JPH0311955Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention transmits high frequency signals received by an antenna to a television receiver (hereinafter abbreviated as TV) and a video tape recorder (hereinafter abbreviated as VTR).
The present invention relates to a high frequency switch that can distribute the output signal of the VTR and the high frequency signal being received by the antenna from interfering with each other.

FIG. 1 is a diagram for explaining the general function of this type of high-frequency switch. A high-frequency signal received by an antenna 1 is taken into a high-frequency switch 2, and then a part of this high-frequency signal is sent to a VTR 3. The remaining signals are distributed to each TV4. Also,
The output signal (high frequency signal) of the VTR 3 is applied to the TV 4 via the high frequency switch 2. At this time, the high frequency switch 2 must ensure that the output signal of the VTR 3 is transmitted to the antenna 1 so that unnecessary side radiation does not occur, and that the signal received by the antenna 1 is not sent to the TV 4.

Although the high frequency switch 2 and the VTR 3 are shown as separate blocks here, the high frequency switch 2 is originally built into the VTR 3, and the signals taken into the VTR 3 referred to here are the signals taken into the tuner. The output signal of the VTR 3 is the signal output from the converter.

FIG. 2 is a basic circuit diagram showing the configuration of a conventional high frequency switch 2 equipped with such a function.
The input terminal 11 to which the antenna 1 related to the first high frequency signal generation source is connected is connected to a high frequency filter 21 for lightning protection and a band elimination filter 2 generally called an FM trap for reducing FM interference.
2 to the primary winding of a high frequency transformer 23. Terminal a at one end and terminal b at the other end of the secondary winding of this high frequency transformer 23 are connected through a resistor, and an intermediate portion of the primary winding and an intermediate portion of the secondary winding are commonly connected and capacitor It is grounded via 24. When a signal sent from the antenna is applied to the primary winding of the high frequency transformer, a signal with a level corresponding to the grounding position appears at terminals a and b. Here, terminal a
is connected to an output terminal 12 for supplying a signal to an input terminal (not shown) of the VTR 3 as a first equipment system, and the other terminal b is connected to four coils 25, 26, 27, 28 connected in series. is connected to an output terminal 13 for supplying a signal to an input terminal (not shown) of a TV 4 as a second equipment system. Furthermore, the anodes of diodes 29, 30, and 31 whose cathodes are grounded are connected to the interconnection points of these coils 25 to 28, respectively, and the cathodes of a diode 32 are connected to the output terminal 13. anode and second
A capacitor 33 is connected between the input terminal 14 which receives the signal of the VTR 3 as a high frequency signal generation source for blocking the DC component, and a capacitor 33 is connected between the anode of the diode 32 and the control terminal 15 which receives the control signal of the VTR 3 to block the AC component. A coil 34 for blocking is connected to each.

Therefore, when the VTR 3 shown in FIG. 1 is not operated in any way, or when only a recording operation is performed, the control terminal 15 is kept at approximately ground potential, and the diodes 29 to 32 are all connected. It is in the off state. Therefore, the high frequency signal taken into the input terminal 11 is distributed to the VTR 3 and TV 4.

Next, when the VTR 3 is operated again,
A DC voltage is applied to the control terminal 15, and the diodes 29 to 32 are all turned on. This results in
The signal induced at one end b of the secondary winding of the high frequency transformer 23 flows into the grounding point side through the diodes 29, 30, 31, and cannot reach the output terminal 13. Instead, the signal is sent to the input terminal 14. The applied signal from the VTR 3 reaches the output terminal 13 via the capacitor 33 and the diode 32.

That is, the high frequency switch shown in Fig. 2 is
The high frequency signal received by the antenna is transmitted to the VTR3 and
Function to distribute to TV4 and output signal of VTR3
It has a function of preventing the high frequency signal being received by the antenna from reaching the TV 4 when being supplied to the TV 4.

In such a conventional high frequency switch, the diodes 29 to 31 in the on state release the signal induced in the secondary winding of the high frequency transformer to the ground side, but the signal is transmitted via the capacitor 33 and the diode 32. It also attenuated the output signal of the VTR 3, which had the disadvantage that the loss was quite large.

On the other hand, when the diodes 29 to 31 are in the OFF state, if the signal induced at one end b of the secondary winding of the high-frequency transformer contains a slightly high-level component, this high-level signal component Therefore, there is a risk that the diodes 29 to 31 may become conductive.
The signal induced at one end b of the secondary winding is
The drawback was that it could not lead to 4.

Furthermore, the current I flowing through the diode is expressed as I=I ₀ (e ^-qV/kT ), where the initial current is I ₀ , the voltage across the capacitance is V, and the time is T, so it is very large. For an input signal, the above equation has a drawback in that when it is expanded by Taylor, terms of the second order and higher order are generated, and a beat signal is generated for an input larger than the signal, resulting in intermodulation.

The present invention was developed in consideration of the above circumstances, and it reduces power loss when the first high-frequency signal is distributed to two systems and the second signal is sent to one system with priority over the other. The purpose of this invention is to provide a high frequency switch that can suppress extremely low frequencies.

Hereinafter, one embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 3 is a circuit diagram showing the configuration of the high frequency switch according to the present invention, and the same reference numerals as in FIG. 2 indicate the same elements. In place of the diodes 29 to 32 in FIG. 2, transistors 41 to 41 constituting the first switching elements are used.
43 and a transistor 44 constituting the second switching element, and variable capacitance diodes 45 and 46 having rectifying characteristics and whose capacitance changes depending on the reverse bias voltage applied between the terminals. The difference from FIG. 2 is that a variable capacitance circuit formed by butt-connecting the cathodes of the coil 28 is provided in series with the coil 28.

Note that transistors 41 to 44 are of NPN type, among which transistors 41 to 43 are
The emitters of these transistors are grounded, and the collectors of these transistors are connected to the interconnection points of the coils 25 to 28, and the bases of these transistors are connected to the control terminal 15 via resistors 47 to 49, respectively. There is. Further, the emitter of the transistor 44 is grounded via a resistor 52 and connected to the input terminal via a capacitor 54, its base is connected to the control terminal 15 via a resistor 51, and its collector is connected to a variable capacitance diode. 46 anodes.

Further, the anode of the variable capacitance diode 45 is connected to the coil 28, the anode of the variable capacitance diode 46 is connected to the output terminal 13 via the high-pass filter 55, and the cathodes of these variable capacitance diodes that are butted against each other are connected to the coil 53 and the resistor. 50 and are respectively connected to the control terminal 15 via a series circuit.

The operation of the high frequency switch of the present invention constructed as described above will be explained below.

First, when the VTR 3 is not operated in any way or when only a recording operation is performed, the control terminal is kept at approximately ground potential, so the transistors 41 to 44 are all off, and the variable capacitance diodes 45, No voltage is applied to the interconnection point c of 46 either. Therefore, since the electrostatic capacitance of the variable capacitance diodes 45 and 46 is large, their impedance becomes low. Therefore, the signal induced in the secondary winding of the high-frequency transformer 23 reaches the output terminal 13 from its terminal b through the coils 25 to 28, the variable capacitance diodes 45 and 46, and the high-pass filter 55.

Note that the impedance of the coils 25 to 28 is relatively small, and conversely, the impedance of the variable capacitance diodes 45 and 46 is
The respective values are appropriately selected so that the impedance of the coil 53 connected to the cathode of the coil 53 is extremely large.

Here, since the transistor is used as a diode in principle, it can be thought of as two diodes connected in reverse, so it will not turn on in response to a large input signal, and intermodulation will not occur easily. A similar effect is obtained for a varistor that is reversely connected to the varistor.

Next, when the VTR 3 is operated for reproduction, a DC voltage is applied to the control terminal 15 and base current is supplied to the transistors 41 to 44, so that all of these transistors are turned on, and the variable capacitance is The voltage at the control terminal 15 is directly applied to the cathodes of the diodes 45 and 46, and the capacitance of these diodes is also significantly reduced. This means that the impedance between the terminal b of the secondary winding of the high-frequency transformer 23 and the ground point becomes extremely small, and the impedance of the variable capacitance diodes 45 and 46 becomes significantly large. Therefore, the signal induced in the secondary winding of the high-frequency transformer 23 is allowed to escape from its terminal b through the transistors 41 to 43 to the installation point, and at the same time, the variable capacitance diodes 45 and 46 prevent the signal from passing through. There is.

On the other hand, the signal from the VTR 3 applied to the input terminal 14 passes through the capacitor 56, the transistor 44 and the high-pass filter 55, and appears at the output terminal 13.
In this case, since the impedance of variable capacitance diodes 45 and 46 is extremely high, this VTR 3
This prevents the signals from leaking to the transistors 41-43.

Note that the resistor 52 provided between the emitter of the transistor 44 and the ground point only needs to supply the base current of the transistor, so a resistor 52 having a large resistance value is used. Therefore, this resistance 52
The signal leaking further is negligible.

Thus, if the VTR3 is not operated in any way,
Or, in the case of only recording operation, the signal loss induced in the secondary winding of the high frequency transformer 23 is extremely small, and when the VTR 3 is played back,
While ensuring that this signal escapes to the grounding point side,
The signal loss of the VTR 3 can be significantly reduced.

Although the above embodiment describes a case where the high frequency signal received by the antenna is distributed to the TV and VTR, and the VTR signal is directly added to the TV, the high frequency switch of the present invention is not limited to such applications. , can be applied when it is necessary to distribute the first signal into two systems and send the second signal to one system with priority over the other, and the video signal is used as the first and second signals. When dealing with relatively low frequencies that do not include It is clear that even if ON/OFF control is performed only by 41, the same effect as described above will be achieved.

Further, in the above embodiment, the variable capacitance diode 4
The cathodes of 5 and 46 are connected together and a positive voltage is applied to this interconnection point. However, when using a negative voltage as a control signal, the anodes of these variable capacitance diodes are connected together and the transistor is It is better to use PNP rather than NPN. .

As is clear from the above explanation, according to the high frequency switch of the present invention, when the first high frequency signal is distributed to two systems and the second signal is sent to one system with priority over the other, power loss can be kept extremely low.

[Brief explanation of the drawing]

Fig. 1 is a block diagram for explaining the general functions of a general high frequency switch, Fig. 2 is a circuit diagram showing the configuration of a conventional high frequency switch, and Fig. 3 is an embodiment of the high frequency switch according to the present invention. FIG. 2 is a block diagram showing the configuration. 1: Antenna, 2: High frequency switch, 3: Video tape recorder, 4: Television receiver, 11: Input terminal (related to the first high frequency signal generation source), 1
4: Input terminal (connected to the second high-frequency signal generation source), 12: Output terminal (connected to the input terminal of the first equipment system), 13: Output terminal (input terminal of the second equipment system) ), 21, 22,
55: High-pass filter, 23: High-frequency transformer, 2
5-28, 34, 53: Coil, 29-32: Diode, 33, 54: Capacitor, 41-4
4: Transistor, 45, 46: Variable capacitance diode, 47-52: Resistor.

Claims (1)

[Claims for Utility Model Registration] (1) A first high-frequency signal is distributed to two systems, and the distributed first high-frequency signal and second high-frequency signal are switched to one distributed output system. The high-frequency switch to which the high-frequency signal is sent includes a high-frequency transformer whose primary winding is connected to the first high-frequency signal generation source, and one end of the secondary winding is connected to the input terminal of the first equipment system; a variable capacitance circuit in which a pair of variable capacitance diodes whose capacitance changes are connected in series in opposite directions to each other, and is provided between the other end of the secondary winding of the high frequency transformer and the input terminal of the second equipment system; a first switching element provided between the other end of the secondary winding of the high frequency transformer and a ground point;
A high frequency switch comprising a second high frequency signal generation source and a second switching element provided between input terminals of the second equipment system. (2) The high frequency switch according to claim 1, wherein transistors are used as the first and second switching elements. (3) On/off control of the first and second switching elements and capacitance control of the variable capacitance diode are performed by a DC power source of the second high frequency signal generation source. A high frequency switch according to claim 1 or 2 of the utility model registration claim.