JPS63312707A - Band-pass filter - Google Patents

Abstract

PURPOSE:To obtain a band-pass filter which is compact and improves a filter characteristic better by capacitorcoupling plural resonators and connecting one place between the resonators with the serial circuit of a coil and a capacitor. CONSTITUTION:Resonators Q1 and Q2 are capacity-coupled by a capacitor Cs. The resonators Q1 and Q2 are connected by a serial circuit composed of a coil L7 and a capacitor C6. The resonators Q1 and Q2 have an equivalent circuit to connect second capacitors C2(C4) in parallel to an LC serial circuit in which coils L1, L2(L3, L4) are serially connected to both sides of capacitors C1(C3). Then, at both sides of a central frequency and close to the central frequency, a pole is formed and a sharp filter characteristic is obtained. Thus, the band-pass filter, which is compact and improves a filter characteristic better, is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a bandpass filter that is suitably used in a frequency range including and exceeding the UHF band.

Conventionally, the filter characteristics of a bandpass filter in the above frequency range are required to have a relatively high sharpness (hereinafter referred to as Q). It was a target.

By the way, the above-mentioned dielectric coaxial resonator is an equivalent circuit consisting of a series circuit consisting of a capacitor and a coil and another capacitor connected in parallel, but the overall shape is cylindrical. Because of this, there was a drawback that the filters became expensive when connected in multiple stages.

As a related invention, the present applicant has realized compactness by forming a conductive pattern constituting a resonator circuit on a single substrate and often capacitively coupling a plurality of the resonator circuits. In the patent application No. 61-97317,
Furthermore, a compact design was proposed by capacitively coupling a plurality of resonator circuits and connecting at least the lfg points between the resonators with a coil.
I have already proposed this on the 27th.

However, although the invention as filed above has become more compact, it cannot be said that its rQJ is necessarily satisfactory in terms of filter characteristics, and there is still room for improvement.

The present invention has been made in view of these problems, and an object of the present invention is to provide a bandpass filter that is compact and has further improved filter characteristics.

In order to achieve the above-mentioned object of calculating the 7' count, the bandpass filter of the present invention has an LC series circuit in which a second capacitor is connected in parallel to an LC series circuit in which coils are connected in series on both sides of a first capacitor. The present invention is characterized in that a plurality of resonators having equivalent circuits are capacitively coupled, and at least one point between the resonators is connected by a series circuit of a coil and a capacitor.

The effects of the invention will be described in the Examples.

Figure 1 shows the configuration of a bandpass filter as an embodiment of the present invention, where Figure (A) is a front view, Figure (B) is a side view,
Figure (c) is a rear view. In the figure, reference numeral 1 denotes a dielectric substrate made of, for example, FRDR material, and U-shaped conductor patterns 2 to 5 are formed on the front surface 1a and the back surface 1b, respectively. The conductive patterns 2 to 5 are two capacitor electrode patterns 2a, 2b, 3a, 3b, 4a, 4b, 5a, 5.
b and one coil pattern 2c, 3c, 4c, 5c. Among these, capacitor electrode patterns 2a and 3a,
2b and 3b, 4a and 5a, 4b and 5b are dielectric substrate 1
The capacitor capacitance is determined by the dielectric constant and thickness of the substrate l and the thickness of the opposing surface of the capacitor electrode pattern. On the other hand, coil pattern 2c,
3c, 4c, and 5c are formed using high frequency at positions that do not face each other, and each coil pattern has an inductance. Of the capacitor electrode patterns 2 to 5, the capacitor electrode patterns 2a and 4a on the side of the substrate surface la have extending portions 2d in a direction in which they approach each other.

4d is formed, and a conductive pattern 16 is formed on the back side of the substrate lb so as to have a capacitor of a predetermined capacity between the extended portions 2d and 4d. Further, a coil pattern 7 extends in an abbreviated shape from the conductive pattern 2 on the side of the substrate surface la, and a conductive pattern 9 and a through hole 10 on the side of the substrate back side lb.
connected via. The conductive pattern 9 on the back side of the substrate Ib faces a part of the conductive pattern 8 extending in an oval shape from the conductive pattern 4 on the front side la of the substrate, forming a capacitor. The inductance of the coil pattern 7 and the capacitor form an LC series circuit. Reference numerals 11 and 13 are input/output lead terminals. 12
．． 14 is a grounding terminal. The conductive patterns 2 and 3 (or the conductive patterns 4 and 5) are represented by an equivalent circuit as shown in FIG. 2, and constitute a resonator Q. That is, the resonator Q is connected to the first capacitor C1 (C3
) on both sides of the coils Ll, L2 . A second capacitor C2 (C4) is connected to the LC series circuit formed by connecting
) are connected in parallel. Here, capacitor C
1 is a capacitor formed by opposing parts of capacitor electrode patterns 2a and 3a, C2 is a capacitor electrode pattern 2
C3 is a capacitor formed by opposing portions of capacitor electrode patterns 4a and 5a, and C4 is a capacitor electrode pattern 4b.

Figure 5b shows a capacitor formed by opposing parts of 5b.

Coil L1 corresponds to coil pattern 3C, and coil L2
corresponds to coil pattern 2C, coil L3 corresponds to coil pattern 5C, and coil L4 corresponds to coil pattern 4C.
corresponds to Further, the capacitor Cs is formed by the extending portions 2d and 4d on the side of the substrate surface la and the conductive pattern 16 on the side of the back surface of the substrate lb.The coil L7 corresponds to the coil pattern 7, and the capacitor C6 A capacitor formed by opposing portions of a conductive pattern 8 on the front surface 1a side and a conductive pattern 9 on the back side Ib of the substrate is shown.

FIG. 3 shows an equivalent circuit of the bandpass filter shown in FIG. 1. That is, the bandpass filter consists of two resonators Q1. Q2 is capacitively coupled by the capacitor Cs, and the resonator Q
1 and C2 are connected by a series circuit consisting of a coil L7 and a capacitor C6. ,L14
is the inductance of the leads [12, 14]. In this bandpass filter, the degree of capacitive coupling can be changed by changing the capacitance of the capacitor Cs, and therefore the passband width can be adjusted thereby.

FIG. 4 shows the frequency characteristics of the band-pass filter having the above configuration, and FIG. 5 shows the frequency characteristics of the band-pass filter without the series circuit of the coil L7 and the capacitor C6. Both center frequencies are 504 MHz. As is clear from the comparison of these two figures, the poles Pi and P2 that occur on both sides of the center frequency are formed closer to the center frequency by coupling the resonators Ql and Q2 through the series circuit of the coil L7 and the capacitor C6. It was confirmed that steep characteristics could be obtained. Specifically, by providing a series circuit of coil L7 and capacitor C6, the position of the lower pole P1 of the center frequency can be set to about 100 MHz, and the position of the upper pole P2 can be set to about 2 MHz.
It was possible to bring the frequency closer to the center frequency by 0Mflz.

Moreover, as described above, the bandpass filter is made of a conductive pattern having the equivalent circuit shown in FIG. 3, and is compact without being bulky.

The dimensions of the substrate 1 and the conductive patterns 2 to 5 to obtain the frequency characteristics shown in FIG. 4 are as follows.

(a) Dielectric band substrate: Thickness 0.4cm, vertical and horizontal dimensions 12x14, dielectric constant 80 (b) Conductive pattern (same for each pattern): ■Capacitor electrode pattern 2a, 2b 7! , =6. 5 (1m) it =1. 5 (m favor) 1, l=6.
5 (tm) 1m = 3. 5 ('m5) CI = 20 (pF) C2 = 44 (pF) ■Coil pattern 2C, 3C 1, = 5. 6 (Seal 1) L1=L2=2.49 (nH) ■Cut the capacitor to the pole 72 d, 4 d, 1
611b=Ilr=1. 5 (■l)1m =
0. 5 (n+) eq =1. 3 (ms) Cs = 1, 0 (pF) ■Series circuit pattern of coil HIF and capacitor C6? ,
8. 9 Lo=0. 5 (m) 11+=2. 0 (fin) ll! =0. 5 (dragon) j2+3=0. 5 (w) 1.4=0. 5 (mm) j2+s=1. 5 (wl) f, 6=1.0 (n) 117=1, 5 (n+) #+a=0.5 (Dragon) β 19=0. 5 (*Seal) 12°=3. 0 (Tsuru) Rz I =0. 5 (m)ezz=3.
5 (IIm) i, #8 (nH) C6= 9 (pH) The width W of the coil pattern is not related to the inductance value, but the larger the width, the smaller the resistance, so Q
It can be said that it is preferable because the value becomes high. In this example W=1
．． 5 (w).

Furthermore, although the above embodiment shows a bandpass filter in which two resonators are coupled together, the present invention can of course be applied to a bandpass filter in which three or more resonators are coupled together. In that case, the LC series circuit may be provided between all the resonators, but it is sufficient if it is provided between at least one resonator. Even when an LC series circuit is provided between one resonator, a pole occurs near the center frequency due to frequency characteristics.

The main group visited the emperor.As detailed above, the bandpass filter of the present invention consists of an LC in which coils are connected in series on both sides of the first capacitor.
In addition to capacitively coupling multiple resonators each having an equivalent circuit in which a second capacitor is connected in parallel to a series circuit, the center frequency is Poles are formed on both sides of the circuit and close to the center frequency, making it possible to obtain steep filter characteristics.Furthermore, since resonators with the above-mentioned unique equivalent circuits are connected in multiple stages, it is possible to Unlike a filter using a dielectric band coaxial resonator, it is not bulky and can be constructed compactly.

[Brief explanation of drawings]

Figure 1 shows a bandpass filter as an embodiment of the present invention, Figure (A) is a front view, Figure (B) is a side view, Figure (C) is a rear view, and Figure 2 is the same as Figure 1. Fig. 3 is an equivalent circuit diagram of the resonator constituting the filter, Fig. 3 is an equivalent circuit diagram of the filter in Fig. 1, Fig. 4 is a frequency characteristic diagram of the bandpass filter in the example, and Fig. 5 is a series circuit of a coil and a capacitor. FIG. 4 is a frequency characteristic diagram showing an example of a case where the RFID is not connected. CI, C3...first capacitor, C2, C4...second capacitor, Ll, L2. L3. L4...Coil, Ll...Coil, C6...Capacitor, Ql, C2...Resonator. Patent applicant: Murata Manufacturing Co., Ltd. Figure 2 Q Figure 3

Claims (1)

[Claims] (1) Capacitively coupling a plurality of resonators having an equivalent circuit in which a second capacitor is connected in parallel to an LC series circuit in which coils are connected in series on both sides of a first capacitor, and
A bandpass filter characterized in that at least one point between the resonators is connected by a series circuit of a coil and a capacitor.