JP2535202B2 - Filter switching circuit - Google Patents

Description

The present invention relates to a filter switching circuit that constitutes an up-down converter or the like used in CATV or the like.

(Prior Art) FIG. 5 shows a configuration of a conventional filter switching circuit. In FIG. 5, 1 is an input terminal, 2 is an output terminal, 3 and 4 are band switching terminals, C _{1 to} C ₁₅ and L _{1 to} L ₆ are filter elements, D _{1 to} D ₄ are switching diodes, R ₁ ~
R ₆ is a bias resistor, F ₁ is a VHF band receiving high-pass filter, F ₂ is a VHF band receiving low-pass filter, and F ₃ is a UHF band receiving high-pass filter.

Next, the operation of the above conventional example will be described. First VHF
The time of band reception will be described. In FIG. 5, when an appropriate positive DC voltage is applied to the band switching terminal 3, the bias resistor R ₃ − the switching diode D ₁ − the bias resistor
R ₁ -ground and bias resistor R ₄ -switching diode D ₂ -bias resistor R _2- DC current flows through ground. That is, the switching diodes D ₁ and D ₂ are brought into an operating state (hereinafter referred to as ON). At this time, no voltage is applied to the band switching terminal 4. Therefore, the switching diodes D ₃ and D ₄ are inactive (hereinafter referred to as OFF). Therefore, the signal input from the input terminal 1 is output from the output terminal 2 through the switching diode D ₁ -VHF band receiving high-pass filter F ₁ -VHF band receiving low-pass filter F ₂ -switching diode D ₂ . The signal input from the input terminal 1 does not flow to the switching diode D ₃ −UHF band receiving high-pass filter F ₃ −switching diode D ₄ .

In the case of receiving in the UHF band, if an appropriate positive DC voltage is applied to the band switching terminal 4, the bias resistor R ₅ − the switching diode D ₃ − the bias resistor R ₁ − the ground and the bias resistor R ₆ − the switching diode D ₄ --Bias resistor
R ₂ − A direct current flows through the ground to turn on the switching diodes D ₃ and D ₄ . At this time, no DC voltage is applied to the band switching terminal 3. Therefore, the switching diodes D ₁ and D ₂ remain off.
Therefore, in this case, the signal input from the input terminal 1, an input terminal _{1-D 3 -F 3 -D 4} - flows through the output terminal 2, to the D ₁ -F ₁ -F ₂ -D ₂ is No signal flows. In this way, band switching can be performed by applying an appropriate DC voltage to the band switching terminals 3 and 4. However, the following development occurs when the signal frequency becomes high.

FIG. 6 is an equivalent circuit when receiving in the VHF band, that is, when the switching diodes D ₁ and D _{2 are} on and the switching diodes D ₃ and D _{4 are} off in FIG. In Fig. 6, VD ₁ is the equivalent power supply of D ₁ when the diode is on, VD ₂ is the equivalent power supply of D ₂ when the diode is on, CD ₃ is the equivalent capacitance of D ₃ when the diode is off, and RD ₃ is the one when diode is off. equivalent resistance of the D _3, CD ₄ is the equivalent capacitance of the D ₄ at the diode off, RD ₄ is an equivalent resistance of the D ₄ at the time of the diode off. A diode can be represented by an equivalent power source when turned on, and can be represented by a parallel circuit of a resistor and a capacitor when turned off. Therefore, in FIG. 6, the switching diode is
Even if D ₃ and D ₄ are turned off, since the switching diodes D ₃ and D ₄ have electrostatic capacitance, the equivalent capacitance CD ₃ · UHF band reception high-pass filter filter element C ₁₁ · C ₁₂ · L ₅ and equivalent Capacity CD ₄
- for the UHF band reception of the high-pass filter filter element C ₁₅ · C
₁₄ · L ₆ is the input terminal 1-switching diode D ₁
-VHF band reception for the high-pass filter F ₁ -VHF band reception low-pass filter F ₂ - switching diode D ₂ - is connected between ground and the filter circuit of the output terminal 2. That is, the CD ₃ , C ₁₁ , C ₁₂ , L ₅ and the CD ₄ , C ₁₅ , C ₁₄ , L ₆
Form a trap circuit for the filter circuit. The C ₁₂ , C ₅ and C ₁₄ , L ₆ are high-pass filters F for UHF band reception.
_Since it is the attenuation pole of ₃ , the center frequency of the attenuation pole exists at a frequency lower than the cutoff frequency of the UHF band reception high-pass filter F ₃ . That is, the center frequency of the attenuation pole of the UHF band receiving high-pass filter F ₃ exists in the VHF band. Therefore, the UHF band receiving high-pass filter F ₃
Due to the attenuation pole of, a trap occurs during reception in the VHF band within the VHF reception band. Next, the reception at the UHF band will be described. FIG. 7 is an equivalent circuit diagram when receiving in the UHF band, that is, when the switching diodes D ₁ and D ₂ are off and the switching diodes D ₃ and D ₄ are on in FIG. In Fig. 7, CD ₁ is the equivalent capacitance of D ₁ when the diode is off, RD ₁ is the equivalent resistance of D ₁ when the diode is off, CD ₂ is the equivalent capacitance of D ₂ when the diode is off, and RD ₂ is the diode off. D _{2 has} an equivalent resistance, VD ₃ is an equivalent power source of D ₃ when the diode is on, and VD ₄ is an equivalent power source of D ₄ when the diode is on. In FIG.
Since the switching diodes D ₁ and D ₂ have capacitance even when they are turned off, the L ₃ C ₇ and L ₄ C ₉ and C ₆ C ₈ C
₁₀ is an input terminal 1-switching diode D ₃ −UHF band receiving high-pass filter F ₃ −switching diode
D ₄ − Connected between the filter circuit of output terminal 2 and ground. That is, L ₃ C ₇ and L ₄ C ₉ and C ₆ C ₈ C ₁₀
Forms a trap circuit for the UHF band receiving high-pass filter circuit. Since the L ₃ · C ₇ and L ₄ · C ₉ is the attenuation pole of the VHF band reception low-pass filter F _2, the center frequency of the attenuation pole is higher than the cut-off frequency of the VHF band reception low-pass filter F ₂ Exists in frequency. That is,
The center frequency of the attenuation pole of the VHF band receiving low-pass filter F ₂ exists in the UHF band. Therefore, when receiving UHF, a trap occurs within the UHF reception band.

(Problems to be Solved by the Invention) However, in the above-described conventional configuration, even when the switching diode is turned off, the electrostatic capacity of the switching diode when the switching diode is turned off causes the electrostatic capacitance of the filter outside the reception time. There is a problem in that a trap circuit is formed for the filter circuit by the attenuation pole and another filter element outside the reception time, and a trap occurs in the reception band.

The present invention solves such a problem, and an object of the present invention is to design a filter having no trap in the reception band and flat insertion loss.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a filter switching in which a filter circuit that allows a plurality of specific signals to pass simultaneously from a signal group of a plurality of television signals is connected in parallel. In the circuit, a diode is connected in series to the front and rear stages of the filter circuit with respect to the filter circuit having the specific plural signals as a pass band, and a diode is connected between the front-stage diode and the filter circuit connected in series. Then, a diode is connected between the filter circuit and the subsequent-stage diode connected in series to ground. Further, among the plurality of filter circuits connected in series, the front-stage and rear-stage diodes connected in series to the filter circuit in the reception state are in the ON state, and the diode between the front-stage and rear-stage diodes in the ON state and the filter circuit is It is off. In addition, the pre-stage and post-stage diodes connected in series to the remaining filter circuit in the non-reception state are in the off state, and the diode connected between the pre-stage and post-stage diodes in the off state and the filter circuit is grounded. The filter switching circuit is configured to be in the ON state.

(Operation) The present invention has the following effects due to the above-mentioned configuration. That is, the diode is connected in parallel with the trap circuit. By turning on the diodes connected in parallel, the trap circuit is short-circuited, and the trap is not generated.

(Embodiment) FIG. 1 shows a filter switching circuit according to an embodiment of the present invention.

In FIG. 1, 1 is an input terminal, 2 is an output terminal, 3 and 4 are band switching terminals, C _{1 to} C ₁₅ and L _{1 to} L ₁₆ are filter elements, D _{1 to} D ₄ are switching diodes, and D ₅ ~ D ₈
Is a diode for trap measures, R _{1 to} R ₆ are bias resistors,
F ₁ is a VHF band receiving high-pass filter, F ₂ is a VHF band receiving low-pass filter, and F ₃ is a UHF band receiving high-pass filter.

FIG. 2 is an equivalent circuit of FIG. 1 when receiving a VHF band signal, that is, the switching diode in FIG.
D ₁ and D ₂ and the diodes D ₇ and D ₈ for trapping are turned on,
The switching diodes D ₃ and D ₄ and the trap countermeasure diodes D ₅ and D ₆ are equivalent circuits in the off state. In Fig. 2, VD ₁ is the equivalent power supply of D ₁ when the diode is on, V
D ₂ is equivalent power D ₂ at the diode ON, CD ₃ is the equivalent capacitance of the D ₃ when the diode off, RD ₃ is D ₃ when the diode off
Equivalent resistance of, CD ₄ is the equivalent capacitance of D ₄ when the diode is off, R
D ₄ is the equivalent resistance of the D ₄ at the diode off, CD ₅ is the equivalent capacitance of the D ₅ at diode off, RD ₅ is D ₅ at diode off
Equivalent resistance of, CD ₆ is the equivalent capacitance of D ₆ when the diode is off, R
D ₆ is the equivalent resistance of D ₆ when the diode is off, VD ₇ is the equivalent power supply of D ₇ when the diode is on, and VD ₈ is D ₈ when the diode is on.
Is the equivalent power source.

The equivalent circuit of FIG. 1 when receiving the UHF signal of FIG. 3, ie, the switching diodes D ₃ and D in FIG.
₄ is an equivalent circuit when the trap countermeasure diodes D ₅ and D ₆ are on, and the switching diodes D ₁ and D ₂ and the trap countermeasure diodes D ₇ and D ₈ are off. In Fig. 3, CD ₁ is the equivalent capacitance of D ₁ when the diode is off, RD ₁
Equivalent resistance, CD ₂ is the equivalent capacitance of the D ₂ at the diode off D ₁ of the time the diode off, RD ₂ is diode-off time of the D ₂ of the equivalent resistance, VD ₃ equivalent power D ₃ when the diode on, VD ₄
Equivalent resistance, the equivalent capacitance of the D ₈ when CD ₈ is diode-off equivalent capacitance, RD ₇ is D ₇ when the diode off of the diode D ₄ equivalent power at the time of ON, CD ₇ is D ₇ when the diode off, RD ₈
Is the equivalent resistance of D ₈ when the diode is off.

Next, the operation of the embodiment of the present invention will be described with reference to FIGS. First, description will be made regarding reception in the VHF band. In FIG. 1, by applying a positive DC voltage (for example, + 12V) to the band switching terminal 3, the switching diodes D ₁ and D ₂ are turned on and the trap countermeasure diodes D ₅ and D ₆ are turned off. V input from input terminal 1
The HF band signal is output from the output terminal 2 through the input terminal 1-switching diode D ₁ -VHF band receiving high pass filter F ₁ -VHF band receiving low pass filter F ₂ -switching diode D ₂ . As it is, the switching diodes D ₃ and D ₄ have equivalent capacitances CD ₃ and CD ₄ in the equivalent circuit at the time of receiving the VHF band shown in FIG. 2 and, as described in the conventional example of FIG. CD ₃・ C ₁₁・ C ₁₂・ L in Fig. 2
₅ and the CD ₄ · C ₁₅ · C ₁₄ · L ₆ trap circuit is formed.
At this time, if a negative DC voltage (for example, −5V) is applied to the band switching terminal 4 of FIG. 1, the diodes D ₇ and D ₈ for preventing trapping are turned off while the diodes D ₃ and D ₄ for switching are kept off. Turn it on. Therefore, the line connecting the anode of the switching diode D ₃ and the filter element C ₁₁ of the UHF band reception high-pass filter F ₃ and the trap countermeasure diode D ₇ are turned on, and therefore are grounded in an alternating current manner.
As a result, the filter elements C ₁₁ , C _12, and L ₅ are short-circuited and a trap circuit is not formed. Similarly, since the trap countermeasure diode D ₈ is turned on, the grounded line connecting the switching diode D ₄ and a filter element C _15, the filter element C ₁₅ · C ₁₄ · L ₆ are also shorted trap occurs do not do.

Next, the reception at the UHF band will be described. In FIG. 1, a positive DC voltage (for example, +12) is applied to the band switching terminal 4.
V), the switching diode D ₃ ,
Since D ₄ turns on and diodes D ₇ and D ₈ for trapping turn off, UHF band signals are output via input terminal 1-switching diode D ₃ −UHF band receiving high-pass filter F ₃ −switching diode D _4. Output from terminal 2. Also in this case, the trap circuit can be formed as it is as described in the conventional example of FIG. At this time, band switching terminal 3
A negative DC voltage (for example, −5 V) is applied to the switching diodes D ₁ and D ₂ while keeping the switching diodes D ₁ and D ₂ off, and the trap countermeasure diodes D ₅ and D ₆ are turned on. Filter elements of the VHF band reception low-pass filter _{F 2 L 3 · C 7 ·} C 6 · C 8 · C 10 and L ₄
Trap circuit for generating an attenuation pole of the _{C 9 · C 6 · C 8} · C 10 , the trap protection diode D _5, D ₆ is to enter in parallel on state, the trap will not occur.

FIG. 4 shows a circuit of another embodiment of the present invention. In FIG. 4, 1 is an input terminal, 2 is an output terminal, 3,
4 is a band switching terminal, D _1a , D _1b , D _{2 to} D ₄ are switching diodes, D _5a , D _5b , D _{6 to} D ₈ are trap countermeasure diodes, R _{1 to} R ₃ , R _4a , R _4b , R _5a , R _5b , R _6a , R _6b are bias resistors, CD _6a , CD _7a , CD _8a , CD _8b are bias capacitors, F ₁
Is a VHF band receiving high-pass filter, F ₂ is a UHF band receiving low-pass filter, and F ₃ is a UHF band receiving high-pass filter.

Next, the operation of the embodiment shown in FIG. 4 will be described. In FIG. 4, a positive DC voltage (for example, +12) is applied to the band switching terminal 3.
V), and a negative DC voltage (for example, -5V) is applied to the band switching terminal 4. As a result, the switching diodes D _1a , D _1b and D ₂ are turned on and D ₃ and D ₄ are turned off. The trap countermeasure diode D _5a, D _5b, D ₆ is turned off, D _7, D ₈ is turned on, VHF radio signal input from the input terminal 1, V
Passes through the high-pass filter F ₁ for HF band reception and the low-pass filter F ₂ for VHF band reception, and the high-pass filter F for UHF band reception
_It does not flow to the ₃ side, and no trap occurs in the reception band. Further, when a negative DC voltage (for example, −5V) is applied to the band switching terminal 3 and a positive DC voltage (for example, + 12V) is applied to the band switching 4, the ON / OFF states of the switching diode and the trap countermeasure diode are The reverse of the case where a positive DC voltage is applied to the band switching terminal 3 and a negative DC voltage is applied to the band switching terminal 4. In other words, the signal flows only on the UHF band reception high-pass filter F ₃ side, and the VHF band reception high and low pass filter F ₁
No signal flows on the F ₂ and F ₂ sides, and no trap occurs in the reception band.

(Effect of the invention) As is apparent from the above-described embodiment of the present invention, in a filter switching circuit in which filter circuits for simultaneously passing a plurality of specific signals are connected in parallel from a signal group of a plurality of television signals, The effect of being able to design a filter having a flat frequency characteristic by preventing the occurrence of traps by providing a diode for preventing traps between the switching diodes connected in series in the front and rear stages of the filter circuit and between the ground Have.

[Brief description of drawings]

FIG. 1 is a filter switching circuit diagram of an embodiment of the present invention, and FIG. 2 is an equivalent circuit diagram of FIG.
In the figure, D ₁ , D ₂ , D ₇ , D ₈ on, D ₃ , D ₄ , D ₅ , D ₆ off), and FIG. 3 is an equivalent circuit diagram of FIG. 1 during reception in the UHF band (FIG. 1 , D ₁ , D ₂ , D ₇ , D ₈ off, D ₃ , D ₄ , D ₅ , D ₆ on), FIG. 4 shows another embodiment of the present invention, and FIG. 5 shows conventional filter switching. Circuit diagram, FIG. 6 is an equivalent circuit diagram of FIG. 5 during reception in the VHF band (D ₁ , D ₂ on, D ₃ , D ₄ off in FIG. 5), 7
The figure is an equivalent circuit diagram of FIG. 5 during reception in the UHF band (in FIG. 5, D ₁ and D _{2 are} off, D ₃ and D _{4 are} on). 1 ... input terminal, 2 ... output terminal, 3,4 ... band switching terminal, C _{1 to} C ₁₅ and L _{1 to} L ₁₆ ... filter element, R ₁ to
R ₆ , R _4a , R _4b , R _5a , R _5b , R _6a , R _6b …… Bias resistance, D ₁ ~
D ₄ , D _1a , D _1b ...... Switching diode, D ₅ ~ D ₈ ,
D _5a , D _5b ...... Trap countermeasure diode, CD _6a , CD _7a , CD
_8a , CD _8b ...... Bias capacitor, CD _{1 to} CD ₈ ...... D _{1 to} D ₈ equivalent capacitance when diode is off, RD _{1 to} RD ₈ ...... D _{1 to} D ₈ equivalent resistance when diode is off, VD _{1 to} VD ₈ ...... Equivalent power supply of D _{1 to} D ₈ when diode is on, F ₁ ...... VHF band receiving high pass filter, F ₂ ...... VHF band receiving low pass filter, F
₃ …… High-pass filter for UHF band reception.

Claims (1)

(57) [Claims] 1. From a signal group such as a plurality of television signals,
In a filter switching circuit in which filter circuits that simultaneously pass a plurality of specific signals are connected in parallel, diodes are connected in series in front of and behind the filter circuit with respect to a filter circuit that has the specific plurality of signals as a pass band. And, in a filter circuit between the front-stage diode and the rear-stage diode, a diode is connected between at least the front-stage diode connected in series with the filter circuit and the ground, and connected in series with the filter circuit. Connect the diode so that the diode between the post-stage and the ground are connected, and of the multiple filter circuits connected in parallel, the front-stage and post-stage diodes connected in series to the filter circuit in the receiving state operate (ON).
The remaining filter in the non-reception state, in which the diode connected between the front and rear diodes in the above-mentioned operation (on) state and the filter circuit and the ground is in the non-operation state (off) The pre-stage and post-stage diodes connected in series to the circuit are inactive (OFF), and the diodes connected between the pre-stage and post-stage diodes in the non-operational (OFF) state and the filter circuit and between the ground operate (ON). ) A filter switching circuit characterized by being in a state.