JPS6354009A - Branching filter - Google Patents

Abstract

PURPOSE:To miniaturize the case for the titled branching filter and to avoid the disturbance from other circuits even with a low level reception signal by using a surface acoustic wave filter enclosed by a metallic member as a reception system band-pass filter and a transmission system band-pass filter and providing the surface acoustic wave filter and an RF amplifier in one and same metallic case. CONSTITUTION:The metallic case 17' is partitioned by a partition 19 and one of two parts from the partition is provided with a reception system wiring board 20a and the other is provided with a transmission system wiring board 20b respectively. The surface acoustic wave filter 22 is provided to the wiring (not shown in figure) provided at the rear side of the board 20a and the surface acoustic wave filter 23 is provided also to the rear side of the board 20b respectively and the surface acoustic wave filter 21 is provided between the boards 20a, 20b while bridging over the partition 19. Moreover, the RF amplifier 3 is provided to the board 20a between the filters 21 and 22 and the board 20b connects to coaxial cables 16a, 16c and the board 20a connects to coaxial cables 16b, 16c. Then the metal-made cover is applied to the surface of the case 17'.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a duplexer suitable for use in cellular radios and the like.

[Conventional technology]

A cellular radio device is an example of a radio device using a duplexer. FIG. 4 is a block diagram showing the transmitting and receiving system of a conventional cellular radio, in which 1 is an antenna, 2 is a branching filter, 2a is a receiving band filter, 2b is a transmitting band filter, and 3 is an RF amplifier (wireless 4 is a bandpass filter, 5 is a mixer circuit, 6 is an IF (intermediate frequency) amplifier/detection circuit, 7 is a VCO (voltage controlled oscillator), 8 is a PLL
(phase-locked loop) synthesizer, 9 is a control circuit, 10 is an isolator, 11 is a transmission power amplifier,
12, the VCO 113 is a PLL.

In the figure, a modulated signal S to be transmitted is supplied to a VCO 12 controlled by a PLL 13 and modulated.

The output signal of the VCO 12 is amplified as a transmission signal by the transmission power amplifier 11 and supplied to the duplexer 2 via the isolator 10. The branching filter 2 is the receiving system bandpass filter 2ah
The transmission signal is supplied to the antenna I via the transmission bandpass filter 2b. On the other hand, the received signal from the antenna 1 passes through the reception system bandpass filter 2a of the duplexer 2, is amplified by the RF amplifier 3, and then is supplied to the mixer circuit 5 via the bandpass filter 4.

In the mixer circuit 5, the received signal is mixed with the output signal of the CO7 controlled by the PLL synthesizer 8, and the IF
The signal is converted twice.

This IF multiplied signal is amplified and detected by the IF amplifier/detection circuit 6 to obtain a demodulated signal SR.

The reception bandpass filter 2a and the transmission bandpass filter 2b of the duplexer 2 have different passbands, and the transmission signal that has passed through the transmission bandpass filter 2b is transferred to the reception bandpass filter 2b.
The received signal is prevented from entering the receiving system by the transmitting system bandpass filter 2b, and the receiving signal is prevented from entering the transmitting system by the transmitting system bandpass filter 2b.

Conventionally, as the receiving band filter 2a and the transmitting band filter 2b of the duplexer 2, for example, dielectric filters such as those described in 1988 Institute of Electronics and Communication Engineers Comprehensive National Conference Material 743 r800 MHz band dielectric-filled compact duplexer have been used. A body filter is used. That is, as shown in FIG. 5, a partition I9 is provided in the metal case I7, and one chamber partitioned by the partition contains a plurality of dielectric cores 142 to 14e, and the other chamber also contains a plurality of dielectric cores 142 to 14e. Body core 15a=1
5e is built-in. These dielectric cores 14a to 14
e, 15a to 1-5e are 800 MHz band resonators, each having an inner conductor (not shown).

Inner conductors of dielectric cores 143-148 are connected to conductor 18a. The dielectric cores 14a to 14e each have passbands that are slightly shifted from each other, and are cascaded to form a dielectric filter having comb filter characteristics. This dielectric filter corresponds to the reception system bandpass filter 2a shown in FIG. The dielectric cores 152 to 15e also
Similarly, a dielectric filter having comb filter characteristics is formed, and this corresponds to the transmission type bandpass filter 2b in FIG. 4.

One end of the conductor 18b to which the dielectric cores 15a to 15e are connected is connected to the antenna 1 (Fig. 4) via a coaxial cable 16a, and the other end is connected to the isolator 10 (Fig. 4) via a coaxial cable 16C. has been done. Further, one end of the conductor 18a to which the dielectric cores 14a to 14e are connected is connected to the coaxial cable 16a via the coaxial cable 16d, and the other end is connected to the RF amplifier 3 via the coaxial cable 16b.
(Fig. 4).

[Problem that the invention seeks to solve]

However, there is a problem in that a duplexer using a dielectric filter is large in size. This is not desirable in cellular radios, etc., where miniaturization is desired.

In addition, there is no problem since the receiving band filter 2a and the transmitting band filter 2b of the duplexer 2 are housed in the metal case 17, but the RF amplifier 3 is not provided with any shielding means from the outside. Since the input signal level is the same low level received by antenna 1,
The received signal in this RF amplifier 3 is interfered with by interference I3 from other circuits.
There was a problem in that the S/N was significantly reduced due to the shadow C of the issue. This problem can be solved by providing a shielding means to the RF amplifier 3, but this is not preferable. It is also conceivable to house the RF amplifier 3 in the metal case 17 of the duplexer 2, but in this case, since the output signal level of the RF amplifier 3 becomes large, its output and dielectric core 14a- 14e will occur, and the S/N of the received signal will deteriorate.

It is an object of the present invention to solve such problems and to
An object of the present invention is to provide a duplexer that can increase /N and can be configured in a small size.

[Means for solving problems]

In order to achieve the above object, the present invention uses a surface acoustic wave filter sealed with a metal member as a reception system bandpass filter and a transmission system bandpass filter, and uses the surface acoustic wave filter and R
F amplifier is installed in the same metal case.

[Effect]

Since surface acoustic wave filters are much smaller than dielectric filters, even if the surface acoustic wave filter and the RF amplifier are housed in the same metal case, the metal case can be made smaller; Since the amplifier is housed in the metal case and the surface acoustic wave filter is sealed with a metal member, the RF amplifier is shielded from other circuits,
Low level received signals are not affected by interfering signals from other circuits.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a configuration diagram showing an embodiment of a duplexer according to the present invention, in which 17' is a metal case, 20a is a receiving system wiring board, 20b is a transmitting system wiring board, and 21 to 23 are surface acoustic wave filters. The parts corresponding to FIGS. 4 and 5 are given the same reference numerals.

In FIG. 1, a partition 19 is provided in a part of the metal case 17', and one of the two partitioned parts is a reception system wiring board 20a, and the other is a transmission system wiring board 20b. It is provided. Receiving system wiring board 2
A surface acoustic wave filter 22 is provided on the wiring (not shown) provided on the back side of the transmission system wiring board 20b in the drawing of 0a, and a surface acoustic wave filter 23 is provided on the wiring (not shown) provided on the back side of the transmission system wiring board 20b. Furthermore, a surface acoustic wave filter 21 is provided so as to straddle the partition 19 between the wiring of the reception system wiring board Fi, 20a and the wiring of the transmission system wiring board 20b. In addition, the receiving system wiring board 20
In a, the RF amplifier 3 is connected to the surface acoustic wave filters 21 and 22.
It is set up in between. A metal lid (not shown) is attached to the metal case 17' so that the RF amplifier 3 and surface acoustic wave filters 21 to 23 are hermetically sealed.

Here, the surface acoustic wave filter 2 in this embodiment corresponds to the cellular radio device shown in the block diagram shown in FIG.
1 is a receiving system bandpass filter 2a, a surface acoustic wave filter 2
3 correspond to the transmission system bandpass filter 2b, and the surface acoustic wave filter 22 corresponds to the bandpass filter 4.

A coaxial cable 16a connected to an antenna (not shown) is connected to one terminal of the wiring on the transmission system wiring board 2Ob, and a coaxial cable 16c connected to the transmission processing system is connected to the other terminal.

In addition, a coaxial cable 16b connected to the reception processing system and a coaxial cable 16e connected to a power source (not shown) are connected to two terminals on the surface acoustic wave filter 22 side of the wiring on the reception system wiring board 2Oa. are connected to each other.

As shown in FIG. 2, the surface acoustic wave filters 21 to 23 are mounted on a metal substrate Fi, 25 via an insulating plate (not shown), and a metal cylinder 24 with a bottom is placed over this. It is sealed by a metal member consisting of the metal substrate 25 and the metal cylinder 24 with a bottom. Both terminals of the surface acoustic wave filters 21 to 23 are external terminals 26a that protrude from the inside of the metal member to the outside through the metal substrate 25;
26b, and these external terminals 26a
, 26b and the metal substrate 25, an insulating member 27a,
27b is provided.

In FIG. 1, external terminals 26a and 26b of the surface acoustic wave filter 22 having the configuration shown in FIG.
The external terminal 2 of the surface acoustic wave filter 23 is connected to the wiring on Oa.
6a and 26b are external terminals 26a of the surface acoustic wave filter 21, which are bonded to the wiring on the transmission system wiring board 2Ob, respectively.

One of the wires 26b is bonded to the wiring of the receiving wiring board 20a, and the other is bonded to the wiring of the transmitting wiring board 20b. The passband of the surface acoustic wave filters 21 and 22 and the passband of the surface acoustic wave filter 230J are different from each other.

Therefore, the transmission signal output by the transmission processing system (not shown) is
The signal is sent through the coaxial cable 16c, passes through the surface acoustic wave filter 23, and then is supplied to an antenna (not shown) through the coaxial cable 16a. Moreover, the reception signal of this antenna is sent via the coaxial cable 16a,
After passing through the surface acoustic wave filter 21, the signal is amplified by the RF amplifier 3, passes through the surface acoustic wave filter 22, and is supplied to a reception processing system (not shown) via the coaxial cable 16b.

FIG. 3 is a block diagram showing the flow of signals in this embodiment, and parts corresponding to those in FIG. 1 are given the same reference numerals.

The surface acoustic wave filters 21 to 23 are sufficiently small compared to conventionally used dielectric filters, and therefore the metal case 17' that houses them is also smaller than that shown in FIG. 5 even if the RF amplifier 3 is housed at the same time. Conventional metal case 1 shown
It should be sufficiently smaller than 7.

Further, the RF amplifier 3 is sealed in the metal case 17' in this way, and the surface acoustic wave filters 21 to 2
3 is also sealed by a metal member consisting of a metal bottomed cylinder 24 and a metal substrate 25, as shown in FIG. 2, so the RF amplifier 3 is not susceptible to interference signals from other circuits. There is no.

〔Effect of the invention〕

As explained above, according to the present invention, very small surface elastic filters are used as bandpass filters for the receiving system and the transmitting system, so the RF amplifier is also housed in the metal case that houses these. However, the metal case can be made much smaller than the above-mentioned conventional technology, and each surface acoustic wave filter is sealed by a metal member.
Coupled with the fact that the RF amplifier is housed within the metal case, there is almost no interference signal to the RF amplifier from other circuits, and the S/N of the received signal is greatly improved.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a duplexer according to the present invention,
Fig. 2 is a structural diagram showing the surface acoustic wave filter in Fig. 1, Fig. 3 is a block diagram showing the signal flow of the embodiment shown in Fig. 1, and Fig. 4 shows a transmission/reception system of a conventional cellular radio. The block diagram in FIG. 5 is a configuration diagram showing the conventional duplexer in FIG. 4. 1... Antenna, 3... Radio frequency amplification circuit, 16a to 16c... Coaxial cable, 17
'...Metal case, 19...Partition,
20a... Receiving system wiring board, 20b...
- Transmission system wiring board, 21-23...Surface acoustic wave filter. Figure 1/7' 3: Radio frequency amplification circuit l? ′: Metal nurse 20σ: Basic lack 20b: Transmission system differential plates 21 to 23: Horizontal wave filter Fig. 2 (a)
(b) Figure 3 Figure 5

Claims (1)

[Claims] 1. a first bandpass filter that passes the transmitted radio frequency signal and a second band pass filter that passes the received radio frequency signal.
In the duplexer equipped with a band-pass filter, the first,
The second band-pass filter is a surface acoustic wave filter sealed with a metal member, and a radio frequency amplification circuit is connected to the second band-pass filter, and the first and second band-pass filters and the radio A duplexer characterized by housing a frequency amplification circuit in the same metal case.