JPH0269012A - Demultiplexer - Google Patents

Abstract

PURPOSE:To make the handling of a demultiplexer in which surface acoustic wave filters are constituted and mounted as a transmission and reception filters easier and, at the same time, to miniaturize the demultiplexer by providing linear inductors to the demultiplexing circuit. CONSTITUTION:Surface acoustic wave filters respectively constituted of piezo-electric substrate 55 which propagate surface acoustic waves and interdigital electrodes 56 for input-output which alternately exchange electric signals and surface acoustic waves are respectively constituted as a transmission and reception filters 41 and 42 and mounted on a substrate 1. In addition, inductors composed of fine lines are formed on the rear of the substrate 1. Namely, inductors 29-31 substituting for the demultiplexing constant line of a demultiplexing circuit are formed. Since the single chip bodies of the surface acoustic wave filters are inserted into a can case for maintaining airtightness, such constitution increases the sealing effect and the need of soldering the can case of the filters to the substrate is eliminated. In addition, handling of the multiplexer becomes easier and the multiplexer can be miniaturized. Moreover, when the inductors are used as the demultiplexing circuit, the line length and the occupying area of the circuit can be reduced as compared with strip lines composed of demultiplexing constant lines.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a duplexer installed in a car telephone device for separating a transmitted signal and a received signal.

(Prior Art) Conventionally, the transmission and reception filters of duplexers used in car telephone devices have mainly been dielectric filters using dielectric resonators. A duplexer used in a car telephone device has an essential function for performing two-way radio broadcasting. In other words, a circuit that separates, within the car phone device, the necessary reception signal of the car phone device and the transmission signal sent out from the car phone device among the signals input by the antenna provided in the car phone device serves as a branching switch. be.

For example, AMPS (Δdbvanced Mobile
In the case of 832CH transmission, the transmission band for car telephone equipment in the United States using the PhoneService method is 824CH.
~849MHz reception band is set to frequencies of 869~894MHz. The dielectric filter described above is used as a filter to cover these bands.

FIG. 2 is a diagram showing a conventional duplexer using a dielectric filter, and FIG. 2(a) is a diagram showing an example of the configuration of the duplexer.
FIG. 2(b) is a back view of the substrate of the duplexer. A duplexer using a dielectric filter includes an insulating substrate 1 made of alumina, glass epoxy, etc., two transmitting dielectric filters (hereinafter referred to as transmitting filters) 6 with different center frequencies mounted on the top surface of the insulating substrate 1, and a receiving filter. It is composed of a dielectric material (hereinafter referred to as a receiving filter) 7. The insulating substrate 1 is provided with a plurality of input/output terminal sections 3 and a ground pattern 2 on its upper and lower surfaces by thick film printing, plating, or the like. A plurality of input/output terminal sections 3 provided on the upper and lower surfaces of the substrate 1 are connected to each other by through holes for connecting the upper and lower surfaces. On the other hand, the dielectric filter 6.7 is, for example, as described in Japanese Patent Application No. 59,201455 filed earlier by the applicant of the present application.
A block-shaped filter body 4.5 made of a homogeneous single dielectric material, and a plurality of dielectric resonators 8, 12 made of cylindrical center conductors embedded in the filter bodies 4, 5 at predetermined intervals. , a plurality of frequency adjustment patterns 9, 13 are connected to the center conductor of each dielectric resonator 8, 12 and formed on one side of the filter body 4.5, and input/output terminal portions 3 are provided at each side end. , and input/output electrodes 10.11.14.15 for connection to the through holes. Also,
The resonant frequency of each dielectric resonator is determined by the height and frequency adjustment pattern of each dielectric resonator, and this adjustment is performed by a mechanical method, an optical method, or the like.

A pair of branching circuits 16 and 17 made of distributed constant lines such as strip lines are formed on the lower surface of the substrate 1 by thick film printing, plating, or the like. Furthermore, a low-pass filter 18 for spurious removal is connected to the branching circuits 16 and 17. Each branching circuit 16.17 has an input/output terminal section 3, an input/output electrode 10
．． 11.14.15 to each filter 6.7 on the top side.

Here, one branching circuit 16 and receiving filter 7 connected in series is connected to the other branching circuit 17 and transmitting filter 6 in order to avoid mutual influence. At the center frequencies of the passbands of the wave circuit 16 and the reception filter 7, the input impedance of one of the branching circuits 17 and the reception filter must be sufficiently high. For this purpose, the line length of each branching circuit 16, 17 is determined as follows.

Consider a case where the demultiplexing circuit 17 and the transmission filter 6 are connected in cascade. SL+ of the S matrix in this case is given by the following equation.

S+ + (1) = [rcos θ −cos θ
+zsin θ+j(sinθ+zcosθ−rsin
θ) 1/ [rcosθ+cosθ−zsinθ+j(
sinθ+zsinθ+rsinθ)l...(1) Here, θ=ββ, β=2π/λ, ρ=line length of the branching circuit 17, input impedance of the transmission filter (zin
) = r + jz.

When the input impedance of the serially connected branching circuit 17 and the transmitting filter 6 is in the passband of the receiving filter,
In order to achieve a sufficiently high value, 5ll(1) in the above formula (1) should be minimized.

That is, cosθ=zsinθ...-(2)
It can be seen that θ should be selected so that In this case, the above equation (1) becomes as follows.

S+ 1(1) = [rcosθ+j(sinθ+z
”sinθ−rsinθ)1/[rcosθ+j(s
inθ+z2sinθ+rsinθ)]...(3) Here, when the above equation is expressed in terms of input impedance (Zin), it becomes as follows.

1in= [(1+j”)/rl −jZ
(4) That is, the input impedance of the series-connected branching circuit 17 and the transmitting filter 6 is set to a sufficiently high input impedance in the pass band of the series-connected branching circuit 16 and receiving filter 7 (if the input impedance is not high enough). It won't happen.

Therefore, the branching circuit 17 and the transmission filter 6 connected in series form an attenuation region. In this case, in equation (4) above, r
It can be considered that <<1. Therefore, the above formula (4) is defined as Zi
n>>1, and they have no influence on each other.

Further, it can be seen that the phase angle of Zin must be used as an example because the real part in the above equation (4) becomes sufficiently large.

In this way, in a duplexer using a dielectric filter for a car phone, the transmitting filter and the receiving filter are inserted into one and the same case, and the case is covered with a lid to provide a shielding effect. Furthermore, in order to obtain sufficient grounding, the board forming the branching circuit and the case must be soldered.

(Problem to be solved by the invention) However, in the duplexer using the conventional dielectric filter with the above configuration, the transmitting filter and the receiving filter are inserted into the same case as described above, and the shielding effect is In addition, it is necessary to solder the board and case that form the branch circuit to ensure sufficient grounding, and it is also necessary to configure a branch circuit using the length of the strip line. However, since the substrate area becomes large, it is difficult to downsize and reduce the cost of the duplexer.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an excellent duplexer that can solve the problems of the prior art, is easy to handle, and can be miniaturized.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides a branching circuit on a substrate, a piezoelectric substrate connected to the branching circuit that propagates at least surface acoustic waves, and an electric signal and a piezoelectric substrate connected to the branching circuit. In a duplexer that is implemented by constructing a surface acoustic wave filter consisting of input and output blind electrodes that mutually convert surface acoustic waves as a transmission filter and a reception filter, a linear inductor is provided in the duplexer circuit. This is what I did.

(Function) According to the present invention, since the duplexer is configured as described above, the transmission filter and the inductor connected in series can be connected by connecting the transmission filter and the reception filter made of the surface acoustic wave filter to the inductor of the branch circuit. At the passband center frequency of the other series-connected receiving filter and inductor, the input impedance of the other series-connected receiving filter and inductor is set to be sufficiently high (and at the passband center frequency of the series-connected receiving filter and inductor, the input impedance of the other series-connected receiving filter and inductor is set to a sufficiently high The input impedance of the transmitted filter and inductor is set to a sufficiently high value, and the transmitted signal and received signal can be separated.

Therefore, by using surface acoustic wave filters as transmitting and receiving filters, surface acoustic wave filters can be made smaller than dielectric filters, and there is no need to provide a lid for shielding effect or to solder the filter case to the branching circuit. Moreover, the branching circuit made of linear inductors on the board has a shorter line length and occupies a smaller area than a conventional strip line.

Therefore, the present invention can eliminate the above-mentioned problems and provide an excellent duplexer that is easy to handle and can be miniaturized.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a configuration diagram of a duplexer showing an embodiment of the present invention, FIG. 1(a) is a diagram showing the configuration of the duplexer, and FIG.
) is a back view of the duplexer board.

In the figure, 1 is a substrate (for example, a glass epoxy resin substrate or an alumina substrate), 41 is a surface acoustic wave filter (Surface Acoustic Pave Fi
2 is a ground pattern, 22 is an antenna terminal, 23 and 25 are Rx (reception filter) terminals, and 24.26 is a Tx (transmission filter) terminal. It is.

Furthermore, an inductor consisting of fine lines is formed on the back surface of the substrate 1. In other words, 29.30.31 is an inductor LAR29, L□30°LR that replaces the distributed constant line in the branch circuit.
It is T31.

FIG. 3 is a diagram showing a typical example of a SAW filter.

In the same figure, the interdigital electrode 5 is placed on one piezoelectric substrate 55.
Two sets of 6 are provided, one for input and one for output. This electrode is created by vapor deposition, sputtering, or the like. This electrode works as an interdigital transducer (TDT) that generates and detects surface acoustic waves.

The operating principle of this SAW filter is that electrical signals input from electrical signal input terminals 51-52 in FIG. 2 are converted into surface acoustic waves by interdigital electrodes 56 provided on the input side. The electrode width (2d) of this interdigital electrode is determined by Vt/4f. Vt is the propagation velocity of the ^ever used as the piezoelectric substrate 55, and fo is generally the center frequency of the filter. Further, the band of the filter is determined by the number of electrode pairs. This elastic wave converted into a surface acoustic wave propagates within the piezoelectric substrate 55 and reaches the electrode 56 on the 7 output side, where it is converted again into an electric signal and supplies energy to the load on the output side.

Next, the present invention will be explained in detail. The duplexer shown in Fig. 1 is, for example, a duplexer for American AMPS car telephones, and has a transmission filter N with a passband 1BW of 824 to 849MHz.
, 41. , BW;869. 894MHz (7
) It consists of a receiving filter N242 and a branching circuit τ. Sending and receiving flaps inserted into the case. - The filters 41 and 42 are SAW filters having a structure as shown in FIG.

FIG. 4 is a block diagram of the above-described branching device. , Receive filter 4; Purchase:, I dialect consists of a SAW filter as I did, input/output terminals 23, 24, 25 in 1.
．． 26, 7I"1., '-('. Next, the input invader +, ;) characteristics of the transmitting/receiving filter will be explained.

Input impedance characteristics (absolute value) diagram of old J transmission filter N, where the horizontal axis shows frequency (%
IHz), the absolute value of input impedance (Ω) is shown on the vertical axis, and the input and output terminal capacitances are 2.3 pF and 2.5 pF.
The case of F is plotted.

As is clear from this figure, the input impedance approximates 50Ω in the passband BW of 824 to 849 MHz of the transmission filter N. Moreover, when the passband is exceeded, the input impedance increases rapidly.

FIG. 6 is a diagram of the input impedance characteristics (phase angle) of the transmission filter N, in which the horizontal axis shows the frequency (MHz), the vertical axis shows the phase angle θ (ω)°, and the input and output terminal capacitances 2. 3
pF and 2.5 pF are plotted 1. As is clear from this figure, the phase angle is close to O in the pass band BW of the transmission filter N, 824 to 849 MHz.

Figure 7 is an input impedance characteristic (absolute value) diagram of the receiving filter N2, where the horizontal axis shows the frequency (MHz), the vertical axis shows the absolute value of the input impedance (Ω), and the input and output terminal capacitances are 1.8 pF and 2. The cases of .0 pF and 2.2 pF are expressed as -1+71.

As is clear from this figure, the input impedance is generally close to 50Ω in the pass band BW of 869 to 894 MHz of the reception nl filter N2.

Figure 8 is a diagram of the input impedance characteristics (phase angle) of the receiving filter N2, where the horizontal axis shows the frequency (MHz), the vertical axis shows the phase angle θ (ω)°, and the input and output terminal capacitance is 1.8P.
The cases of F, 2.0 pF and 2.2 pF are plotted.

As is clear from this figure, the phase angle is generally close to O in the passband BW of 869 to 894 MHz of the reception filter N2.

By the way, one of the points in which the present invention differs from the prior art shown in FIG. 2 is that instead of the distributed constant circuit, inductors LAR29, LRE30, . This is especially true when installing LRT31.

The invention will be described in detail below based on the operation of this inductor.

First, inductors LAR29, LRE30. LRT
Consider the case where there is no 31. For convenience of explanation, the center frequency f of each passband of the transmission filter N1 and the reception filter N2.

Only 836.5 MHz, f, and 881.5 MHz will be described.

B I [fO=836.5MHzl, B2 [f
Regarding O=881.5 MHzl, the following can be considered from FIGS. 5 to 8.

B: r+=50. Ox+=Orz; o xz
=-j30B2: r+=o X2”-186
,0r2=50. Oxz=0 When a duplexer is configured with this transmitting/receiving filter, B l rf,=836.5MH
zl, B, [f, = 881.5 MHzl, the input impedance Zin and the mismatch attenuation RL seen from the ANT end are determined by the transmission filter N1. It is degraded compared to the case where the reception filter N2 is used alone.

B, : Zin =13.254-j22.06
8RL =3.88dB B2: Zin =46.62-j12.541
RL = 17.5 dB From the above equation, it can be seen that the problem is that X2 in the B band is small. Under the condition that X2 in the B1 band is small, LR
=5nH is added. Input impedance Zin at this time
And the mismatch attenuation RL is as follows.

B+: Zin = 17.9-j28.66
44RL = 4.67dB B2: Zin = 45.4545. 114
．． 341RL = 16.15dB Next, LRE will be explained.

If this LRE is LIIE:"20nH, this LR
After addition of t, Bl, Zin and RL in B2 are as follows.

B, : Zin =32.2633-j31.8
74RL =7.67dB B2: Zin =49.14 +j6.7125
RL = 23.34 dB It can be seen that this LRE operates to make the imaginary part of Zin(f) relatively small compared to the real part in the B, ., B2 bands.

Next, LAR will be explained. This L-ori...:4
When nH is assumed, LRE and RL at B, , B2 are as follows.

B+: Zin=32.2633-jlo
, 888RL=12.01dB Bz: Zin=49.14 +j28.
834RL = 11.08dB In other words, this LAR makes the imaginary part of Zin smaller on average in the B, B2 bands. Therefore, this L
By using RA, LIIE, and LAR, a duplexer satisfying RL>1OdB, which is required as a duplexer for a car telephone, can be obtained.

This Lp+7. L□ and LAR were explained using an example, but
island.

Similar operations can be performed as long as the trend of Zin of N2 does not change.

In addition, when actually forming LR and LREIAR on a glass epoxy substrate (permittivity 4.8, thickness 1.6 mm), when fo = 850 (MHz), the inductance is when the line length is β. , is shown by the following equation.

(1) When W (width) is 0.3 mm, L (nH)
= 1.389 jN+r, 11) - 5,3443 Therefore, for example, in the case of LRT = 5 nH as described above, A = 7.45 mmL,!
= 20 nH, A = 18.25 mm LA,
= 4nH, ρ" is 6.73mm.

(2) When W (width) 0.5mm, L (nH)
=1.092 0 (mm) -2,4726(3)
When W (width) is 0.7 mm, L (nH) = 1.
0135° C. (mm) −2,1753 Furthermore, if it is formed on an alumina substrate (dielectric constant 9.3), the line length β can be further shortened.

Note that the present invention is not limited to the above embodiments,
Various modifications are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

(Effects of the Invention) As explained in detail above, according to the present invention, the single SAW filter chip is inserted into the can case to maintain airtightness, so this plays the role of a shielding effect.
There is no need to solder the SAW filter's can case to the board, making it easier to handle and expected to be smaller than conventional dielectric filters. Furthermore, by using an inductor in the branching circuit, the line length is shorter than that of a strip line using a conventional distributed constant line, so the area occupied by the branching circuit is expected to be smaller (or so on). Can be made smaller.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of a turnout showing one embodiment of the present invention;
Figure 3 is a block diagram of a conventional duplexer, Figure 3 is a diagram showing a typical example of a SAW filter, Figure 4 is a block diagram of the duplexer in Figure 1, and Figure 5 is a transmission filter N. Figure 6 shows the input impedance characteristics (absolute value), Figure 6 shows the input impedance characteristics (phase angle) of the transmitting filter NI, Figure 7 shows the input impedance characteristics (absolute value) of the receiving filter N2, and Figure 8 shows the input impedance characteristics (absolute value) of the receiving filter N2. It is a figure which shows the input impedance characteristic (phase angle) of reception filter N2. 1... Board, 2... Earth pattern,
22... Antenna terminal, 23, 25... Rx (reception filter) terminal, 24
, 26... Tx (transmission filter) terminal, 29...
・Inductor LAR130...Inductor RE, 3
1... Inductor LR, 41... Transmission filter (N1), 42... Reception filter (N2). Patent applicant Oki Electric Industry Co., Ltd. Patent application agent

Claims (2)

[Claims] (1) An elastic surface consisting of a branching circuit on a substrate, a piezoelectric substrate connected to the branching circuit that propagates at least surface acoustic waves, and input/output interdigital electrodes that mutually convert electric signals and surface acoustic waves. What is claimed is: 1. A duplexer in which a wave filter is configured as a transmission filter and a reception filter, and a linear inductor is provided in the duplexer circuit. (2) The duplexer according to claim 1, wherein the duplexer circuit is formed on the back surface of a substrate on which the surface acoustic wave filter is configured and mounted as a transmission filter and a reception filter.