JP3513010B2 - RF modulator signal switching circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a PAL signal and SE.
R used for video cassette decks for CAM signals
The present invention relates to an F modulator, and more particularly, to a signal switching circuit that sends a signal input to an antenna input terminal to a television output terminal without attenuating the power when the power is not consumed.

[0002]

2. Description of the Related Art An RF modulator provided in a video cassette deck, a video disc reproducing device, a BS receiving device, a personal computer or the like is configured to execute the following functions. That is, in order to send the internally generated video signal and audio signal to a television receiver that does not have a terminal for inputting a video signal and an audio signal, the video signal and the audio signal of the television broadcast are transmitted. It is converted to a signal of the same format as the signal format and sent to the television receiver. Also, when the connected TV receiver receives a television broadcast, it sends the signal received by the antenna to the TV receiver connected to the outside (in the case of a video cassette deck, it is received by the antenna. Signal is distributed to the externally connected TV receiver and internal tuner).

4 to 6 show a configuration proposed as a conventional technique for executing the above-mentioned functions.

The configuration shown in FIG. 4 has an RF off-through
It is a switch system. That is, the RF signal guided to the antenna input terminal 1 is distributed to two RF signals using the balun 51, and one of the distributed RF signals is guided to the tuner output terminal 3. Further, the other of the distributed signals is guided to the a contact of the electronic switch 52. The modulator 4 is connected to the b contact of the electronic switch 52.
, And the RF signal sent from the c contact is led to the television output terminal 2.

With the above configuration, when the television receiver connected to the television output terminal 2 receives a television broadcast, the c contact is connected to the a contact and the RF distributed by the balun 51 is connected. The signal is led to the TV output terminal 2. At this time, the modulator 4 is set in the operation stopped state. On the other hand, when reproducing the video tape, the modulator 4 is set to the operating state and c
The contact is connected to the b contact. Therefore, the RF signal from the modulator 4 is sent to the television output terminal 2.

In the above configuration, from the relationship between the distribution loss of the balun 51 and the loss of the electronic switch 52,
The pass characteristic from the antenna input terminal 1 to the tuner output terminal 3 is about -4db, and the pass characteristic from the antenna input terminal 1 to the television output terminal 2 is about -6db. Therefore, it is for strong electric field areas, mainly NTS
Used for C type video cassette deck (for VHF band).

On the other hand, in Europe, since a plurality of countries are densely clustered with each other, the output power of television broadcasting is set to a small value for the purpose of avoiding interference and interference. Therefore, since the electric field strength is weak, if there is a loss in the pass characteristic of the RF modulator, the S / N ratio deteriorates and the image quality deteriorates. Therefore, PAL video cassette deck (for VHF band and UHF band), S
ECAM video cassette deck (for UHF band)
Then, the configuration shown in FIG. 5 or the configuration shown in FIG. 6 is adopted. 5 and 6, the pass characteristic from the antenna input terminal 1 to the tuner output terminal 3 is about 4 db, and the pass characteristic from the antenna input terminal 1 to the television output terminal 2 is 0 to 2 db. ing.

The configuration shown in FIG. 5 is an RF booster switch system. That is, the antenna input terminal 1
The RF signal guided to is amplified by using the booster 53. Then, the amplified RF signal is distributed to two RF signals by using the balun 51, and one of the distributed RF signals is guided to the tuner output terminal 3. Further, the other of the distributed signals is guided to the a contact of the electronic switch 52. Then, the output from the modulator 4 is guided to the b contact of the electronic switch 52, and the c contact is connected to the television output terminal 2
Connected to.

With the above configuration, when the television receiver connected to the television output terminal 2 receives the television broadcast, the c contact is connected to the a contact and the balun 5 is connected.
The RF signal distributed by 1 is led to the television output terminal 2. At this time, the modulator 4 is set in the operation stopped state. On the other hand, when reproducing the video tape, the modulator 4 is set to the operating state and the c contact is connected to the b contact. Therefore, modulator 4
The RF signal from is output to the television output terminal 2. The booster 53 is always set to the operating state.

The configuration shown in FIG. 6 is of the RF / booster / mixer type. That is, the RF signal guided to the antenna input terminal 1 is amplified by using the booster 53. Then, the amplified RF signal is distributed to two RF signals using the balun 51, and one of the distributed RF signals is
Leads to tuner output terminal 3. Further, the other of the distributed signals is guided to the booster 54 and amplified, and the amplified RF signal is guided to the electronic switch 55. Further, the output of the modulator 4 is guided to the electronic switch 55, and the output of the electronic switch 55 is connected to the television output terminal 2.

With the above configuration, when the television connected to the television output terminal 2 receives the television broadcast, the RF signal amplified by the booster 54 is transmitted via the electronic switch 55 to the television. It leads to the output terminal 2. At this time, the modulator 4 is set in the operation stopped state. On the other hand, when reproducing the video tape, the modulator 4 is set to the operating state, and the RF signal from the modulator 4 and the RF from the booster 54 are set.
The signal is mixed in the electronic switch 55.
Then, the mixed RF signal is sent to the television output terminal 2. The boosters 53 and 54 are always set to the operating state.

[0012]

However, when the above technique is used, the following problems occur. That is, in the standby state where the video cassette deck is not used, it is necessary to maintain the pass characteristic from the antenna input terminal 1 to the television output terminal 2 to a value of 0 to 2 db. For this purpose, in the configuration shown in FIG. 5, it is necessary to operate the booster 53, and in the configuration shown in FIG. 6, it is necessary to operate both the booster 53 and the booster 54. . Therefore, even in the standby state, the RF modulator consumes power, so that the power consumption of the video cassette deck in the standby state is large.

The present invention was devised to solve the above problems, and an object of the present invention is to provide a switch circuit for opening and closing a connection between an antenna input and a television output when power is not consumed. Circuit to close the connection,
The switch circuit for opening / closing the connection between the antenna input and the tuner output and the switch circuit for opening / closing the connection between the modulator input and the television output are circuits for opening the connection when the power is not consumed, thereby making the RF in the standby state.
An object of the present invention is to provide a signal switching circuit for an RF modulator that can reduce the power consumption of the modulator to zero.

[0014]

[0015]

Further object of the invention of claim 2, wherein, in addition to the above object, to provide a signal switching circuit of the RF modulator, which may be zero power consumption in standby state RF modulator of the PAL system and the SECAM system It is in.

[0017]

[Means for Solving the Problems] To solve the above problems
A signal switching circuit of an RF modulator according to the present invention includes an antenna input to which a signal from an antenna is input, a television output to which a signal is sent to a television, a tuner output to which a signal is sent to a tuner, and a modulator output. Applied to a signal switching circuit of an RF modulator having a modulator input to which the signal of (1) is guided, and a first switch circuit for opening and closing the connection between the antenna input and the TV output, and for opening and closing the connection between the antenna input and the tuner output A second switch circuit, a third switch circuit that opens and closes the connection between the modulator input and the television output, and control for applying a predetermined voltage
And a first switch circuit, the first FET,
2FET, first capacitor, second capacitor, first resistor
It consists of an anti resistor, a second resistor, a third resistor, and a fourth resistor.
And the second switch circuit includes a first diode and a third capacitor.
It consists of a resistor, a first resistor, a second resistor, and a fifth resistor.
The third switch circuit includes a second diode and a fourth diode.
With a capacitor, a third resistor, a fourth resistor, and a sixth resistor
Is configured .

The antenna input is the first capacitor.
The source of the 1st FET and the diode of the 1st diode
Connected to the sword and the anode of the first diode is
Connected to the tuner output via a capacitor and
5 is connected to the control terminal via a resistor,
The data input is connected to the second diode via the fourth capacitor.
Connected to the anode, the anode of the second diode is
The second diode is connected to the control terminal via a 6-resistor.
The cathode of the cathode is connected to the source of the second FET.
Is connected to the TV output via a second capacitor,
The drain of the first FET and the drain of the second FET are mutually
The gate of the first FET is connected to
Connected to the source of the first FET and via the second resistor
Grounded, the gate of the second FET is connected through the fourth resistor
It is connected to the source of the second FET and also through the third resistor.
Grounded.

The first FET and the second FET are connected to the source and
When the potential of the gate is the same as the potential of the drain
And an N-channel FET, which is a modulator
Supply to the control terminal is stopped and the power supply to the control terminal is 0
When it becomes V, the saw of the first FET and the second FET
Between the drain and drain is in the ON state, and the first switch circuit
When turned on, the first diode and the second diode
The cathode and anode are in the off state between the second
Switch circuit and the third switch circuit are turned off,
Power is supplied to the modulator, and the control terminal
When a predetermined voltage is applied to the first FET and the second FET
The FET source and drain are turned off and the first switch
The switch circuit is turned off and the first diode and the second diode are turned on.
ON state between cathode and anode of each diode
The second switch circuit and the third switch circuit are
Turn on .

That is, in the state where power is not consumed
The antenna input and TV output are closed,
The connection between the tuner input and tuner output is opened and the module
The connection between the data input and the TV output is opened. Therefore,
Tuner output disconnected from antenna input
Input is disconnected from the TV output. Therefore, the power
R led to the antenna input when the
The F signal is sent to the TV output without any attenuation.
It

The gates of the first FET and the second FET are also included.
Voltage to generate a negative potential with respect to the source
The generated first resistance and fourth resistance are connected to respective gates.
When connected to the source, the first switch circuit
The connection is closed when no current flows through the first and fourth resistors.
The connection is opened when a current is applied. In other words, the power consumption is 0
The configuration is such that the connection is closed when
The first and fourth resistors, and the passage of current through these resistors
Path (fifth resistance, first diode, first resistance, second resistance
A path, a sixth resistor, a second diode, a fourth resistor, a
3 resistance paths).

Further , the first and second diodes are
The connection is opened when current is not applied, and the connection is closed when current is applied.
Jijiru Therefore, the configuration that opens the connection when the power consumption becomes 0
To the first and second diodes and these diodes
Current flow path (fifth resistor, first diode, first resistor
Anti-, second resistance path, and sixth resistance, second diode
, The fourth resistance, and the path of the third resistance).
Becomes

The signal switching circuit of the RF modulator according to the second aspect of the present invention has a configuration used for RF signals of the PAL system or SECAM system in addition to the above configuration.

That is, PAL led to the antenna input
System or SECAM system RF signals are sent out from the television output without being attenuated.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing an electrical connection of an embodiment of a signal switching circuit of an RF modulator according to the present invention, and more specifically, an RF used in a PAL system and SECAM system video cassette deck. It is a modulator. The parts having the same functions as those of the conventional technology shown in FIGS. 4 to 6 are designated by the same reference numerals. Further, FIG. 2 shows an equivalent circuit of the configuration shown in FIG.

This embodiment is roughly divided into three blocks of a signal switching circuit 5, a booster 6 and a modulator 4. The signal switching circuit 5 is a block for switching the RF signal, and includes an antenna input 11 to which the RF signal from the antenna input terminal 1 is guided, a television output 12 for sending the RF signal to the television output terminal 2, and a booster 6. It has a tuner output 13 for transmitting an RF signal and a modulator input 14 to which the RF signal from the modulator 4 is introduced.

The booster 6 is a block that amplifies the RF signal sent from the tuner output 13, and sends the amplified RF signal to the tuner output terminal 3. In addition, the modulator 4 includes a video signal 7 and an audio signal 8
Is a block for converting the RF signal into an RF signal according to the television broadcasting format, and the converted RF signal is sent to the modulator input 14.

More specifically, the signal switching circuit 5
Is a first switch circuit 21 that opens and closes the connection between the antenna input 11 and the television output 12, and a second switch circuit 2 that opens and closes the connection between the antenna input 11 and the tuner output 13.
2 and a third switch circuit 23 that opens and closes the connection between the modulator input 14 and the television output 12.

Then, the first switch circuit 21 is connected to the antenna input 11 and the television output 1 without consuming power.
It is a circuit that closes the connection between the two. Also, the second
The switch circuit 22 is a circuit that opens the connection between the antenna input 11 and the tuner output 13 without consuming power, and the third switch circuit 23 does not consume power, and the modulator input 14 and It is a circuit that opens the connection with the TV output 12.

The first to third switch circuits 21 to 21 will be described below.
The configuration of 23 will be described in detail.

The antenna input 11 is connected to the source of the FET 18 and the cathode of the diode D2 via the capacitor C1. The anode of the diode D2 is connected to the tuner output 13 via the capacitor C3. The modulator input 14 is also connected to the anode of the diode D3 via the capacitor C4. The cathode of the diode D3 is FE
It is connected to the source of T19 and is also connected to the television output 12 via the capacitor C2. Also, FE
The drain of T18 and the drain of FET 19 are connected to each other.

The gate of the FET 18 is connected to the source of the FET 18 via the resistor R1 and is also grounded via the resistor R2. The gate of the FET 19 is connected to the source of the FET 19 via the resistor R4 and is also grounded via the resistor R3. Also,
The anode of the diode D2 is connected to the control terminal 9 via the resistor R5, and the anode of the diode D3 is connected to the control terminal 9 via the resistor R6.

The first switch circuit 21 is composed of two FETs 18 and 19, two capacitors C1 and C2, and four resistors R1 to R4. Also,
The second switch circuit 22 includes a diode D2, a capacitor C3, and three resistors R1, R2, and R5, and the third switch circuit 23 includes a diode D3, a capacitor C4, and three resistors R3, R4, and R6. It is composed by. That is, the resistors R1 and R2 are
Is a device shared by the switch circuit 21 and the second switch circuit 22, and the resistors R3 and R4 are devices shared by the first switch circuit 21 and the third switch circuit 23. There is. The capacitors C1 to C4 are
It is an element for cutting the DC component.

Further, as the FETs 18 and 19, N-channel FETs are used in which the source and the drain are turned on when the voltage between the source and the gate is 0V. Further, as the diodes D2 and D3, diodes having a small junction capacitance such as pin diodes or Schottky diodes are used.

Further, the FET 18 and the FET 19 are switch elements of the first switch circuit 21, the diode D2 is a switch element of the second switch circuit 22, and the diode D3 is a switch of the third switch circuit 23. It is an element. Therefore, the FET 18 is
The FET 19 corresponds to the switch S1a shown in FIG. The diode D2 corresponds to the switch S2, and the diode D3 is the switch S3.
Will correspond to.

Next, the operation of the signal switching circuit having the above configuration will be described. When the video cassette deck is set to the standby state, the power supply to the booster 6 and the modulator 4 is stopped. Further, the voltage of the control terminal 9 becomes 0V. That is, the RF modulator is set to a state in which the power consumption of the operating power supply is zero.

In the above state, the diodes D2, D
No current flows through both sides. Therefore, the connection between the anode and the cathode of the diode D2 is open. Further, the connection between the anode and the cathode of the diode D3 is opened. Also, since no current flows through the resistor R1, the gate of the FET 18 has the same potential as the source,
The FET 18 is turned on between its source and drain. In addition, since no current flows through the resistor R4, the gate of the FET 19 has the same potential as the source, and the source of the FET 19
The drain is turned on.

That is, the circuit shown in FIG.
The circuit is equivalent to the circuit shown in (1), and the state between the antenna input 11 and the television output 12 is turned on. Further, the booster 6 is disconnected from the antenna input 11, and the modulator 4 is disconnected from the television output 12. for that reason,
The RF signal guided to the antenna input terminal 1 is transmitted from the television output terminal 2 without being attenuated.

On the other hand, when the video cassette deck is set to an operating state such as a reproducing operation, operating power is supplied to the booster 6 and the modulator input 14. Further, a predetermined voltage (for example, 12V) is applied to the control terminal 9.

When a predetermined voltage is applied to the control terminal 9, a current flows through the path composed of the resistor R5, the diode D2, the resistor R1 and the resistor R2. Therefore, the cathode and anode of the diode D2 are turned on. In addition, FET18
Since the potential of the gate of is lower than the potential of the source,
The source-drain of ET18 is turned off. Further, a current flows through a path formed by the resistor R6, the diode D3, the resistor R4, and the resistor R3. Therefore, the cathode and anode of the diode D3 are turned on. In addition, FET19
Since the potential of the gate of is lower than the potential of the source,
The source and drain of ET19 are turned off.

That is, the circuit shown in FIG.
The RF signal, which is equivalent to the circuit shown in (1), is guided to the antenna input terminal 1, is guided to the booster 6, is amplified, and is then transmitted from the tuner output terminal 3. In addition, the RF signal transmitted from the modulator input 14 is the TV output terminal 2
Be led to.

At this time, the antenna input 11 and the television output 12 have two FETs 18 and 1 in the off state.
Antenna input terminal 1 because it is separated by 9
Sufficient isolation is secured between the TV output terminal 2 and the TV output terminal 2.

In this embodiment, two FETs 18 and 19 are connected between the antenna input 11 and the television output 12, but this is necessary because of the isolation between the source and drain of one FET. If it is possible to secure a high isolation value, one FE
It is possible to use T as a capacitor having a capacitance having a small impedance with respect to the RF signal.

[0045] Figure 3 is a circuit diagram showing the electrical connection of the reference example of the signal switching circuit of the R F modulator. Note that FIG.
The same reference numerals as in FIG. 1 are given to the portions having the same functions as those of the configuration shown in FIG.

In this configuration, the signal switching circuit 10 is composed of switches 16 and 17 for mechanically switching and connecting the c contact to the a contact or the b contact. That is, the antenna input 11 is connected to the c contact of the switch 16, and the a contact of the switch 16 is connected to the tuner output 1
Connected to 3. The c contact of the switch 17 is
It is connected to the television output 12 and the a contact of the switch 17 is connected to the modulator input 14. The b contact of the switch 16 and the b contact of the switch 17 are connected to each other.

That is, the switch constituted by the c-contact and the b-contact of the switch 16 and the switch constituted by the c-contact and the b-contact of the switch 17 correspond to the first switch according to claim 3. It is composed. Further, the switch formed by the c contact and the a contact of the switch 16 corresponds to the second switch, and the switch 17 has the c contact.
The switch composed of the contact and the a contact corresponds to the third switch.

The switches 16 and 17 may be switches whose connections are switched manually, and the c contact is connected to the b contact when the relay coil is not driven. When the relay coil is driven, the c contact is connected. Can be a relay connected to the a contact.

Next, the operation of the signal switching circuit having the above configuration will be described. When the video cassette deck is set to the standby state, the power supply to the booster 6 and the modulator 4 is stopped. The c contacts of the switches 16 and 17 are connected to the b contacts. Therefore, the antenna input 11 and the television output 12 are connected to each other. Further, the booster 6 is disconnected from the antenna input 11, and the modulator 4 is disconnected from the television output 12. Therefore, the RF signal guided to the antenna input terminal 1 is transmitted from the television output terminal 2 without being attenuated. Further, the power consumption of the RF modulator at this time becomes zero.

On the other hand, when the video cassette deck is set in an operating state such as a reproducing operation, operating power is supplied to the booster 6 and the modulator input 14. The c contacts of the switches 16 and 17 are connected to the a contacts.
Therefore, the RF signal guided to the antenna input terminal 1 is
After being guided to the booster 6 and amplified, it is sent out from the tuner output terminal 3. Further, the RF signal transmitted from the modulator input 14 is guided to the television output terminal 2.

At this time, the antenna input 11 and the television output 12 are separated by the gap between the c contact and the b contact of the switch 16 and the gap between the c contact and the b contact of the switch 17. Has been. Therefore, switch 1
Even when 6 and 17 are small-sized manual switching switches or small-sized relays, sufficient isolation is secured between the antenna input terminal 1 and the television output terminal 2.

[0052]

The signal switching circuit of the RF modulator according to the present invention comprises a first switch circuit for opening and closing the connection between the antenna input and the television output, and a second switch circuit for opening and closing the connection between the antenna input and the tuner output. A circuit and a third switch circuit for opening and closing the connection between the modulator input and the television output, wherein the first switch circuit is a circuit for closing the connection when power is not consumed, and the second switch circuit and the third switch circuit are provided. The switch circuit is a circuit that opens the connection when power is not consumed. Therefore, in a state in which power is not consumed, the connection between the antenna input and the TV output is closed, the connection between the antenna input and the tuner output is opened, and the connection between the modulator input and the TV output is opened. Therefore, in a state where power is not consumed, the RF signal guided to the antenna input is sent to the television output without being attenuated, so that the power consumption of the RF modulator in the standby state can be reduced to zero. In addition, the first
The switch element of the switch circuit has the same source and gate.
N-channel that turns on between drain and source when
As a channel FET and a switch element of the second switch circuit
And a diode as a switch element of the third switch circuit
I am trying. That is, the gate of the FET with respect to the source
The resistance that generates the voltage to set the negative potential.
Connected between the gate and the source, the first switch circuit
Closes the connection when no current is flowing through this resistor,
The connection is opened when the current flows. That is, when the power consumption becomes 0
The configuration that closes the connection is the FET, the resistor, and the resistor.
It is composed of a flow path. Also, the diode is
Open the connection when current is not flowing, and connect when current is flowing
Close. Therefore, open the connection when the power consumption becomes 0.
The configuration consists of a diode and a path for passing current through the diode.
It will be composed by. This allows the entire circuit
The configuration can be simple.

[0053]

[0054]

Further, the signal switching circuit of the RF modulator according to the present invention is configured to be used for the PAL system or SECAM system RF signal. That is, the PAL or SECAM RF signal guided to the antenna input is transmitted from the television output without being attenuated. Therefore, it is possible to reduce the power consumption of the PAL and SECAM RF modulators in the standby state.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an electrical connection of an embodiment of a signal switching circuit of an RF modulator according to the present invention.

FIG. 2 is an equivalent circuit diagram of the configuration shown in FIG.

3 is a circuit diagram showing the electrical connection of the reference example of the signal switching circuit of the R F modulator.

FIG. 4 is a circuit diagram showing a conventional electrical connection.

FIG. 5 is a circuit diagram showing a conventional electrical connection.

FIG. 6 is a circuit diagram showing a conventional electrical connection.

[Explanation of symbols]

1 Antenna Input Terminal 2 Television Output Terminal 3 Tuner Output Terminal 4 Modulator 5 Signal Switching Circuit 6 Booster 7 Video Signal 8 Audio Signal 10 Signal Switching Circuit 11 Antenna Input 12 Television Output 13 Tuner Output 14 Modulator Input 16 First Switch and Second Switch 17 constituting the first switch and switch 18 constituting the third switch, and FET 19 which is the switching element of the first switch circuit 21 first switch circuit 22 second switch circuit 23 third switch Switch circuit D2 Diode which is a switch element of the second switch circuit D3 Diode which is a switch element of the third switch circuit

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H04N 5/38-5/46 H04B 1/16-1/24

Claims (2)

(57) [Claims] 1. An antenna input to which a signal from an antenna is input, and a television output to which a signal to a television is transmitted,
In a signal switching circuit of an RF modulator having a tuner output for transmitting a signal to a tuner and a modulator input for guiding a signal from a modulator, a first switch circuit for opening and closing a connection between an antenna input and a television output. , a second switch circuit for opening and closing a connection between the antenna input and the tuner output, and a third switching circuit for opening and closing a connection between the modulator input and TV output, where
And a control terminal for applying a constant voltage , wherein the first switch circuit includes a first FET, a second FET, and a first FET.
Capacitor, second capacitor, first resistance, second resistance, second
It is composed of a third resistor and a fourth resistor, and has a second switch.
The H circuit includes a first diode, a third capacitor, and a first resistor.
The anti-, the second resistance, and the fifth resistance, and the third resistance
The switch circuit includes a second diode, a fourth capacitor, a
It is composed of a third resistor, a fourth resistor, and a sixth resistor, and the antenna input has a first FE through a first capacitor.
Connected to the source of T and the cathode of the first diode,
The anode of one diode is connected via a third capacitor.
It is connected to the tuner output and the above-mentioned control is performed via the fifth resistor.
The modulator input is connected to the control terminal.
Connected to the anode of the second diode via a capacitor,
The anode of the second diode is controlled by a sixth resistor.
The second diode cathode connected to the second terminal.
It is connected to the source of the FET and via the second capacitor
Connected to the TV output and the drain of the first FET
And the drain of the second FET are connected to each other, and the first FE
The gate of T is connected to the source of the first FET through the first resistor.
Connected and grounded via a second resistor, the second FE
The gate of T is connected to the source of the second FET through the fourth resistor.
The first FET and the second FET are connected to each other and grounded via the third resistor, and the source and the gate are the same.
When the potential is turned on, the N
It is a channel FET, the power supply to the modulator is stopped,
When the power supply of the control terminal becomes 0V, the first FET and
The source-drain of the second FET is turned on and the first
Switch circuit is turned on and the first diode and
Off between cathode and anode of each second diode
The second switch circuit and the third switch
The circuit is turned off, power is supplied to the modulator, and the control end
When a predetermined voltage is applied to the child, the first FET and the first FET
The first FET is turned off between the source and drain of the two FETs.
The switch circuit is turned off and the first diode and the first diode
ON state between cathode and anode of each 2 diodes
Second switch circuit and third switch circuit
The signal switching circuit of the RF modulator, which is turned on . 2. A PAL or SECAM RF
The RF according to claim 1, wherein the RF is used for a signal.
Signal switching circuit for modulator.