JPS60154706A - Surface acoustic wave filter device - Google Patents

Abstract

PURPOSE:To suppress the increase in a direct wave spurious radiation by making a passing phase amount of two stages of surface acoustic wave filters different by pi(2n+1) radians (where; n=0, + or -1, + or -2,...) substantially. CONSTITUTION:The 1st reed screen transducer input IDT32 transducing an electrical signal into a surface wave and the 1st output IDT33 transducing the surface acoustic wave into the electrical signal are provided to a piezoelectric substrate 30 so as to constitute a surface acoustic wave filter F1. A surface acoustic wave filter F2 is constituted by providing the 2nd inout IDT42 and the 2nd outout IDT43 on the piezoelectric substrate 31. The input IDTs 32, 42 are weighted by apodized form, the output IDTs 33, 43 are of normal type and have identical structure. In the distance between the input and output IDTs, the filter F2 is shifted from the filter F1 by (2n+1)lambda0/2 (where; n=0, + or -1, + or -2,...).

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to a surface acoustic wave filter device.

[Technical background of the invention and its problems]

Conventionally, in order to obtain the amount of attenuation in the stopband of a surface acoustic wave filter, a first interdigital transducer (1) for converting an electrical signal into a surface wave is placed on a piezoelectric substrate (1) as shown in FIG.
(hereinafter referred to as IDT) (2) and this first IDT (2)
) that converts the surface waves into electrical signals.
(3) are arranged together to form a surface acoustic wave filter,
For the second IDT (3), an avocado-type weighting structure or an axial weighting structure is used.

In addition, when using a piezoelectric substrate with large bulk spurious waves, as shown in Fig. 2, an avocized type or axially weighted first waveguide is placed on the piezoelectric substrate (11) to convert the electric signal into a surface wave. IDT (Apodized weighting that converts surface waves into electrical signals, which are arranged facing each other so as to have axes different from the 13 axes, and a second one that converts surface waves that have been weighted in the axial direction into electrical signals. A multi-strip coupler I was installed between the IDT ([3), the first IDT (12), and the second IDT (13) to change the track of the surface wave.

However, bulk spurious and first] IDT can be achieved at low cost.
(2) aD,! : 2nd (7) IDT (3
) <13 Due to problems such as electrical leakage, a single-stage surface acoustic wave filter configuration achieves only an attenuation of approximately (iQ dB).

As a countermeasure to this problem, as shown in Figure 3, a two-stage surface acoustic wave filter consisting of an amplifier CD, a surface acoustic wave filter (product), an amplifier (c), and a surface acoustic wave filter (product) are connected in series. There are configurations that achieve the amount of attenuation, but electrical leakage generated by the surface acoustic wave filter (24) and the surface acoustic wave filter Q4 (direct wave acid), such as electrostatic induction or electromagnetic induction in which unnecessary waves directly propagate through space, etc. The pre-ghost component (
For example, the main signal is also a component that appears earlier in time)
There is a danger that it will appear as

[Purpose of the invention]

In view of the above-mentioned problems, an object of the present invention is to provide a surface acoustic wave filter device capable of suppressing an increase in direct wave spurious even if a two-stage surface acoustic wave filter is used.

[Summary of the invention]

In order to achieve the above object, the present invention provides an arrangement in which the amount of passing phase at frequency f1 within the passband of surface acoustic wave filter F2 is equal to the frequency f of surface acoustic wave filter F1.

π(2n+1) for the amount of passing phase in -
Since the surface acoustic wave filter devices are set to differ by radians (n=0.±l]±2. . . ), direct wave spurious waves can be attenuated.

[Embodiments of the invention]

Embodiments of the surface acoustic wave filter device of the present invention will be described below with reference to the drawings.

In FIG. 4, a first interdigital transducer (hereinafter referred to as a first transducer) for converting an electrical signal into a surface wave is placed on a piezoelectric substrate (top).
C3D and the first input IDT (referred to as the input IDT of
A second interdigital transducer (hereinafter referred to as first output IDT) C31, which is disposed on a piezoelectric substrate (top) opposite to C32 and converts a surface wave into an electric signal, is connected to a surface acoustic wave filter. F1 is configured. Further, a third interdigital transducer (hereinafter referred to as the second input IDT) (42 and this The piezoelectric substrate 01 faces the second input IDT 14a.
A fourth interdigital transducer (J
A surface acoustic wave filter F2 is constructed from the second output IDT (43).The first input IDT 33 and the second input IDT f42 are weighted in an avoidized manner and have the same structure. The first output IDT e3) and the second output IDT (43 are normal IDTs and have substantially the same structure.Furthermore, the first input IDT of the surface acoustic wave filter F1 The interval between @■ and the first output IDT (c) is the distance between the second input IDT (421) and the second output IDT (421) of the surface acoustic wave filter F2.
The distance from 33 is also shifted by 2n+1 □·λ0 (although 1n=0.±1.±2. . . in the figure, n=0). Here, λ. is the wavelength of the surface acoustic wave corresponding to the center frequency f0 of the surface acoustic wave filters F1 and F2. In this way, the surface acoustic wave filter device shown in FIG. 4 is constructed.

Next, with reference to FIG. 5, an example of use of the surface acoustic wave filter device shown in FIG. 4 will be described.

In FIG. 5, in the circuit actually used, the left side of the surface acoustic wave filter F15υ and the surface acoustic wave filter F26 are cascade-connected via a coupling circuit, for example, an amplifier.

Furthermore, with reference to FIG. 6, the temporal position and magnitude of the response of each part of the circuit shown in FIG. 5 will be explained.

In FIG. 6, the input signal (61) as °C, (e,) is applied to the first output (eou) of the first surface acoustic wave filter F1.
jl), a first main signal (62) delayed by a delay time (r 2 ) of the first surface acoustic wave filter F1 and a direct wave component (63) with a delay time of 0 are output signals. This output signal is input to the surface acoustic wave filter F2 via the amplifier 69 shown in FIG. (e
The input signal (62) as ln2) is input as the second output (eont2) of the second surface acoustic wave filter F2.
The first main signal (64) delayed by the delay time (r) of the surface acoustic wave filter F2 and the direct wave component (65) with a delay time O
The input signal (63) generated from the direct wave component of the first surface acoustic wave filter F1 is outputted as the second output (eo,
t□), a second main signal (66) delayed by the delay time (τ,) of the second surface acoustic wave filter F2 and a direct wave component (67) with a delay time of 0 are output. Here, since rl and τ2 differ by a negative phase amount, the direct wave component (65) and the second main signal (66) have opposite phases and cancel each other out, and the direct wave spurious is attenuated. Ru.

If we consider this mathematically, eont -A (6-jo" + B) e 1.
, -(1) However, eout...Output e of the first surface acoustic wave filter...Input of the first surface acoustic wave filter...Loss B of the first surface acoustic wave filter
... Suppression of the main signal of the direct wave of the first surface acoustic wave filter -jωT2 e, u, = A (e + B) eo,, ・-(
2) However, eont2...The outputs A and B of the second surface acoustic wave filter F2 are the same as the first surface acoustic wave filter F1, and the setting amplifier is ignored (11, +21 to equation (3), τ, =τ, 10-, then the 21st in ()
0 term is at f = fo, -jωτ1-jωτ2 B(e +e) 1'°" -7g(r, +-; πゝ), -B(e 4-e -jωτ1 = t e (1+e' snow) -j0r1.f.) -B-e, (1+.-j-tytl,,--jωτ1 x13-e-(1+e-kawaza+x).

−jωτ.

wB −e ・(1+cos(−π(zn+x) )+
jsin (-π (2-+1))) J 6) r + = B-e (1-1) ; 0, so the formula (3) - At (e-ja + (r, + r2) t + B
)・ell becomes.

That is, the phase relationship at the center frequency of the response corresponding to each term in equation (3) is as shown in FIG. 7, and the direct wave spurious (65) and the direct wave spurious (66) are in opposite phase. be canceled out. Therefore, direct wave spurious waves are attenuated. However, in FIG. 7, the first surface acoustic wave filter Fl
Passing phase rotation amount 2mπ100 (m
is an integer).

As described above, in the embodiment of the surface acoustic wave filter device of the present invention,
In FIG. 4, the first input I of the surface acoustic wave filter F1
The interval between DT (to) and the first output IDT (to) is
The second input IDT of the surface acoustic wave filter P2 (43
Although the explanation has been given using an example in which the distance between the second output IDT (43) and the second output IDT (43) is even □・λ0, the surface acoustic wave filter device of the present invention is not limited to this. The second input IDT 143 and the second output IDT (
431 is substantially the same as that of the first surface acoustic wave filter F1, the surface acoustic wave filter F2
The amount of passing phase at the frequency fl within the passband of the surface acoustic wave filter F1 is the frequency f! substantially π(2n+1) radians (where n=0.
±1. ±2. ...It would be good if the settings were set differently only for the heat.

Furthermore, the effect is the same even if the surface acoustic wave filter F1 and the surface acoustic wave filter F2 are constructed from the same piezoelectric substrate or from different piezoelectric substrates. Furthermore, if the piezoelectric substrate of the surface acoustic wave filter Fl and the piezoelectric substrate of the surface acoustic wave filter F2 are different substrates, it is possible to make a difference whether these piezoelectric substrates are made of the same material or different materials. The effect is the same.

〔Effect of the invention〕

By adopting the above-mentioned configuration, the present invention can sufficiently attenuate direct wave spurious waves when surface acoustic wave filters are connected in series in order to ensure a sufficient amount of guaranteed attenuation. is extremely large.

[Brief explanation of drawings]

FIG. 1 is a plan view of a main part showing a first example of a conventional surface acoustic wave filter, FIG. 2 is a plan view of a main part showing a second example of a conventional surface acoustic wave filter, and FIG. FIGS. 4 to 7 are block circuit diagrams using two-stage series-connected surface acoustic wave filters, each showing an embodiment of the surface acoustic wave filter of the present invention. FIG. 4 is a plan view showing two stages of surface acoustic wave filters with different delay times formed on a piezoelectric substrate, and FIG.
Fig. 6 is an explanatory diagram showing the response position of each signal of the surface acoustic wave filter of Fig. 4. Fig. 7 is an explanatory diagram showing the response position of each signal of the surface acoustic wave filter of Fig. 4. FIG. 3 is an explanatory diagram that does not show the phase relationship of responses. (1), αn, (g), 01)...Piezoelectric substrate (21,
(121, Zeng... 1st IDT (3), (13)
, 4331-Second IDT(4), C1,4)
, (aZ-$3 <2) IDT03...
・4th IDT Agent Patent Attorney Kensuke Chika (and 1 other person) 3rd
Figure 4 Figure 5 Figure 6 Figure 7 Figure 270゛31-

Claims (4)

[Claims] (1) A first interdigital transducer comprising a first interdigital transducer disposed on a piezoelectric substrate and a second interdigital transducer disposed opposite to the first interdigital transducer. a surface acoustic wave filter F1, a third interdigital transducer disposed on the piezoelectric substrate, and a fourth interdigital transducer disposed opposite to the third interdigital transducer. In a surface acoustic wave filter device in which a second surface acoustic wave filter F2 consisting of It should be noted that it is set to be substantially different from the amount of passing phase at frequency f1 of surface acoustic wave filter F1 by π(Zfl+1) radians (however, n-0, ±1, ±2,...). Surface acoustic wave filter device with % characteristics. (2) The surface acoustic wave according to claim 1, wherein the first surface acoustic wave filter and the second surface acoustic wave filter are disposed on the same piezoelectric substrate. filter device. (3) The elastic surface according to claim 1, wherein the first surface acoustic wave filter and the second surface acoustic wave filter are disposed on different piezoelectric substrates. Wave filter device. (4) Claim 3, characterized in that the piezoelectric substrate of the first surface acoustic wave filter and the piezoelectric substrate of the second surface acoustic wave filter are made of different materials.
2. The surface acoustic wave filter device described in 2.