JP2005340994A - Antenna tuning circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an antenna tuning circuit capable of finely adjusting the capacity of the antenna tuning circuit within a wide range and capable of being changed into an IC. <P>SOLUTION: Either of variable-capacity diodes VC1, VC2, VC3 and VC4 is connected to a resistor R by each semiconductor switch S1, S2, S3 and S4. The variable-capacity diodes VC2, VC3 and VC4 are connected in parallel with each two, four and eight variable capacity diodes VC1. Consequently, a synthetic capacity is controlled digitally. The synthetic capacity is adjusted finely by applying a voltage to the variable-capacity diode connected from the terminal TA side, and the resonance frequency of the antenna tuning circuit is maintained continuously at a specified value. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an antenna tuning circuit capable of having a high gain in a wide frequency band used for television broadcasting, for example.

  In recent years, with the spread of portable terminals capable of receiving television broadcasts, it is desired to reduce the size of antennas. In particular, in terrestrial digital television broadcasting, the center frequency is as high as 500 MHz (wavelength of about 60 cm), and active antenna technology that covers a wideband frequency while using a small antenna attracts attention.

  As an example, a method for controlling the frequency characteristics of an antenna using a variable capacitance diode is known. Hereinafter, a conventional antenna tuning circuit 200 will be described with reference to the block diagram of FIG. In the figure, 21 is a small dielectric antenna unit that receives a broadcast wave of a television signal, 22 is a variable capacitance diode having one end connected to one end of the dielectric antenna unit 21 and the other end grounded, and 23 has a one end dielectric. A tuner unit 24 connected to the other end of the body antenna unit 21 includes a central processing unit (not shown) for processing a signal from the tuner unit 23 and a digital / analog converter (not shown). 2 is a voltage generation circuit that generates a voltage suitable for the above and supplies it to the variable capacitance diode 22 from the other end of the dielectric antenna unit 21.

  The operation of the antenna tuning circuit 200 having the above configuration will be described. The television signal received by the dielectric antenna unit 21 including the inductor component is received by the tuner unit 23 in a desired channel. Here, the reception capacity of the dielectric antenna unit 21 is extremely narrow in the receivable frequency band as compared with a general rod antenna. Therefore, since it is necessary to tune each broadcast channel in the antenna circuit, a variable capacitance diode 22 is provided in series with the dielectric antenna unit 21, and the voltage generation circuit 24 applies a voltage suitable for each channel to the variable capacitance diode. 22, the frequency band with high gain is shifted and tuned and received (see, for example, Patent Document 1).

  However, since the antenna tuning circuit 200 relies on the capacitance change of the variable capacitance diode 22 for tuning, a variable width of a desired capacitance to cope with a wide band can be obtained unless a high voltage (0 to 30 V) is applied. There was a problem that could not be taken. Further, since the relationship between the voltage applied to the variable capacitance diode 22 and the capacitance is not linear, the process (or control) for obtaining the voltage applied from the (tuning) frequency is complicated.

  In order to avoid the problem of power consumption and the complexity of control, a method has been proposed in which a plurality of capacitors are used instead of the variable capacitance diode 22 and switching is performed by a switch element.

  The capacitor switching type antenna tuning circuit 210 will be described below with reference to the equivalent circuit of FIG. In the figure, L is the inductance of the tuning circuit including the antenna, R is the resistance of the tuning circuit including the antenna, C0, C1, C2, and C3 are capacitors, each having one end connected in common and connected to the terminal TA. The other end of the capacitor C0 is connected in series to one end of the inductance L via the resistor R, and the other end of the inductance L is connected to the terminal TB.

  S1, S2, and S3 are semiconductor switches, and TC is a control terminal. These semiconductor switches S1, S2, and S3 are controlled to be opened and closed by a control circuit (not shown) so as to maintain the resonance frequency of the antenna tuning circuit at a predetermined value. Yes. The other ends of the capacitors C1, C2, and C3 are connected to one end sides of the corresponding semiconductor switches S1, S2, and S3, and the other ends of the semiconductor switches S1, S2, and S3 are connected to the other end side of the capacitor C0. Yes.

According to the antenna tuning circuit 210 configured as described above, the capacitor C0 and any one of the capacitors C1, C2, and C3 are connected in parallel, so that if the capacitors C1, C2, and C3 are different from each other, the combined capacitance can be made variable. can do. In the illustrated example, the capacitances of the capacitors C1, C2, and C3 are set to be twice, four times, and eight times that of the capacitor C0, respectively. Thus, the resonance frequency of the antenna tuning circuit is maintained at a predetermined value step by step, and a wideband frequency is covered while using a small antenna (see, for example, Patent Document 2).
JP-A-10-224698 (page 3, FIG. 1) JP 2001-344574 A (3rd page, FIG. 1)

  However, the conventional antenna tuning circuit 210 has a problem in that the capacitance synthesis is digital and fine adjustment cannot be performed. Further, in order to make each capacitor with a semiconductor, the occupied area becomes large, which is disadvantageous in terms of IC implementation.

  In view of the above problems, an object of the present invention is to provide an antenna tuning circuit that can finely adjust the capacitance of the tuning circuit over a wide range and can be integrated into an IC.

The invention according to claim 1 is an antenna including an antenna element capable of receiving a terrestrial signal, a capacitive element connected to the antenna element, and a semiconductor switch element for selecting the capacitive element according to the reception frequency band. In the tuning circuit,
The capacitive element is a plurality of variable capacitance diodes having one end commonly connected, and the other ends of the one or more variable capacitance diodes are commonly connected to form a plurality of variable capacitance diode groups, and one end of each corresponding semiconductor switch element. The antenna tuning circuit is characterized in that the other end of each semiconductor switch element is connected in common.

  A second aspect of the present invention is the antenna tuning circuit according to the first aspect, wherein the antenna element has a length that is substantially a quarter of the reception wavelength.

  The invention according to claim 3 is the antenna tuning circuit according to claim 1, wherein the number of variable capacitance diodes constituting each variable capacitance diode group is a geometric sequence of 2 starting from 1. .

  According to a fourth aspect of the present invention, in the antenna tuning circuit according to the first aspect, each semiconductor switch element is a switch control by light.

  According to the fifth aspect of the present invention, the combined capacitance of each variable capacitance diode group is finely adjusted by applying a voltage from a voltage generation circuit that detects a difference between the resonance frequency and the desired frequency and matches the desired frequency. The antenna tuning circuit according to claim 1, wherein:

According to a sixth aspect of the present invention, there is provided an antenna element having a length that is approximately a quarter of a reception wavelength capable of receiving a terrestrial signal, a capacitive element connected to the antenna element, and a capacitive element according to a reception frequency band. An antenna tuning circuit comprising a semiconductor switch element that is switch-controlled by light for selection,
The capacitive element is a plurality of variable capacitance diodes with one end connected in common, and the other end is connected in common with the number of geometric sequences of 2 starting from 1 to form a plurality of variable capacitance diode groups, and a plurality of variable capacitances. Connected to one end of each semiconductor switch element corresponding to the diode group, each other end of each semiconductor switch element is connected in common, and the combined capacitance of each variable capacitance diode group detects the difference between the resonance frequency and the desired frequency Then, the antenna tuning circuit is characterized in that a voltage by a voltage generation circuit that matches a desired frequency is applied and finely adjusted.

  According to the antenna tuning circuit of the present invention, since a plurality of variable capacitance diodes are connected in parallel and selectively switched by a semiconductor switch, the capacitance of the tuning circuit can be finely adjusted over a wide range and an IC can be realized. And it is possible to cover a wide frequency range while using a small antenna.

  The purpose of making an IC that can finely adjust the capacitance of the antenna tuning circuit over a wide range is realized by connecting a plurality of variable capacitance diodes in parallel and selectively switching them with a semiconductor switch.

  Hereinafter, an antenna tuning circuit 100 according to a first embodiment of the present invention will be described with reference to FIG. In the figure, L is the inductance of the tuning circuit including the antenna, R is the resistance of the tuning circuit including the antenna, VC1, VC2, VC3, and VC4 are variable capacitance diodes, one end of which is connected in common and connected to the terminal TA. .

  S1, S2, S3, S4 are semiconductor switches, TC is a control terminal, and these semiconductor switches S1, S2, S3, S4 are controlled by a control circuit (not shown) so as to maintain the resonance frequency of the antenna tuning circuit at a predetermined value. Open / close controlled. The other ends of the variable capacitance diodes VC1, VC2, VC3, VC4 are connected to one ends of the corresponding semiconductor switches S1, S2, S3, S4, and the other ends of the semiconductor switches S1, S2, S3, S4 are resistors R. Is connected in series to one end of the inductance L, and the other end of the inductance L is connected to the terminal TB.

  According to the antenna tuning circuit 210 configured as described above, the variable capacitance diodes VC1, VC2, VC3, and VC4 are connected to the resistor R by the respective semiconductor switches.

  By connecting the variable capacitance diodes VC2, VC3, and VC4 in parallel with two, four, and eight variable capacitance diodes VC1, respectively, the capacitance of each variable capacitance diode becomes a geometric sequence of 2 starting from 1. The composite capacitor can be digitally controlled from 1 to 15 levels by suitably selecting a semiconductor switch to be conducted. Since the combined capacitance changes linearly, it is easy to control when tuning the resonance frequency of the antenna tuning circuit from a wide frequency range.

  Furthermore, the combined capacitance can be finely adjusted by applying a voltage to the variable capacitance diode connected from the terminal TA side, and the resonance frequency of the antenna tuning circuit is continuously set to a predetermined value while using a small antenna. Can be maintained. In addition, since the tuning circuit has a variable capacitance diode, it can be integrated into an IC.

  Next, the antenna tuning circuit 110 according to the second embodiment of the present invention will be described with reference to FIG. The difference from the antenna tuning circuit 100 shown in FIG. 1 is that the semiconductor switches (S1, S2, S3, S4) are optical MOSFETs (P1, P2, P3, P4).

  According to the second embodiment, the control signal is light, and the control circuit (not shown) can be electrically disconnected from the antenna tuning circuit. Therefore, it is possible to minimize the influence of the control circuit which affects the high frequency characteristics such as the impedance of the tuning circuit and Q (Quality factor).

  The antenna tuning circuit of the present invention can be widely applied to the antenna tuning circuit of a receiving apparatus that covers high-frequency and wide-band frequencies used in digital TV broadcasting that will be expanded in the future.

1 is a circuit diagram showing a configuration of an antenna tuning circuit 100 according to a first embodiment of the present invention. The circuit diagram which shows the structure of the antenna tuning circuit 110 of Example 2 of this invention. The block diagram which shows the structure of the antenna tuning circuit 200 of the prior art Example. The circuit diagram which shows the structure of the antenna tuning circuit 210 of another conventional example.

Explanation of symbols

21 Dielectric antenna unit 22 Variable capacitance diode 23 Tuner unit 24 Voltage generation circuit L Inductance R Resistance TA, TB, TC Terminals S1, S2, S3, S4 Semiconductor switches P1, P2, P3, P4 Optical MOSFET
C0, C1, C2, C3 Capacitors VC1, VC2, VC3, VC4 Variable capacitance diodes 100, 200, 210 Antenna tuning circuit

Claims (6)

An antenna element capable of receiving a terrestrial signal;
A capacitive element connected to the antenna element;
In an antenna tuning circuit comprising a semiconductor switch element for selecting the capacitive element according to a reception frequency band,
The capacitive element is a plurality of variable capacitance diodes having one end commonly connected, and the other ends of the one or more variable capacitance diodes are commonly connected to form a plurality of variable capacitance diode groups. An antenna tuning circuit, wherein the antenna tuning circuit is connected to one end of an element, and the other ends of the semiconductor switch elements are connected in common.   The antenna tuning circuit according to claim 1, wherein the antenna element has a length that is approximately a quarter of a reception wavelength.   2. The antenna tuning circuit according to claim 1, wherein the number of variable capacitance diodes forming each variable capacitance diode group is a geometric sequence of 2 starting from 1.   2. The antenna tuning circuit according to claim 1, wherein each of the semiconductor switch elements is switch control by light.   The combined capacitance of each of the variable capacitance diode groups is finely adjusted by applying a voltage from a voltage generation circuit that detects a difference between a resonance frequency and a desired frequency and matches the desired frequency. 5. The antenna tuning circuit according to any one of 1 to 4. An antenna element having a length that is approximately a quarter of the reception wavelength capable of receiving a terrestrial signal;
A capacitive element connected to the antenna element;
An antenna tuning circuit including a semiconductor switch element that is switch-controlled by light for selecting the capacitive element according to a reception frequency band,
The capacitive element is a plurality of variable capacitance diodes having one end connected in common, and the other end is connected in common with the number of two geometric sequences starting from 1 to form a plurality of variable capacitance diode groups. Connected to one end side of each semiconductor switch element corresponding to the variable capacitance diode group, each other end of each semiconductor switch element is connected in common, and the combined capacitance of each variable capacitance diode group has a resonance frequency and a desired frequency. The antenna tuning circuit is characterized in that a voltage generated by a voltage generation circuit that detects a difference between the two and matches a desired frequency is applied and finely adjusted.

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