JPS59117311A - Elastic surface wave filter device - Google Patents

Abstract

PURPOSE:To attenuate reflected spurious radiation by connecting two elastic surface wave filters in series via a coupling circuit and making a delay time of the said filter at the poststage side different from that of the prestage by (2n+1)/ (4f0), (where: f0 is the center frequency). CONSTITUTION:The center distance between the 1st input IDT (reed screen transducer) 32 of the elastic surface wave filter F1 and the 2nd output IDT 33 is shifted by (2n+1)lambda/4 from the center interval between the 3rd input IDT42 of the elastic surface wave filter F2 and the 4th output IDT43. When a signal is inputted to the filter F1, the 1st signal having delay time tau1 and the 1st TTE (spurious component) having delay time 3tau1 are filtered to the filter F2. The filter F2 outputs the 2nd signal having delay time tau2 and the 2nd TTE having delay time 3tau2 to the 1st signal and outputs the 3rd signal having delay time tau2 and the 3rd TTE having delay time 3tau2 to the 1st TTE. Since there is a relation of tau2=tau1+(2n+1)/(4f0), the 3rd signal and the 2nd TTE are cancelled, resulting in that the reflected spurious component is reduced.

Description

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

[Technical background of the invention and its problems]

Conventionally, in order to reduce the attenuation of the surface acoustic wave filter, as shown in FIG. A surface acoustic wave filter consisting of a second interdigital transducer (hereinafter referred to as output IDT) (3) arranged opposite to (2) (hereinafter referred to as input IDT) and which converts a surface wave into an electrical signal. Quick second output IDT (3) i Nearbodies type weighting or axial weighting structure is used.

In addition, when using a small pressure substrate with large bulk spurious, as shown in Figure 2, an apodized type or axially weighted piezoelectric substrate αυ that converts electrical signals into surface waves is used.(12) output IDTs (13) that convert surface waves that have been subjected to apodized weighting or axial weighting that convert surface waves into electrical signals, which are disposed facing each other so as to have an axis different from the axis of Human power fD
Two multi-strip couplers were installed between the TQ2) and the output IDTα3) to perform surface wave track changes.

In a configuration with one stage of surface acoustic wave filter, approximately 5
QdB attenuation is achieved. As a countermeasure, as shown in Figure 3, amplifier 09, surface acoustic wave filter element 4 (22), amplifier (tough, surface acoustic wave filter
A structure using two stages of surface acoustic wave filters in which two (2 = l) are connected in series has been considered, and a sufficient amount of attenuation is achieved by these two stages of surface acoustic wave filters. It suppresses reflection components mainly from TTFj, is not affected by changes in load resistance, and has a constant loss of approximately -20 dB per stage without performing electrical impedance matching.
It will be used to some degree. For this reason, the amplifier (2])
(23) is required, which results in an extremely complex structure and a large size.

[Purpose of the invention]

The present invention was made in view of the problems mentioned above, and provides a surface acoustic wave filter device with a large guaranteed attenuation area without introducing an increase in constant loss even if a two-stage surface acoustic wave filter scheme is used. is intended to provide.

[Summary of the invention]

That is, the present invention includes a first interdigital transducer on a piezoelectric substrate that converts an electric signal into a surface wave, and a transducer disposed opposite to the first interdigital transducer that converts the surface wave into an electric signal. a second lattice-shaped transducer that converts electrical signals into surface waves; In a surface acoustic wave filter device, a surface acoustic wave filter F2 is connected in series via a coupling circuit with a fourth interdigital transducer disposed facing each other to convert a surface wave into an electric signal. , the passbands of the surface acoustic wave filter Fl and the surface acoustic wave filter are set to be almost the same, and the delay time at the center frequency f of the surface acoustic wave filter F2 is different from the delay time at the center frequency f0 of the surface acoustic wave filter F2. , habojodan (however, n-0+±1.±2.....
・) will move 4f.

This surface acoustic wave filter device is characterized in that it is set as follows.

[Embodiments of the invention]

Next, a fourth embodiment of the surface acoustic wave filter device of the present invention will be described.
This will be explained using figures.

That is, a first input IDTC 32+ for converting an electric signal into a surface wave and this first input IDTU are placed on the small pressure substrate 6υ.
A surface acoustic wave filter ≠ sheep (F l ) consisting of a second output IDT (1) arranged opposite to z and converting a surface wave into an electric signal, and this surface acoustic wave filter group −Il
The structure is almost the same as j (Fl), that is, the third input IDT (42+) that converts the electric signal into a surface wave and the input IDT (421) of this third input which converts the surface wave into an electric A surface acoustic wave filter (F2) consisting of a fourth output IDT that converts into a signal is provided, and an output IDT (C) (all four are apotized-type weighted and have almost the same structure). .That is, a little output IDT (43
is the output 1. It may be formed substantially longer than D T (33).

In addition, the distance between the center position of the first input IDT (, +21 and the output IDTi of 'A'r 2) of the human-powered IDTC 321 (the 4 units have the same structure, but the surface acoustic wave filter ≠ competition (Fl), +21 and 'A'r 2 output IDTi) is The center position of the third input IDT of the surface wave filter Rinhaya (F2) (・1 Enoki and the fourth output IDT (
It is shifted by 2n+1 - χ (however, n-0 in the figure) from the interval of 43. here(
λ) is a typical surface wave filter #sheep (F t ) (F'2
) is the wavelength of the surface wave corresponding to the center frequency.

The circuit actually used is an amplifier c39 as shown in Figure 5.
, surface acoustic wave filter ≠ support, ';li''l) and surface acoustic wave filter ≠≠ (F2) are connected in series via a coupling circuit (to), and the input signal ( e in) as a surface acoustic wave filter ≠ sheep (F
The first output signal (eo
utl) is further changed to constant loss -I QdB using a surface acoustic wave filter≠'+(F2).The second output signal (eout2)
It is designed to be.

Further, the coupling circuit (G) has a configuration in which, for example, L and R are connected in parallel. In this configuration, L is approximately the center frequency f. surface acoustic wave filter (F l )
output parallel capacitance M (C+.) and surface acoustic wave filter valve (
F 2 ) takes a value that satisfies the parallel resonance condition with the input parallel capacitance fit (C24). (R) is for loss adjustment, and the lowest loss is obtained when R is not inserted.

Figure 6 shows the temporal position of the response of each part of the circuit shown in Figure 5, and the input signal (51) is filtered as the first output signal of the surface acoustic wave filter ≠ sheep (FL) The first main signal (52
), (3τ,) and sends the first T T E (53) to the surface acoustic wave filter competition (F2) with a delay of (3τ,), as the second output signal of the surface acoustic wave filter competition (F' 2 ) with The second main signal (54) is delayed by the delay time (F2) of the surface acoustic wave filter (F2), the second T T E (55) of the first main signal (52) is delayed by (3τ2), and 1st
T T E (53) (F2) delayed first 'I
'Third main signal (56) from T E (53).

The third T T E (57) is output after a delay of (3τ2).

In this case, the most problematic reflection spurious is the relationship between the second J″T E (55) and the third main signal (56), and these signals (55) and (56) are inverted in phase. Surface acoustic wave filters by canceling each other, t=l
=-(Fl), (F2) Constant loss of approximately -20 dB due to TTE E suppression. For example, constant loss of approximately -20 dB even if not used.
Even when used under a coupling condition of 1QdB, anti-body spurious can be sufficiently suppressed.

If we devised this using a mathematical formula, we get eoutl "'A (e-j"r+ -1-B6-4
0):3'r, ) ein ++・, ■) However, e.

utl...Output e, n of filter F1...Input A of filter F1...Loss B of filter Fl-...Suppression of the main signal of TTE of filter F1 eout 2 "" ( e−”π2+Be−jω3T
2) eoutl -=-(2) eout2...
- Outputs A and B of filter F2 are set to be the same as filter F' from formula (1) + 2). out 2 :A2(.-Jω(τ1+τ2)+B
e−jω(τ1+3τ2)+Be−jω(3τ1+τ2
)−1−B2e−jω(3τ1+3τ2) )e+n
1. (3) Here, assuming τ2-τ and 107, the second term in parentheses.

The third term is f: Be-JOJO(τ, 1τ2) (e-jω.2 F2
+e7 jωo2τ1)=:, +36−1ω. (τ, +
τ2 ) e−Jωo2τ+(1+, −j(2n+1)
n)=0 and are canceled.

That is, the phase relationship at the center frequency of the response corresponding to each term is as shown in FIG. 7, with the second T T E (55) and the third main signal (56) corresponding to the spurious response.
will be in opposite phase and will be cancelled.

Figure 7 shows the phase difference between the main signal of the surface acoustic wave filter (Fl) and TTE.

Note that in this embodiment, a surface acoustic wave filter '#+ (F l
) and (F2) are substantially the same constant loss, but surface acoustic wave filters # (F l ) and (
It goes without saying that the constant loss may be different from F2).

〔Effect of the invention〕

As mentioned above, when two stages of surface acoustic wave filters are connected in series to ensure sufficient attenuation, the structure of the present invention allows constant loss to be kept at the same level as when using one stage. Its industrial value is significant because spurious signals can be effectively eliminated and the number of amplifiers can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a plan view of the main part showing an example of Ml in a conventional surface acoustic wave filter≠≠, and Fig. 2 is a conventional surface acoustic wave filter! −
Figure 3 is a block diagram of a surface acoustic wave filter device using conventional two-stage series-connected surface acoustic wave filters, Figures 4 and 7 are FIG. 4 is a plan view showing a state in which ten surface acoustic wave filters with different delay times are formed on a piezoelectric substrate, and FIG. 5 is a block circuit diagram showing an embodiment of the surface acoustic wave filter device of the present invention. 6 is an explanatory diagram showing the response position of each signal when two stages are connected in series, and FIG. 7 is an explanatory diagram showing the phase relationship of the responses of each signal when two stages are connected in series. 1.11.31... Piezoelectric substrate 2.12, 32.42..., input IDT 3.13, 33
．． 43...Output IDT36...Coupler agent Patent attorney Inoue -kirij Figure 3 t,=rodBθ=-zotls Q=zodB 5=
-zodBFigure 4Figure 5

Claims (2)

[Claims] (1) W, l that converts electrical signals into surface waves on a piezoelectric substrate
a surface acoustic wave filter Fl comprising a transducer in the form of a transducer and a second transducer in the form of a transducer, which is disposed opposite to the first transducer in the form of a transducer and converts a surface wave into an electrical signal; A third interdigital transducer for converting an electrical signal into a surface wave; and a fourth interdigital transducer for converting a surface wave into an electrical signal, which is disposed opposite to the third interdigital transducer. A surface acoustic wave filter device in which a surface acoustic wave filter F2 consisting of
The passbands of the surface acoustic wave filter Fl and the surface acoustic wave filter F2 are set to be substantially the same, and the delay time at the center frequency fo of the surface acoustic wave filter F2 is the delay at the center frequency f0 of the surface acoustic wave filter Fl. What about 2n+1 in time? Y 1q (however, n=0.±1.±2....
A surface acoustic wave filter device characterized in that the settings are different by...). (2) Surface acoustic wave filter F1 and surface acoustic wave filter F
2. The surface acoustic wave filter device according to claim 1, wherein the loss is set to be substantially the same as that of the surface acoustic wave filter device.