JPS5915319A - Filter circuit device - Google Patents

Abstract

PURPOSE:To ensure the stable working despite the impedance variation of a varactor element that is used to vary the attenuation characteristics of a filter, by using a coplanar line to filter circuit to obtain a constant impedance. CONSTITUTION:A coplanar transmission line is formed with a center conductor 17 on the same level as a dielectric substrate 16 and earth conductors 18 printed at both sides of the conductor 17 with a prescribed space. In such a case where the conductors 18 are set on the same level as the conductor 17, the characteristic impedance is equal to a fixed impedance value which is decided by a ratio between a1 and b1 as long as the effective dielectric constant including the substrate 16 is constant. Therefore the impedance of the transmission line itself has no variation despite the impedance variation of a variable capacity element 13 which varies the attenuation characteristics of a filter. This can maintain good filter characteristics.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a filter circuit device, and particularly to a printed circuit device equipped with a filter circuit for selecting high frequency signals. damping characteristics)
The present invention relates to a filter circuit device that obtains impedance characteristics.

[Technical background of the invention]

In general, TV tuners and CATV
In a high frequency receiving device such as a tuner for (CABLE EVISI○N), a filter circuit is disposed in the high frequency panono part in order to deal with interference including cross modulation interference and heat interference.

Since this filter circuit is located at the input stage of the receiving device, it has a large influence on the interference characteristics, noise figure, impedance characteristics, etc. Therefore, regarding such a filter circuit,
It is desirable that the pass frequency band has as small a loss as possible and the impedance characteristics are constant, and that the attenuation frequency band has as large an amount of attenuation as possible. For this reason, for example, in a tuner for a television receiver, an adjustment signal generator 3 is connected to the input terminal 2 of the tuner 1 as shown in FIG.
After passing through a filter load 5 such as an amplifier or a mixer, the output is measured using a detection device 6 and adjusted to optimize the pass loss characteristics and impedance characteristics of the filter circuit section. Technological Problems] By the way, television reception using the super-heterodyne system or the double super-heterodyne system
In high-frequency receiving devices such as tuners for L tuners, CATV, and inverters, when the above-mentioned filter circuit is composed of a wideband filter, an interference signal called a backtalk component is generated in the mixer, and this backtalk component is generated in the mixer. - There is a problem that talk components leak to the input terminal. Next, the generation process of the back-1 to -re components will be explained with respect to a tuner for a CATV converter.

FIG. 2 is a block diagram showing the main parts of a tuner for a CAT' V converter, and a characteristic diagram showing a pass frequency band of its input filter circuit portion.

As shown in FIG. 2(a), the received signal is input from the input terminal 7 to the input filter circuit 8, and the signal that has passed through the input filter circuit 8 is generated in the air-fuel mixture 9 by local oscillation from the local oscillation circuit 10. It is mixed with the signal and converted into an intermediate frequency signal. This intermediate frequency signal further passes through an intermediate frequency band filter circuit 11, and then is output to the next stage circuit.

In such a configuration, the signal frequency received in CATV broadcasting is 55 to 440 MHz (transmission on 58 reception channels), and the signal is introduced into the input terminal 7 of the converter/tuner. As shown in FIG. 2(b), the input filter circuit 8 has a passband that includes all of the above transmission frequency bands, so all of the above transmission signals are input to the mixer 9 in the next stage. Become. On the other hand, a prescribed local oscillation frequency signal is injected from the local oscillation circuit 10 into the mixer 9, and a predetermined intermediate frequency signal is obtained.However, in reality, the intermediate frequency band filter circuit 11, which is the load of the mixer, selects the local oscillation frequency signal. By doing this, an intermediate frequency signal is obtained. Therefore, inside the mixer, all the frequencies mentioned above are frequency-converted by the local oscillation frequency signal. In this case, the frequency characteristics of the intermediate frequency band filter circuit 11 are usually designed to be steep, so that almost no frequency components other than the desired signal are output to the next stage circuit.

However, the frequency components reflected by the intermediate frequency band filter circuit 11 (back and 1-to-1 forward components) are reflected by the mixer 9.
Proceeds in the opposite direction and reaches the manual filter circuit 8. If the reflected frequency component is in the passband of the input filter circuit 8, that signal component appears at the input terminal 7 of the converter tuner and is further transmitted to the signal supply cable, causing interference to many receiving equipment. Become.

Next, the above matters will be explained using mathematical formulas.

The input frequency range reaching the mixer 9 is defined as "d1~"d2,
Corresponding to this frequency, the local oscillation frequency range for converting to an intermediate frequency in the mixer 9 is foI~fO2, a certain reception frequency is fdx, the local oscillation frequency at that time is fax, and the intermediate frequency is 'IF. + If the back talk frequency is "U," then the frequency conversion of the desired signal is expressed as f IF = fox - fdx, and the frequency conversion of the interfering signal (back talk component) is expressed as fu = fox : (f ~ fox + fd2
It is expressed as Therefore, when receiving a certain channel, frequency-converted components are generated between fox-fdt and fOX+fd2, and among these, the signal component that passes within the passband of the input filter circuit 8 is The interference actually occurs as a back talk component. Furthermore, the local oscillation frequency is the reception frequency [accordingly, fo + ~ f
Since it changes up to o2, countless interference signals are generated.

Figure 3 shows a reception frequency range of 55 to 440 MHz, a local excavation frequency range of 667 to 1052 MHz, and an intermediate frequency of 61 MHz.
2M1-(Z) is an explanatory diagram illustrating the generation of back talk components.

In Figure 3, the part B is the signal frequency range generated by the sum of the local excavation frequency and the input frequency, the part B is the signal frequency range generated by the difference between the local excavation frequency and the input frequency, and the part C is the signal frequency range generated by the difference between the local excavation frequency and the input frequency.
The diagonally shaded range in the part B is within the band of the received signal, that is, the range in which the back talk component appears at the input terminal 7. In addition, the straight line indicated by the sign indicates the frequency at which the input filter circuit 8 must be at least in the pass band, and the sign E indicates the reception frequency range, frequencies below the line are the pass band, and frequencies above the line are attenuated. It shows that it can be a band. Therefore, when the receiving frequency is 270 MHz or less, the shaded area is the range that passes through the passband of the input filter circuit 8 as a back component, and is the area where it appears at the input terminal 7 and causes interference. .

However, for example, if the reception frequency is 55MHz, the interference generation frequency will be 230MHz or higher, and there is a certain frequency difference between the reception frequency and the interference signal frequency, so it is possible to deal with the above interference by using a variable attenuation filter. will be possible.

Figure 4 shows an input filter circuit 8 using a variable attenuation filter.
It is a circuit diagram showing an example.

In FIG. 4, the filter circuit is constructed by combining an input band pass filter with a pass band covering the entire reception frequency range and a variable attenuation filter. The received signal is input to the input terminal 12 of the converter/tuner, and a high-speed circuit consisting of capacitors C)~C3° and coils L+~2 is input to the converter/tuner input terminal 12.
Pass filter, capacitor C4 to CIO, coil L
After passing through a low pass filter consisting of L3 to L5,
The signal is guided to the output terminal 14 through a variable attenuation filter consisting of coils 16 to La, a resistor R++ capacitor C11, and a variable capacitance element 13 such as a varactor diode. A control voltage for varying the capacitance of the varactor diode 13 of the variable attenuation filter is applied to the terminal 15.

In this way, by configuring the input filter circuit using a variable attenuation filter, it is possible to attenuate the interference component frequency. However, in this circuit, the varactor
There is an element called a diode whose impedance changes depending on the magnitude of the control voltage, so even if the loss characteristics or impedance characteristics within the pass frequency range are adjusted at a certain control voltage, the impedance value of the varactor diode will change in the interest rate t111 pressure range. In contrast, the loss characteristics and impedance characteristics have large fluctuations, making it difficult to obtain a good receiving device.

[Purpose of the invention]

The purpose of the present invention is to address the above-mentioned points, and to solve the problem of using an element whose impedance fluctuates, such as a varactor diode, in the filter circuit of the input stage in a receiving device such as a tuner for a television receiver or a tuner for a CATV converter. Even if there is a filter circuit, the purpose is to provide a filter circuit with little variation in loss characteristics, impedance characteristics, etc. over the entire pass frequency band.

[Summary of the invention]

The filter circuit device of the present invention has a center 3 on one side of a wiring board.
81* and ground conductors on both sides thereof to form a planar line, all Noirta elements or a part thereof are arranged on this planar line to constitute a filter circuit, and at least One variable capacitance element is used as an element of the filter circuit, and a control voltage is applied to the variable capacitance element to make the filter characteristics (passage loss characteristics and impedance characteristics) variable. In fact, in reality, the center conductor of the coplanar shadow line is divided into a plurality of pieces, and the filter element is connected between the center conductor and the ground conductors on both sides thereof, or between each center conductor.

[Embodiments of the invention]

Hereinafter, the present invention will be described in detail based on the drawings.

FIG. 5 is a plan view showing the substrate pattern surface of the filter circuit device according to the present invention, FIG. 6 is a sectional view taken along line A-A shown in FIG. 5, and FIG. 7 is the opposite side of the substrate shown in FIG. 5. FIG. 3 is a plan view showing a state in which filter circuit components are attached to the filter circuit component.

As shown in FIGS. 5 and 6, a center conductor (conductive pattern) 17 is placed on the same plane of the dielectric substrate 16, and ground conductors (earth conductors) are placed on both sides of the center conductor 17 at predetermined intervals.
Pattern) 18 is printed to form coplanar transmission lines. In this case, the center conductor 17 is divided into a plurality of pieces. Then, the conductive pattern 17 surface and the ground
Component mounting holes 19 penetrating the board 16 on the pattern 18 surface
Through these holes 19, as shown in FIG. 7, insert the filter elements shown in FIG. 4 (capacitors C1 to C11, coils L1 to L8, resistors R+,
A varactor diode 13) is connected to form a circuit. However, 12 is an input terminal, 14 is an output terminal, 1
5 is a control voltage application terminal.

In the printed circuit board of the above-mentioned military planar track structure, the ground conductor 18 is printed at a predetermined interval on both sides of the center conductor 17, which is arranged separately, and the ground conductor 18 is printed between the center conductors and between the center conductors. The filter element is connected between the ground conductor and the ground conductor. In this way, when the ground conductor 18 and the center conductor 17 are on the same plane, if the effective M electric current including the substrate 16 is constant, the characteristic impedance is the center conductor width al shown in FIG.
It is determined by the ratio of the distance between the center conductor 17 and the ground conductor 18. Therefore, the characteristic impedance of the transmission line can be freely selected by changing the ratio of a and bl.

When a loop/loop circuit is formed using a coplanar transmission line in this way, the transmission line itself has a constant impedance, so even if the impedance of the elements that make up the filter circuit changes slightly, the effect will be It is possible to obtain 1q of good characteristics with almost no damage.

Figure 8 shows the insertion loss characteristics and impedance characteristics (with the same load on the output terminal 14) of a device in which the filter circuit is configured with a coplanar transmission line and a filter device in a conventional printed pattern configuration as shown in FIG. FIG.

In Fig. 8, the characteristic impedance of the coplanar transmission line is designed to be 750, and the insertion loss N (dB) of the filter when viewed from the input terminal 12 at an impedance of 75Ω.
and return loss T (dB). However, the solid line is for the filter circuit device of the present invention, and the chain line is for the conventional filter circuit device.

In this way, compared to a filter circuit constructed using a conventional printed pattern, a filter circuit constructed using a coplanar transmission line has a smaller insertion loss N and a larger reflection loss T, so that the input filter circuit It is possible to effectively reduce back talk components generated in the latter stage. Also,
As mentioned above, coplanar transmission lines have conductors on the same plane, so there is no need to use a board with conductors on both sides like micro slip lines, which simplifies the manufacturing process. Therefore, it is advantageous in terms of cost.

For example, frequency conversion circuits used in tuners for 0ATV converters are usually balanced mixers or double mixers using diodes or 1-transistors.
Balanced mixers are used to suppress the leakage of local oscillation frequency components and the generation of unnecessary frequency components, but a filter circuit device like the one shown in Figure 7 is installed before these balance mixers or double balance mixers. It is more effective to use C.

In addition, in the super-heterotine system tuner,
It always has a local oscillator, and a varactor diode is used to control the oscillation frequency of this local oscillator. Therefore, the varactor used in this local oscillator
If the control voltage of the diode and the control voltage of the varactor diode used in the variable attenuation filter shown in Fig. can be tracked.

〔Effect of the invention〕

As described above, according to the present invention, all or part of the elements constituting the filter circuit are configured using coplanar shadow lines, and at least one variable capacitance element is used as the element of the filter circuit. Since this variable capacitance element is controlled by a control voltage to make the filter characteristics variable, it is possible to effectively reduce the back talk component generated in the latter stage of the filter circuit, and improve the pass loss characteristics.

A filter circuit device with significantly improved impedance characteristics can be realized. In addition, in the military planar line structure, ground patterns are provided on both sides of the conductive pattern, making it easy to ground one end of the filter element.
Part arrangement becomes easy.

For this reason, this filter circuit device is used as a television receiver [1
If applied to the filter part of a tuner or a tuner for a CATV converter, it is possible to realize a receiving device that is advantageous in manufacturing and has excellent performance.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a conventional adjustment method for a filter circuit, Fig. 2 is a block diagram of the main parts of a tuner for a CATV converter and a frequency characteristic diagram showing the pass band of the input filter circuit, and Fig. 3 is a back filter circuit diagram. 4 is a circuit diagram showing an example of an input filter circuit using a variable attenuation filter; FIG. 5 is a plan view showing a substrate pattern surface of a filter circuit device according to the present invention; FIG. 6 is a cross-sectional view of A-/Vigil shown in FIG. 5, FIG. 7 is a plan view showing a state in which filter circuit components are attached to the opposite side of the board shown in FIG. 5, and FIG. 8 is a plan view of the present invention. FIG. 2 is a frequency characteristic diagram showing insertion loss characteristics and impedance characteristics of the device of FIG. 1 and a conventional device. 01-Cu... Capacitor, 1-L8... Coil, R+... Resistor, 12... Input terminal, 13... Variable capacitance element (varactor diode), 14... Output terminal, 15...Control [1? [f pressure application terminal, 16...
・Dielectric substrate, 17...center conductor (S electric pattern),
18...Grounding conductor (earth pattern), 19...
Holes for mounting parts. Patent applicant Tokyo Shibaura Electric Co., Ltd.

Claims (5)

[Claims] (1) A plurality of center conductors are extended and arranged on a board, and ground conductors are arranged on both sides of the center conductor along the extension direction of the center conductor on the board, and ground conductors are arranged between the center conductors and at the center. A plurality of elements constituting a filter circuit are connected between a conductor and a ground conductor, at least one of these elements is a variable capacitance element, and a control voltage is applied to this variable capacitance element to vary the filter characteristics. A filter circuit device L characterized by (2) A patent claim characterized in that the filter circuit is composed of a band pass filter consisting of a high pass filter section and a low pass filter section, and a variable filter using a variable capacitance element. The filter circuit device according to item 1. (3) The filter circuit device according to claim 1 or 2, wherein the filter circuit is disposed between a high frequency input terminal of a tuner and a mixer. (4) A patent claim characterized in that the filter circuit avoids passing at least the desired signal frequency and sets the variable attenuation frequency of the variable capacitance element to the back-to-one component frequency generated by the mixer. The filter circuit device according to the second and third ranges. (5) A frequency control voltage of a local oscillator to be injected into the mixer is used as a control voltage of a variable capacitance element of the filter circuit, and the input frequency and the variable attenuation frequency are racked to 1. A filter circuit device according to claim 3 or 4, characterized in that the filter circuit device comprises: