DE1920078C - Electromechanical filter arrangement - Google Patents

Description

Filtering of the type in question occurs, FIG. 9 the reactance diagram of the two-pole, justifies that it is extremely difficult to achieve the exact which the longitudinal and diagonal branches of the cross-degree of that mass load, which link according to FIG. 5 in the event that the resonance frequency in each electrode of the filter according to F i g. 4 massed and leads intermediate resonator. It is known that pre-5 are arranged at a distance from one another that a precision adjustment is available, for example with the aid of weak coupling.
Laser cutting beams to achieve a certain F i g. 10 shows a diagram to illustrate the Ande-Elektrodenmas.se \ erwendet and that ments of the real part of the characteristic impedance dei the resonance frequency at the electrodes of this circuit according to FIG. 4 and 5 can be measured simultaneously in the two Passsonators. If io range under the conditions of Figs. 9. But then the frequency measuring device is dis- F i g. 11 is a diagram showing the Überfernt is, the resonance frequency shifts of the tragungskennlinie the circuits of F i g. 4 and 5 resonators something and it must then largely be based on the conditions of FIG. 9 and 10, namely calculations based on empirical principles at the end with a fixed resistor, which is the right one for and subsequent additional adjustments.
can be taken in order to arrive at the desired theoretical frequency. Clarification of a test method for measuring the

The object of the invention is, accordingly, such coupling between the resonators, which by the

Eliminate resonance frequency shifts and create electrode pairs of the F i g. 1 and 2 are formed, and

thus the adjustment of these crystal filters significantly to 20 Fig. 13, 14 and 15 diagrams to illustrate the

simplify. Parameter relationships for determining the

According to the invention, this task is for the measurements of the filter arrangement according to FIG. 1 and 2.

electromechanical filter arrangement of the introductory In the case of the in FIG. 1 shown embodiment

described type solved in that the two of the filter are 8 pairs of electrodes 12, 14; 16, 18;

Electrodes of each intermediate resonator via 25, 20, 22; 24, 26; 28, 30; 32, 34; 36, 38; 40, 42 in alignment

outer switching means conductively connected to one another with the crystallographic Z-axis on one

are. rectangular / -ir cut quartz crystal flake 44

In the simplest case, a connection is simply vapor-deposited or plated on. The thickness of the electrical conductors between the two electrodes. This erodes and the platelets are shown in FIG. 2 For the sake of clarity, it is sufficient that no displacement of the resonance is shown on an enlarged scale. The electrodes of a frequency occurs when the frequency measuring devices of each pair face each other. A source S after adjusting the mass loading of the electrodes supplies a high frequency voltage to the input removed. As a result, the actually measured electrodes 12 and 14 match and generate thickness shear vibrations in the crystal precisely with the actually existing resonance plates 44 at the piezoelectric resonance frequency of each intermediate resonator. The vibrations correspond in the crystal frequency as this was set. A much closer correspondence is obtained between pairs of 12 to 42 oscillations at ui <d on the En _L throw data and the actual data of the electrodes 40 and 42 in turn electrical energy filters, so that optimally a constant frequency response is obtained. Each pair of electrodes, together with the 40 optimally steep platelets within the pass band, forms a resonator that can be reached at neighboring ReFlanken. is coupled to sonators. An output resistance R ₀

The invention is illustrated below with reference to the drawing which receives the output electrodes 40 and 42

explanation explained in detail; it shows occurring electrical energy. The middle elec-

F i g. 1 shows a schematic plan view of a pair of invention electrodes 16 to 38, filters 45, which are designed according to the short term, are all closed and grounded.

F i g. 2 a sectional view of the arrangement according to The masses of the electrodes 12 to 42 are made of F i g. 1, large enough to absorb the vibrational energy in the platelet F i g. 3 a diagram to show the excess on the volume of the platelet between the elec-

load characteristic of the filter according to FIG. 1 and 2, trod each couple to focus and energize

F i g. Figure 4 is a schematic view of a filter such as 50 with increasing distance from the one being viewed

according to FIG. 1 and 2, but only with two pairs of electrodes to attenuate exponentially. This limits that

pair, effect of the platelet limits on the

F i g. 5 the conditions within the platelet, which can be reproduced by a cross member. At the same time is the Equivalent circuit diagram of the filter according to FIG. 4, distance between pairs of electrodes, together F i g. 6 the reactance diagram of the two-poles, 55 with the degree of the mass loading so that the pairs

which the longitudinal and diagonal branches of the cross are coupled to each other in order to be given with a certain

member according to F i g. 5 in the event that in FIG. 4 Passband within the bandwidth limits (Fig. 3)

The filters shown have no masses and are compliant.

a distance are arranged such that a In addition, the masses and the distance

there is strong coupling between them, 60 chosen so that any two adjacent electrode

F i g. 7 is a diagram showing the frequency pairs are in a defined coupling relationship,

of the real part of the wave resistance of the This means that if the we-

Circuit according to FIG. 4 for the conditions of the kings of all other electrodes the real part of the

F i g. 6, wave resistance that any two neighboring

F i g. 8 shows a diagram to represent the over 65 pairs with increasing frequency, to effective

load characteristic for the circuits according to FIG. 4 resistance ranges, each in separate frequency

and 5 under the conditions of FIG. 6 and 7, in areas leads, with in a frequency range the

Termination with a fixed resistance, real part of the wave resistance a finite maximum

mum between two zeros of the resistance and wherein in the other separate frequency range the characteristic impedance is a minimum between has two poles of the effective resistance. This effect is brought about by sufficiently massive Forming any two pairs of adjacent electrodes and providing one sufficiently large Distance between them such that the otherwise undisturbed coupling between them is such that cine Frequency bandwidth from a resonance at an impedance zero to a resonance at a Another impedance zero point (coupling bandwidth) is available, which is smaller than the smallest frequency range between resonance and anti-resonance frequency of one of the two coupled pairs. In the embodiment according to FIG. 1 the effect is emphasized, so that any two adjacent electrode pairs are coupled weaker than a third of the maximum definitive coupling. That is, they are sufficient massive and sufficiently spaced that the otherwise undisturbed coupling between them is such that the coupling band width is smaller than one third of the smallest resonance frequency-anti-resonance frequency range one of the coupled resonators.

The effects in the case of only two such pairs of electrodes can be demonstrated on the basis of such a filter with two resonators of a source S and a load resistor R ₀ (FIG. 4) and of the equivalent circuit diagram formed by a circuit (FIG. 5). to be viewed as. The equivalent circuit diagram shows electrically the coupling effect of two resonators on filters that only have two coupled resonators. Here the capacitors C ₁ A and C ₁ B control the resonance frequencies of Za and Zb and change with the coupling. For the non-coupled case, C ₁ A is equal to C ₁ B. The stronger the coupling, the greater the C ₁ A and the smaller the C ₁ B. In FIG. 5 is the characteristic impedance of the filter Z _(- | z "z _K, where Zoc the impedances when the load or is open shorted g for the cross member to F i 5 \ _ζ Λ ζ Β · Since the crystal body 44.. has a high 2-value, the values of Za and Zβ consist almost exclusively of their reactances Xa and Xr. Therefore, the characteristic impedance Zi is equal to YXaXb-

In the case of crystal arrangements which are not loaded with mass by the electrodes , vibrations generated by the source S excite large areas of the crystal body. The coupling is then much stronger than electrodes loaded with masses. In the case of a very strong coupling, the reactances Xa and Xb then change with the frequency as shown in FIG. 6 is shown

Since Xa and X _{B are} imaginary numbers , that is to say that they are equal to jX'a and jXa, their product is negative if they have the same sign, but positive if they have different signs. Only the square root of a positive number is real. _{The filter therefore only has characteristic impedances Z 1} which are positive and real in the frequency ranges in which X _A and Xb appear on opposite sides of the abscissa. This real positive wave resistance is the effective resistance Rt. As shown by the curves of the real part of Ζ * in FIG. 7, there are two real positive wave resistances or effective resistances R _t for the strong coupling according to FIG. 6. They each extend over the lower resonance frequency-antiresonance frequency range / a to / _ü a and over the upper resonance frequency-antiresonance frequency range / b to barrel of the resonators, which are represented by the individual impedances Za and Z _n . Since the insertion loss is a minimum when the terminating resistance R ₀ is matched to the real wave resistance Rt , the insertion loss for such a device is very high in the wave blind resistance range / _o , i to Jb - it is only low in the vicinity of the two frequencies where R ₀ crosses the value Ri . For low load resistances, the curves in FIG. 6 shows the insertion loss or the transmission characteristic as shown in FIG.

If the electrodes are given sufficient mass, the thickness vibration energy in the plate is increased 44 concentrated between the electrodes of the respective pairs, so that the crystal body 44 exponentially with it decreasing amplitude oscillates outside the volume between the electrodes. the Coupling between the resonators therefore decreases. It prevents significant energy from the Limits of the body reached. Such

»5 The mass loading of the electrodes creates two reso. nators when two pairs of electrodes are used.

If each resonator is placed in the effective field of the other, they work similarly to one

Transformer.

3 «Line increase in the distance between the fiectrode pairs and an increase in the electrode mass reduces the coupling between the resonators. When this occurs, the resonance frequencies / a and Jb approach each other. If the coupling is low enough that / β is smaller than / „a, the individual reactance curves Xa and Xb get those from FIG. 9 visible form. The resonance frequency-antiresonance frequency ranges overlap there. Therefore / b- / a is smaller than / „α- / α · The resulting wave resistance Zt, ie Ri appears in the real plane of F i g. 10. As shown in FIG. 10, the resistance Ri has two positive real ranges. One area extends between the resonance frequencies and has a maximum between the values of zero. A second range is between f _aA and / _aB . There Rt begins in infinity and becomes finite again when the frequency increases. Signal energy in one of the two frequency ranges can be blocked

So by terminating the electrode within the resistance range of one resistor Rt but away from the other. Since in FIG. 10 A _{0 is} well matched to the wave resistance within the lower range, the system lets signal energy through at frequencies between f _A and / β with little attenuation. The curve showing the insertion loss for a filter under these conditions and at a load with a resistor / 2 , is shown in FIG. 11 shown.

The conditions of Fig. 9, 10 and 11 can be ensured by applying a control voltage with a source impedance to one pair of electrodes and by short-circuiting the other in a monolithic filter with two electrodes mate. The input voltage to the controlled pair is then noted.

The frequencies at which the noted input voltage is lowest are then measured.

7 8

This then sets the frequencies Ja and Jb distances d, to d ₇ between neighboring edges,

. When the coupling bandwidth century-Yes, this measure in the longitudinal direction, are in centimeters the fol-

is the bandwidth of one point of resonance for the following:
the impedance zero to the other, is smaller
as the anti-resonant frequency-resonant frequency range S <A = 0.0945, rich JaA-Jα of each of the two coupled d _s = 0.1059,

Resonators, then the conditions exist </ ₃ _ 0.10823,

the F i g. 9, 10 and 11. This is the condition ^ _ q'iO87

which here as the definitive coupling condition ⁴ _ _n ' _inR9 ~

bc7cichnet is. The resonators or electrodes- to "s ~ 0.10823, pairs are therefore» definitely coupled. If Jb-Ja ^ e ~ 0.1059,

is equal to or greater than JaA-Jα , the conditions d, - 0.0945 apply.

the F i g. 6, 7 and 8. The coupling coefficient k between these pairs is then equal to (Jb-Ja) I \ f _A fu- These distance measurements have tolerances of

For practical purposes lies to the maximum 15 -i 0.000254 cm. The electrode masses are so

Impedance value between / «and Yes much smaller than that selects that relative frequency shifts of 3.0 ° / ₀

the minimum impedance value between JaB-JaA can be achieved. These relative frequency differences

machcn, the value Jb-Ja generally below both exercises represent a measure of the effect of the masses

(/ «« - // 0/3 as well as (JaA-J, \) ß- This represents one of the electrodes

quatc rejection of a band and an adequate 20 around the drop (J-Jr) IJ in the resonance frequency / _r

Passage of the other with suitable termination - one with a single pair of electrodes in contact -

evaluate the resistance R ₀ safely. crystal body compared to the thickness shear

In Fig. 1 and 2 are adjacent pairs of electrodes, oscillation frequency / of the uncontacted crystal

When viewed on its own, also in the upper body due to the increasing electrode masses,

Finished "definitive" coupling state. That is, »5 based on the size /. This contributes to that

they obey the rules shown in Figs. 9, 10 and U take account of the fact that with increasing electrical

provided rule. These conditions can therefore affect the resonance frequency of the individual

Any pairs that can be identified are assured of sonators, measured when other resonators are out of tune.

By supplying a variable frequency drive voltage, it is lowered.

tion to one of the neighboring P; are. by Kurz- 30 The resulting normalized Kopplunexschlii ßc 1 of the other neighboring pair and by coefficients k between successive pairs of offeilases of the fading pairs. An example from left to right in Fig. 1 and 2 are 0.7277; a useful arrangement for testing the 0.5451; 0.51560; 0.5101; 0.5160; 0.5451 and 0.7277. Coupling between two adjacent pairs is shown in the arrangement of FIG. 1 and 2 leave a middle fig. 12 shown. Here a variable frequency band frequency of 8.141830 megahertz is through and has test source 60 connected to the electrodes 20 and 22, a transmission frequency bandwidth of about 3.2 kHz. and electrodes 24 and 26 are short-circuited. The resonator inductance is 44.2 mHy and sen. The other pairs of electrodes are open. The voltage applied to the quality factor Q of the resonator is about 160,000, electrodes 20 and 22 are measured by a voltmeter 62 around a good frequency response within the passage. The applied frequency 40 frequencyb; ndbnite. The source S has quenz the source 60 is at Hen two lowest a resistance of 36 ohms, and the output voltages indicated by the voltmeter 62 measured, the voltage of the electrodes 40 and 42 is the ohm when the frequency output of the source 60 is changed see load Λ _ο from 736 ohms is supplied. These two measured frequencies are the result of the electrodes being matched. Frequencies J _A and Jn- In F i g. 1 is Jb-Ja less than 45 while at the middle of the desired band it is short as JaA-Jα or JaB-Jb- Therefore the two pairs are closed, | In fact, only those frequencies in the definitive coupling state. which are assigned to the low impedance.

The remaining electrodes are not able to influence them by the on inanderfe Igenden electrode pairs measurements appreciably because the KAPA transmitted Aufeinanderfclgende resonators capacity C ₉ of the metal electrodes, the frequencies of these 5 ° each by a short-circuited electrode pair gePaare far enough from the frequency spectrum Jb-Ja weg · forms are similar to arbi Hen until the last electrode pushes in order to avoid significant interference which gives the voltage to the load R _0. In the process of determining the coupling

If necessary, an additional inductance between adjacent pairs (Fig. 12), it is the liveness parallel to the remaining electrodes 12 55 capacitances C _{0 of} the open pairs that these are switched sufficiently to 18 and 28 to 42 to their Fre- detune, so as not to quench the measurement of f _A and Jb further away from the range Jb-Ja . If the disgruntlement is caused by some grande, mung as a result of the open state »is not sufficient

An example of suitable dimensions for the connection is an inductance parallel to those elec-

order according to fig. 1 and 2 is the following. These 60 trodes switched, their coupling not measured

Dimensions are illustrative only, not being made to detune them or C to be anti-resonant

but to be understood in a limiting sense. Make this one.

For example, the crystal body consists of a 3.480 cm. In operation, the source S supplies an alternating voltage long, 0.118 cm wide and approximately 0.019827 cm to the electrodes 12 and 14. These electrodes are thickened / cut quartz crystal bodies. The dimensions 65 produce acoustic energy in a piezoelectric way . Because of the length of the crystal body, that is, the Z 'axis of its mass loading, which is the relative frequency and 0.2H8 cm perpendicular / ur /' axis. The electrode shift creates, these electrodes catch most of the time

9 'ίο

the vibrational energy within the crystal body speaks, namely by having the desired

44 into the volume between the electrodes and mid-band frequency f _m - fr makes. Hence applies

draw this vibrational energy from the edges of the · f - ff-f

Body 44. However, the vibrations Pb ~ - = ■ -——

between the first pair of electrodes on top of each other- 5 ff

following into the acoustic area of the following f _m

Electrode pairs and excite within the load / = ■ ·

range vibrations of the ^{B between these electrodes}

same frequency. The vibrations at the end of the manufacturing process begins with cutting Electrode pairs generate piezoelectrically io a plate 16 of a quartz crystal of the appropriate electrical output voltage, the desired crystallographic orientation on the load, z. B. appears. a / ίΓ-cut. The platelet is then on a

The term "thickness shear vibrations" or thickness t ground and etched that of the desired

"Thickness shear mode" is used in the sense of the fundamental frequency / the shear oscillation, either <'er \

uses how this in McCraw-Hill Encyclopedia of 15 parallel or the torsional shear vibration, i

Science and Technology, published by M> G raw- corresponds to. Generally the thickness is inversely pro- Hill Book Company of New York, 1966, Volume 10, proportional to the desired frequency. Masks with Pp. 220, 221 and 222; it thus includes corresponding sections on each surface

the vibrations under which the opposing crystal platelets are arranged serve

the surfaces along their planes in relation to one another for depositing the electrodes. The geometry

oscillate in opposite directions, and close the electrodes is made by the considerations on the

the vibrations, in which the parts of the desired bandwidth and the appropriate relative

same area both in and out of phase or frequency shift.

swing out of phase. The latter form of thickness The correct distances ind d between the electrodes

Shear vibrations is sometimes called the thickness- 25 can be based on curves, for example the in

torsional waveform referred to. It occurs in the manner shown in Figs. 13, 14 and 15, be determined

if on a ΛΓ-cut quartz crystal the electrodes the dependency of the coupling for different

troden are aligned in the Z 'direction. Dar In- Relationship of electrode spacing to chip thickness

The phase state occurs when on this crystal the and for various relative frequency shifts _w

fclektroden are aligned in the Ä-direction. 30 also for different values of rji in one

Show thickness shear oscillations and thickness shear oscillation center frequency.

shape also relate to vibration, which in order to achieve the desired relative frequency shift

occur when the electrodes get on the examples, gold or nickel is for example

adhere ΛΓ-cut crystal in directions between wise by layer-by-layer vapor deposition through the

are aligned in the X and Z 'directions. 35 Mask thrown down in order to also

An example of curves that allow for arrangements, at- conclusions and nearly total for example the one shown in FIG. 4, which work in the desired relative frequency shift with respect to the basic thickness shear waveform. Energy is given separately for each pair of electrodes has been wrapped and fed to the design of the crystal, and Misse will be the electrodes for so long arrangement are useful, are supplied in Figs. 13, 14 40, until a: frequency shift accordingly and 15 shows the desired overall relative frequency difference

The crystal arrangement according to FIG. 1 and 2 will shift occurs. This is done until

produced by first coming into resonance with the whole of the pair at the frequency / »,.

Bandwidth Bw selects and based on the during this lowering procedure, the

habitual circuit theory detuned the coupling coefficient 45 other pairs of electrodes by leaving them open

zient {fs-fA) IVfλ / β remain between each pair of electrodes. However, it may be necessary to use the influence

calculated. Electrode sizes and a suitable change of the other pairs dadu-ch zu ver.niidjn that one

lative frequency shift value (from 0.3 per cent until it terminates inductively. The middle electrodes

3%) is made from curves, e.g. B. the one in Fig. 13, 14 and 15 are then short-circuited. The coupling and

type shown, selected. Does t mean the platelets - so does the frequency response of each »pair of coupled resonances ·

Thickness and t the width of the electrodes, so will rft in gates are then measured, and the desired

generally equal to 12, although in practice bandwidths should lead. Settings can

any value between 20 and 6 is usable A by slightly changing everyone's plateback

Value of 15 1 is often made as the length of the electrodes electrodepiares

used perpendicular to the coupling axis to avoid good un- 55 So a reliable energy transfer is obtained.

to have suppression of other forms of vibration. arrangement for selected frequency bands

The DickenscheTS fundamental oscillation frequency / is so and filter that on only one crystal in small

determines that it can be produced according to the selected plateback Pb sizes.

For this 2 sheets * .sluiung

Claims (1)

piezoelectric crystal platelets, both of which Patent claims: each side is provided with an electrode are. Resonators of this type are generally Electromechanical filter arrangement for the known and are described, for example, in "Physical passage of a selected frequency band. 5 Acoustics and the Properties of Solids ", p. 146, with a piezoelectric body (44, Fig. 1 D. Van Nostrand Co., New York, 195K of and 2). the one with opposite surfaces \ er VV. P. M as ο η. The Herstel.ung a ^r plurality of such see, for operation in Dickenseherschwin- resonators is in the USA. Patent 3,384,768 is cut conditions, and described a resonator. According to this, a large number of independent arrangements can be made on the crystal body with a suspended resonator by means of a Be input resonator. an output resonator and fixing pairs of electrodes on a common at least one intermediate resonator, each piezoelectric plate. In this known resonator through that part of the 11th-order crystal, neither an electrical nor a body is formed which is provided with a mechanical coupling between the resonators opposite the two surfaces of the crystal body. on standing arranged pair of electrodes (12-14, there has been no lack of attempts to a elektio- ! 6-18 ..., 36-38, 40-42) , and to manufacture each mechanical filter by using a P.esonntor loaded with ground and with its pair of input electrodes and a pair of output each neighboring resonator acoustically coupled electrodes on a common piezoelectric is such that the frequency response of the real part of the 20 platelets is arranged so close to one another Characteristic impedance (FIG. 10) of the filter can be converted into a mechanical, i.e. H. acoustic steadily running part of the curve to ensure the coupling between them from zero. The one increases to a maximum value and then the relevant state of the art is the following: decreases to zero, within a limited Has impedance range, and such that 25 ^L " ^{New Method of} Providing Coupling Between the filter - seen as a whole - a replacement resonator in an Electromechanical Filter, «by circuit diagram in the form of a cross-link network M. R e d w ο ο d and N. H. C. R e 1 1 1 y, elec- (Fig. 5) with a reactance frequency response ^{tromcs Letters} ' ^Bd · ² ' ^{June 1966} > ^s · ²² ° ^{to 222} '> (Fig. 9 ;. has, at which the two resonance frequency 2. »A Method for Measuring Equivalent Circuit Antiresonant frequency-ßoreiche {fa-faA and / _ß -30 Constants of Electromechanical Filters, «by faß) overlap each other, thereby making M. Onoe, The Journal of the Institute of indicates that the two electrodes Electrical Communication Engineers of Japan, (16-18 ..., 36-38) of each intermediate resonator Volume 43, No. 8, August 1960, pp. 884 to 889 and conductive through external switching means comparable with each other ■, _{A., iU} λ e »R ■ r- ■ 1 * / - · ... j 3. “A Method for Measuring Equivalent Circuit Dunaen sina. 35 Parameters of Electromechanical Filters, «by M. O η ο e, The Jouritd! of the Institute of Elec- trical Communication Engineers of Japan - Abstracts, Volume 43, No. 8, August 1960, pp. 3 and 4. 40 In addition, in the above work The invention relates to an electromechanical and also the possibility of using a twin filter arrangement for the passage of a frequency band selected from the input and output resonator, with a piezoelectric and also acoustically coupled Resotric body with opposing surfaces nators suggested. 45 According to an older proposal, a band-pass filter with two resonators can be produced on the crystal body with an input resonator, using an input electrode, an output resonator and at least one pair and one of these at a spaced Ausschenresonator, whereby each resonator is formed by the pair of passage electrodes as the two resonators that part of the crystal body, which 5 <> on a common piezoelectric plate, between one on the two faces of the crystal if to fulfill the body described in the introduction opposite arranged electrode conditions a load of each resonator is located with a pair, and each resonator with mass precisely determined mass (mass load) in Verlastet as well as with its respective neighboring resonator binding with a likewise precisely determined en is acoustically coupled in such a way that the frequency response 55 stic degree of coupling is provided. The equal of the real part of the characteristic impedance of the filter, if provided, use of one or more continuously running curve part, which increases a maximum value from zero to intermediate resonators according to the older one and then increases again on suggestion, the order of the filter decreases in maihe-NuIl, within a limited Impedance-matic sense and leads, accordingly, to a surrounding area, as well as in such a way that the filter - as a ^6o settlement characteristic, which seen a flatter passage whole - an equivalent circuit diagram in the form of an area (pass band) with steeper edges compared to cross-member network rr. it shows a reactance-frequency case in which only a single gear is used in which the two resonance-frequency-anti-resonator pairs are used. Each of the intermediate resonance frequency ranges overlap one another. resonators is characterized also by mass Piezoelectric resonators have long been ⁶ 5 load and acoustic coupling with as frequency determining Vonichtungen adjacent in electronic resonators.
niche circuits have been used. The basic A problem associated with the additional resonator device consists of a position of composed of many resonators