CN85101813A - Surface acoustic wave filter - Google Patents
Surface acoustic wave filter Download PDFInfo
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- CN85101813A CN85101813A CN 85101813 CN85101813A CN85101813A CN 85101813 A CN85101813 A CN 85101813A CN 85101813 CN85101813 CN 85101813 CN 85101813 A CN85101813 A CN 85101813A CN 85101813 A CN85101813 A CN 85101813A
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- interdigital
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- admittance
- acoustic wave
- surface acoustic
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Abstract
A surface acoustic wave filter comprises uni-directional cross finger-type input and output transducer, wherein should have one at least and have incomplete one-way, and comprise being mounted to can produce a geometric phase difference φ between them
MThe pair of cross finger electrodes.These two electrodes can produce an electric phase difference by one between them
EPhase shifter be connected to each other phase difference
MWith φ
EDiscord be not equal to the π radian so that incomplete one-way to be provided.Thereby enlarged the admittance of external load or be used to suppress undesirable triple range of choice of getting over the essential unidirectional transducer radiation admittance of echo level, but kept relatively low insertion loss simultaneously.
Description
Background of invention
The invention relates to a kind of unidirectional surface wave filter,, can reduce the surface acoustic wave filter of volume again particularly about a kind of degree of freedom that both can increase design.
In order to reduce the insertion loss of surface acoustic wave filter, the suggestion that a unidirectional transducer is set among surface acoustic wave filter was once arranged, for example, northeastward in the mountain of the electric communication of university research institute and people Suo Zhuan And such as a man of virtue and ability be stated from the IEEE(IEEE) ultrasonic wave discussion scientific research reports in 1975 years concentrate " using the low insertion loss surface acoustic wave filter of type uni-directional cross finger-type transducer in groups " (the Low Insertion Loss Accoustic Surface Wave Filter Using Group-Type Unidirectional Interdigital Transducer) of (IEEE at#75 CHO 994-4SU pp317-321) and by hillside plot pure and hold under the arm between the United States Patent (USP) 4 of hard application " unidirectional surface acoustic wave device " (Unidirectional Surface Accoustic Wave Device With Meadering Electrode) with meander electrode, this suggestion is all proposed in 422, No. 000.Above-mentioned United States Patent (USP) was invested in December 20 nineteen eighty-three, and And has transferred Hitachi Co., Ltd.
Since its both sides tropism, a common surface acoustic wave transducer, and even do minimum estimation, its intrinsic insertion loss is 6 decibels, and a desirable loss with complete unidirectional surface acoustic wave transducer is zero.
In order to explain the operation principle of unidirectional transducer, existing referring to Fig. 1.The simplification pattern that this figure has drawn an interdigital input converter and its peripheral circuit.Although do not draw the interdigital output translator in the drawings, the structural similarity of its structure device to that indicated in the drawings has only replaced the signal source 3 among Fig. 1 with a load.In Fig. 1, an interdigital sender electrode 5 and an interdigital reflecting electrode 6 have constituted the interdigital input converter.Interdigital sender electrode 5 is connected with signal source 3 by a phase shifter 2.This phase shifter produces the electric phase difference of pi/2 radian, and one of reference number 4 expression signal sources 3 drives admittance G
lThe interdigital reflecting electrode 6 ， And that directly links to each other with signal source 3 selects distance between interdigital sender electrode 5 and the interdigital reflecting electrode 6, so that geometric phase difference therebetween is the pi/2 radian.Reference number 7 and 8 represent respectively forward the direction of propagation and the direction of propagation backward.
During work, from forwards to, along forwards having two respectively from the surface acoustic wave W of interdigital sender electrode 5 and reflecting electrode 6 emissions to 7
SFAnd W
RFIt is poor that ， And and this two sound waves all postpone the electric phase difference or the geometric phase of pi/2 radian than the signal phase of signal source 3, makes two signal homophases on the position of interdigital sender electrode 5, thereby make the interdigital transducer forwards equal W to the surface acoustic wave of propagating
SFAnd W
RFAnd.Aspect backward directions, from the surface wave W of interdigital reflecting electrode 6 with backward directions 8 propagation
RRBe in same phase place with the signal of signal source 3, and by the surface acoustic wave W of interdigital sender electrode 5 with the surface acoustic wave of backward directions 8 propagation
SRThe locational phase place of interdigital reflecting electrode 6 than the signal delay of signal source 3 the π radian, make ripple W
RRAnd W
SRDifferent Xiang And cancels out each other, and making the synthetic surface ripples with 8 propagation rearward is zero, thereby obtains one-way.
Moreover, with regard to common bidirectional transducer in fact, since surface acoustic wave along electrode assembly or transducer with forwards to propagating equably with backward directions, thereby one 3 decibels loss must be arranged, the result, when output and input converter when all taking in, are certainly existed a total insertion loss that is at least 6 decibels.
In the unidirectional transducer of Fig. 1,, thereby produce complete one-way because electricity and geometric phase difference are the pi/2 radian., it should be noted, though electric phase difference that produces because of phase shifter and the geometric phase difference between interdigital sender electrode and the reflecting electrode and be not the π radian, still can obtain complete one-way, this is disclosed like that as No. 4,422,000, United States Patent (USP) above-mentioned.
Shown in Figure 2 is the structure of a typical prior art unidirectional transducer.In Fig. 2, represent that with identical reference number And no longer describes in detail with the corresponding to parts of Fig. 1.Can see a unidirectional transducer 1 from Fig. 2, pi/2 phase shifter 2, signal source 3, the driving admittance 4 of signal source 3, its value is G
l, interdigital sender electrode 5 ' and interdigital reflecting electrode 6 '.The propagation forward of surface acoustic wave and the direction that backward directions are propagated are respectively with reference number 7 and 8 expressions.Selected interdigital sender electrode 5 ' and interdigital reflecting electrode 6 ' between distance to make their geometric phase difference be the pi/2 radian.
Use this prior art transducer, if the input admittance G that looks from the signal source aspect of transducer (comprising the admittance of pi/2 phase shifter)
aNot the driving admittance G that is substantially equal to signal source
l, it is impossible check undesirable transducer anti-She And to keep low insertion loss.Therefore to the volume and the shape of unidirectional transducer and drive admittance value and do some restrictions, so just cause the inconvenience that brings because of the destruction of design freedom.More particularly, when Quasi made the input admittance of transducer consistent with the big driving admittance of signal source fully, the aperture length W of transducer shown in Figure 2 must increase, thereby causes the increase of device slice, thin piece size, improved manufacturing cost.And, when unidirectional transducer is used for mass-producted product, for example, when being used in the intermediate-frequency filter of color TV set, following problem will take place, the input admittance that is signal source admittance (for example, the output admittance of tuner) and unidirectional transducer can change because of the central value that has been predetermined in the manufacture process of variation around tuner and pi/2 phase shifter that constitutes the pi/2 phase shifter component values.So, for the admittance of adjusting signal source or the input admittance of unidirectional transducer, then must or insert a variable admittance element in the signal source circuit, or adjust the constant of phase shifter circuit or the fine setting of transducer.These inconveniences also can betide on the output admittance of adjusting admittance and unidirectional transducer, and therefore, above-mentioned any adjustment all is essential.
Summary of the present invention
An object of the present invention is to provide one improved, need not to regulate the surface acoustic wave filter little with volume, this filter can be eliminated the shortcoming of prior art surface acoustic wave filter.
Another object of the present invention is that a surface acoustic wave filter will be provided, and this surface wave filter can be expanded the range of choice of the emission admittance or the external loading admittance of unidirectional transducer.
On the one hand, the present invention should have a transducer to comprise that 2 make geometric phase difference φ is arranged between them in interdigital input and output transducer at least
MThe interdigital electrode of radian, and one connect these 2 electrodes and produce φ
EThe phase shifter of radian electricity phase difference.These two phase differences and (φ
M+ φ
E) and be not equal to the π radian.That is to say that the present invention is one-way transducer fully intentionally.
On the other hand, in the present invention, if the number of degrees of the one-way a of definition unidirectional transducer are
a＝ (1+Cos(φ
M+φ
E))/(1+Cos(φ
M+φ
E))
The value of a when the scope of 0≤a≤9/11, signal source or load admittance G
lEmission admittance G with the interdigital transducer
aThe selection of ratio need satisfy following formula:
(9（a+1）)/(11-9a) ≤G
l/G
a≤ (11（a+1）)/(9-11a)
And and, when number of degrees a as defined above is in scope 9/11≤a≤1, G
lAnd G
aThe selection of ratio need satisfy:
(9（a+1）)/(11-9a) ≤G
l/G
a
If when using surface acoustic wave filter in the television receiver intermediate-frequency filter, must will be undesirable triplely get over echo (TTE) and be suppressed to less than-40 decibels, this numerical value is the threshold level (threshold level of ghost detection) of phantom detection.When satisfying above-mentioned condition, this requirement just can reach, and reduce the volume of filter simultaneously and can not cause the excessive increase of inserting loss, and eliminate for make prior art interdigital unidirectional transducer can be under unidirectional fully condition operation and the trouble that must adjust.
The schematic illustration of accompanying drawing
Fig. 1 is the operating principle schematic diagram that helps to explain unidirectional transducer.
Fig. 2 is the circuit diagram of prior art unidirectional transducer.
Fig. 3 represents in prior art unidirectional transducer and the bidirectional transducer at loss and triple characteristic curve of getting over the mark Quasi admittance effect on the echo inhibition level.
Fig. 4 represents that unidirectional transducer of the present invention is at loss and triple characteristic curve of getting over the mark Quasi admittance effect on the echo inhibition level.
Fig. 5 is the filter circuit figure of example of the present invention.
The narration of preferable embodiment
Before the narration example of the present invention, earlier the prior art unidirectional transducer is done more detailed narration.
When the transducer of being considered was one 3 pairs opening paraphase networks (three ported network), triple relations of getting over echo between loss and unidirectional transducer electrode can assign to represent by the transmission and the reflecting part of collision matrix.In the prior art, this is well-known.Under this condition, can be with reference to hillside plot pure and hold under the arm between hard " the insertion loss of surface acoustic wave (SAW) unidirectional transducer and triple relation of getting over echo " (Relation of the Insertion Loss and The Tripple Transit Echo in SAW Unidirectional Transducers) literary composition of being shown, this article is seen in the scientific research collection of thesis of the ultrasonic wave electronics seminar that nineteen eighty-two holds in the Tokyo, and Japanese applicating physical magazine, volume 22(1983 published on the 7th), supplementary issue 22-3, page or leaf 163-164(Jun Yamada and Katashi Hazama, Proceedings of 3rd Symposium on Ultrasonics Electronics, TOKYO 1982, JAPAN; Japanese Journal of Applied Physics, VOL22(Published July, 1983) Supplement 22-3, PP163-164.).
Fig. 3 represents by the prior art unidirectional transducer that the author analyzed of the above-mentioned paper characteristic curve of (with both sides' transducer).Among Fig. 3, curve 9 and 10 is represented the loss in the unidirectional transducer respectively and is triplely getted over echo and suppress level.Characteristic curve shown in Figure 3 is the result of Theoretical Calculation that a unidirectional transducer is done.If the input and output transducer all is an one-way type, then the loss of representing with decibel on the longitudinal axis will increase by 1 times.Transverse axis is represented the driving admittance G by signal source
lWith transducer admittance G
aThe defined normalized admittance b of ratio.
Because phantom is surveyed the requirement of threshold level, generally must get over-40 decibels or the following degree that echo is suppressed at main signal with triple.Here, so-called " phantom detection threshold " is meant and is the appreciable critical mirage phantom of human eye on the color television picture, and the intensity of mirage phantom is then determined by triple amplitudes of getting over echo that if bandpas filter produced of color TV set.
When each input and output transducer was all used unidirectional transducer, each transducer triple getted over the echo inhibition level are minimum and should be 20 decibels.Among Fig. 3, a mark Quasiization admittance b who meets this requirement is in the scope of 9/11≤b≤11/9.
As previously mentioned, for the value that makes b is limited in this scope, must be to adjusting aspect the signal source and in the admittance aspect the transducer, and this adjustment is very bothersome.
Loss in the prior art bidirectional transducer that curve 9 among Fig. 3 ' and 10 ' the above-mentioned authors analysis of expression goes out and triplely get over echo and suppress level., the bidirectional transducer of it should be noted that here to be analyzed is a kind of prior art bidirectional transducer with single cross interdigitated transducer, is different from incomplete unidirectional transducer of the present invention fully.Transducer of the present invention has the input and/or the output translator ， And that comprise transmission and reflecting electrode incomplete one-way is arranged.
From above narration as can be known, in known unidirectional transducer, people have sought complete one-way, but inventor of the present invention has then invented mass production first a kind ofly has an incomplete unidirectional unidirectional transducer, has solved the above-mentioned intrinsic variety of issue of complete one-way unidirectional transducer.
Compare with the prior art unidirectional transducer, a transducer of the present invention has incomplete one-way, this incomplete one-way is that cost brings to reduce some loss characteristics slightly, so as to the scope of expansion b, thereby has eliminated the necessity that requires adjustment in the prior art transducer.
Refer now to according to Fig. 4 and Fig. 5 the present invention is done detailed explanation.In Fig. 4 and Fig. 5, represent with identical reference number with Fig. 1 to Fig. 3 same section, no longer narration.
At first, not exclusively one-way can be by selecting the geometric phase difference φ between interdigital sender electrode and the reflecting electrode
MWith the electric phase difference that produces because of phase shifter
EAnd obtain, make this two phase difference De with And is not equal to the π radian exactly.
Secondly, will be by the defined direction degree of the ratio a of the power of the surface acoustic wave of forwards propagating to the power of the surface acoustic wave of propagating and backward directions as a parameter, loss L
31Get over echo and suppress level L with triple
11Can be with deciding, promptly shown in following equation with aforementioned paper similar methods:
L
31=-10 log { (4b)/((1+a) (1+b)
2) (decibel)
L
11=-10 log { ((a-r)
2)/((a+1)
2) (decibel)
Here, r=| (b-1)/(b+1) |.This result draws at Fig. 4, dotted line 11 expression losses, and solid line 12 is represented triple echo inhibition level of getting over.By using the geometric phase φ that produces owing to the position difference between interdigital sender electrode and reflecting electrode
MRadian and produce with electric phase difference because of phase shifter
ERadian, direction degree a can be expressed as
a＝ (1+Cos(φ
M+φ
E))/(1+Cos(φ
M+φ
E))
Because interdigital send and reflecting electrode on when applying unit voltage, forwards to rear backward upwards the surface wave bending of excitement be respectively e-j φ
E+ e-j φ
MWith e-j φ
E+ e
J φM, therefore, the transmitting power on forward and backward directions is respectively
2 (1+cos(φ
M-φ
E)) and 2 (1+cos(φ
M+ φ
E)).
In the prior art example, work as φ
M=φ
E=0 o'clock, can obtain a=1, represent a bidirectional transducer forwards to backward directions on transmitting power is all arranged.Work as φ
M=φ
EDuring=pi/2 radian, then a=0 represents that this transducer has complete one-way.
(b → ∞) triplely gets over echo and suppresses level L when finite value b becomes infinity
11To provide (unit is not a decibel) by following formula
L
11＝（ (1-a)/(1+a) ）
2。
If use the scope of above-mentioned finite value, make formula L with decision b
11≤/A
2Set up in this scope (A 〉=1 here), and that is petty, as a during greater than (A-1)/(A+1), and L
11=1/A
2Have only unique separating, the result, b drops in the semo-infinite field., when the value of a during less than (A-1)/(A+1), L
11=1/A
2Have two to separate, at this moment, the value of b is in a limited field, and here, A is determined by a value that depends on the threshold level of the phantom detection that will narrate below.Above result can obtain by computational methods, at first, and from (a-r)
2/ (a+1)
2≤ 1/A
2Obtain the scope of r, i.e. (aA-a-1)/(A)≤r≤(aA+a+1)/(A), and the scope of b can b=(1+r)/(1-r) calculate ， And to obtain following result:
(a) for 0≤a≤(A-1)/(A+1), the result is
(A+（aA-a-1）)/(A-（aA-a-1）) ≤b≤ (A+（aA+a+1）)/(A-（aA+a+1）)
(b) for (A-1)/(A+1)≤a≤1, the result is
(A+（aA-a-1）)/(A-（aA-a-1）) ≤b。
That is petty, and the requirement of surveying the threshold level from phantom inputs or outputs transducer for any one interdigital as can be known, must satisfy L
11〉=20, i.e. A=10.Therefore, above-mentioned (a) and result (b) can be reduced to:
(a) when 0≤a≤9/11,
(9(a+1))/(11-9a)≤b≤(11(a+1))/(9-11a) and
(b) when 9/11≤a≤1,
(9（a+1）)/(11-9a) ≤b。
As shown in Figure 4, the direction degree increase to 0.3 → 0.6 → 0.8 → 1.0, predetermined triplely to get over echo and suppress the b value scopes of level (in this being 20 decibels) and change b into and satisfy
a=0 → b
a=0.3 → b
a=0.6 → b
a=0.8 → ba=1, thereby the respective value (a=0) of the value of b during greater than complete one-way.
Thereby interdigital electrode become the phase difference that can provide predetermined with phase shifter configuration to realize incomplete one-way, thereby enlarge the range of choice of external loading admittance or transducer radiation admittance, undesirable triple to get over the gratifying level of echo to be essential and this radiation admittance is to suppressing.
Thereby eliminated in the prior-art devices adjustment that must do impedance.
Because the scope of mark Quasiization admittance is transferred to a number range bigger than prior art numerical value, the radiation admittance of having lowered transducer, the result has reduced the volume of filter itself greatly.
Though by L
31The loss of expression has increased, but this numerical value Yi Ban And is unlikely to big to the degree that in fact can not use this device.
Figure 5 shows that an instantiation filter of the present invention.Make its X axis the direction of propagation of surface acoustic wave as Piezoelectric Substrates 13 ， And one 128 ° single crystalline substrate of rotating the lithium niobate of Y-axis cutting.An interdigital input converter 14 and an interdigital output translator 15 respectively have group type unidirectional transducer parts that comprise 4 pairs 2 groups.Interdigital input converter 14 comprises interdigital sender electrode 18 and interdigital reflecting electrode 19.The interdigital output translator has identical Jie Gou And and is connected with load 21 by phase shifter 20.Yet, should have one at least in two transducers and have incomplete one-way.Phase shifter 16 is Bezier type phase shifters, and it and the inductor of one 1.99 microhenry and one 105.2 ohm resistor are in series.The inductance of above-mentioned inductor and resistor and resistance value should be chosen to be and make phase shifter 16 that one 120 ° electric phase difference be arranged.The distance 17 of the center to center between interdigital sender electrode and interdigital reflecting electrode is chosen to be 183.1 microns, thereby provides one 120 ° geometric phase poor.Therefore, electric phase difference and geometric phase difference and be about 1.33 π radians.Each transducer is to make by photoetching is carried out in the aluminium vacuum coating of 6000 dusts, and its centre frequency is 56.5 megahertzes.
Because signal source admittance and load admittance all equal 5 to 6 millimhos, so the hole length of transducer is set at 1200 microns, are 3.3 millimhos thereby make output/input admittance.Under certain conditions, can obtain a filter with 2.7 decibels of undesirable reflected wave level that insert losses and-44 decibels (triple get over echo).
As mentioned above, by the present invention as can be known, when comparing with the prior art wave filter, the present invention not only need not to make signal source or load admittance fully with consistent to inputing or outputing admittance, and can enlarge inconsistent tolerance band, thereby omitted the set-up procedure to signal source or load admittance. Also have, because the inputing or outputing admittance and can reduce in the above-mentioned tolerance band of contracting of surface acoustic wave filter, therefore, its volume also can dwindle. In above-mentioned object lesson, volume Reduce to reach 42%. When comparing with complete directional filter, although loss slightly increases, when comparing with the prior art bidirectional filter, it is quite low that loss remains.
In other words, the free degree ， And that the present invention can improve design of filter and side circuit design has realized the adjustment-free filter circuit, has reduced manufacturing cost, can make the commercial filter circuit that uses thereby provide.
Claims (3)
1, a surface acoustic wave filter is characterized by and has
One is used for the substrate of propagation surface sound wave;
The interdigital input converter that at least one constitutes on said substrate, said input converter are to be used for and signal source Lian And and change the signal of telecommunication of said signal source into surface acoustic wave Xiang;
At least one interdigital that constitutes on said substrate is failed parallel operation, and said output translator is to be used for and load Lian And and change a surface acoustic wave into the said signal of telecommunication Xiang; With
At least one said interdigital inputs or outputs transducer and comprises interdigital sender electrode parts and interdigital reflecting electrode parts, and above-mentioned interdigital sender electrode and reflecting electrode are mounted to and can produce a geometric phase difference φ between them
MHu Du And is connected to each other by a phase shifter, and this phase shifter can produce an electric phase difference between them
E, said phase difference and (φ
M+ φ
E) And is not equal to the π radian.
2, claim 1 desired surface acoustic wave filter is characterized in that, when by following formula
a＝ (1+Cos(φ
M+φ
E))/(1+Cos(φ
M+φ
E))
The value of defined number of degrees a is in the scope of 0≤a≤9/11 time, and G is received at least one said signal source or load
lWith said interdigital transducer admittance G
aRatio should meet the following conditions:
(9（a+1）)/(11-9a) ≤G
l/G
a≤ (11（a+1）)/(9-11a)
3, claim 1 desired surface wave filter is characterized in that, when by following formula
a＝ (1+Cos(φ
M+φ
E))/(1+Cos(φ
M+φ
E))
When the value of defined number of degrees a drops in the scope of 9/11≤a≤1, said signal source load admittance G
lWith said interdigital transducer emission admittance G
aRatio should satisfy following conditions:
(9（a+1）)/(11-9a) ＜G
l/G
a。
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN85101813A CN85101813B (en) | 1985-04-01 | 1985-04-01 | Surface acoustic wave filter |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN85101813A CN85101813B (en) | 1985-04-01 | 1985-04-01 | Surface acoustic wave filter |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN85101813A true CN85101813A (en) | 1987-01-10 |
| CN85101813B CN85101813B (en) | 1987-05-20 |
Family
ID=4792080
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN85101813A Expired CN85101813B (en) | 1985-04-01 | 1985-04-01 | Surface acoustic wave filter |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN85101813B (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6882249B2 (en) | 2000-06-27 | 2005-04-19 | Murata Manufacturing Co., Ltd. | Surface acoustic wave device |
| CN100474773C (en) * | 2004-11-23 | 2009-04-01 | 三星电子株式会社 | Monolithic duplexer and producing method thereof |
| CN108292912A (en) * | 2015-12-24 | 2018-07-17 | 株式会社村田制作所 | Acoustic wave device |
-
1985
- 1985-04-01 CN CN85101813A patent/CN85101813B/en not_active Expired
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6882249B2 (en) | 2000-06-27 | 2005-04-19 | Murata Manufacturing Co., Ltd. | Surface acoustic wave device |
| CN100474773C (en) * | 2004-11-23 | 2009-04-01 | 三星电子株式会社 | Monolithic duplexer and producing method thereof |
| CN108292912A (en) * | 2015-12-24 | 2018-07-17 | 株式会社村田制作所 | Acoustic wave device |
| CN108292912B (en) * | 2015-12-24 | 2021-10-08 | 株式会社村田制作所 | Elastic wave device |
Also Published As
| Publication number | Publication date |
|---|---|
| CN85101813B (en) | 1987-05-20 |
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