JP4672500B2 - Antenna input device - Google Patents

Description

  The present invention relates to an antenna input device including an impedance matching circuit for matching an input impedance between an antenna and a receiver, and more particularly to an antenna for a glass antenna incorporated in a window glass of an automobile or the like that receives an AM broadcast reception wave. It relates to an input device.

  In general, the medium wave AM broadcast wave has a very long wavelength of about 180 to 600 m. Therefore, it is necessary to increase the length of the antenna accordingly. Only a length of m can be realized.

  Therefore, in order to receive the AM band with a relatively short antenna, various antenna input devices including an impedance matching circuit that matches the input impedance between the antenna and the receiver have been developed.

  Conventionally, as this type of antenna input device, as shown in FIG. 9A, a device having a μ tuning circuit that tunes to a desired frequency by variably adjusting the effective permeability μ value of inductive reactance is provided. However, there is a problem that the mechanism for moving the coil core and the mechanism for applying the operating force to move the coil are required, which complicates the apparatus.

  Further, as shown in FIG. 9B, a desired frequency can be obtained by variably adjusting the capacitance by controlling the reverse voltage of the diode by using a variable capacitance element such as a varicap diode VC for the capacitive reactance. Although it has been proposed to have an electronic tuning circuit that can be tuned to a constant frequency, it is impossible to obtain a constant reception sensitivity over the entire reception frequency due to the variable capacitance limit of the variable capacitance element and the change in the combined capacitance at low frequencies. There was a problem.

  Furthermore, as shown in FIG. 9C, an electronic tuning circuit having an impedance conversion circuit using an FET or the like before the tuning circuit has been proposed to reduce input loss from the antenna. Since the reception frequency band is amplified, there is a problem that it is easily affected by an interference wave and distortion due to strong input interference occurs.

  By the way, it is known that when the antenna is made shorter than the wavelength, the reactance is increased. This reactance has a capacitance of several tens of pF to several hundreds of pF, and in the case of AM band reception, the impedance is about 1 kΩ to 4 kΩ, which is about a fourfold change. In order to cancel out this capacitive reactance, it is necessary to give the inductive reactance a change width of about 10 times ranging from about 100 μH to 1000 μH. However, the capacity change ratio is limited in the current device, which is not sufficient.

Therefore, Patent Document 1 discloses that an antenna unit that is disposed on a window glass and receives an AM charging wave has a high impedance when the radio side is viewed from the antenna side and a low impedance when the antenna side is viewed from the radio side. An AM band window glass antenna device including an impedance matching circuit in which circuit constants are set so that the impedance matching circuit includes a variable capacitance rectifier in series that cancels the equivalent reactance of the antenna unit. A window glass antenna device for AM band has been proposed.
JP-A-6-177628

  However, according to the device described in Patent Document 1 described above, since it is difficult to obtain the best matching in a wide frequency range, there is a problem that stable practical sensitivity that is stable in the entire frequency band cannot be obtained. .

  An object of the present invention is to provide an antenna input device capable of ensuring a relatively stable practical sensitivity in the entire reception frequency band in view of the above-described conventional drawbacks.

In order to achieve the above object, a first characteristic configuration of an antenna input device according to the present invention includes an impedance matching circuit for matching an input impedance between an antenna and a receiver, and an antenna input installed in the vicinity of the antenna. The impedance matching circuit includes a series circuit of a plurality of inductive reactance elements and switches, a series circuit of a variable capacitance element and a capacitive reactance element whose reactance is continuously variable, and the antenna. Connected in parallel between the ground, and both ends of the variable capacitance element are connected via capacitive reactance elements, respectively , and the LC circuit using the connection as an output end, and the tuning frequency band to be received , the connection mode switching control child of the inductive reactance element via the respective switches of the LC circuit Optionally with changing the reactance in steps, in that it includes a control circuit for continuously switching control the reactance of the variable capacitance element in response to each connection mode.

  According to the above-described configuration, the connection mode of the reactance element is switched by the switching circuit controlled by the impedance control circuit so as to obtain an appropriate reactance corresponding to the tuning frequency band to be received. Since switching is performed in a stepwise manner, a predetermined practical sensitivity can be ensured corresponding to the entire reception frequency band without providing a large number of reactance elements. Then, due to the practical sensitivity characteristic by reactance indicating the sawtooth characteristic output from the connection point between the inductive reactance element and the variable capacitance element, and by the reactance indicating the reverse sawtooth characteristic output from the other of the variable capacitance element. Practical sensitivity characteristics are combined with each other, so that practical sensitivity differences are small, that is, extremely stable practical sensitivity can be secured in the entire reception frequency band.

  The second characteristic configuration is that, in addition to the first characteristic configuration described above, an attenuator is provided in the preceding stage of the impedance matching circuit.

  According to the above configuration, even if there is an interference wave in the vicinity of the tuning frequency to be received, the level of the interference wave by the attenuator in the previous stage is sufficiently attenuated, so that the occurrence of cross modulation is effectively prevented. You will be able to do it.

  The third feature configuration is that, in addition to the first feature configuration described above, an attenuator is provided in the subsequent stage of the impedance matching circuit, and the input impedance of the attenuator is matched with the output impedance of the impedance matching circuit. is there.

  According to the above-described configuration, it is possible to reliably obtain the desired frequency by avoiding the deviation of the tuning frequency when the attenuator is operating and when the attenuator is not operating, while avoiding the occurrence of cross modulation.

  The fourth feature configuration is that, in addition to any of the first to third feature configurations described above, the switching circuit is configured by an RF-MEMS that switches the connection mode of the reactance elements.

  According to the above-described configuration, the device can be significantly reduced in size by using an RF-MEMS (Micro Electro Mechanical System) as the switching circuit.

  As described above, according to the present invention, it is possible to provide an antenna input device capable of ensuring a relatively stable practical sensitivity in the entire reception frequency band.

  Hereinafter, embodiments of an antenna input device according to the present invention will be described. As shown in FIG. 1, the antenna input device 3 includes an attenuator 4 and an impedance matching circuit 5 connected between the glass antenna 1 and the receiver 2 embedded in the car window and connected to the subsequent stage of the attenuator 4. Has been.

  The impedance matching circuit 5 is a circuit for matching an input impedance between the antenna 1 and the receiver 2 and switches a plurality of reactance elements (L1 to Ln) whose connection modes can be switched and a connection mode of the reactance elements. Thus, a switching circuit 51 that changes the reactance stepwise and an impedance control circuit 52 that controls the switching circuit 51 according to the tuning frequency band to be received are provided.

  The receiver 2 amplifies a high-frequency amplifier circuit 21 that amplifies a high-frequency signal that is received by the antenna 1 and includes a signal component in the vicinity of the frequency of a desired wave to be received, tuned in the impedance matching circuit 5, and the amplified reception A mixer circuit 24 that mixes the signal and the local oscillation signal from the local oscillation circuit 22, a narrowband filter 25 that separates a component containing an audio signal from the mixed intermediate frequency signal, and an intermediate frequency that amplifies the output signal An amplifying circuit 26 and a detecting circuit 27 for detecting an audio signal are provided, and the audio signal output from the detecting circuit 27 is power amplified and output to a speaker.

  The local oscillation circuit 22 is configured by a voltage controlled oscillator or the like, and is configured to output a local oscillation signal having a frequency corresponding to a tuning voltage from a phase lock loop (hereinafter abbreviated as “PLL”) circuit. The PLL circuit includes a frequency divider that divides the local oscillation signal by a frequency division ratio N corresponding to the frequency of the desired wave input from the control unit 6 realized by a microcomputer, and a predetermined reference frequency. A reference signal source that generates a reference signal, a comparator that compares the phase of the reference signal with the divided local oscillation signal and generates an error output corresponding to the difference, and an error output from the comparator Is smoothed into a direct current voltage and provided as a tuning voltage to the local oscillation circuit 22.

  Therefore, when a desired frequency is set and input to the control unit 6 from an operation input unit (not shown), an N value corresponding to the desired frequency is referred to in the ROM table and then output from the control unit 6 to generate the local oscillation signal. The desired wave can be received by changing the tuning voltage so that the phase difference between the signal obtained by dividing the signal by the N value and the reference signal becomes zero.

  As shown in FIG. 1, the impedance matching circuit 5 includes a plurality of coils L1, L2, L3,. A pair of varicap diodes VC1 and VC2 connected so that their cathodes face each other are also connected in parallel.

  Switches S1, S2,... Sn as switching circuits 51 that switch the connection mode of the reactance elements are connected to the ground side terminals of the coils L1, L2,. The reactance is configured to change stepwise by controlling the switching circuit 51 with a selection signal.

  The cathodes of the varicap diodes D1 and D2 are provided with a D / A converter as a switching circuit 51 for converting a control signal output from the control unit 6 into an analog control signal, and the control signal is applied to the cathode. Thus, the reactance is continuously changed.

  The controller 6 refers to the ROM table, acquires data relating to the combination of the switches S1, S2,... Sn corresponding to the desired frequency and the target control voltage, and controls the switching circuit 51 based on the data. Thus, the reactance of the impedance matching circuit 5 is adjusted to a reactance appropriate for the desired frequency.

  That is, the ROM table stores N-value data for the desired frequency and setting data for the target reactance.

  As shown in FIGS. 2A to 2C, the reactance by the coil L is changed stepwise by selectively controlling the switches S1, S2,... By adjusting the control voltage for the diode VC and changing it continuously or stepwise, the impedance is adjusted to tune to the desired frequency.

  Furthermore, a level detector 28 for detecting an output level from the high frequency amplifier circuit 21 is provided, and the control unit 6 is configured to maintain the reception level detected by the level detector 28 at a predetermined level. By finely adjusting the switching circuit 51, signal distortion is prevented and adjustment control is performed to a stable reception level.

  That is, the block that controls the switching circuit 51 in accordance with the tuning frequency band to be received in the control unit 6 is configured to function as an impedance control circuit.

  Further, the control unit 6 operates the attenuator 4 to avoid cross modulation when the reception level detected by the level detector 28 is higher than a predetermined level or when a strong input disturbance wave exists. Attenuate the level. Here, the attenuator 4 may be arranged at the subsequent stage of the impedance matching circuit 5.

  Hereinafter, another embodiment of the present invention will be described.

  In the embodiment described above, the reactance element includes the variable capacitance element VC (VC1, VC2) whose reactance is continuously variable as the impedance matching circuit 5, and the switching circuit 51 includes the inductive reactance elements L1, L2,. Although the connection mode of Ln is configured to be switchable and the reactance of the variable capacitance element VC is configured to be continuously switchable according to each connection mode, the impedance matching circuit is shown in FIG. As shown in (a), the switching circuit 51 may be configured so that at least only the connection mode of the inductive reactance elements L1, L2,... Ln can be switched.

  Further, as shown in FIG. 4B, the switching circuit 51 is configured such that at least the capacitive reactance elements C1, C2,... Cm can be switched by switches S1, S2,. As shown in FIG. 4 (c), the inductive reactance elements L1, L2,... Ln and the capacitive reactance elements C1, C2,. It may be a thing.

  As shown in FIG. 3A, the switch constituting the switching circuit 51 is configured using an RF-MEMS (Micro Electro Mechanical System) manufactured by a micromachining technology, thereby greatly reducing the size of the apparatus. Can be planned. Furthermore, as shown in FIG. 3B, by adopting one or both of a tapped one package transformer LP as an inductive reactance element and a tapped one package capacitor CP as a capacitive reactance element, as shown in FIG. It is also possible to reduce the mounting area of the apparatus.

  As shown in FIG. 5A, the inductive reactance elements L1, L2,... Ln and the variable capacitance element VC are connected in parallel, and outputs OUT1 and OUT2 from both ends of the variable capacitance element VC are combined. It may be configured to include a combining circuit. In this case, the practical sensitivity characteristic (shown in FIG. 6B) for the output OUT1 of the impedance matching circuit shown in FIG. 5B and the practical sensitivity for the output OUT2 of the impedance matching circuit shown in FIG. A practical sensitivity characteristic as shown in FIG. 6A obtained by combining the characteristics (shown in FIG. 6C) is obtained, the fluctuation range of the practical sensitivity is greatly reduced, and a low-level input signal is obtained. In addition, reception characteristics with a high S / N ratio can be obtained.

  Further, as shown in FIG. 7A, an attenuator 4 is provided at the subsequent stage of the impedance matching circuit 5 so that the input impedance of the attenuator 4 is matched with the output impedance of the impedance matching circuit 5. It is preferable to reduce the reception sensitivity by attenuating the impedance so as not to cause an impedance mismatch even if there is a strong input disturbance.

  Specifically, the capacitor C7 is set to an appropriate value, the capacitance of the capacitor C8 is determined so as to be equal to the impedance on the impedance matching circuit side viewed from the capacitor C8 with a predetermined attenuation, and further viewed from the capacitor C9. An appropriate value can be obtained by determining the capacitance of the capacitor C9 so as to be equal to the impedance on the impedance matching circuit side.

  For example, as shown in FIG. 7B, when the values of the capacitor C7 are set to 22 pF while ignoring the capacitors C3 and C6 that have a sufficiently large capacitance and an error range, the combined capacitance Ccom1 becomes Ccom1 = (Cant + Cf ) · C7 / (Cant + Cf) + C7, 18.03 pF is obtained. When the attenuation is set to 20 dB, C8 is obtained as 162 pF from the capacitance ratio X = Ccom1 / (Ccom1 + C8), 20logX = −20. Further, the combined capacitance Ccom2 seen from C9 is obtained as 180 pF by Ccom2 = C8 + Ccom1, and Ccom3 = (Ccom2 · C9) / Ccom2 + C9 = Cant + Cf so that the combined capacitance seen from the tuning circuit does not change depending on the presence or absence of the attenuator. , C9 = 225 pF. Cant is an antenna capacitance, L1 and Cf are reactance values of the impedance matching circuit, and C3 is a wiring capacitance.

  Further, as shown in FIG. 8, the impedance matching circuit described above is disposed in the vicinity of the antenna 1, for example, at the rear pillar portion of the vehicle body, so that the influence of the wiring capacity is reduced and stable reception characteristics can be ensured. Similarly, an antenna input device including the impedance matching circuit and the attenuator may be disposed in the vicinity of the antenna 1.

  Note that the above-described embodiment is merely an example of the present invention, and it is needless to say that the specific configuration and the like of each block can be changed and designed as appropriate within the scope of the effects of the present invention.

The circuit block block diagram of the receiver containing the antenna input device by this invention Explanatory diagram of frequency characteristics of impedance matching circuit shown in FIG. Configuration diagram of impedance matching circuit showing another embodiment Configuration diagram of impedance matching circuit showing another embodiment Configuration diagram of impedance matching circuit showing another embodiment Performance sensitivity characteristic diagram of the impedance matching circuit shown in FIG. Attenuator circuit diagram Explanatory drawing showing an implementation example of the antenna input device Illustration of conventional impedance matching circuit

1: Antenna (glass antenna)
2: Receiver 3: Antenna input device 4: Attenuator 5: Impedance matching circuit 6: Control unit (control circuit)
51: Switching circuit 51
52: Impedance control circuit L1... Lc: Inductive reactance element (coil)
D1, D2: Capacitive reactance elements (varicap diodes)
C1... Cm: Capacitive reactance element (capacitor)

Claims (4)

An antenna input device provided with an impedance matching circuit for matching input impedance between an antenna and a receiver, installed near the antenna,
The impedance matching circuit is:
A series circuit of a plurality of inductive reactance elements and switches and a series circuit of a variable capacitance element and a capacitive reactance element whose reactance is continuously variable are connected in parallel between the antenna and the ground, and the variable An LC circuit that connects both ends of the capacitive element via capacitive reactance elements, and uses the connection as an output end ,
According to the tuning frequency band to be received, the reactance is changed stepwise by switching the connection mode of the inductive reactance element via each switch of the LC circuit, and the variable according to each connection mode. A control circuit that continuously switches and controls the reactance of the capacitive element;
An antenna input device comprising:   The antenna input device according to claim 1, wherein an attenuator is provided upstream of the impedance matching circuit.   The antenna input device according to claim 1, wherein an attenuator is provided at a subsequent stage of the impedance matching circuit, and an input impedance of the attenuator is matched with an output impedance of the impedance matching circuit.   The antenna input device according to claim 1, wherein the switch is configured by RF-MEMS.

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