SIST EN 61019-2:2005

Surface acoustic wave (SAW) resonators -- Part 2: Guide to the use

Gives practical guidance to the use of surface acoustic wave (SAW) resonators which are used in telecommunications, radio equipments and consumer products. Is to be used in conjunction with EN 61019-1. The features of SAW resonators are small size, light weight, adjustment-free and high stability. operating frequencies extend to the VHF and UHF ranges.

Oberflächenwellenresonatoren (OFW-Resonatoren) -- Teil 2: Leitfaden für die Anwendung

Résonateurs à ondes acoustiques de surface (OAS) -- Partie 2: Guide d'emploi

Gives practical guidance to the use of surface acoustic wave (SAW) resonators which are used in telecommunications, radio equipments and consumer products. Is to be used in conjunction with EN 61019-1. The features of SAW resonators are small size, light weight, adjustment-free and high stability. operating frequencies extend to the VHF and UHF ranges.

Resonatorji za površinske akustične valove – 2. del: Vodilo za uporabo (IEC 61019-2:2004)

General Information

• Status: Published
• Publication Date: 30-Nov-2005
• ICS: 31.140 - Piezoelectric devices
• Technical Committee: SS EIT - Technical Board for the electrotechnical, information technology and telecommunications fields
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 01-Dec-2005
• Due Date: 01-Dec-2005
• Completion Date: 01-Dec-2005
• Ref Project: EN 61019-2:2005 - Surface acoustic wave (SAW) resonators - Part 2: Guide to the use

Relations

• Replaces: SIST EN 61019-2:2002 - Surface acoustic wave (SAW) resonators -- Part 2: Guide to the use
• Effective Date: 29-Jan-2023
• Revised: SIST EN 61019-2:2002 - Surface acoustic wave (SAW) resonators -- Part 2: Guide to the use
• Effective Date: 13-May-2010

Standards Content (Sample)

SLOVENSKI SIST EN 61019-1:2005

STANDARD
december 2005
Resonatorji za površinske akustične valove – 1. del: Generična specifikacija
(IEC 61019-1:2004)
Surface acoustic wave (SAW) resonators – Part 1: Generic specification (IEC
61019-1:2004)
ICS 31.140 Referenčna številka
SIST EN 61019-1:2005(en)
©  Standard je založil in izdal Slovenski inštitut za standardizacijo. Razmnoževanje ali kopiranje celote ali delov tega dokumenta ni dovoljeno

---------------------- Page: 1 ----------------------

EUROPEAN STANDARD EN 61019-2
NORME EUROPÉENNE
EUROPÄISCHE NORM June 2005

ICS 31.140 Supersedes EN 61019-2:1997


English version


Surface acoustic wave (SAW) resonators
Part 2: Guide to the use
(IEC 61019-2:2005)


Résonateurs à ondes acoustiques  Oberflächenwellenresonatoren
de surface (OAS) (OFW-Resonatoren)
Partie 2: Guide d'emploi Teil 2: Leitfaden für die Anwendung
(CEI 61019-2:2005) (IEC 61019-2:2005)






This European Standard was approved by CENELEC on 2005-06-01. CENELEC members are bound to
comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on
application to the Central Secretariat or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CENELEC member into its own language and
notified to the Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Cyprus, Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden,
Switzerland and United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Central Secretariat: rue de Stassart 35, B - 1050 Brussels


© 2005 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.

Ref. No. EN 61019-2:2005 E

---------------------- Page: 2 ----------------------

EN 61019-2:2005 - 2 -
Foreword
The text of document 49/714/FDIS, future edition 2 of IEC 61019-2, prepared by IEC TC 49,
Piezoelectric and dielectric devices for frequency control and selection, was submitted to the
IEC-CENELEC parallel vote and was approved by CENELEC as EN 61019-2 on 2005-06-01.
This European Standard supersedes EN 61019-2:1997.
The main changes with respect to EN 61019-2:1997 are listed below:
– at the end of 5.1, the edge reflector has been added. Its reference literature has been inserted in
the bibliography;
– in Table 1, the propagation properties of LiNbO3 (64° Y) have been added;
– in Table 3, the clause and subclause numbers have been corrected in order to be consistent with
EN 61019-1:2005.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2006-03-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2008-06-01
Annex ZA has been added by CENELEC.
__________
Endorsement notice
The text of the International Standard IEC 61019-2:2005 was approved by CENELEC as a European
Standard without any modification.
__________

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- 3 - EN 61019-2:2005
Annex ZA
(normative)

Normative references to international publications
with their corresponding European publications
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
NOTE Where an international publication has been modified by common modifications, indicated by (mod), the relevant
EN/HD applies.
Publication Year Title EN/HD Year
IEC 61019-1 2004 Surface acoustic wave (SAW) resonators EN 61019-1 2005
Part 1: Generic specification

IEC 61019-3 1991 Part 3: Standard outlines and lead - -
connections

---------------------- Page: 4 ----------------------

INTERNATIONAL IEC


STANDARD 61019-2





Second edition
2005-05


Surface acoustic wave (SAW) resonators –
Part 2:
Guide to the use

 IEC 2005  Copyright - all rights reserved
No part of this publication may be reproduced or utilized in any form or by any means, electronic or
mechanical, including photocopying and microfilm, without permission in writing from the publisher.
International Electrotechnical Commission, 3, rue de Varembé, PO Box 131, CH-1211 Geneva 20, Switzerland
Telephone: [phone] Telefax: [phone] E-mail: [e-mail] Web: www.iec.ch
PRICE CODE
Commission Electrotechnique Internationale U
International Electrotechnical Commission
МеждународнаяЭлектротехническаяКомиссия
For price, see current catalogue

---------------------- Page: 5 ----------------------

– 2 – 61019-2  IEC:2005(E)
CONTENTS

FOREWORD.3
INTRODUCTION.5

1 Scope.6
2 Normative references .6
3 Technical considerations .6
4 Fundamentals of SAW resonators.7
4.1 Basic structure .7
4.2 Principle of operation .7
5 SAW resonator characteristics.8
5.1 Reflector characteristics .8
5.2 SAW resonator characteristics.10
5.3 Spurious modes .14
5.4 Substrate materials and their characteristics .15
5.5 Available characteristics.17
6 Application guide.19
6.1 Oscillator circuits and oscillation condition .19
6.2 Practical remarks for oscillator applications.21
7 Checklist of SAW resonator parameters for drawing up specifications .22

Bibliography.25

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61019-2  IEC:2005(E) – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

SURFACE ACOUSTIC WAVE (SAW) RESONATORS –

Part 2: Guide to the use


FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61019-2 has been prepared by IEC technical committee 49:
Piezoelectric and dielectric devices for frequency control and selection.
This second edition cancels and replaces the first edition published in 1995. This edition
constitutes a technical revision.
The main changes with respect to the previous editon are listed below:
• at the end of 5.1, the edge reflector has been added. Its reference literature has been
inserted in the bibliography;
• in Table 1, the propagation properties of LiNbO (64° Y) have been added;
3
• in Table 3, the clause and subclause numbers have been corrected in order to be
consistent with IEC 61019-1 (2004) which has replaced IEC 61019-1-1 (1990) and IEC
61019-1-2 (1993).

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– 4 – 61019-2  IEC:2005(E)
The text of this standard is based on the following documents:
FDIS Report on voting
49/714/FDIS 49/723/RVD

Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
IEC 61019 consists of the following parts, under the general title Surface acoustic wave
(SAW) resonators
Part 1: Generic information
Part 2: Guide to the use
Part 3: Standard outlines and lead connections
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.

A bilingual version of this publication may be issued at a later date.

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61019-2  IEC:2005(E) – 5 –
INTRODUCTION
This part of IEC 61019 gives practical guidance to the use of SAW resonators which are used
in telecommunications, radio equipments and consumer products. IEC 61019-1 can be referred
to for general information, standard values and test conditions.
The features of these SAW resonators are small size, light weight, adjustment-free and high
stability. In addition, the operating frequency of SAW resonators extends to the VHF and UHF
ranges.
This part has been compiled in response to a generally expressed desire on the part of both
users and manufacturers for a guide to the use of SAW resonators, so that the resonators
may be used to their best advantage. To this end, general and fundamental characteristics
have been explained in this guide.

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– 6 – 61019-2  IEC:2005(E)
SURFACE ACOUSTIC WAVE (SAW) RESONATORS –

Part 2: Guide to the use



1 Scope
SAW resonators are now widely used in a variety of applications: VCR RF-converters, CATV
local oscillators, measuring equipment, remote control and so on. While SAW resonators are
also applied to narrow bandwidth filters, the scope of this part of IEC 61019 is limited to SAW
resonators for oscillator applications
It is not the aim of this guide to explain theory, nor to attempt to cover all the eventualities
which may arise in practical circumstances. This guide draws attention to some of the more
fundamental questions, which should be considered by the user before he places an order for
a SAW resonator for a new application. Such a procedure will be the user's insurance against
unsatisfactory performance.
Standard specifications, such as those of the IEC of which this guide forms a part, and
national specifications or detail specifications issued by manufacturers, will define the
available combinations of resonance frequency, quality factor, motional resistance, parallel
capacitance, etc. These specifications are compiled to include a wide range of SAW
resonators with standardized performances. It cannot be over-emphasized that the user
should, wherever possible, select his SAW resonators from these specifications, when
available, even if it may lead to making small modifications to his circuit to enable the use of
standard resonators. This applies particularly to the selection of the nominal frequency.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 61019-1:2004, Surface acoustic wave (SAW) resonators – Part 1: Generic specification
IEC 61019-3:1991, Surface acoustic wave (SAW) resonators – Part 3: Standard outlines and
lead connections
3 Technical considerations
It is of prime interest to a user that the resonator characteristics should satisfy particular
specifications. The selection of oscillating circuits and SAW resonators to meet such
specifications should be a matter of agreement between user and manufacturer.
Resonator characteristics are usually expressed in terms of resonance frequency, motional
resistance, quality factor and parallel capacitance (for the one-port type) and centre
frequency, insertion attenuation, loaded and unloaded quality factor, input capacitance and
output capacitance (for the two-port type). A standard method for measuring resonator
characteristics is described in 8.5 and 8.6 of IEC 61019-1. The specifications are to be
satisfied between the lowest and highest temperatures of the specified operating temperature
range and before and after environmental tests.

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61019-2  IEC:2005(E) – 7 –
4 Fundamentals of SAW resonators
4.1 Basic structure
SAW resonators consist of interdigital transducers (IDT) and of grating reflectors, which are
placed on the surface of a piezoelectric substrate. In most cases, the grating reflectors are
made of thin metal (such as Al, Au) film while, in some cases, they are constructed with
periodic grooves. The die is bonded by an adhesive agent into a sealed enclosure, and the
IDT is electrically connected to the terminals with bonding wires. There are two SAW
resonator configurations. One is a one-port SAW resonator. The other is a two-port SAW
resonator. The former has a single IDT between two reflectors, as shown in Figure 1. The
latter has two IDTs between two reflectors, as shown in Figure 2. In the figures, l is the
eff
resonator cavity length, as described in 5.2 c).

l
eff
S
Grating reflector Grating reflector
d = λ /2
0
IDT
IEC  694/05

Figure 1 – One-port SAW resonator configuration
l

eff
S
Grating reflector Grating reflector
IDT
d = λ /2
0
IEC  695/05

Figure 2 – Two-port SAW resonator configuration
4.2 Principle of operation
The resonance phenomenon for SAW resonators is achieved by confining the SAW vibration
energy within grating reflectors. The SAW, excited by an alternating electrical field between
IDT electrode fingers, propagates outside the IDT to be reflected by grating reflectors.

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– 8 – 61019-2  IEC:2005(E)
The grating reflectors feed the perturbation to the SAW, owing to the discontinuity in electrical
or mechanical impedance. When the SAW is incident on such grating reflectors, the incident
wave is gradually converted into a reflected wave. Although the amount of perturbation per
unit reflective element may be very small, a large number of such elements, arranged
periodically, reflect the SAW in phase, and maximize coherent reflection.
These grating configurations can form effective reflecting boundary, creating a standing wave
between the reflectors and make resonance with a very high Q. Figure 3 shows the
displacement distribution for this standing wave for a one-port SAW resonator. As shown in
the figure, the SAW energy is maximum near the centre of the IDT, and gradually decays
towards the edges of the grating reflectors. The resonance frequency, f , is approximately
r
determined by
f ≈ v /(2d) = v /λ
r s s 0
where
v is the SAW propagation velocity;
s
d is the distance between electrode centres;
λ is the SAW wavelength at the stop band centre frequency.
0

IDT
Grating reflector Grating reflector
d
Substrate
SAW energy
distribution
IEC  696/05

Figure 3 – Standing wave pattern and SAW energy distribution
5 SAW resonator characteristics
5.1 Reflector characteristics
The reflector for SAW resonators consists of a periodically arranged array of reflective
elements, called a grating reflector. As cross-sections show in Figure 4, possible array
elements are:
a) metal strips or dielectric ridges;
b) grooves;
c) ion-implanted or metal-diffused strips.
For example, an aluminum strip on ST-cut quartz, whose thickness h is 1 % of wave length
λ(h/λ ) and whose width w is half the spatial period (w = d/2 = λ /4), has a small reflection
0 0
coefficient ε of approximately 0,5 %. A groove with 1 % depth has almost the same ε. This
periodic perturbation causes efficient reflection of SAW energy, if its wavelength equals twice
its periodicity.

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61019-2  IEC:2005(E) – 9 –

h
d
IEC  697/05

4a – Metal strips or dielectric ridges

IEC  698/05

4b – Grooves

IEC  699/05

4c – Ion-implanted or metal diffused strips
Figure 4 – Grating reflector configurations
A grating reflector without loss with a finite number of array elements has a frequency range
of nearly total reflection called the stop band. The fractional stop bandwidth to centre
frequency is 2ε/π, where ε is the reflection coefficient for one element. Figure 5 indicates the
frequency dependency on the total reflectivity |Γ| for the grating reflector with a finite number
N of array elements. Theoretically, the reflectivity maximum value is derived as:
R
|Γ| = tanh(N × ε)
max R
at the centre frequency f of the stop band. A greater reflectivity makes SAW resonator Q
0
value higher, due to decreasing the leakage of SAW energy stored in the cavity between two
grating reflectors.

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– 10 – 61019-2  IEC:2005(E)

1,0
N × ε = 2
R
0,5
0,0
–4 –2 0 2 4
(f – f )
0
Frequency × ε/π
f
0
IEC  700/05

Figure 5 – Reflectivity response for grating reflection
For obtaining a greater reflectivity, it is clear, from the preceding equation, that N × ε should
R
be larger. Increasing reflector element number N is the easiest way to obtain a higher
R
reflectivity. However, in practice, a greater element number, i.e. longer reflector size, requires
a larger SAW chip size and means an expensive SAW resonator. Generally, N × ε = 4 is
R
adequate for practical SAW resonators.
For obtaining greater reflectivity, increasing the reflection from one element is also effective.
To accomplish this, strips should be thicker or grooves should be deeper. For the most part,
ε is proportional to the thickness or the depth h/λ . Thicker strips or deeper grooves require
0
less element number N for the same reflection coefficient and realize greater stop
R
bandwidth. However, a reflector with a large h/λ has the following disadvantages:
0
a) the mode conversion loss from SAW to bulk wave tends to increase, which may degrade
the quality factor;
b) stopband centre frequency deviation from the frequency v /(2d) increases, because the
s
centre frequency is a function of the square of h/λ . This may cause mass production
0
difficulties.
For a substrate material supporting shear wave, reflection at the edge of a substrate can be
utilized as a substitute for a grating reflector. This gives the advantage of size reduction
corresponding to the size of array elements.

5.2 SAW resonator characteristics
a) One-port SAW resonators
A one-port SAW resonator has the transmission characteristics shown in Figure 6.
Reflection coefficient  |Γ|

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61019-2  IEC:2005(E) – 11 –

Spurious
resonance
Frequency
Frequency
of maximum of minimum
admittance (f ) admittance (f )
m n
Frequency  MHz
IEC  701/05

Figure 6 – Typical frequency characteristics for a one-port SAW resonator,
inserted into a transmission line in series
The equivalent circuit in Figure 7 represents this one-port SAW resonator resonance.
Comparing SAW resonators made from different piezoelectric materials, the figure of merit
M = Q/r derived from the equivalent circuit can be used. For example, SAW resonators on
a quartz substrate have a high Q factor and a large r, while the values on X-cut LiTaO
3
are both smaller. Both resonators have similar figure of merit values. Considering only Q
or the capacitance ratio r is insufficient for comparison purposes.
The equivalent circuit in Figure 7 can be replaced by a reactance with a series resistance:
R (f) + jX (f), where X and R are an equivalent series reactance and an equivalent series
e e e e
resistance, respectively. The frequency dependencies for these values are shown in
Figure 8, where the value X /R reaches the maximum at the arithmetic mean of
e e
resonance and anti-resonance frequencies of zero susceptance.

L R
1 1
C
1
C
0
IEC  702/05

1
 is the motional (series) resonance frequency;
f =
s
2π L × C
1 1
Q = 2πf × L /R is the quality factor;
s 1 1
r = C /C is the capacitance ratio;
0 1
M = Q/r is the figure of merit;
L , C , R are the motional inductance, motional capacitance and motional resistance respectively;
1 1 1
C is the static capacitance.
0
Figure 7 – Equivalent circuit for a one-port resonator
Attenuation  dB

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– 12 – 61019-2  IEC:2005(E)

X
e
≈ M
R
e
4
R
e
Resonance frequency
of zero susceptance (f )
r
X
e
Anti-resonance frequency
of zero susceptance (f )
a
X
e
Frequency
IEC  703/05

Figure 8 – Frequency response for series equivalent resistance (R ),
e
reactance (X ) and X /R
e e e

The maximum value can be derived from the equivalent circuit as:
(X /R ) ≈ (Q/r) /4
e e max
In order to achieve oscillation more easily, resonators should show high Q reactance.
Consequently, the figure of merit is adequate to compare SAW resonators.
Resonator impedance is inversely proportional to the aperture design. However, an over-
narrow aperture resonator tends to increase r, due to the stray capacitance, and to
degrade Q, due to the diffraction loss. On the other hand, an over-wide aperture resonator
has a relatively low Q, due to electrode resistance.
b) Two-port SAW resonators
Two-port resonator transmission characteristics are shown in Figure 9.
(arbitrary unit)

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61019-2  IEC:2005(E) – 13 –

Minimum insertion
attenuation
Spurious
response
rejection
Centre frequency (f )
c
Frequency  MHz
IEC  704/05

Figure 9 – Insertion attenuation and spurious response characteristics
for a two-port resonator
An equivalent circuit for a two-port SAW resonator, in the vicinity of the centre frequency,
is shown in Figure 10. It is constructed with a motional arm with motional inductance (L ),
1
capacitance (C ), and resistance (R ) in series, two parallel capacitances (C and C )
1 1 IN OUT
shunting the input and output ports and an ideal transformer. The turns ratio φ for the ideal
transformer is derived from the input and output transducer structures. When both
structures are the same, the φ value is unity; a 0° phase shift type is expressed as φ = 1
and a 180° type is expressed as φ = –1. Two-port SAW resonators, with different input
and output impedances, have a |φ| value, which is not equal to unity.

C
1
L R
1 1 1:φ
C C
IN OUT
IEC  705/05

Key
L motional inductance C input capacitance
IN
1
C motional capacitance C output capacitance
OUT
1
R motional resistance φ  turns ratio
1
Figure 10 – Equivalent circuit for a two-port resonator
For two-port resonators, there is no evident index as figure of merit as for one-port
resonators. Easy-to-oscillate resonators are devices with low loss in the specific circuit
and with the appropriate phase transition of 0° or 180°. Small motional resistance R is
1
essential for low loss. A lower impedance resonator (larger C and C ) has lower loss,
IN OUT
in most cases.
Attenuation  dB

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– 14 – 61019-2  IEC:2005(E)
c) Equivalent circuit parameters
Equivalent circuit parameters for a one-port SAW resonator can be represented as follows,
when SAW reflection at IDT fingers is neglected:

l /λ
eff 0

L = × R
1 a
4 f Γ
0
1− Γ
R = × R
1 a
Γ
2
1
C =
1
2
(2πf ) L
0 1
C = N × w(1+ ε )× ε
0 r 0
where
1
R = is the IDT radiation resistance at f ;
a
0
2
8k f NC
s 0 0
f = v /(2d);
0 s
N is the IDT finger pair number;
w is the aperture;
2
k is the SAW coupling coefficient;
s
ε is the relative permittivity of a piezoelectric substrate;
r
ε is the permittivity of vacuum;
0
Γ is the reflection coefficient of a reflector;
λ is the SAW wavelength at the centre frequency;
0
l is the resonator cavity length shown in Figures 1 and 2 (l ≈ S + λ /(2ε)), where S
eff eff 0
is a separation of grating reflectors.
For two-port SAW resonators, C shall be replaced by C or C respectively. Other
0 IN OUT
equations are the same as the above equations.
5.3 Spurious modes
SAW resonators have many kinds of spurious modes. One is higher-order SAW resonance
modes, called longitudinal and transverse modes. Other types of SAW modes, such as leaky
SAW, SSBW, Love waves, may be excited by the IDT. Another mode is bulk wave modes.
Figures 6 and 9 show the typical spurious characteristics for one-port and two-port
resonators, respectively. These spurious modes can be reduced by applying several
techniques to the resonators.
When used in an oscillator circuit, these spurious modes rarely cause problems. However,
should there be spurious responses near the main mode or responses with relatively large
amplitude, oscillation problems at those spurious frequencies could occur.
These spurious responses could result in anomalous frequency-temperature, resistance-
temperature and frequency pulling characteristics. Even very small perturbations of this type
can have very deleterious effects for VCO (voltage controlled oscillator) applications. It is
more difficult to eliminate these spurious responses from the resonators. However, these
resonators seldom give trouble, because the spurious resonance resistance is in general
larger than that for the main mode. Manufacturers' standard products involve design
measures which mini
...