JPS6121608A - Print filter - Google Patents

Abstract

PURPOSE:To realize desired characteristics by providing a tap to an inductor of one set of parallel resonance circuit inserted in series with an input/output terminal in an FM radio receiver and adopting simple circuit constitution where a capacitor is connected between the tap and ground to produce an attenuating poles at high frequencies. CONSTITUTION:The circuit is constituted by selecting values of an inductor L2 and capacitors C2, C4 so that the tap 5 is provided to the inductor L2 of the 2nd parallel resonance circuit inserted in series with the input/output terminal 1, the capacitor C4 is added between the tap 5 and ground 2, the 1st attenuation pole is produced in a frequency range of nearly 1.2 time to 1.6 time of the high frequency cut-off frequency f2 of pass band and the 2nd attenuation pole is produced in the frequency range of nearly 1.9 time to 3 times of the cut-off frequency f2, and the frequency band between the 1st attenuation pole and the 2nd attenuation pole is used as the pass band. The figure shows the circuit constituted by printing a circuit pattern comprising an inductor and capacitor to both sides of a dielectric board 8.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a printed filter used as a bandpass filter inserted between an antenna and a tuner of an F'M radio receiver.

Conventional configuration and its problems The required characteristics of the bandpass filter inserted between the antenna and the tuner are that the attenuation should be about 20 to 30 dB in a frequency region that is approximately twice the frequency used in the passband. Ru. For example, if the frequency used is 76 MHz ~ 1
At 0.08 MHz, the required attenuation amount on the high frequency side is
Approximately 150 corpses - 20-30 in the frequency range of 230 pm
It is about dB. Therefore, as a filter, there is an attenuation pole on the high frequency side, and the high frequency (1411 power cut-off frequency f
It is preferable that the slope of two or more damping parts is negative.

Therefore, a circuit shown in FIG. 4 is available as a hand-held filter with a small number of parts and an attenuation pole in the high frequency range 1111. Fourth
In the figure, 1 is an input terminal, 2 is a ground terminal, and 3 is an output terminal. Ll(I'i) is an inductor, C1 is a capacitor and constitutes a first parallel resonant circuit. L2 is an inductor, and C2 is a capacitor and constitutes a second parallel resonant circuit. C3 is a capacitor.

FIG. 5 is a characteristic curve diagram showing the output characteristics of FIG. 4. fl is the lower cutoff frequency, fl1 is the lower limit frequency used, fl2 is the upper limit frequency used, f
2 indicates the cutoff frequency on the high frequency side, and f3 indicates the frequency of the attenuation pole on the high frequency side. This characteristic has a small amount of attenuation in the frequency range from 2f'1 (twice the lower limit usable frequency f'1) to 2f'2 (twice the upper limit usable frequency f'2), As the frequency increases to 2f'2, the amount of attenuation increases to about 10 to 16 dB, making it impossible to satisfy the above-mentioned required characteristics.

In order to satisfy the characteristics, bandpass filters may be connected in series in multiple stages, but this increases the number of parts, resulting in an increase in price and the problem that only miniaturization is possible.

OBJECTS OF THE INVENTION It is an object of the present invention to overcome the above-mentioned problems with a simple circuit.

Structure of the Invention In order to achieve the above-mentioned object, the present invention provides an input terminal, an output terminal, and a ground terminal on a dielectric substrate, and provides a first parallel connection consisting of a first inductor and a first capacitor in parallel with the input terminal. A resonant circuit is deposited, and a second parallel resonant circuit consisting of a second inductor and a second capacitor is deposited in series with the input terminal, and the second inductor has a linear pattern formed in a helical manner. A wire ground pattern is provided which is wound into a shape and overlaps diagonally with a part of the inductor pattern, and the second inductor and the ground terminal are connected by capacitive coupling of the wire ground pattern. A capacitor is formed between them.

DESCRIPTION OF THE EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 to 3.
51!1"j.

Fig. 1 is a circuit diagram of a printed filter according to an embodiment of the present invention, and this circuit consists of a second parallel resonant circuit inserted in series with the input/output terminal 1 in the circuit of Fig. 4 shown in the conventional example. A tap 5 is provided in the inductor L2, and a capacitor C4 is added between the tap 5 and the ground 2, and a first inductor is provided in the frequency range of about 1.2 to 1.6 times the high-side cutoff frequency f2 of the passband. The intactor L2. Capacitor c2. Select and configure the value of c4 to set the first attenuation pole and the second attenuation to 2
It can be set to 0 to 35d13.

However, 2f'1 is a frequency that is 02 times the lower limit usable frequency f'1, which is 2J/? indicates a frequency twice the upper limit usable frequency f/2.

From then on, fl, f2. fl1. The numbers attached before f'2 are fl, f2. fl1. Let it represent how many times fl2 it is.

Hereinafter, the circuit within the frame 4 surrounded by the broken line will be described in detail. L3 in Figure 1. L4. Y-Δ conversion of c4 to 6-
The impedance 2 of the series arm between 7 and 7 can be expressed as follows.

Since the attenuation pole occurs at the frequency where impedance 2 is maximum, finding this frequency is 1 ro2C4
C2Σ=.

It becomes good. f4 is the frequency that produces the first attenuation pole, and f5
is the frequency that produces the second attenuation pole.

Therefore, in order to obtain the desired characteristics, the frequency f should be approximately 12f.
In the frequency range of about 2 to 1.6 f2, the frequency f5
The capacitor c4. The value of c2 is 02〉q(L3-L4
). Then, depending on your peace of mind, inductor L3. It is a good idea to adjust L4. The area between the first attenuation pole and the second attenuation pole forms a stop band, so if the band is narrowed to 1, the amount of attenuation will increase. For example, if the passband frequency is 70 to 12014 (about z), the frequency f4 is 140 to 1'90 MHz.
If the frequency f5 is set to about 230 to 350 MHz, a stop band will be formed between f4 and f5, and the output characteristics shown in FIG. 2 can be realized, thereby satisfying the above-mentioned required characteristics.

Next, considering that the circuit of FIG. 1 is constructed as a planar circuit, the capacitor C4 can be constructed isometrically. The configuration of the planar circuit is shown in a plan view in FIG.

In FIG. 3, circuit patterns such as inductors and capacitors are formed on both sides of a dielectric substrate 8.

The solid line in FIG. 3 shows the circuit pattern formed on the A side of the dielectric substrate 8, and the dotted line shows the circuit pattern formed on the third side.

9 in Figure 3 is the pattern of terminal 1 in Figure 1;
0 is pattern T of terminal 2 in FIG.

11.12 in Fig. 3 is the coil pattern forming the inductor L1, and it is connected to the through hole 13, l:tte, 11 and 12.
or connected. The capacitor C1 in FIG. 1 is formed entirely by the opposite portion of the pattern 9.10.

The inductor L3 in FIG. 1 is the coil pattern 1 in FIG.
4, and the inductor L4 in FIG. 1 is substantially in phase with the coil pattern 15 in FIG.

Even though 14.15 can be connected through the through hole 18, the capacitor C2 in Fig. 1 has a small capacitance value compared to the value of 01, so it is mainly formed isometrically at the opposing portions of the coil patterns 14 and 15. has been done.

Coil pattern 14. Parts of j5 are diagonally opposed to capacitor C2, inductor L3. This is to adjust the value of L4. (Adjust the electrostatic and magnetic coupling.) The tag 5 in FIG. 1 is approximately parallel to the tag 19 in FIG. 3.

The capacitor C4 in FIG.
is formed isometrically by the electrostatic coupling of . The reason why the pattern 20 and the opposing pattern are oblique is that the value of capacitive coupling can be set by adjusting the position where the pattern 20 resonates with the tag 5 and the length of the pattern 2Q.

Reference numeral 16 in FIG. 3 is the pattern of the output terminal 3 in FIG.

Capacitor C3 is completely formed in the opposing portions of patterns 16 and 17.

As described above, the circuit shown in FIG. 1 has the advantage that it can be easily constructed as a planar circuit.

As described in detail, the invention has a simple circuit configuration in which a tap is provided to the inductor of a set of parallel resonant circuits inserted in series to the input/output terminals, and a capacitor is connected to the tap and the ground m1.
It is possible to generate two attenuation poles in the high frequency band.

Since the stopband is between these two attenuation poles, the desired characteristics can be achieved, and the value of the added capacitor is
Since the capacitance may be smaller than the capacitance of the capacitor constituting the pair of parallel resonant circuits, it does not pose an obstacle to miniaturization.

In addition, since the capacitor connected between the tap and the ground can be constructed using an equivalent circuit when realized using a planar circuit, there is an advantage that the number of parts does not appear to increase.

By slanting the opposing parts of the circuit pattern, the electrostatic or magnetic coupling state can be easily changed, and the circuit constants can be easily realized.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing one embodiment of the present invention, and Fig. 2 is a circuit diagram showing an embodiment of the present invention.
Figure 3 is a pattern diagram obtained by actually applying Figure 1 to a planar circuit, Figure 4 is a circuit diagram of a conventional bandpass filter, and Figure 5 is an output characteristic diagram of Figure 4. . 1...Input/output terminal, 2...Earth, 5...
Tap, 8...Dielectric substrate, 9...Input/output terminal pattern, 1o゛...Earth terminal pattern, 11.
12゜14.16... Coil pattern, 13.18
...Through hole, 16. River...Output terminal putter y.

Claims (1)

[Claims] An input terminal, an output terminal, and a ground terminal are provided on a dielectric substrate, and a first parallel resonant circuit consisting of a first inductor and a first capacitor is deposited and formed in parallel with the input terminal, and in series with the input terminal. A second parallel resonant circuit including a second inductor and a second capacitor is formed by depositing a second parallel resonant circuit, the second inductor is formed by winding a filament pattern in a helical shape, and the second inductor has a linear pattern wound in a helical shape. A printed filter characterized in that a linear ground pattern is provided that faces the part and overlaps diagonally, and a capacitor is formed between the second inductor and the ground terminal by electrostatic coupling of the linear ground pattern. .