JP2014033375A - Matching circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a matching circuit that allows reducing the loss of an input signal with respect to an amplifier circuit and increasing the output of the amplifier circuit.SOLUTION: A matching circuit 10 connected to an input of an amplifier circuit for amplifying a reception signal from an antenna is composed of a variable control LC circuit 20 and a control section 30. The variable control LC circuit 20 is composed of a variable capacitance 22 and a coil 21 that are connected in series. The variable control LC circuit 20 has its one end connected to an input of a collector-grounded transistor amplifier circuit 40 so as to branch and has its other end connected to the ground. The control section 30 controls the variable capacitance 22 of the variable control LC circuit so that the impedance viewed from the antenna side is matched.

Description

  The present invention relates to a matching circuit, and more particularly to a matching circuit connected to an input of an amplifier circuit that amplifies a received signal from an antenna.

  The matching circuit is connected to the input of an amplifier circuit that amplifies the received signal from the antenna. This is intended to match the impedance viewed from the antenna side with the input impedance of the amplifier circuit. By performing impedance matching, a received signal from the antenna can be efficiently input to the amplifier circuit. Such a matching circuit is composed of, for example, an LC circuit in which L (coil) and C (capacitor) are combined.

  Recently, terrestrial digital broadcasting and the like have begun, and wireless devices such as mobile phones, radios, and GPS have been diversified. For this reason, a matching circuit capable of matching over a wide frequency band is desired.

  For example, Patent Literature 1 and Patent Literature 2 disclose matching circuits connected in series to an antenna. This is composed of a parallel LC circuit connected in series to the antenna, and the capacitor of the parallel LC circuit is composed of a variable capacitance element.

JP 2004-320611 A JP 2008-113233 A

  However, these conventional matching circuits are connected in series between the antenna and the amplifier circuit, and the loss of the input signal by the matching circuit itself is large. That is, since the matching circuit is connected in series and the impedance of the control unit of the matching circuit is visible from the antenna input path, the antenna input path is affected.

  In view of such circumstances, the present invention seeks to provide a matching circuit that can reduce the loss of an input signal to the amplifier circuit and increase the output of the amplifier circuit.

  In order to achieve the above-described object of the present invention, the matching circuit according to the present invention is a variable control LC circuit comprising a variable capacitor and a coil, a capacitor and a variable coil, or a variable capacitor and a variable coil connected in parallel or in series. The variable control LC circuit, one end of which is connected so as to branch to the input of the collector grounded transistor amplifier circuit and the other end is grounded, and the variable capacitance and / or variable coil of the variable control LC circuit are connected to the antenna side. And a control unit that performs control so as to match the impedance as viewed from above.

  Here, the variable control LC circuit may be any circuit in which a coil and a variable capacity varicap are connected in series, the anode of the varicap is grounded, the cathode is connected to the coil, and the controller is connected. .

  The variable control LC circuit includes a parallel connection of a coil and a variable capacity varicap, the anode of the varicap is grounded, the cathode is connected to one end of the coil, and the control unit is connected to the other end of the coil. May be grounded.

  In addition, a series LC filter circuit and a DC cut capacitor are connected in series to the input of the common collector transistor amplification circuit, and one end of the variable control LC circuit is interposed between the series LC filter circuit and the DC cut capacitor. It may be connected and the other end grounded.

  The matching circuit of the present invention has an advantage that the loss of the input signal to the amplifier circuit can be reduced and the output of the amplifier circuit can be increased.

FIG. 1 is a circuit diagram for explaining a matching circuit of the present invention. FIG. 2 is an amplifier circuit output frequency response graph when the capacitance value of the variable capacitor of the series variable control LC circuit shown in FIG. 1 is changed. FIG. 3 is a circuit diagram when the variable control LC circuit of the matching circuit of the present invention is connected in parallel. FIG. 4 is an amplifier circuit output frequency response graph when the capacitance value of the variable capacitor of the parallel variable control LC circuit shown in FIG. 3 is changed.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described together with illustrated examples. FIG. 1 is a circuit diagram for explaining a matching circuit of the present invention. As shown in the figure, the matching circuit 10 of the present invention is mainly composed of a variable control LC circuit 20 and a control unit 30. The matching circuit 10 is connected to the input of an amplifier circuit 40 that amplifies the received signal from the antenna 1.

  Here, the amplifier circuit 40 is composed of a grounded collector transistor amplifier circuit. The common collector transistor amplification circuit 40 has a high impedance input impedance. By connecting the matching circuit 10 to the high impedance amplifier circuit 40, it is possible to reduce the loss of the input signal. As shown in the figure, in the collector grounded transistor amplifier circuit 40, the collector of the transistor 41 is connected to the power supply 44 of the amplifier circuit via the first resistor 43. The base is connected to the collector via the second resistor 45. The emitter is grounded via the third resistor 46. Note that the third resistor 46 may be configured by an inductance. In the illustrated example, the collector of the transistor 41 is grounded via a capacitor 42 which is a bypass capacitor provided as necessary. Furthermore, in the illustrated example, a bipolar transistor is shown as the transistor 41. However, the present invention is not limited to this, and a grounded drain type using a MOSFET may be used.

  In the example shown in FIG. 1, the variable control LC circuit 20 includes a variable capacitor and a coil connected in series. As shown in the figure, the variable control LC circuit 20 has a variable capacitor (C) 22 connected in series to a coil (L) 21. One end of the variable control LC circuit 20 in series with the LC, that is, one end of the coil 21 is connected to the input of the amplifier circuit 40. The other end of the variable control LC circuit 20 in series with LC, that is, the other end of the variable capacitor 22 is grounded.

  The control unit 30 controls the variable capacitor 22 of the variable control LC circuit 20 so as to match the impedance viewed from the antenna 1 side. In this method, impedance matching is performed in accordance with the selected reception frequency, and the capacitance value of the variable capacitor 22 is controlled to be large and small so that the output peak comes in the reception frequency band.

  In the illustrated example, a series LC filter circuit 2 as an input filter circuit is inserted in series at the input of the common collector transistor amplifying circuit, and a DC cut capacitor 3 is connected in series thereto. The variable control LC circuit 20 is connected to be branched between the series LC filter circuit 2 and the DC cut capacitor 3.

Hereinafter, an example in which the variable capacitor 22 of the variable control LC circuit 20 is formed of a varicap as shown in the drawing will be described in more detail. The variable control LC circuit 20 includes a series connection of a coil 21 and a variable capacitor 22 that is a varicap. An anode of the varicap is grounded, a cathode is connected to the coil, and a control unit 30 is connected. In order to vary the capacity of the varicap, the control unit 30 has a configuration in which a control bias 32 that is a negative bias is applied to the varicap via a resistor 31. That is, the resistor 31 is connected between the series-connected coil 21 and the variable capacitor 22. Here, the resistor 31 may have a resistance value large enough to make the control bias 32 of the control unit 30 invisible from the antenna input path. By varying the control bias 32, the capacitance value of the variable capacitor 22 may be controlled to perform impedance matching. With this configuration, the matching circuit of the present invention is connected so as to branch from the input path of the antenna, and the control bias 32 is connected to the control unit 30 via the resistor 31. Accordingly, since the control unit of the matching circuit is not visible from the input path of the antenna, it is possible to eliminate the loss of the input signal to the amplifier circuit. That is, it is possible to adjust the impedance by controlling the variable capacitance without worrying about the impedance of the control unit itself.
Become.

  In the illustrated example, the variable capacitor 22 is formed of a varicap, but the present invention is not limited to this. For example, in the case of a matching circuit for a radio broadcast receiving antenna, the frequency band is set so as to be skipped for each radio station, so that the capacitance value of the variable capacitor does not need to be continuously variable. Therefore, for example, it is possible to use a configuration in which the capacitance value can be switched by a switch using capacitors of various capacities, and the switch can be switched by the control unit according to each station so that impedance matching can be performed in a jumping manner.

  In the above example, the variable control LC circuit has been described using a variable capacitor and a coil. However, the present invention is not limited to this, and a configuration using a variable coil and a capacitor may be used. Of course, both a variable capacitor and a variable coil may be used. When using a variable coil, for example, it is only necessary to use a coil with various inductances so that the inductance can be switched by a switch so that impedance matching can be performed.

  FIG. 2 shows an output frequency response graph of the amplifier circuit when the capacitance value of the variable capacitor of the series variable control LC circuit shown in FIG. 1 is changed. In the figure, the solid line represents the frequency response when the capacitance value is 17 pF, the dotted line is 11 pF, and the alternate long and short dash line is 7.5 pF. As can be seen from the figure, the peak of the amplifier circuit output changes according to the capacitance value of the variable capacitor. That is, it can be seen that the output of the amplifier circuit can be maximized if the capacitance value of the variable capacitor is set so as to match the peak in accordance with the selected frequency band.

  In the illustrated example described above, the variable control LC circuit 20 is connected in series. However, as described below, the variable control LC circuit 20 may be connected in parallel. FIG. 3 is a circuit diagram when the variable control LC circuit of the matching circuit of the present invention is connected in parallel. In the figure, the parts denoted by the same reference numerals as those in FIG. In the illustrated example, since the amplifier circuit, the antenna, and the like are the same as those in FIG. 1, only the variable control LC circuit is shown.

  As shown in the figure, the variable control LC circuit 20 in the case of parallel connection includes a coil 21 and a variable capacitor 22 that is a varicap, which are connected in parallel, the anode of the varicap is grounded, and the cathode is connected to one end of the coil 21. At the same time, the control unit 30 is connected, and the other end of the coil 21 is grounded. In the illustrated example, a DC cut capacitor 25 is connected between the cathode of the varicap, which is the variable capacitor 22, and the coil 21. This is provided to prevent a short circuit through the coil 21. Also in this example, in order to vary the capacity of the varicap, the control unit 30 has a configuration in which a control bias 32 that is a negative bias is applied to the varicap via a resistor 31. That is, the resistor 31 is connected between the parallel-connected coil 21 and the varicap cathode that is the variable capacitor 22. By varying the control bias 32, the capacitance value of the variable capacitor 22 may be controlled to perform impedance matching.

  In addition, even if it is a variable control LC circuit in the case of parallel connection, it is not limited to the structure using a variable capacity | capacitance and a coil, The structure using a variable coil and a capacity | capacitance may be sufficient. Of course, both a variable capacitor and a variable coil may be used.

  FIG. 4 shows an amplifier circuit output frequency response graph when the capacitance value of the variable capacitor of the parallel variable control LC circuit shown in FIG. 3 is changed. In the figure, the solid line represents the frequency response when the capacitance value is 17 pF, the dotted line is 11 pF, and the alternate long and short dash line is 7.5 pF. As can be seen from the figure, as in the case of the configuration of the series variable control LC circuit, the peak of the amplifier circuit output changes according to the capacitance value of the variable capacitor. That is, it can be seen that the output of the amplifier circuit can be maximized if the capacitance value of the variable capacitor is set so as to match the peak in accordance with the selected frequency band.

  Furthermore, since the matching circuit of the present invention can arbitrarily match the impedance by the control unit, it is also possible to perform feedback control so that the control bias for the variable control LC circuit is changed depending on the temperature. For example, when a varicap is used as the variable capacitor of the variable control LC circuit, the temperature characteristics of the varicap may be poor, and the capacitance value with respect to the control bias may vary depending on the ambient temperature. If the capacitance value changes from the intended value, the output peak may not come to the reception frequency band. In order to avoid such a situation, the ambient temperature is detected, and the control bias may be feedback-controlled so as to obtain an optimum capacitance value depending on the temperature.

  It should be noted that the matching circuit of the present invention is not limited to the above-described illustrated examples, and various modifications can be made without departing from the scope of the present invention.

1 Antenna 2 Series LC Filter Circuit 3 DC Cut Capacitor 10 Matching Circuit 20 Variable Control LC Circuit 21 Coil 22 Variable Capacitance 25 Capacitor 30 Control Unit 31 Resistor 32 Control Bias 40 Amplifier Circuit 41 Transistor 42 Capacitor 43 First Resistor 44 Power Supply 45 Second 2 resistance 46 3rd resistance

Claims (4)

A matching circuit connected to an input of an amplifier circuit for amplifying a received signal from an antenna,
A variable control LC circuit consisting of a variable capacitor and a coil, a capacitor and a variable coil, or a variable capacitor and a variable coil, connected in parallel or in series, and connected so that one end branches to the input of the collector grounded transistor amplifier circuit A variable control LC circuit whose other end is grounded;
A control unit for controlling the variable capacitance and / or the variable coil of the variable control LC circuit so as to match the impedance viewed from the antenna side;
A matching circuit comprising:   2. The matching circuit according to claim 1, wherein the variable control LC circuit comprises a series connection of a coil and a variable capacity varicap, the anode of the varicap is grounded, the cathode is connected to the coil, and the control unit is connected. A matching circuit.   2. The matching circuit according to claim 1, wherein the variable control LC circuit comprises a parallel connection of a coil and a variable capacitance varicap, the anode of the varicap is grounded, the cathode is connected to one end of the coil, and the control unit. Is connected, and the other end of the coil is grounded. In the matching circuit according to any one of claims 1 to 3, a series LC filter circuit and a DC cut capacitor are connected in series to an input of the common collector transistor amplification circuit,
One end of the variable control LC circuit is connected between the series LC filter circuit and the DC cut capacitor, and the other end is grounded.
A matching circuit characterized by that.