JP2008227729A - Bandwidth variable filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the size and the number of components of a high frequency filter capable of switching a pass band or block band. <P>SOLUTION: In a bandwidth variable filter, first to third capacitors C1 to C3 are serially connected between an input terminal 1 and an output terminal 2; a first inductor L1 and a fourth capacitor C4 are serially connected between contact points of the first and the second capacitors C1 and C2 and the ground; and a first diode D1 is connected between the fourth capacitor C4 and the first inductor L1. A second inductor L2 and a fifth capacitor C5 are serially connected between the second and the third capacitors C2 and C3 and the ground. A third inductor L3 is connected between one ends of the first and the second inductors L1 and L2 and the ground, and an eighth capacitor C8 and a third diode D3 are connected in parallel to a third inductor L3. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a variable band filter capable of switching a pass band or a stop band.

2. Description of the Related Art Conventionally, there is a filter in which a plurality of filters are provided in parallel so that at least one of the filters is turned on / off, and the pass band (or stop band) is switched (see, for example, Patent Document 1). The high-frequency filter shown in FIG. 8 includes a high-frequency high-pass filter (or high-frequency band-pass filter) 103 and a high-frequency low-pass filter 104 provided in parallel. Are connected to each other as input terminal 101, and the output terminal of high-frequency high-pass filter 103 and the output part of high-frequency low-pass filter 104 are connected as output terminal 102. In addition, a switch circuit 105 is provided in front of the high-frequency high-pass filter 103 in order to make the pass band of the high-frequency high-pass filter 103 a stop band.
JP 2002-204135 A

  However, in a configuration in which a plurality of filters are provided in parallel and at least one of them is turned on / off by a switch, there is a problem that the number of parts increases and it is difficult to reduce the size.

  The present invention has been made in view of this point, and an object of the present invention is to provide a band-variable filter that can switch the pass band or the stop band with a small number of parts and can be easily reduced in size.

  The variable band filter of the present invention includes a first capacitor having one end connected to an input terminal, a second capacitor having one end connected to the other end of the first capacitor, and the other end of the second capacitor. A third capacitor connected between the first capacitor and the output terminal; a first inductor having one end connected to a connection point between the first capacitor and the second capacitor; the first inductor and the ground A fourth capacitor connected between the first capacitor, a first switch for connecting or disconnecting the fourth capacitor to one end of the first inductor, the second capacitor, and the second capacitor. 3, a second inductor having one end connected to a connection point with the capacitor, a fifth capacitor connected between the second inductor and the ground, and the fifth capacitor connected to the second inductor. A second switch that is connected to or disconnected from one end of the first inductor; a third inductor connected between the other end of the first inductor and the other end of the second inductor and the ground; A third switch connected in parallel with the third inductor and short-circuiting both ends of the third inductor in a high frequency manner, turning on the first and second switches and the third switch A high pass filter having a pass band higher than the band pass filter by turning off the switch to form a band pass filter, turning off the first and second switches and turning on the third switch It is characterized by forming.

  According to this configuration, a high frequency filter capable of selecting the VHF broadcast band and the UHF broadcast band of the television tuner can be realized with a simple configuration. For example, a band-pass filter that attenuates both the FM band and the UHF broadcast band when the VHF broadcast band is selected, and a high-pass filter that attenuates the VHF broadcast band that covers the FM band when the UHF broadcast band is selected. The switching can be performed by three diodes that are three switches, and the number of parts can be reduced.

  According to the present invention, in the variable band filter, a sixth capacitor connected between a connection point of the first and second capacitors and one end of the first inductor, and the second and third capacitors A seventh capacitor connected between a connection point of a capacitor and one end of the second inductor; turning on the first and second switches and turning off the third switch; When the band-pass filter is formed, a trap circuit having an attenuation pole at a frequency lower than the pass band of the band-pass filter is formed, and the first and second switches are turned off and the third switch is turned on. A trap circuit having an attenuation pole at a frequency lower than the pass band of the high pass filter when a high pass filter having a higher pass band than the band pass filter is formed when turned on Characterized in that it is formed.

  With this configuration, when the first and second switches are turned on and the third switch is turned off to form a band-pass filter for the VHF broadcast band, for example, the first and third capacitors in the FM radio broadcast band Circuits except for can be resonated in series, and traps can be formed in the FM radio broadcast band. In addition, when the first and second switches are turned off and the third switch is turned on to form a high-pass filter for the UHF broadcast band, for example, a specific low power radio of 322 MHz, an analog cordless telephone base phone Traps can be formed at 330 MHz.

  According to the present invention, in the band-variable filter, the first and second switches are configured by first and second switch diodes each composed of a diode, and the first switch diode is connected to the anode at the fourth switch diode. Is connected to one end of the first inductor, and the second switch diode is connected to the fifth capacitor at the anode and to the cathode at one end of the second inductor. And a control voltage is applied to the anodes of the first and second switch diodes.

  With this configuration, the control voltage of the first and second switch diodes flows to the ground through the first (second) inductor and the third inductor, and the anodes of the first and second switch diodes are the fourth ( Since it is separated from the ground in a DC manner by the fifth capacitor, no DC cut capacitor or choke (AC cut) inductor is required for controlling the first and second switch diodes, reducing the number of parts and reducing the size. Can be achieved.

  According to the present invention, in the band-variable filter, the third switch includes a third switch diode made of a diode, and an eighth capacitor for DC cut having one end connected to the anode of the third switch diode. The third switch diode has a cathode connected to a connection point of the first, second, and third inductors, one end of the eighth capacitor connected to the ground, and the third switch diode. A control voltage is applied to the anode of the switch diode.

  With this configuration, when the third switch diode is off, the control circuit for controlling the anode of the third switch diode to switch between the band pass filter and the high pass filter is disconnected from the band variable filter, When the third switch diode is on, the anode of the third switch diode is grounded at a high frequency, so that the band variable filter can be prevented from being affected by the control circuit.

  According to the present invention, in the band variable filter, when the first and second switches are turned on and the third switch is turned off, a pass band is a VHF broadcast band, and the first and second switches When the third switch is turned off and the third switch is turned on, the pass band is equal to or higher than the UHF band.

  With this configuration, the VHF broadcast band has interference waves (FM radio broadcast waves and UHF broadcast band broadcast waves) on the high frequency side and the low frequency side. Can be attenuated. Further, since the UHF broadcast band has an interference wave (broadcast wave in the VHF broadcast band) on the low frequency side and the band is wide, the interference wave can be attenuated by using a high-pass filter that is higher than the UHF broadcast band.

  According to the present invention, it is possible to reduce the number of components of the high-frequency filter that can switch the pass band or the stop band, thereby achieving downsizing.

  Hereinafter, an embodiment in which a variable band filter of the present invention is applied to a high frequency filter of a television tuner capable of selecting a VHF broadcast band and a UHF broadcast band will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a circuit configuration diagram of a variable band filter according to the present embodiment. In the variable band filter shown in FIG. 2, a high frequency signal is introduced from the antenna side to the input terminal 1, and a high frequency signal in a desired band extracted by the filter is output from the output terminal 2. First, second, and third capacitors C1, C2, and C3 are connected in series between the input terminal 1 and the output terminal 2. One end of the first inductor L1 is connected to a connection point between the first capacitor C1 and the second capacitor C2. A fourth capacitor C4 is connected between one end of the first inductor L1 and the ground, and a first PIN diode D1 is connected between the fourth capacitor C4 and one end of the first inductor L1. Yes. A fifth capacitor C5 is connected between one end of the second inductor L2 and the ground, and a second PIN diode D2 is connected between the fifth capacitor C5 and one end of the second inductor L1. Has been.

  In the present embodiment, a sixth capacitor C6 is connected between the connection point of the first capacitor C1 and the second capacitor C2 and one end of the first inductor L1, and the second capacitor C2 and the third capacitor C2 are connected to each other. A seventh capacitor C7 is connected between the connection point of the capacitor C3 and one end of the second inductor L2.

  The other ends of the first and second inductors L1 and L2 are connected to one end of the third inductor L3, and the other end of the third inductor L3 is connected to the ground. An eighth capacitor C8 for cutting direct current is connected in parallel with the third inductor L3, and a third PIN diode D3 is connected between the eighth capacitor C8 and one end of the third inductor L3.

  In addition, a switching circuit 3 for switching between a high band (UHF broadcast band) and a low band (VHF broadcast band) is provided. The fixed end of the switching circuit 3 is connected to the power source 4, one switching terminal 3a is connected to the anode of the third PIN diode D3, and the other switching terminal 3b is the anode of the first and second PIN diodes D1 and D2. It is connected to the. In the switching circuit 3, the high band is selected when the fixed end is connected to the switching terminal 3a, and the low band is selected when the fixed end is connected to the switching terminal 3b.

Next, the operation of the variable band filter according to the present embodiment configured as described above and the set filter characteristics will be described.
First, the case where the low end (VHF broadcast band) is selected by connecting the fixed end to the switching terminal 3b in the switching circuit 3 will be described. FIG. 2A shows the on / off states of the first, second, and third PIN diodes D1, D2, and D3 in the low band selection. A voltage is applied to the anodes of the first and second PIN diodes D1 and D2 via the switching circuit 3, and the first and second PIN diodes D1 and D2 are turned on. Thus, one end of the first and second inductors L1 and L2 is connected to the ground via the fourth and fifth capacitors C4 and C5. Further, since the anode of the third PIN diode D3 is turned off at 0V, the eighth capacitor C8 is not connected in parallel to the third inductor L3.

  FIG. 2B is an equivalent circuit diagram in a state where the first, second, and third PIN diodes D1, D2, and D3 are set as shown in FIG. The first inductor L1, the third inductor L3, the sixth capacitor C6, and the fourth capacitor C4 constitute an LC resonance circuit, and the second inductor L2, the third inductor L3, and the seventh capacitor. The LC resonance circuit is configured by C7 and the fifth capacitor C5. Then, the two resonant circuits are M-coupled by the third inductor L3, thereby forming a double-tuned circuit having a trap.

  FIG. 3 is a frequency characteristic diagram that is simulated by setting the numerical values shown in FIG. 2B to the respective components constituting the double-tuned circuit. As shown in the figure, the attenuation of the VHF broadcasting band is extremely small, and the adjacent area on the low side of the VHF broadcasting band is attenuated by about 30 dB, while the adjacent area on the high side of the VHF broadcasting band is attenuated by about 10 dB. Thus, it can be seen that bandpass filter characteristics having a VHF broadcast band as a pass band are obtained. In addition, traps are formed in the FM band, and the FM band that becomes an interference wave in the television tuner can be sufficiently attenuated.

  Next, the case where the high band (UHF broadcast band) is selected by connecting the fixed end to the switching terminal 3a in the switching circuit 3 will be described. FIG. 4A shows the on / off states of the first, second, and third PIN diodes D1, D2, and D3 when the high band is selected. A voltage is applied to the anode of the third PIN diode D3 via the switching circuit 3, and the third PIN diode D3 is turned on. As a result, the eighth capacitor C8 is connected in parallel to the third inductor L3. Since the anodes of the first and second PIN diodes D1 and D2 are turned off at 0V, the fourth and fifth capacitors C4 and C8 are connected in parallel to the first and second inductors L1 and L2. It will not be done.

  FIG. 4B is an equivalent circuit diagram in a state where the first, second, and third PIN diodes D1, D2, and D3 are set as shown in FIG. 4A. A connection point between the first capacitor C1 and the second capacitor C2 is connected to the ground via the sixth capacitor C6 and the first inductor L1, and a connection point between the second capacitor C2 and the third capacitor C3. Are connected to the ground via the seventh capacitor C7 and the second inductor L2, and a π-type high-pass filter is formed as a whole.

  FIG. 5 is a frequency characteristic diagram that is simulated by setting the numerical values shown in FIG. 4B to the constituent elements of the π-type high-pass filter. As shown in the figure, there is almost no attenuation in the UHF broadcast band and higher bands, and it is attenuated by about 30 dB toward 300 MHz at the lower end of the UHF broadcast band, and a desired high-pass filter characteristic is obtained. It has been. In addition, traps are formed in the specific low-power radio band (322 MHz) and the use band (330 MHz) of the analog cordless telephone master unit.

  As described above, according to the present embodiment, the VHF broadcast band and the UHF broadcast band are set in parallel without providing a bandpass filter having the VHF broadcast band as a pass band and a high-pass filter having the UHF broadcast band as the pass band. A selectable high-frequency filter can be realized, and the size and cost can be reduced by reducing the number of components. A first and second bandpass filter that attenuates both the FM band and the UHF broadcast band when the VHF broadcast band is selected, and a highpass filter that attenuates a band including the FM band and the VHF broadcast band when the UHF broadcast band is selected. The third PIN diodes D1, D2, and D3 can be switched, and the number of diode components can be reduced.

  Note that there is no problem even if the attenuation of the FM band at the time of selecting the VHF broadcasting band, or the attenuation of the specific low power wireless band and the band used for the analog cordless telephone base unit (around 322 to 330 MHz) at the time of selecting the UHF broadcasting band is not a problem. If so, the sixth and seventh capacitors C6 and C7 can be deleted.

  FIG. 6 is a configuration diagram of a band-variable filter in which the sixth and seventh capacitors C6 and C7 (24 pF) are omitted. Instead of the switching circuit 3, two power supplies 5a and 5b in which high / low are reversed are used. The numerical values of the constituent elements constituting the variable band filter are the same as those in the above embodiment.

  FIG. 7A shows a low-band filter in which the first and second PIN diodes D1 and D2 are turned on (power supply 5b = H) and the third PIN diode D3 is turned off (power supply 5a = L). It is a frequency characteristic figure at the time of selecting. As shown in the figure, band pass filter characteristics having a VHF broadcast band as a pass band are shown. However, no trap is formed in the FM band.

  FIG. 7B is a band-variable filter of FIG. 6 in which the first and second PIN diodes D1 and D2 are turned off (power supply 5b = L) and the third PIN diode D3 is turned on (power supply 5a = H). It is a frequency characteristic figure at the time of selecting. As shown in the figure, a high-pass filter characteristic having a pass band above the UHF broadcast band is shown. However, the attenuation is not sufficient in the specific low power wireless band and the band used in the analog cordless telephone base unit (near 322 to 330 MHz).

  In this way, even if the sixth and seventh capacitors C6 and C7 are deleted, a bandpass filter having a VHF broadcast band as a passband and a highpass filter having a UHF broadcast band as a passband are not provided in parallel. A high frequency filter capable of selecting a VHF broadcast band and a UHF broadcast band can be realized.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the gist of the present invention. For example, the first, second, and third switches are not limited to PIN diodes, and other switch components can be used. Further, the positional relationship between the first, second, and third PIN diodes D1, D2, and D3 and the fourth, fifth, and eighth capacitors C4, C5, and C8 may be reversed.

  In the above-described frequency characteristic simulation, optimized values are set based on the VHF broadcast band and UHF broadcast band in Japan. However, appropriately optimized values are set according to the application and purpose. be able to. Further, as long as the bandpass filter and the highpass filter are switched, the present invention can be applied to other than the high frequency filter of the television tuner.

  The present invention is applicable to a high-frequency filter that switches between a band-pass filter and a high-pass filter.

1 is a circuit configuration diagram of a variable band filter according to an embodiment of the present invention. (A) Circuit configuration diagram when the low band is selected by the variable band filter of FIG. 1, (b) Equivalent circuit diagram when the low band is selected Frequency characteristic diagram at low band selection simulated with the equivalent circuit of FIG. (A) Circuit configuration diagram when the high-band is selected by the variable band filter of FIG. 1, (b) Equivalent circuit diagram when the high-band is selected Frequency characteristics diagram when selecting high band simulated with the equivalent circuit of FIG. The circuit block diagram of the modification of the band variable filter which concerns on the said one embodiment (A) Frequency characteristic diagram when low band is selected by the band variable filter of FIG. 6, (b) Frequency characteristic diagram when high band is selected by the band variable filter of FIG. Schematic diagram of conventional high-frequency filter

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Input terminal 2 ... Output terminal C1-C8 ... 1st-8th capacitor | condenser D1-D3 ... 1st-3rd PIN diode L1, L2 ... 1st, 2nd inductor 3 ... Switching circuit 4 ... Power supply

Claims (5)

A first capacitor having one end connected to the input terminal;
A second capacitor having one end connected to the other end of the first capacitor;
A third capacitor connected between the other end of the second capacitor and the output terminal;
A first inductor having one end connected to a connection point between the first capacitor and the second capacitor;
A fourth capacitor connected between the first inductor and ground;
A first switch for connecting or disconnecting the fourth capacitor to one end of the first inductor;
A second inductor having one end connected to a connection point between the second capacitor and the third capacitor;
A fifth capacitor connected between the second inductor and ground;
A second switch for connecting or disconnecting the fifth capacitor to one end of the second inductor;
A third inductor connected between the other end of the first inductor and the other end of the second inductor and the ground;
A third switch connected in parallel with the third inductor and short-circuiting both ends of the third inductor at a high frequency,
Turning on the first and second switches and turning off the third switch to form a band-pass filter, turning off the first and second switches and turning on the third switch A band-variable filter that forms a high-pass filter having a higher pass band than the band-pass filter. A sixth capacitor connected between a connection point of the first and second capacitors and one end of the first inductor;
A seventh capacitor connected between a connection point of the second and third capacitors and one end of the second inductor;
When the first and second switches are turned on and the third switch is turned off to form a band pass filter, a trap circuit having an attenuation pole at a frequency lower than the pass band of the band pass filter Formed,
When the first and second switches are turned off and the third switch is turned on to form a high-pass filter having a higher pass band than the band-pass filter, the high-pass filter passes therethrough. A trap circuit with an attenuation pole at a frequency lower than the band is formed.
The band-variable filter according to claim 1. The first and second switches are respectively composed of first and second switch diodes composed of diodes,
The first switch diode has an anode connected to the fourth capacitor, and a cathode connected to one end of the first inductor.
The second switch diode has the anode connected to the fifth capacitor, and the cathode connected to one end of the second inductor.
3. The band variable filter according to claim 1, wherein a control voltage is applied to anodes of the first and second switch diodes. The third switch is composed of a third switch diode made of a diode, and an eighth capacitor for DC cut whose one end is connected to the anode of the third switch diode.
The third switch diode has a cathode connected to a connection point of the first, second, and third inductors,
One end of the eighth capacitor is connected to ground,
The band-variable filter according to any one of claims 1 to 3, wherein a control voltage is applied to an anode of the third switch diode. When the first and second switches are turned on and the third switch is turned off, the pass band is a VHF broadcast band,
5. The passband when the first and second switches are turned off and the third switch is turned on is equal to or higher than the UHF band. 6. Band-variable filter.

Images