadvantage is the substantially equal amplitude response of a double electrode transducer at both its fundamental and third harmonic modes. In the . .. .
case of a transducer having the conventional electrode geometry of Figure 2A, i.e. where the electrodes are at an effective spacing of half a wavelength at a frequency fo, the width of the electrodes is the same as the gaps between them and the electrodes are alternately connected to the two bus bars, the individual electrode response is zero at the frequency 3fo and so the response of the transducer at that frequency is suppressed. However in the case of a transducer having the double electrode geometry of Figure 2B, i.e. where the electrodes are at an effective spacing lS of a quarter of a wavelength at a frequency _o, the width of the electrodes is ~he same as the gaps between them and ; ~ . : . . .
~` the electrodes are connected in pairs to the two bus bars, the individual electrode response is not zero at the fre-quency 3fo and so the response of the transducer at that frequency is not suppressed. Thus in the case of an acoustic surface wave device which is required to have a band-pass frequency response;about a frequency fo, e.g. an interme-dlate frequency~te~levision filter, more stringent require-ments may be placed on the external electrical circuits 25 associated~with the acoustic surface wave de~ice to ensure that they do~not respond~at frequency~3fo and spoll the stop-band response~of the filter~
.~
7 -- -:
:. -1089~3 PHB 32,514 The problem of wavefront distortion arises with "length-weighted" interdigital array acoustic surface wave transducers, in which the length of the overlapping elec-trode parts varies along the line of acoustic surface wave propagation through the transducer. Referring to Figure 1, the wavefronts of acoustic surface waves travelling from the transducer 2 both towards and away from the transducer 3 are made up of waves generated at the position o~ each elec-trode 5 within the transducer. The velocity of acoustic surface waves is altered by travelling under a metallised surface on a piezoelectric material, and thus the waves generated from the position of each electrode 5 suffer a velocity change which varies across the aperture of the transducer 2 as the number of metal electrodes 5 in the path of these waves varies across the aperture. In the case -~
of the particular overlap envelope of the transducer 2 in Figure 1 the waves midway across the aperture A travel :
`I under approximately double the number of electrodes as the -`~
:
waves at the outer edges of the aperture A. The resulting wavefront distortion affects the performance of an acoustic surface wave device which~is designed under the assumption that the wavefronts are straight. -.
In Applied Physics Letters, 1st December 1971, :
` Volume l9,~Number~11, at~pages~456 to 459, the above-des-; 25 cribed problem of wavefront distortion is recognised and a solution proposed which is to insert extra electrodes which ~ are connected to the bus bars but which are not "active".
-' : ' : ~ . :
,........................................................................ ''' ,`. ~ : .' ; - 8 -"' ~' 39~83 PHB 3 2, 514 These extra electrodes are outside the existing overlap envelope, i.e. both their adjacent electrodes are connected to the same bus bar, and so they do not contribute to the generation of acoustic surface waves by the transducer.
~owever, they equalise the "metal path length" across the aperture of the transducer and serve to keep the wavefront plane. Figure 3 of the accompanying drawings shows a 'length-weighted' interdigital array acoustic surface wave trans-ducer as illustrated in the Applied Physics Letters paper 1~ having the above-mentioned extra electrodes 14 outside the overlap envelope (shown in dotted outline). -We have found that whilst the introduction of extra electrodes as suggested in the pre~ious paragraph into the 'length-weighted' transducer 2 of the conventional filter shown in Figure 1 does indeed reduce wavefront dis-tortion it has the disadvantage of increasing those ripples in the amplitude-frequency and phase-frequency response of the transducer in the region of the frequency fo which are due to "interactions ~
.
In an article in Electronics Letters, 14th November 1974 Vol. 10 No. 23, pages 489-90, we have described a : , "length-weighted" transducer with low "interactions" which - -enables the provision of acoustic surface wave devices with a good yield in manufacture. This transducer includes an interdigital array of two sets of eIectrodes~ Each set is connected to one of two~opposite bus bars and each electrode -:
~ has a~part which ouerlaps a part of an adjacent electrode ~ -,' :
,. ~ ~: :
.~ .
. .
. . .
," ' .
~089~83 PHB 32,514 of the opposite set. The overlapping electrode parts are at an effective spacing of a half wavelength of acoustic surface waves at a frequency fo, and the length of the overlapping electrode parts varies along the line of acoustic surface wave propagation through the transducer, the limits of the envelope of the overlapping electrode parts normal to the propagation line defining the acoustic aperture of the transducer. Furthermore, groups of metallic strips normal to the propagation line extend outside the - lO envelope and within the aperture so as to at least partly compensate for wavefront distortion due to the varying length -of the overlapping electrode parts, the strips of each ; group being electrically connected in common, and adjacent ; strips within each group being at an effective spacing of a quarter sic wavelength of acoustic surface waves at the -~
frequency fo. The metallic strips of each group are connect-ed to one of the bus bars, and some of the metallic strips of each group are in pa-irs whiah form part of one of the sets of electrodes, each said pair connecting an overlapping ` 20 electrode part to its respective bus bar.
.. . .
The number of groups of~metallic strips, the number of strips within each group, and the length of each ~
. . .
strip are such that with a second transducer arranged in an acoustic surface wave path with~the first transducer, - :
in the case of the first transducer acting as a launching :~ :
transducer, compensation for wavefront distortion is pro-vided for waves launched toward~s the seoond transducer but ",.j : ~ ~ : - 1 0 - ' , : :
.~ .
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:, : ' ' :`:' ' ' ': ~,' :
10t39`S~83 PHB 32,541 ' ' not for waves launched away from the second transducer.
The above-described transducer is also described in our Canadian Patent 1,033,049 which issued on June 13, 1978 where it is explained that the design of the trans-ducer depends upon the appreciation of a certain combina-tion of properties of a conventional "length-weighted"
transducer. Firstly, only ~hose parts of the elec~rodes within the overlap envelope contribute to the generation or reception of acoustic surface waves. Secondly, it is the varying length of those electrode parts which results ;
in wavefront distortion. Thirdly, those parts of the electrodes outside the envelope partly compensate for . .
that wavefront distortion. Fourthly, those parts of the electrodes outside the envelope contribute to r ' .
"interactions". Therefore, if those parts of the elec- -trodes outside the envelope are split into double electrodes, ''interactî~ons'' will be significantly reduced ^ ~ ~ but the yield of good devices will not be signif;cantlyreduced since the overlapping electrode parts are not ; 20 ~ split and the charge on an overlapping electrodq part ~ .
will not be affected by either a break in one of the -. ~ split parts or a~short between them. The extra elec-~ trodes introduced outside the overlap envelope to ,, ~
provide further compensation for wavefront distortion ~ do not significantly increase "interactions'' since these extra~electrodes are split into double electrodes.
. . . .
.. ~ ~ :: - .
, . . .
, : , :: B
-1089~83 PHB 32,514 Referring now to Figure 4, a body 1 in the form of a wafer of piezoelectric material has applied to ;ts upper surface a launching transducer 2 and a receiving transducer 3. The transducers include 5 interdigital arrays of electrodes formed on the surface of the body 1, suitably by photolithography from a vapour-deposited layer of metal. ;
The interdigital electrode array of the launching transducer 2 is adapted to direct acoustic -surface waves parallel to the line of acoustic surface wave propagation 4 through that transducer. The interdigital electrode array of the receiving trans-ducer 3 is arranged in an acoustic surface wave path with the transducer 2 and is adapted to receive 15 acoustic surface waves~launched towards it by the transducer 2. Each interdigital array comprises two --sets of strlp electrodes 5,~ each set being connected ~ : .
to one o~ two oppos1te bus bars. The bus bars 6, 7 lead to respective input terminals 8, 9 of the 20 launching transducer 2, and the bus bars lO, ll lead , to respective output terminals 12, 13 o~ the receiv-ing transducer 3.
Each electrode 5 has a part which overlaps a part ., - :~
~, : ~ . ...
; ~
1~9~3 PHB 32,514 of an adjacent electrode 5 connected to the opposite bus bar. The overlapping parts of the electrodes 5 of each transducer are at an effective spacing of a half wavelength of acoustic surface waves at a frequency fo, which frequency may be the same or different for the two transducers. The width of the overlapping electrode parts 5 and the gaps between them are a quarter of the wavelength of acoustic surface waves at the frequency fo.
The shape of the envelope of the overlapping electrode ;~
parts of each transducer, shown in dotted outline, is designed to produce a required amplitude-frequency response for each transducer. ~he frequency response of the filter is the combination of the frequency responses of the two transducers.
The limits of the envelope of the overlapping electrode parts normal to the propagation line 4 define the acoustic aperture A of each transducer. The transducer 2 , ~
is "length-weighted" i.e. the length of the overlapping ` ~ ~ parts of the~electrodes S varies along the propagation line 4 through that transducer, and the transducer 3 is a ~ "uniform" transducer i.e. the length of the overlapping - ~ parts of the electrodes 5 does not vary along the propaga tion line 4 through that transducer.
Considering the "length-weighted" trans-25~ ~ ducer 2 in more~detail,~the~bus bars 6 and 7 are shaped to follow the overlap envelope so that the electrodes 5 are ;~
connected to~the~bus bars~,immediately outside the envelope.
The advantages of~ this~feature~are as follows. Firstly, as - ;~
has ~
''~ ~ : : '. ,,' :
~0~ 3 PHB 32,514 been previously mentioned in the introductory part of this specification, in a conventional "length-weighted" trans-ducer such as the transducer 2 of Figure 1, and also in a "length-weighted" transducer with extra inactive electrodes .
as shown in Figure 3, the electrode parts outside the over-lap envelope contribute to "interactions". As shown in Figure 4 there are substantially no electrode parts outside :~
the overlap envelope which contribute to "interactions" and so the performance of the device shown in Figure 4 is im-proved having regard to this effect compared with a device :
incorporating a "length-weighted" transducer as shown in Figure 1 or Figure 3. Secondly, the closer connection of the overlapping parts of the electrodes 5 to their respective bus bars reduces the chances of breaks in those electrodes or shorts between them compared with a conventional "length-. .
weighted" transducer and should thus improve the yield in `:.-~ manufacture. Thirdlyr the terminals 8 and 9 are accommodated -:~ : :: within the length of the transducer 2, so sa~ing cost on : ~ .. ..
the slze of the piezoelectric body 1 required for the device.
- Two approximately triangular shaped metallised ~:
areas 15, 16 are located outside the overlap envelope and within the aperture A on the side o~ the transducer 2 near- :
est the transducer 3. The location, size and shape of these - :
:i ... .
: 25 ~areas 15, 16 is such that:they~provide a substantial degree of ~compensation for wavefront dlstortion for waves launched ~ :
from the transducer 2:towards th~e transducer 3 as will now .,: ~ :: : :
. : ~ . . .:
,-~: , . ' 5: " ' ' '''' , ,' ,,, . ,.. .... . . . ' . ' , ' . ' ' . ' . "'.' '. ' . ' ' . "`.' , '," '~" . '."'.''.` .. ' PH~ 32,514 ~108~0B3 ., .
be explained in more detail. Considering waves generated from the long overlapping electrode part 51 near the centre of the transducer 2 towards the transducer 3, then midway .
across the aperture A those waves will travel through the transducer 2 under a 'Imetal path length" equal to the sum of the widths of the electrodes S in their path in the transducer 2 be~ore proceeding towards the transducer 3.
However, at the edges of the aperture A those waves would not, in the absence of the metallised areas 15, 16, travel under any metal (other than the bus bars) before proceeding towards the transducer 3. This 'Imetal path length'l for the waves generated ~rom the electrode 51 varies across the aperture A as the number of metal electrodes in the path of these wave varies acxoss the aperture A. Equalisation of this variation in "metal path length" is provided by the ~ .
areas 15, 16 which extend over a distance along the line 4 of acoustic surface wave propagation through the transducer .. . .. .
substantially equal to the sum of the widths of the elec-trodes 5 in the transducer 2 between the~electrode 51 and :~
the transducer 3. The width of the areas 15, 16 varies from : . .
a maximum equal to this distance at the edges of the aper- .
~ ture A to a minimum of zero near the middl.e of the aperture A.
.~ Figure 5 shows that the metallised areas 15 and ~ :
,. : : ~ ; : .
~: : 16 do not have to~be formed integrally with the bus bars of :
.. . .
the transducer 2 as long as they are in the acoustic surface wave path between the transducer 2 and the transducer 3. - .
Figure 6 shows that the metallised areas 15 and 16 could ,:
.' ~ ' ~; : ':
. - . . .
~, ' ': .:
. :. .
A
10~9083 PHB 32,514 be formed as a single metallised area.
The location, size and shape of the metallised areas 15, 16 of the length-weighted transducer 2 as shown in Figures 4 to 6 is such as to provide compensation for wavefront distortion of waves launched towards a second transducer but not for waves launched away from that second transducer. If required, however, e.g. in the case of a three transducer arrangement, metallised areas can be ar-ranged such as to provide compensation for wavefront dis-tortion of waves launched in both directions along the lineof propagation through the length-weighted transducer. The invention has been described above in terms of a length-weighted transducer which is a launching transducer. The length-weighted transducer can, of course, equally well; ~
be operated as a receiving transducer. ~-:
. : :
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' ' ., ~ . ., . ~, .1, ~ ' '.
:: ~
~, : .... ~ .
-.: :: , -.
: : ~ :, :
~ 16 ~
:::
,~ ,, .
!
devices.
The use of acoustic surface waves has enabled -devices, such as frequency selective filters, to be manu-factured which are small, compact and are moreover compa-tible with integrated circuit manufacturing techniques. ~;
Such devices enable difficulties such as bulk and manufact-uring cost associated with the provision of inductors to be avoided.
An acoustic surface-wave filter is commonly formed `~ by a thin wafer of piezoelectric material on one surface of -~
which a launching and a receiving transducer are arranged respectively to launch and to receive an acoustic surface '!'~ wave propagating over the surface. Each transducer normally - ~ 15 comprises an interdigital array of strip electrodes, the arrays being formed, for examplei by a photolighographic process from a layer of a suitable metal deposited on the~
surface of the wafer.~ ~
The frequency response of the filter is determined 20 ~ by the number, spacing and d~imensional configuration of the electrodes making up each transducer. For convenlence of computation, a mathematical model of the array is consider-.
ed~1n~which~each e~lectrode i~s regarded as representing anindividual~acoust~ic~wave~source~and;the results~ obtained -~25 ~ from this mode1 are found~ to~be generally satisfactory~in -~
.,-:
. : ~:
:, : . . . ~ -~LQ8~083 PHB 32514 ~ ~
'.':', '-' ' practice for design purposes. By employing techniques of Fourier synthetis and computer optimisat;on on this mathe-matical model, a suitable relative distribution of magni-tude and spacing of such sources in the launching and receiving transducer arrays can be determined which can prov~de a good approximation to a desired band-pass response. The spacing of the launching and receiving transducers along the line of propagation of the acoustic surface waves will introduce a delay in the signal path;
however, in many applications such a delay is not im-portant or can be allowed for. For example, in the case of an intermediate frequency filter for a television receiver, since the entire received signal receîves the same delay, this delay is simply equivalent to displacing the receiving aer;al further from the transmitter.
. ;
-o ~ ~ ~ Alternativel`y, this property of the -devi~ce~can be employed to provide a desired delay. ~ ~-Within an interdigltal array acoustic surface wave transducer, the electrodes partially reflect ~ acoustic surface waves and are also caused by the acoustic surface waves to generate an electrical signal and reradiate. These~reflections and re-radiations, which~can together~be~called "interactions" will be additive in a conventiona;l transducer having its 25 ~ ~ electrodes~at an~effectlve;spaclng of half a wavelength of acoustic~surface waves~at a frequency fo, so as to produce~ripples~ln the~ampl~itude-frequency and phase-requency response~of th;e transducer in the ~egion of that frequency fo.
, :
~1~89~83 An object of this invention is to provide an alternative acoustic surface wave device having a "length-weighted" transducer with low "interactions", compensation ; ~
for wavefront distortion and a good yield of devices in ~ :
manufacture.
According to the invention there is provided an :
acoustic surface wave device including a body of piezo-electric material on one surface of which is formed a launch-ing or receiving transducer including an interdigital array :
of two sets of electrodes, in which each set is connected to one of two opposite bus bars and each electrode has a part which overlaps a part of an adiacent electrode of the opposite set, in which the length of the overlapping electrode parts .. ~:
`~ varies along the line of acoustic surface wave propagation through the transducer, the~limits of the envelope o~ the 1 overlapping electrode parts normal to the propagation line. defining the acoustic aperture oF the transducer, in which the two bus bars are shaped to follow the overlap envelope so that the electrodes are connected to the bus bars immedla~ely out-side the envelope, and in:which at least one conductive area is provided outside the envelope and wlthin the aperture such : that the or:each conductive area compensates at least partly for wavefront distortion due to the varying length of the ~ -overlapping:parts:o~ some of the electrodes, the or each con-25 ~ ductive area extending over a:distance along the line of acoustic surface~wave propagation through the transducer sub-stantially~equal~to~the sum of~the widths of those electrodes for whose varying length it provides compensation. : -3 (a) ;:
~ . -,j ~ .
,'.. ::: : .'-, .,:, ~ , '':
-, ~ .:. .-: .
~08~3 The invention will now be descrlbed ;n more detail with reference to the drawing in which Fig. 1 shows a conventional acoustic surface wavefilter.
Figs. 2A and 2B show two alternative electrode geo~etrics and Fig. 3 a transducer having additional electrodes outside the overlap envelope.
Fig. 4 shows in plan view an acoustic surface wave device according to the invention, and Figs. 5 and 6 illustrate modifications of the arrangement -of the length-weighted transducer and compensating metallised area of the device shown in Figure 4.
Figure 1 of the accompanying drawing shows schematically in plan view a conventional acoustic surface wave filter which can be used as~an intermediate frequency filter for a television receiver. A body 1 in the form of a wafer of piezoelectric material has applied to its upper surface a launching transducer 2 and a receiving transducer - ~.
3. The transducers include interdigital arrays of electrodes ,~ 20 formed on the surface of the body 1, suitably by photo- -.. . .
lithography from a vapour-deposi~ed layer of metal.
The interdigital electrode array of the launching transducer 2 is adapted to direct acoustic surfac~ waves ~-. . . .
,, : :
', : : ' "
!~ 3 ~. .: : : : .:
, ~089~83 PHB 32,514 parallel to the line of acoustic surface wave propagation -~-4 through that transducer. The interdigital electrode array of the receiving transducer 3 is arranged in an acoustic surface waves path with the transducer 2 and is adapted to receive acoustic surface waves launched towards it by the transducer 2. Each interdigital array comprises two sets of strip electrodes 5, each set being connected to one of two opposite bus bars. The bus bars 6, 7 lead to respect-ive input terminals 8, 9 of the launching transducer 2, and 10 the bus bars 10, 11 lead to respective output terminals 12, 13 of the receiving transducer 3.
The frequency response of the filter is the combi-nation of the frequency responses of the two transducers.
~ .
The electrodes 5 are at an effective spacing of a half :
` 15 wavelength of acoustic surface waves at a frequency fo, ~;
which frequency may be the same or different for the two~
transducers. Each electrode 5~has a part which overlaps a - part of an adjacent electrode 5 connected to the opposite bus bar, and the shape of the envelope of the overlapping .
electrode parts of each transducer, shown in dotted outline, is designed to produce a required amplitude-frequency res-ponse~for each~transduce~r~. ~
The~limits of~the envelope of the overlapping ;., electrode parts normal to the propagation line 4 define ^~ 25~ the acoustic aperture A~of~each transducer. In figure l the transducer 2~ lS 'length-weighted' i.e. the length of the overlapping~parts of the~electrodes 5 varies along the ,~.: , :
~ 4 `: '~ ~ ' ' '~
: ,- -~08!!~0~33 PHB 32,514 propagation line 4 through that transducer, and the trans- -ducer 3 is a 'uniform' transducer i.e. the length of the ~ `
overlapping parts of the electrodes 5 does not vary along the propagation line 4 through that transducer.
The conventional acoustic surface wave filter described above with reference to Figure 1 is designed to - have a desired frequency response. However, it is subjectto various secondary effects which can produce unwanted perturbations in that frequency response and so degrade its performance. Two of these secondary effects, i.e. "inter-actions" and wavefront distortion, will now be discussed in turn.
Within an interdLgital array acoustic surface wave transducer, the electrodes partially reflect acoustic surface waves and are also caused by the acoustic surface waves to generate~an electrical signal and reradiate. These ~ reflections and re-radiations, which can together be called `~ ; "interactions" will be additive in a conventional trans-`` ; ducer having its electrodes at an effective spacing of half;a wavelength of acoustic surface waves at a frequency fo, so as to produce ripples in the amplitude-frequency and .
phase - frequency response of~ the transducer in the region of~that frequency~fo.
The above described problem of reflections is re- ;
~ cognised and a solution proposed ln~a paper entitled "Appli-cations of double electrodes in acoustic surface wave device , ~ ~ , ..
~ designi' by T.W.~ Bristol et al presented to the Proc. IEEE
,, ;: , : . :
.. , ~ :: : ' '. .. ' , ~ , . .
1089083 PHB 32, 514 Ultrasonics Symposium, October 1972, where it is said that by dividing each electrode into a split pair the reflections cancel at the centre frequency, since the periodicity of the discontinuities is doubled. It is also said that double electrodes couple to both the fundamental and third harmonic modes with essentially equal strength while retaining the inherent reflection suppression for both modes. Figures 2A
and 2B of the accompanying drawings show a conventional acoustic surface wave transducer geometry and a double elec-trode transducer geometry respectively as illustrated in theProc. IEEE paper.
We have found that there are two main disadvan-tages to the above-proposed double electrode transducer geometry. -The first disadvantage is that fabrication errors are more likely to result in breaks in the electrodes or shorts between them, and so the yield of good devices in manufacture is reduced. In particular, a break which severs ;
a major part of only one of the long electrodes in the 'length-weighted' transducer of the filter shown in Figure l mayi throw the filter out of the desired response speci-~ fication. ; ;~
-~ In an intermediate frequency television filter fabricated on a chip of bismuth silicon oxide, the width :
of the electrodes and the gaps~between~them are 10 /u using the conventional electrode geometry of Figure 2A, but are 5 /u using the double~electrode geometry of Figure 2B. In : :.
~ this casé the use of a double electrode geometry can result -~ ~ : '.'`.'"
: ~ : 6 ' . .
'.
108,.~83 PHB 32, 514 `:' in a significant reduction in the yield of good devices.
The second disadvantage is the substantially equal amplitude response of a double electrode transducer at both its fundamental and third harmonic modes. In the . .. .
case of a transducer having the conventional electrode geometry of Figure 2A, i.e. where the electrodes are at an effective spacing of half a wavelength at a frequency fo, the width of the electrodes is the same as the gaps between them and the electrodes are alternately connected to the two bus bars, the individual electrode response is zero at the frequency 3fo and so the response of the transducer at that frequency is suppressed. However in the case of a transducer having the double electrode geometry of Figure 2B, i.e. where the electrodes are at an effective spacing lS of a quarter of a wavelength at a frequency _o, the width of the electrodes is ~he same as the gaps between them and ; ~ . : . . .
~` the electrodes are connected in pairs to the two bus bars, the individual electrode response is not zero at the fre-quency 3fo and so the response of the transducer at that frequency is not suppressed. Thus in the case of an acoustic surface wave device which is required to have a band-pass frequency response;about a frequency fo, e.g. an interme-dlate frequency~te~levision filter, more stringent require-ments may be placed on the external electrical circuits 25 associated~with the acoustic surface wave de~ice to ensure that they do~not respond~at frequency~3fo and spoll the stop-band response~of the filter~
.~
7 -- -:
:. -1089~3 PHB 32,514 The problem of wavefront distortion arises with "length-weighted" interdigital array acoustic surface wave transducers, in which the length of the overlapping elec-trode parts varies along the line of acoustic surface wave propagation through the transducer. Referring to Figure 1, the wavefronts of acoustic surface waves travelling from the transducer 2 both towards and away from the transducer 3 are made up of waves generated at the position o~ each elec-trode 5 within the transducer. The velocity of acoustic surface waves is altered by travelling under a metallised surface on a piezoelectric material, and thus the waves generated from the position of each electrode 5 suffer a velocity change which varies across the aperture of the transducer 2 as the number of metal electrodes 5 in the path of these waves varies across the aperture. In the case -~
of the particular overlap envelope of the transducer 2 in Figure 1 the waves midway across the aperture A travel :
`I under approximately double the number of electrodes as the -`~
:
waves at the outer edges of the aperture A. The resulting wavefront distortion affects the performance of an acoustic surface wave device which~is designed under the assumption that the wavefronts are straight. -.
In Applied Physics Letters, 1st December 1971, :
` Volume l9,~Number~11, at~pages~456 to 459, the above-des-; 25 cribed problem of wavefront distortion is recognised and a solution proposed which is to insert extra electrodes which ~ are connected to the bus bars but which are not "active".
-' : ' : ~ . :
,........................................................................ ''' ,`. ~ : .' ; - 8 -"' ~' 39~83 PHB 3 2, 514 These extra electrodes are outside the existing overlap envelope, i.e. both their adjacent electrodes are connected to the same bus bar, and so they do not contribute to the generation of acoustic surface waves by the transducer.
~owever, they equalise the "metal path length" across the aperture of the transducer and serve to keep the wavefront plane. Figure 3 of the accompanying drawings shows a 'length-weighted' interdigital array acoustic surface wave trans-ducer as illustrated in the Applied Physics Letters paper 1~ having the above-mentioned extra electrodes 14 outside the overlap envelope (shown in dotted outline). -We have found that whilst the introduction of extra electrodes as suggested in the pre~ious paragraph into the 'length-weighted' transducer 2 of the conventional filter shown in Figure 1 does indeed reduce wavefront dis-tortion it has the disadvantage of increasing those ripples in the amplitude-frequency and phase-frequency response of the transducer in the region of the frequency fo which are due to "interactions ~
.
In an article in Electronics Letters, 14th November 1974 Vol. 10 No. 23, pages 489-90, we have described a : , "length-weighted" transducer with low "interactions" which - -enables the provision of acoustic surface wave devices with a good yield in manufacture. This transducer includes an interdigital array of two sets of eIectrodes~ Each set is connected to one of two~opposite bus bars and each electrode -:
~ has a~part which ouerlaps a part of an adjacent electrode ~ -,' :
,. ~ ~: :
.~ .
. .
. . .
," ' .
~089~83 PHB 32,514 of the opposite set. The overlapping electrode parts are at an effective spacing of a half wavelength of acoustic surface waves at a frequency fo, and the length of the overlapping electrode parts varies along the line of acoustic surface wave propagation through the transducer, the limits of the envelope of the overlapping electrode parts normal to the propagation line defining the acoustic aperture of the transducer. Furthermore, groups of metallic strips normal to the propagation line extend outside the - lO envelope and within the aperture so as to at least partly compensate for wavefront distortion due to the varying length -of the overlapping electrode parts, the strips of each ; group being electrically connected in common, and adjacent ; strips within each group being at an effective spacing of a quarter sic wavelength of acoustic surface waves at the -~
frequency fo. The metallic strips of each group are connect-ed to one of the bus bars, and some of the metallic strips of each group are in pa-irs whiah form part of one of the sets of electrodes, each said pair connecting an overlapping ` 20 electrode part to its respective bus bar.
.. . .
The number of groups of~metallic strips, the number of strips within each group, and the length of each ~
. . .
strip are such that with a second transducer arranged in an acoustic surface wave path with~the first transducer, - :
in the case of the first transducer acting as a launching :~ :
transducer, compensation for wavefront distortion is pro-vided for waves launched toward~s the seoond transducer but ",.j : ~ ~ : - 1 0 - ' , : :
.~ .
', ~: : : -:.-. ~ .. .:
:, : ' ' :`:' ' ' ': ~,' :
10t39`S~83 PHB 32,541 ' ' not for waves launched away from the second transducer.
The above-described transducer is also described in our Canadian Patent 1,033,049 which issued on June 13, 1978 where it is explained that the design of the trans-ducer depends upon the appreciation of a certain combina-tion of properties of a conventional "length-weighted"
transducer. Firstly, only ~hose parts of the elec~rodes within the overlap envelope contribute to the generation or reception of acoustic surface waves. Secondly, it is the varying length of those electrode parts which results ;
in wavefront distortion. Thirdly, those parts of the electrodes outside the envelope partly compensate for . .
that wavefront distortion. Fourthly, those parts of the electrodes outside the envelope contribute to r ' .
"interactions". Therefore, if those parts of the elec- -trodes outside the envelope are split into double electrodes, ''interactî~ons'' will be significantly reduced ^ ~ ~ but the yield of good devices will not be signif;cantlyreduced since the overlapping electrode parts are not ; 20 ~ split and the charge on an overlapping electrodq part ~ .
will not be affected by either a break in one of the -. ~ split parts or a~short between them. The extra elec-~ trodes introduced outside the overlap envelope to ,, ~
provide further compensation for wavefront distortion ~ do not significantly increase "interactions'' since these extra~electrodes are split into double electrodes.
. . . .
.. ~ ~ :: - .
, . . .
, : , :: B
-1089~83 PHB 32,514 Referring now to Figure 4, a body 1 in the form of a wafer of piezoelectric material has applied to ;ts upper surface a launching transducer 2 and a receiving transducer 3. The transducers include 5 interdigital arrays of electrodes formed on the surface of the body 1, suitably by photolithography from a vapour-deposited layer of metal. ;
The interdigital electrode array of the launching transducer 2 is adapted to direct acoustic -surface waves parallel to the line of acoustic surface wave propagation 4 through that transducer. The interdigital electrode array of the receiving trans-ducer 3 is arranged in an acoustic surface wave path with the transducer 2 and is adapted to receive 15 acoustic surface waves~launched towards it by the transducer 2. Each interdigital array comprises two --sets of strlp electrodes 5,~ each set being connected ~ : .
to one o~ two oppos1te bus bars. The bus bars 6, 7 lead to respective input terminals 8, 9 of the 20 launching transducer 2, and the bus bars lO, ll lead , to respective output terminals 12, 13 o~ the receiv-ing transducer 3.
Each electrode 5 has a part which overlaps a part ., - :~
~, : ~ . ...
; ~
1~9~3 PHB 32,514 of an adjacent electrode 5 connected to the opposite bus bar. The overlapping parts of the electrodes 5 of each transducer are at an effective spacing of a half wavelength of acoustic surface waves at a frequency fo, which frequency may be the same or different for the two transducers. The width of the overlapping electrode parts 5 and the gaps between them are a quarter of the wavelength of acoustic surface waves at the frequency fo.
The shape of the envelope of the overlapping electrode ;~
parts of each transducer, shown in dotted outline, is designed to produce a required amplitude-frequency response for each transducer. ~he frequency response of the filter is the combination of the frequency responses of the two transducers.
The limits of the envelope of the overlapping electrode parts normal to the propagation line 4 define the acoustic aperture A of each transducer. The transducer 2 , ~
is "length-weighted" i.e. the length of the overlapping ` ~ ~ parts of the~electrodes S varies along the propagation line 4 through that transducer, and the transducer 3 is a ~ "uniform" transducer i.e. the length of the overlapping - ~ parts of the electrodes 5 does not vary along the propaga tion line 4 through that transducer.
Considering the "length-weighted" trans-25~ ~ ducer 2 in more~detail,~the~bus bars 6 and 7 are shaped to follow the overlap envelope so that the electrodes 5 are ;~
connected to~the~bus bars~,immediately outside the envelope.
The advantages of~ this~feature~are as follows. Firstly, as - ;~
has ~
''~ ~ : : '. ,,' :
~0~ 3 PHB 32,514 been previously mentioned in the introductory part of this specification, in a conventional "length-weighted" trans-ducer such as the transducer 2 of Figure 1, and also in a "length-weighted" transducer with extra inactive electrodes .
as shown in Figure 3, the electrode parts outside the over-lap envelope contribute to "interactions". As shown in Figure 4 there are substantially no electrode parts outside :~
the overlap envelope which contribute to "interactions" and so the performance of the device shown in Figure 4 is im-proved having regard to this effect compared with a device :
incorporating a "length-weighted" transducer as shown in Figure 1 or Figure 3. Secondly, the closer connection of the overlapping parts of the electrodes 5 to their respective bus bars reduces the chances of breaks in those electrodes or shorts between them compared with a conventional "length-. .
weighted" transducer and should thus improve the yield in `:.-~ manufacture. Thirdlyr the terminals 8 and 9 are accommodated -:~ : :: within the length of the transducer 2, so sa~ing cost on : ~ .. ..
the slze of the piezoelectric body 1 required for the device.
- Two approximately triangular shaped metallised ~:
areas 15, 16 are located outside the overlap envelope and within the aperture A on the side o~ the transducer 2 near- :
est the transducer 3. The location, size and shape of these - :
:i ... .
: 25 ~areas 15, 16 is such that:they~provide a substantial degree of ~compensation for wavefront dlstortion for waves launched ~ :
from the transducer 2:towards th~e transducer 3 as will now .,: ~ :: : :
. : ~ . . .:
,-~: , . ' 5: " ' ' '''' , ,' ,,, . ,.. .... . . . ' . ' , ' . ' ' . ' . "'.' '. ' . ' ' . "`.' , '," '~" . '."'.''.` .. ' PH~ 32,514 ~108~0B3 ., .
be explained in more detail. Considering waves generated from the long overlapping electrode part 51 near the centre of the transducer 2 towards the transducer 3, then midway .
across the aperture A those waves will travel through the transducer 2 under a 'Imetal path length" equal to the sum of the widths of the electrodes S in their path in the transducer 2 be~ore proceeding towards the transducer 3.
However, at the edges of the aperture A those waves would not, in the absence of the metallised areas 15, 16, travel under any metal (other than the bus bars) before proceeding towards the transducer 3. This 'Imetal path length'l for the waves generated ~rom the electrode 51 varies across the aperture A as the number of metal electrodes in the path of these wave varies acxoss the aperture A. Equalisation of this variation in "metal path length" is provided by the ~ .
areas 15, 16 which extend over a distance along the line 4 of acoustic surface wave propagation through the transducer .. . .. .
substantially equal to the sum of the widths of the elec-trodes 5 in the transducer 2 between the~electrode 51 and :~
the transducer 3. The width of the areas 15, 16 varies from : . .
a maximum equal to this distance at the edges of the aper- .
~ ture A to a minimum of zero near the middl.e of the aperture A.
.~ Figure 5 shows that the metallised areas 15 and ~ :
,. : : ~ ; : .
~: : 16 do not have to~be formed integrally with the bus bars of :
.. . .
the transducer 2 as long as they are in the acoustic surface wave path between the transducer 2 and the transducer 3. - .
Figure 6 shows that the metallised areas 15 and 16 could ,:
.' ~ ' ~; : ':
. - . . .
~, ' ': .:
. :. .
A
10~9083 PHB 32,514 be formed as a single metallised area.
The location, size and shape of the metallised areas 15, 16 of the length-weighted transducer 2 as shown in Figures 4 to 6 is such as to provide compensation for wavefront distortion of waves launched towards a second transducer but not for waves launched away from that second transducer. If required, however, e.g. in the case of a three transducer arrangement, metallised areas can be ar-ranged such as to provide compensation for wavefront dis-tortion of waves launched in both directions along the lineof propagation through the length-weighted transducer. The invention has been described above in terms of a length-weighted transducer which is a launching transducer. The length-weighted transducer can, of course, equally well; ~
be operated as a receiving transducer. ~-:
. : :
~: -:: -,: , : .
' ' ., ~ . ., . ~, .1, ~ ' '.
:: ~
~, : .... ~ .
-.: :: , -.
: : ~ :, :
~ 16 ~
:::
,~ ,, .
!
Claims (2)
EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An acoustic surface wave device including a body of piezoelectric material on one surface which is formed a launch-ing or receiving transducer including an interdigital array of two sets of electrodes, in which each set is connected to one of two opposite bus bars and each electrode has a part which overlaps a part of an adjacent electrode of the opposite set, in which the length of the overlapping electrode parts varies along the line of acoustic surface wave propagation through the transducer, the limits of the envelope of the overlapping electrode parts normal to the propagation line defining the acoustic aperture of the transducer, in which the two bus bars are shaped to follow the overlap envelope so that the electrodes are connected to the bus bars immediately outside the envelope, and in which at least one conductive area is provided outside the envelope and within the aperture such that this conductive area compensates at least partly for wavefront distortion due to the varying length of the overlapping parts of some of the electrodes, the said conductive area extending over a distance along the line of acoustic surface wave propagation through the transducer substantially equal to the sum of the widths of those electrodes for whose varying length it provides compensation.
2. An acoustic surface wave device as claimed in Claim 1, in which the transducer is a first transducer, in which a second transducer is arranged in an acoustic surface wave path with the first transducer, and in which the location, size, and shape of the conductive area or areas are such that, in the case of the first transducer acting as a launching transducer, compensa-tion for wavefront distortion is provided for waves launched towards the second transducer but not for waves launched away from the second transducer.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB34234/75 | 1975-08-18 | ||
| GB3423475A GB1512686A (en) | 1975-08-18 | 1975-08-18 | Acoustic surface wave devices |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1089083A true CA1089083A (en) | 1980-11-04 |
Family
ID=10363100
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA258,899A Expired CA1089083A (en) | 1975-08-18 | 1976-08-11 | Acoustic surface wave devices |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS5224444A (en) |
| CA (1) | CA1089083A (en) |
| DE (1) | DE2635192C2 (en) |
| FR (1) | FR2321802A1 (en) |
| GB (1) | GB1512686A (en) |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1585087A (en) * | 1976-07-29 | 1981-02-25 | Plessey Co Ltd | Surface acoustic wave filters |
| NL7810674A (en) * | 1977-12-21 | 1979-06-25 | Tektronix Inc | ACOUSTIC SURFACE WAVE DEVICE. |
| US4205285A (en) * | 1978-11-03 | 1980-05-27 | Gte Laboratories Incorporated | Acoustic surface wave device |
| JPS55125713A (en) | 1979-03-22 | 1980-09-27 | Toshiba Corp | Surface elastic wave device |
| JPS5654114A (en) * | 1979-10-11 | 1981-05-14 | Nec Corp | Reed screen shape converter of elastic surface wave |
| CN114611533B (en) * | 2022-01-28 | 2022-12-06 | 金陵科技学院 | Interdigital unilateral inclined weighted surface acoustic wave type Morlet wavelet processor |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1360235A (en) * | 1971-04-17 | 1974-07-17 | Marconi Co Ltd | Acoustic surface wave devices |
| GB1430725A (en) * | 1974-08-02 | 1976-04-07 | Mullard Ltd | Acoustic surface wave devices |
| GB1499330A (en) * | 1974-09-26 | 1978-02-01 | Plessey Co Ltd | Acoustic surface wave filters |
-
1975
- 1975-08-18 GB GB3423475A patent/GB1512686A/en not_active Expired
-
1976
- 1976-08-05 DE DE19762635192 patent/DE2635192C2/en not_active Expired
- 1976-08-11 CA CA258,899A patent/CA1089083A/en not_active Expired
- 1976-08-18 JP JP9783476A patent/JPS5224444A/en active Granted
- 1976-08-18 FR FR7625074A patent/FR2321802A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| FR2321802A1 (en) | 1977-03-18 |
| JPS5224444A (en) | 1977-02-23 |
| DE2635192A1 (en) | 1977-03-03 |
| FR2321802B1 (en) | 1982-03-12 |
| JPS5753003B2 (en) | 1982-11-10 |
| GB1512686A (en) | 1978-06-01 |
| DE2635192C2 (en) | 1985-08-08 |
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