JPH06334463A - Band changeover circuit - Google Patents

Abstract

PURPOSE:To reduce number of switching elements without decreasing a switchable band characteristic. CONSTITUTION:An input terminal 11 is connected to an output terminal 14 via the series connection of 1st and 2nd HPFs 12,13. Furthermore, the input terminal 11 is connected to one terminal of the 1st switching element SW 1. The other terminal of the 1st switching element SW1 is connected to the output terminal 14. Third and fourth switching elements SW3, SW4 are used to turn on/off the resonance circuit sections of the 1st and 2nd HPFs 12,13. Through the connection above, number of switching elements is reduced without decreasing the band characteristic to be switched.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a band switching circuit for passing a band selected and switched to a signal guided to an input terminal and guiding it to an output terminal, and more particularly to a band switching circuit capable of simplifying the circuit. Regarding the circuit.

[0002]

2. Description of the Related Art Generally, in a cable television system (hereinafter referred to as a CATV system), since multi-channel television signals are transmitted on a cable,
In a CATV tuner intended for wideband reception, it is a major problem to prevent interference due to second-order distortion and third-order distortion generated by an amplifier and a mixer. Therefore, such CA
In a TV tuner, a band switching circuit is often used on the input side.

FIG. 8 is a circuit diagram showing such a conventional band switching circuit.

In FIG. 8, reference numeral 71 is an input terminal to which the television signal a3 of the CATV system is input. The input terminal 71 includes a switching element SW21,
It is connected to one terminal of SW22, SW23, and SW24. Switching elements SW21, SW22, SW23,
The other terminal of the SW 24 has first to fourth band pass filters (hereinafter referred to as BPFs) 81, 82, 83,
Switching elements SW31, SW32, S via 84
It is connected to one end of W33 and SW34. The other ends of the switching elements SW31, SW32, SW33, SW34 are
It is connected to the output terminal 72.

The BPFs 81, 82, 83 and 84 are adapted to perform first to fourth band filtering of different bands.

Switching elements SW21, SW22, S
W23 and SW24 are turned on by a control circuit (not shown).
The switching elements are turned off, and when one switching element is turned on, the other switching elements are turned off.

Switching elements SW31, SW32, S
W33 and SW34 are switching elements SW21, SW22, SW23, and
The switch 24 is turned on and off at the same time.

As the switching element is turned on and off in this manner, the television signal b3 whose band is switched and selected is guided to the output terminal 72.

In such a conventional band switching circuit, a CATV is used.
When extracting the first band from the television signal of the system, an ON signal from a control circuit (not shown)
The switching elements SW21, SW31 are turned on, and the switching elements SW22, SW23, SW24, SW3.
2, SW33 and SW34 are turned off. As a result, the television signal a3 guided to the input terminal 71 has the first band signal extracted by the first BPF 81, and the television signal b3 having the first band switched and selected is outputted to the output terminal 72. Get burned.

When the second band is to be extracted, the switching element S is turned on by an ON signal from a control circuit (not shown).
W22 and SW32 are turned on, and switching elements other than these are turned off. As a result, the second BPF 82 extracts the signal in the second band from the television signal a3 guided to the input terminal 71, and the output terminal 72 outputs the television signal b3 in which the second band is switched and selected. Get burned.

When extracting the third band, the switching elements SW23 and SW33 are turned on, and the other switching elements are turned off. As a result, the television signal a3 guided to the input terminal 71 is transmitted to the third BPF.
The signal of the third band is extracted by 83, and the output terminal 72
The television signal b3 in which the third band is switched and selected is introduced to.

When extracting the fourth band, the switching elements SW24 and SW34 are turned on, and the other switching elements are turned off. As a result, the television signal a3 guided to the input terminal 71 is transmitted to the fourth BPF.
The signal of the fourth band is extracted by 84, and the output terminal 72
The television signal b3 in which the fourth band is switched and selected is guided to.

According to such a conventional band switching circuit,
Since only the necessary band can be extracted from the television signal of the CATV system and guided to the circuit in the subsequent stage, it is possible to prevent the interference due to the second-order distortion and the third-order distortion generated by the amplifier and the mixer in the subsequent stage, but In the case of extraction, two switching elements have to be passed, insertion loss is large, and two switching elements must be provided for each band, which is a problem that the number of components is too large.

[0014]

As described above, in the conventional band switching circuit, when each band is extracted, two switching elements must be passed and the insertion loss is large, and each band has a large insertion loss. Since two switching elements must be provided, there is a problem that the number of parts is too large.

An object of the present invention is to solve the above problems and to provide a band switching circuit capable of reducing the number of switching elements without reducing the band characteristic that can be switched.

[0016]

A band switching circuit according to the present invention is a band switching circuit which passes a band selected and switched for a signal guided to an input terminal and guides it to an output terminal.
A first serially connected between the input terminal and the output terminal
And a second high-pass filter, and a first switching element that is provided between the input terminal and the output terminal and that turns on / off bypass of a signal from the input terminal to the output terminal,
It is provided between the connection point of the first and second high pass filters and the output terminal, and turns on / off the bypass of the signal from the connection point of the first and second high pass filters to the output terminal. And a third switching element for turning on and off the respective resonant circuit portions of the first and second high-pass filters, respectively.

[0017]

According to such a configuration, by switching the first to fourth switching elements on and off, the individual band characteristics are switched and selected, and the signals guided to the input terminals are switched and selected. Since the selected band can be passed and guided to the output terminal, the number of switching elements can be reduced without reducing the band characteristic that can be switched.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to illustrated embodiments.

FIG. 1 is a block diagram showing an embodiment of a band switching circuit according to the present invention.

In FIG. 1, reference numeral 11 is an input terminal through which the television signal a1 is guided, and the input terminal 11 is the first terminal.
And a second high pass filter (hereinafter referred to as HPF) 1
It is connected to the output terminal 14 through a series connection of 2 and 13. The input terminal 11 is connected to the first switching element S
It is connected to one terminal of W1. The other terminal of the first switching element SW1 is connected to the output terminal 14. With such a connection, the first switching element SW1 is
In the ON state, the signal from the input terminal 11 is bypassed to the output terminal 14. First and second HPF1
The connection point of 2 and 13 is connected to one terminal of the second switching element SW2. Second switching element SW2
The other terminal of is connected to the output terminal 14. With this connection, the second switching element SW2 outputs the signal from the connection point of the HPFs 12 and 13 to the output terminal 14 in the ON state.
It is designed to be bypassed.

More specifically, the first HPF1
2 includes capacitors C1, C2, C3, a coil L1 and a third switching element SW3. The input terminal of the first HPF 12 connected to the input terminal 1 is connected to the first HPF 1 through the series connection of the capacitors C1 and C2.
2 is connected to the output terminal. The connection point of the capacitors C1 and C2 is connected to the third switching element SW3 through the series connection of the capacitor C3 and the coil L1 which form the resonance circuit section.
Connected to one of the terminals. Third switching element S
The other terminal of W3 is connected to the reference potential point. As a result, the third switching element SW3 is connected to the capacitor C3.
And the coil L1 serve as a switching element for turning on / off the resonance circuit section.

The second HPF 12 includes capacitors C4 and C4.
5, C6, coil L2 and fourth switching element SW
It is composed of 3. The input terminal of the second HPF 13 connected to the output terminal of the first HPF 12 has a capacitor C
It is connected to the output terminal of the second HPF 13 through a series connection of 4 and C5. The connection point of capacitors C4 and C5 is
It is connected to one terminal of the fourth switching element SW4 through the series connection of the capacitor C6 and the coil L2 which form the resonance circuit section. The other terminal of the fourth switching element SW4 is connected to the reference potential point. As a result, the fourth
The switching element SW4 is a switching element that turns on / off the resonance circuit section including the capacitor C6 and the coil L2.

The capacitors C1 and C of the first HPF 12
2, C3 and the coil L1 and the capacitors C4, C5 and C6 and the coil L2 of the second HPF 13 have individual capacitances and inductances set, and the first HPF 12 and the second HPF 13 each have individual bands. It becomes a characteristic.

The band switching circuit according to the present embodiment is configured to derive the band-switched television signal b1 at the output terminal 14 by such a configuration.

The operation of such an embodiment will be described below.

When the band switching circuit of FIG. 1 is operated in the first band, the first and fourth switching elements SW1,
SW4 is turned on, and the second and third switching elements SW
2, SW3 is turned off.

FIG. 2 is a circuit diagram for explaining an equivalent circuit when the band switching circuit of FIG. 1 is operated in the first band.

In FIG. 2, the input terminal 11 is the output terminal 1
4 directly connected. Further, the input terminal 11 is connected to the capacitor C6 through the series connection of the capacitors C1, C2 and C4.
One of the electrodes of the capacitor C6 is connected to one of the electrodes of the capacitor C6 via the capacitor C5. The other electrode of the capacitor C6 is connected to the reference potential point via the coil L2. As a result, the equivalent circuit shown in FIG. 2 constitutes a high band rejection type trap filter. In this case, since the first switching element SW1 (see FIG. 1) in the turned-on state connects the output terminal 11 and the input terminal 12, a loss equivalent to that of the switching element SW31 of FIG. The switching element SW4 is a coil L2.
Since it is connected between the point and the reference potential point, it gives almost no loss. As a result, the loss when the band switching circuit is operated in the first band can be suppressed to half that of the conventional example.

When the band switching circuit of FIG. 1 is operated in the second band, the second and third switching elements SW2 and
SW3 is turned on, and the first and fourth switching elements SW
1, SW4 is turned off.

FIG. 3 is a circuit diagram for explaining an equivalent circuit when the band switching circuit of FIG. 1 is operated in the second band.

In FIG. 3, the input terminal 11 is connected to the output terminal 14 through the series connection of the capacitors C1 and C2. The connection point of the capacitors C1 and C2 is connected to the reference potential point via the series connection of the capacitor C3 and the coil L1. As a result, the equivalent circuit shown in FIG.
HPF1 composed of 1, C2, C3 and coil L1
It has only 5 characteristics. In this case, the second switching element SW2 (see FIG. 1) in the turned-on state is the HPF1.
Since it is connected to the output side of No. 5, a loss equivalent to that of the switching element SW32 of FIG. 8 is given, but the fourth switching element SW4 is connected between the coil L1 and the reference potential point, so that the loss is reduced. Hardly give. As a result, the loss when the band switching circuit is operated in the first band can be suppressed to about half that of the conventional example.

When the band switching circuit of FIG. 1 is operated in the third band, the third and fourth switching elements SW3 and SW3 are used.
SW4 is turned on, and the first and second switching elements SW
1, SW2 is turned off.

FIG. 4 is a circuit diagram for explaining an equivalent circuit when the band switching circuit of FIG. 1 is operated in the second band.

In FIG. 4, the input terminal 11 is connected to the output terminal 1 through the series connection of capacitors C1, C2, C4 and C5.
4 is connected. The connection point of the capacitors C1 and C2 is connected to the reference potential point via the series connection of the capacitor C3 and the coil L1. The connection point of the capacitors C4 and C5 is connected to the reference potential point via the series connection of the capacitor C6 and the coil L2. As a result, in the equivalent circuit shown in FIG. 4, the characteristics of the HPF 15 including the capacitors C1, C2, C3 and the coil L1 and the characteristics of the HPF 16 including the capacitors C4, C5, C6 and the coil L2 are superimposed. Have characteristics. In this case, since the third switching element SW3 is connected between the coil L1 and the reference potential point, and the fourth switching element SW4 is connected between the coil L2 and the reference potential point, it causes almost no loss. As a result, the loss when the band switching circuit is operated in the third band can be significantly suppressed as compared with the conventional example.

When the band switching circuit of FIG. 1 is operated in the fourth band, the first to fourth switching elements SW1,
SW2, SW3 and SW4 are turned off.

FIG. 5 is a circuit diagram for explaining an equivalent circuit when the band switching circuit of FIG. 1 is operated in the fourth band.

In FIG. 5, the input terminal 11 is connected to the output terminal 1 through the series connection of capacitors C1, C2, C4 and C5.
4 is connected. The connection point of the capacitors C1 and C2 is connected to the reference potential point via the series connection of the capacitor C3, the coil L1 and the capacitor C7. Conden C4, C5
The connection point is connected to the reference potential point through the series connection of the capacitor C6, the coil L2, and the capacitor C8. Condenses C7 and C8 indicate equivalent circuits in the off state of the third and fourth switching elements SW3 and SW4 of FIG. 1, respectively. As a result, the equivalent circuit shown in FIG. 5 has characteristics of the HPF 17 including the capacitors C1, C2, C3, C7 and the coil L1 and the capacitors C4, C5, C6.
And a characteristic of the HPF 18 composed of the coil L2 are superposed, and the HPF has a higher cutoff frequency than the equivalent circuit shown in FIG. Since the first to fourth switching elements SW1, SW2, SW3 and SW4 are all turned off, almost no loss is given. As a result, the loss when the band switching circuit is operated in the fourth band can be significantly suppressed as compared with the conventional example.

FIG. 6 shows the first to fourth band switching circuits of FIG.
3 is a graph showing the band characteristic of, where the vertical axis represents the amplitude gain and the horizontal axis represents the frequency.

Since the equivalent circuit shown in FIG. 2 constitutes a high band rejection type trap filter, when the band switching circuit of FIG. 1 is operated in the first band, as shown by the solid line,
The amplitude gain of the lowest first band is 0 dB, and the amplitude gain becomes higher than 0 dB in the higher range beyond that.

Since the equivalent circuit shown in FIG. 3 constitutes one HPF 15, when the band switching circuit of FIG. 1 is operated in the second band, as shown by the broken line, the amplitude gain is increased in the first band. Becomes smaller than 0 dB, and the amplitude gain becomes 0 dB in the second band higher than the first band.

The equivalent circuit shown in FIG. 4 is the HPF 15 and the HPF.
When the band switching circuit of FIG. 1 is operated in the third band, the amplitude gain is 0 in the first and second bands as shown by the alternate long and short dash line.
The amplitude gain becomes 0 dB in the third band which is smaller than dB and higher than the second band.

Since the equivalent circuit shown in FIG. 5 is an HPF having a higher cutoff frequency than the equivalent circuit shown in FIG. 4, when the band switching circuit is operated in the fourth band, as shown by the solid line, the first circuit is used. Through the third band, the amplitude gain becomes smaller than 0 dB, and in the fourth band higher than the third band, the amplitude gain becomes 0 dB.

According to such an embodiment, the loss when the band switching circuit is operated can be reduced, and the number of switching elements is four, so that the manufacturing cost can be reduced. In addition to the combinations of switching elements on and off other than those described above, 12 combinations of band characteristics other than those described above are possible.

FIG. 7 is a block diagram showing another embodiment of the band switching circuit according to the present invention. The same components as those in FIG. 1 are designated by the same reference numerals and their description is omitted.

In FIG. 7, HPF12 and HPF13 have the same structure as that of the embodiment of FIG. The difference of the present embodiment is that instead of providing one switching element between the input terminal 11 and the output terminal 14, the switching element SW5 on the input side, a low pass filter (hereinafter referred to as LPF) 21.
And the switching element SW6 on the output side are provided, and 1 is provided between the connection point of the first and second HPFs 12 and 13 and the output terminal.
Instead of providing two switching elements, an input-side switching element SW7, LPF22 and an output-side switching element SW8 are provided.

More specifically, the input terminal 11
Is connected to one terminal of the switching element SW5 on the input side. The other terminal of the switching element SW5 is connected to the input terminal of the LPF 21. LPF21
Is a coil L11, L12, L13 and a capacitor C11.
And its input terminal is coil L11,
It is connected to the output terminal through the series connection of L12. The connection point of the coils L11 and L12 is connected to the reference potential point via the series connection of the coil L13 and the capacitor C11.
The output terminal of the LPF 21 is a switching element S on the output side.
It is connected to one terminal of W6. The other terminal of the switching element SW6 is connected to the output terminal 14.

The connection point of the HPFs 12 and 13 is connected to one terminal of the switching element SW7 on the input side.
The other terminal of the switching element SW7 is connected to the input terminal of the LPF 22. LPF22 is coil L1
4, L15, L16 and a capacitor C12, the input terminal of which is connected to the output terminal through the series connection of the coils L14, L15. Coils L14, L1
The connection point of 5 is connected to the reference potential point through the series connection of the coil L16 and the capacitor C12. The output terminal of the LPF 22 is connected to one terminal of the switching element SW8 on the output side. The other terminal of the switching element SW8 is connected to the output terminal 14. The band switching circuit of this embodiment is configured to derive the band-switched television signal c1 at the output terminal 14 by such a configuration.

According to this embodiment, the switching element SW5 and the switching element SW6 are turned on and off at the same time, and the switching element SW7 and the switching element SW8 are turned on and off at the same time.
It turns on independently between the other switching elements.
Since it is turned off, 16 kinds of band switching can be performed as in the embodiment of FIG. Also, when these switching elements are turned on,
With the combination of OFF, the LPF and HPF can be connected in series or in parallel, and the band can be narrowed as compared with the embodiment of FIG.

[0049]

As described above, according to the present invention, it is possible to reduce the number of switching elements without reducing the band characteristic that can be switched, so that it is possible to reduce the loss when the band switching circuit is operated. The cost of the band switching circuit can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a band switching circuit according to the present invention.

FIG. 2 is a circuit diagram illustrating an equivalent circuit when the band switching circuit of FIG. 1 is operated in a first band.

FIG. 3 is a circuit diagram illustrating an equivalent circuit when the band switching circuit of FIG. 1 is operated in a second band.

4 is a circuit diagram illustrating an equivalent circuit when the band switching circuit of FIG. 1 is operated in a third band.

5 is a circuit diagram illustrating an equivalent circuit when the band switching circuit of FIG. 1 is operated in a fourth band.

FIG. 6 is a graph showing first to fourth band characteristics of the band switching circuit of FIG.

FIG. 7 is a block diagram showing another embodiment of the band switching circuit according to the present invention.

FIG. 8 is a block diagram showing a conventional band switching circuit.

[Explanation of symbols]

11 Input Terminals 12, 13 First and Second HPFs 14 Output Terminals SW1, SW2, SW3, SW4 First to Fourth Switching Elements

Claims (1)

[Claims] 1. A band switching circuit for passing a band selected and switched to a signal guided to an input terminal and guiding it to an output terminal, wherein the band switching circuit is connected in series between the input terminal and the output terminal. 1
And a second high-pass filter, a first switching element that is provided between the input terminal and the output terminal, and that turns on and off a bypass of a signal from the input terminal to the output terminal; Second switching provided between the connection point of the second high-pass filter and the output terminal and for turning on / off the bypass of the signal from the connection point of the first and second high-pass filters to the output terminal. A band switching circuit comprising: an element; and third and fourth switching elements for respectively turning on and off the respective resonant circuit sections of the first and second high pass filters.