JPH04243306A - Image frequency and local frequency trap circuit - Google Patents

Abstract

PURPOSE:To reduce number of components and to make the performance stable with respect to a trap circuit attenuating an image frequency and a local frequency so as not to give adverse effect on a desired signal. CONSTITUTION:First and 2nd strip lines 11a, 11b having a distributed constant are formed by printed circuit wiring and one terminal of both strip lines 11a, 11b connects directly ground and the other terminal connects to ground via lumped constant components 12a, 12b respectively. One point of the 1st strip line 11a connects to an input terminal 14 via a lead inductor 13. An image frequency is attenuated by the coupling between both strip lines 11a, 11b and the lead inductor 13. The 2nd strip line 11b is provided with an output terminal 15. The local frequency is attenuated by the coupling between the end strip line 11b and the lead inductor 13.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a trap circuit that attenuates the power of image frequencies and local frequencies in electronic circuits so as not to adversely affect desired signals.

0002

2. Description of the Related Art In recent years, it has been desired to improve the quality of video signals and audio signals. For example, in a double superheterodyne tuner such as a CATV converter, an image frequency that is twice as low as the first intermediate frequency, and a local frequency that is higher than the second intermediate frequency than the first intermediate frequency adversely affect the desired signal. was giving. Conventionally, as a countermeasure of this kind, in order to attenuate the image frequency signal, an inductance 22 (22a to 22d) and a capacitance 21 using lumped constants are used as shown in FIG. 2(a).
(21a to 21i), and in order to attenuate the local frequency signal, inductance 24 and capacitance 23 (23a
~23c) A circuit for attenuating the local frequency signal having 23c) was constructed separately to trap the image frequency and the local frequency.

0003

However, when a circuit using lumped constant components as shown in FIG. 2 is constructed, there are problems in that the cost of the components is high and it takes time and effort to insert the components. Furthermore, there are also disadvantages in that performance deteriorates due to variations in components, it takes time and effort to adjust components, and manufacturing the circuit is expensive.

The present invention solves the above problems by creating an image frequency/local frequency trap circuit that not only reduces the number of lumped constant components and eliminates the trouble of inserting and adjusting components, but also stabilizes performance. is intended to provide.

[0005]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a first method having distributed constants using printed wiring.
constitutes a strip line with one end connected to earth,
A second strip line having a capacitance at the other end and having a distributed constant by printed wiring is placed at a distance to couple with the first strip line, and is the same as the side connected to the ground of the first strip line. The side has a configuration in which one end of the second strip line is grounded via a capacitance, and the other end of the second strip line is connected to ground, and between the first strip line and the second strip line. The first intermediate strip line has an input end having a lead inductance or an inductance due to printed wiring from a part of the first strip line, and an output end having inductive coupling connected to the second strip line. In this embodiment, trapping of an image frequency twice lower than the second intermediate frequency and filtering of a local frequency higher than the first intermediate frequency by more than the second intermediate frequency can be easily achieved at the same time.

[0006]

[Operation] The image frequency/local frequency trap circuit of the present invention configured as described above utilizes distributed constants provided by printed wiring, reduces the number of parts, and simultaneously attenuates the image frequency and local frequency signals with stable performance.

[0007]

Embodiment An embodiment of the present invention will be described below with reference to FIG.

As shown in the figure, the image frequency/local frequency trap circuit has strip lines 11a and 11b having distributed constants formed by printed wiring. Both strip lines 11a and 11b have one end connected to ground 1.
6, and the other end is connected to ground 16 via lumped constant components 12a and 12b.In the input section, an input terminal 14 is connected from one point of the printed wiring strip line 11a via a lead inductance 13. death,
Input lead inductance 13 and strip line 11a
, 11b to adjust the frequency and attenuation of the image frequency signal 18, and the output section has an output end 15 from the strip line 11b, and a lead inductance connected to the output end 15 or a distribution by printed wiring. The frequency and attenuation of the local frequency trap signal 19 can be adjusted by the degree of coupling between the constant inductance and the strip line 11b, and the induction between the distributed constant inductance and the strip line 11b using a lead inductance with one end connected to the ground or printed wiring can be used. The output end 15 is a coupling portion, and the frequency and attenuation amount of the local frequency trap signal 19 can be adjusted depending on the degree of coupling.

In addition, the image frequency is determined by the length, width, and thickness of the strip line formed by printed wiring, the distance between the strip lines, and the dielectric constant of the substrate, and by the ground terminal placed at a distance connected to the strip line.・The structure allows the frequency and attenuation of the local frequency trap to be adjusted.

0010

Effects of the Invention As is clear from the above description, the image frequency/local frequency trap circuit of the present invention is constructed using a strip line having a distributed constant by printed wiring, and the inductance component at the input end and The frequency and attenuation amount of the image frequency signal can be adjusted depending on the coupling condition with the first strip line and the second strip line. In addition, by adding a ground terminal from the inductively coupled output end of the strip line or from the ground near the strip line, it is possible to adjust the frequency and attenuation of the image frequency signal and local frequency signal by the coupling component that is coupled to the strip line. can. Moreover, according to the above configuration, it is possible to provide an image frequency/local frequency trap circuit that can simultaneously and simply configure an image frequency trap and a local frequency trap with stable performance without any cost.

[Brief explanation of the drawing]

[Figure 1] (a) is a configuration diagram of the image frequency/local frequency trap circuit of the present invention in a practical state (b) is a frequency characteristic diagram of the image frequency trap and local frequency trap

[Figure 2] (a) is a block diagram of a conventional image frequency trap circuit using lumped constants (b) is a block diagram of a local frequency attenuation circuit using conventional lumped constants

[Explanation of symbols]

11a, 11b Strip line with printed wiring 12 Lumped constant component 13 Input lead inductance 14 Input end 15 Output end 16 Ground

Claims (3)

[Claims] 1. A second strip having a first strip line formed by printed pattern wiring, one end of which is connected to ground, the other end of which is connected to ground through a capacitance, and is located at a coupling distance with the strip line. a second strip line connected to the ground via a capacitance on the same side as the first strip line connected to the ground, and the other end of the second strip line connected to the ground; An input end is provided between the first strip line and the second strip line via a lead inductance as a tap from a part of the first strip line, and an output end is provided to the second strip line. Image frequency/local frequency trap circuit with. 2. The image frequency/local frequency trap circuit according to claim 1, wherein the lead inductance connecting a part of the first strip line and the input end is an inductance formed by a printed pattern. 3. The image frequency/local frequency trap circuit according to claim 1, wherein the output terminal is inductively coupled.