JP2005286974A - T-type filter circuit and reception device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a T-type filter circuit in which resonance caused by an influence of capacitance between a transmission line connected to one of two coils and the ground is reduced, and to provide a reception device capable of stabilizing frequency characteristics of a reception signal. <P>SOLUTION: The T-type filter circuit 18 has: two coils L and L which are connected in series between an input terminal IN and an output terminal OUT; and a capacitor C connected to a mutual connection point of the coils L and L, wherein resistances R and R are connected in parallel to the coils L and L, and the T-type filter circuit and a tuner are connected by a feeder. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a T-type filter circuit having two coils connected in series and a capacitor connected to a connection point between the coils, and a receiving apparatus including the T-type filter circuit.

  AM broadcasts are received using a receiving device such as a car radio. FIG. 3A is a block diagram illustrating an example of the AM broadcast receiving apparatus 10. The receiving device 10 is connected to the filter unit 12 via the filter unit 12 that passes the signal of the AM broadcast band among the signals received by the antenna and the feeder 14 that is a high-frequency coaxial filter, and has passed through the filter unit 12. And an AM tuner unit 16 for selecting a frequency for the signal of the AM broadcast band.

As a filter circuit used for the filter unit 12, there is a T-type filter circuit (see, for example, Patent Document 1). FIG. 4A is a circuit diagram illustrating an example of the T-type filter circuit 2. The T-type filter circuit 2 includes two coils L and L connected in series between the input terminal IN and the output terminal OUT, and a capacitor C connected between a connection point between the coils L and L and the ground. .
Japanese Utility Model Publication No. 7-29925

  FIG. 3B is a circuit diagram showing an equivalent circuit of the feeder 14. The feeder 14 has a capacitance between the transmission line and the ground, and it can be considered that a capacitor Cf is connected between the transmission line and the ground as shown in FIG. Since the feeder 14 is connected to the output terminal OUT of the filter unit 12, resonance may occur in the AM broadcast band due to one or both of the two coils L and L of the filter unit 12 and the capacitor Cf of the feeder 14.

  FIG. 4B is a diagram illustrating an example of the frequency characteristics of the antenna gain of the receiving apparatus 10 illustrated in FIG. However, a solid line shows the case where the feeder 14 is connected, and a broken line shows the case where the feeder 14 is not connected. When the feeder 14 is connected, resonance occurs at the frequency f1.

  Further, the capacitance of the capacitor Cf increases in proportion to the length of the transmission path of the feeder 14. When the capacitance increases, the resonance frequency f1 shown in FIG. 4B decreases. Therefore, the larger the capacitor Cf of the feeder 14 is, the more easily resonance occurs in the AM broadcast band. When resonance occurs in the AM broadcast band, the AM tuner unit 16 may select a frequency near the resonance frequency f1, and the antenna gain varies depending on the selected frequency, and the reception sensitivity of the AM tuner unit 16 varies. Problems arise.

  The present invention has been made in view of such circumstances, and by connecting a resistor in parallel to one or both of two coils, the capacitance of the transmission line connected to one of the coils and the one or both An object of the present invention is to provide a T-type filter circuit that can reduce the influence of resonance due to the inductance of the coil.

  The present invention also provides a receiving apparatus that can stabilize the frequency characteristics of a signal input to a tuner by using a T-type filter circuit in which a resistor is connected in parallel to one or both of two coils. The purpose.

  A T-type filter circuit according to a first aspect of the present invention is a T-type filter circuit having two coils connected in series and a capacitor having one end connected to a connection point between the coils, and one of the two coils. Alternatively, resistors are connected in parallel to both.

  A receiving apparatus according to a second invention is a receiving apparatus for transmitting a signal received by an antenna to a tuner via a feeder, wherein the T-type filter circuit described in the first invention is connected between the antenna and the feeder. And

  In the first invention, when there is a capacitance between the transmission line connected to one of the two coils and the ground, resonance due to the capacitance and the inductance of one or both of the two coils, May occur in the pass frequency band. The height of the peak portion generated by resonance increases when the Q value of the coil is large, and decreases when the Q value of the coil is small. When a resistor is connected in parallel to one or both of the two coils, the Q value of the one or both coil portions is lowered, so that resonance is suppressed and the influence of resonance can be reduced.

  In the second invention, the feeder connecting the T-type filter circuit and the tuner has a capacitance with the ground, and resonance caused by the capacitance and the inductance of the coil of the T-type filter circuit is the reception frequency of the tuner. Although there is a possibility of occurrence in the band, resonance is suppressed as described above by the T-type filter circuit in which a resistor is connected in parallel to one or both of the two coils, and the influence of resonance can be reduced.

  According to the first invention, when a transmission line having a capacitance is connected between one of the two coils and the ground, the influence of resonance due to the capacitance and the inductance of one or both of the two coils is reduced. it can.

  According to the second invention, it is possible to reduce the influence of resonance due to the inductance of the coil of the T-type filter circuit and the capacitance of the feeder, and to stabilize the frequency characteristics of the signal input to the tuner.

Hereinafter, the present invention will be specifically described with reference to the drawings showing embodiments thereof.
FIG. 1 is a block diagram showing a configuration example of an audio device including a receiving device 10 according to the present invention that receives an AM broadcast. The receiving device 10 is connected to the filter unit 12 via a filter unit 12 that passes signals in the AM broadcast band among signals received by the antenna and a feeder 14 that is a high-frequency coaxial filter, and has passed through the filter unit 12. And an AM tuner unit 16 having a tuning circuit for selecting a frequency for a signal in the AM broadcast band, a high-frequency amplifier circuit, and the like.

  The signal selected by the AM tuner unit 16 is amplified by the amplifier unit 22 and output from the speaker 24. A microcomputer 20 is connected to the AM tuner unit 16 and the amplifier unit 22, and an operation unit 26 is connected to the microcomputer 20. The microcomputer 20 controls the selection of the frequency of the AM tuner unit 16 and the amplification factor of the amplifier unit 22 in accordance with the operation received by the operation unit 26. The amplifier unit 22 may be connected to another device that outputs an audio signal such as a CD (Compact Disk) player or an MD (Mini Disc) player.

  FIG. 2A is a circuit diagram illustrating an example of the T-type filter circuit 18 used in the filter unit 12. The T-type filter circuit 18 includes two coils L and L connected in series between an input terminal IN to which a signal received by an antenna is input and an output terminal OUT to which the feeder 14 is connected, and the coils L and L And a capacitor C connected between the connection point and the ground, and two resistors R and R connected in parallel with the two coils L and L, respectively. The resistance value of the resistor R is several hundred Ω, the inductance of the coil L is several μH, and the capacitance of the capacitor C is several tens of pF.

  FIG. 2B is a diagram illustrating an example of frequency characteristics of the antenna gain of the receiving apparatus 10 illustrated in FIG. The resistances R and R added to the conventional T-type filter circuit 18 reduce the Q value of the coils L and L, so that the height of the peak portion generated by resonance is reduced. For this reason, the resonance shown in FIG. 4B, which has occurred in the past, is suppressed, the frequency characteristics become flat, and there is no variation in reception sensitivity of the AM tuner section 16 that has occurred in the past.

  In the embodiment described above, the two resistors R and R are connected in parallel to the two coils L and L, respectively, but it is also possible to connect the resistor R in parallel to only one of the two coils L and L. . However, since resonance due to the inductance of each of the two coils L and L and the capacitance of the feeder 14 may occur in the AM broadcast band, it is preferable to connect resistors to both coils in parallel.

  In the embodiment described above, the case where the T-type filter circuit 18 according to the present invention shown in FIG. 2A is used in the AM broadcast receiving apparatus 10 has been described as an example. 18 can be used for any device that needs to select a frequency range.

It is a block diagram which shows the structural example of the audio equipment containing the receiver which concerns on this invention which receives AM broadcast. (A) is a circuit diagram which shows the example of the T-type filter circuit used for the filter part shown in FIG. 1, (b) is a figure which shows the example of the frequency characteristic of the antenna gain of the receiver shown in FIG. (A) is a block diagram which shows the prior art example of the receiver of AM broadcast, (b) is a circuit diagram which shows the equivalent circuit of a feeder. (A) is a circuit diagram which shows the example of the conventional T-type filter circuit, (b) is a figure which shows the example of the frequency characteristic of the antenna gain of the receiver shown to Fig.3 (a).

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Receiving device 12 Filter part 14 Feeder 16 AM tuner part 18 T type filter circuit 20 Microcomputer 22 Amplifier part 24 Speaker 26 Operation part

Claims (2)

In a T-type filter circuit having two coils connected in series and a capacitor having one end connected to a connection point between the coils,
A T-type filter circuit, wherein a resistance is connected in parallel to one or both of the two coils. In a receiving device that transmits a signal received by an antenna to a tuner via a feeder,
A receiving apparatus, wherein the T-type filter circuit according to claim 1 is connected between an antenna and a feeder.

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