JPH0545113B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a high frequency signal selection output circuit. In particular, RF modulator units for video tape recorders (VTRs)
(Reference) relates to a high frequency signal selection output circuit used for.

(b) Prior Art A general VTR with a built-in tuner receives a high frequency signal (first high frequency signal) from an antenna. Then, this VTR uses this first high frequency signal and a high frequency signal (second high frequency signal) from the RF modulator.
selectively output to a television receiver.

Figure 5 shows an outline of this VTR.

In Figure 5, 10 is an antenna, 12 is
14 is a VTR, 14 is a 2-way distributor, 16 is a VTR built-in tuner, and 18 is a recording/reproducing circuit (VTR body).
22 is an RF modulator that converts the video signal into a 3-channel or 4-channel (this is used in the United States, and is 1 channel or 2 channel in Japan) high frequency signal. 24 is a two-way divider 14
26 is a second switch means for cutting off a second high frequency signal from the RF modulator 22. 10
0 is a television receiver (TV).

A is the antenna input terminal, B is the output terminal for the VTR built-in tuner, C is the input terminal for the distributed first high frequency signal, D is the TV output terminal, E is the first and second
This is a control terminal to which a control voltage for controlling the switch means 24 and 26 is applied. In addition, in a normal VTR 12, a control voltage is applied to the control terminal E, and the first and second
The RF modulator 22 is operated only when the switch means 24 and 26 are turned on to output the second high frequency signal to the TV 100. Therefore, the control terminal E is usually also used as a power supply voltage supply terminal of the RF modulator 22. F is TV100
This is the antenna input terminal.

Reference numeral 1 denotes a first transmission line that transmits a first high-frequency signal from an input terminal C to an output terminal D for TV. This first
The first switch means 24 is inserted into the transmission line 1. Reference numeral 2 denotes a second transmission line for transmitting a second high frequency signal from the RF modulator 22 to the TV output terminal D. The second switch means 26 is inserted into the second transmission line 2.

The first and second switch means 24 and 26 complementarily cut off the first and second high frequency signals. When selectively outputting the first high frequency signal to the TV 100, the control terminal E
is at a low level, and the first and second switch means 2
4 and 26 are both turned off, and the second switch means 2
6 cuts off the second transmission line 2, and the first switch means 24 transmits the first high frequency signal to the first transmission line 1. Also, the RF modulator 22 becomes inoperable. The first high frequency signal from the antenna 10 is applied to the TV output terminal D via the antenna input terminal A, the two-way divider 14, the input terminal C, and the first transmission path 1, and
It is input to the TV 100.

Further, when selectively outputting the output of the recording/reproducing circuit 18 to the TV 100, the control terminal E is at a high level, and both the first and second switch means 24 and 26 are turned on. Therefore, the second switch means 26 conducts the second transmission line 2, and the first switch means 24 conducts the first transmission line 2.
The first high frequency signal is attenuated by grounding the transmission line 1, thereby substantially cutting off the first transmission line 1. Further, the power supply voltage is applied to the RF modulator 22, and the RF modulator 22 becomes operational. The signals (Video, Sound) output from the recording/reproducing circuit 18 are converted into 3-channel or 4-channel high frequency signals (second high frequency signals) by the RF modulator 22 and output. This second high frequency signal is output to the TV output terminal D via the second transmission line 2, and is then output to the TV output terminal D.
100 is input.

Next, the circuit of the RF modulator unit is shown in Figure 6. The RF modulator unit 30 is a fifth
The two-way divider 14 shown in the figure, the first and second transmission lines 1 and 2,
A high frequency circuit such as an RF modulator 22 is housed in a shielded housing 33.

In FIG. 6, the same parts as in FIG. 5 are given the same reference numerals. In FIG. 6, 22 is an RF modulator IC. E is a power supply terminal (control terminal), 22V is a video output terminal to which a video signal (second high frequency signal) converted to a 3-channel or 4-channel high-frequency signal is output, and 22S is a 3-channel or 4-channel high-frequency signal. The audio output terminal 22F is the RF modulator 22 where the converted audio signal (second high frequency signal) is output.
This is a terminal for setting whether the conversion to a high frequency signal at 3 channels or 4 channels is to be performed.

R1 and R2 are respectively video/audio output terminals 22V,
This resistor is used to attenuate the level of the signal from 22S in accordance with the product specifications. C1 and C2 are capacitors for DC cut, and R3 is a resistor to set the output impedance to 75Ω. g is a connection point.

32 is a low pass filter that allows frequencies below 72 MHz to pass. This low-pass filter 32 is composed of coils L1, L2, and capacitors C3, C4, and C5. This low-pass filter 32 functions to pass the 3-channel or 4-channel (60 MHz to 72 MHz) second high frequency signal output from the RF modulator 22. The low-pass filter 32 removes high-order harmonic components (for example, the second-order harmonic components are 120 to 150 MHz) from the second high-frequency signals of the three or four channels. Q3 constitutes the second switch means 26
It is an NPN type transistor.

A is an antenna input terminal into which a television broadcast signal (first high frequency signal) in the VHF and UHF bands (54 MHz to approximately 900 MHz) is input. 14 is a two-way divider. 34 is a high pass filter that allows, for example, 50 MHz or more (50 MHz to 1000 MHz) to pass when the transistors Q1 and Q2 are off. This high pass filter 34 consists of capacitors C6, C7, C8 and coils L3, L5.

When transistor Q3 is on, that is, power supply terminal E
When the power supply voltage (+B) is applied to the transistors Q1 and Q constituting the first switch means 24
2 is also in the on state. At this time, the connection point h is dropped to the ground potential (reference potential). That is, by turning on the transistor Q1, the first transmission line 1 is grounded. However, in the high frequency signal band, the on-characteristic (conductivity) of the transistor Q1 is not perfect, and the first high frequency signal from the two-way divider 14 may be attenuated and transmitted. Furthermore, when the transistor Q2 is turned on, the capacitor C7 and the coil L4 are connected in parallel to form a parallel resonant circuit 36 (Utility Model No. 61-7134).
issue, H03K17/60). The values of the capacitor C7 and the coil L4 are set in advance so that the resonance frequency of this parallel resonant circuit 36 is in the band of 3 channels and 4 channels (60 MHz to 72 MHz). Therefore, this parallel resonant circuit 36 blocks transmission of high frequency signals in the 3rd and 4th channel bands.

In other words, this parallel resonant circuit 36 prevents the second high frequency signal from the RF modulator 22 from flowing backward through the first transmission line 1 and leaking to the antenna input terminal A and the output terminal B to the VTR built-in tuner. Furthermore, this parallel resonant circuit 36 receives a first high frequency signal (50~
The signal components of channels 3 and 4 (60 to 72MHz) of the frequency (900MHz) leak to the TV output terminal D via the first transmission line 1 and interfere with the second high frequency signal from the RF modulator 22. prevent.

When selectively outputting the first high frequency signal of the antenna input terminal A to the TV output terminal D, no power supply voltage is applied to the control terminal E. At this time, the RF modulator 22 does not operate. Transistor Q1, Q
2, Q3 is off. At this time, capacitor C
6, C7, and C8 and coils L3 and L5 constitute a high-pass filter 34 that allows signals of 50 MHz or higher to pass. This high-pass filter 34 allows the first high frequency signal in all bands of VHF and UHF inputted to the antenna input terminal A to pass therethrough.

Therefore, the first signal input to the antenna input terminal A
The high frequency signal is passed through a high pass filter 34.
Output to TV output terminal D.

It should be noted that the first high frequency signal, which is always input to the antenna input terminal A, is divided into two and supplied to the VTR built-in tuner output terminal B.

3 is the power supply voltage of control terminal E at each part Q1, Q.
This is a signal line for supplying signals to Q2 and Q3. 4 is a signal line for supplying power supply voltage to the RF modulator 22.

R4, R5, R6 are transistors Q3, Q2,
This is a bias resistor for controlling on/off of Q1. L6 is a virtual coil formed by the distributed inductance of the signal line 4. This coil L6
Describe the effects of The RF modulator 22 has a built-in high frequency carrier signal oscillation circuit for converting a video signal or the like into a high frequency signal of 60 to 72 MHz. And, as a matter of course, high frequency signals tend to leak. Therefore, this carrier frequency component and the high-order harmonic components of this carrier leak to the terminal 22B in a very large amount. If this carrier frequency component etc. goes outside the shield plate, it will adversely affect other circuits as unnecessary radiation. Therefore, the coil L6 prevents transmission of carrier frequency components and the like. Further, the capacitors C9 and C10 attenuate the high frequency carrier frequency component by grounding it. Incidentally, the coil L6 is actively created by bending the signal line 4.

(c) Problems to be solved by the invention As mentioned above, the second
When selectively outputting a high frequency signal to the TV output terminal D [when transistors Q1, Q2, and Q3 are on],
A parallel resonant circuit 36 is formed to prevent the second high frequency signal from leaking to the antenna input terminal A.

By the way, the high-order harmonic component (second-order harmonic) of the second high-frequency signal output from the RF modulator 22
120 to 146 MHz and tertiary high frequency (180 to 220 MHz) are removed by the low-pass filter 32. However, this removal is not complete.

Furthermore, the parallel resonant circuit 36 does not block passage of high-order harmonic components. Furthermore, the ground fault caused by the transistor Q1 is not perfect. As a result, high-order harmonic components leak to the antenna input terminal A and the VTR built-in tuner output terminal B.

Further, the transistor Q2 has a capacitance between its base and emitter when it is off. (This value is typically twice the collector-emitter capacitance). Due to this capacitance, when the transistor Q2 is off, that is, when the first high frequency signal from the antenna input terminal A is output from the TV output terminal D, the first high frequency signal in the first transmission line 1 is transmitted between the base and emitter of the transistor Q2. Attenuated by capacitance.

As an improvement on this, it is conceivable to perform the ground fault of the first transmission line 1 by using three transistors, as schematically shown in FIG. In this way, the attenuation of the signal passing through the transmission line 1 can be increased.
Note that the low-pass filter 32 and the like are not shown in FIG. 7.

In this circuit, a predetermined amount of attenuation (3 channels, 4
Three transistors are used to obtain -60dB in the channel. However, transistor Q
has a capacitance between the collector and emitter when it is off. Therefore, when the transistor Q is off, that is, when the first high frequency signal of the antenna input terminal A is output from the TV output terminal D, the first high frequency signal in the first transmission path 1 is transmitted to the transistor Q.
It is attenuated by the collector-emitter capacitance of .

That is, by increasing the number of transistors Q that ground the first transmission line 1 when selectively outputting the second high-frequency signal, it is possible to prevent the high-frequency signal from the RF modulator 22 from flowing back to the antenna input terminal A. However, if this is done, the passage characteristics from the antenna input terminal A to the TV output terminal D will deteriorate when the first high frequency signal is selectively output.

(d) Means for Solving the Problems The present invention provides a pair of transistors Q1 and Q2 for grounding the first transmission line 1 at both ends of a capacitor C15, and connects the capacitor between the bases of the transistors Q1 and Q2. It is characterized by providing a coil L15 that forms a parallel resonant circuit 37 in cooperation with C15.

(e) Effect Since the present invention has the above-described configuration, the ground fault at the two points p and g of the first transmission line 1 and the formation of the parallel resonant circuit 37 can be simultaneously performed by the pair of transistors Q1 and Q2.

(F) Embodiment An embodiment of the present invention will be described with reference to FIG. In FIG. 1, the same parts as in FIGS. 6 and 7 are designated by the same reference numerals, and redundant explanation will be omitted.

In Fig. 1, Q1 and Q2 are switching transistors, and these transistors Q1 and Q2 are switching transistors.
2 is a first switch means 24;

The collectors of the transistors Q1 and Q2 are connected to both ends p and q of a capacitor (first electronic component) C15, respectively, and the emitters are grounded (connected to a reference potential point). L15 is this transistor Q1, Q2
A coil (second electronic component) is connected and inserted between the bases of the . This coil L15 and the capacitor C15 form a parallel resonant circuit 37 when the transistors Q1 and Q2 are turned on, and the 3-channel and 4-channel
Channel (60MHz to 72MHz) signals are prevented from passing through the first transmission path 1.

R7 is a bias resistor for supplying a control voltage to the base of transistor Q2. This control voltage is also applied to the base of transistor Q1 via coil L15.

In the above circuit, the first antenna input terminal A
When selectively outputting a high frequency signal to the TV output terminal D, no power supply voltage is applied to the control terminal E.

Therefore, transistors Q1, Q2, Q3 and
The RF modulator 22 is turned off, and the first high frequency signal at the antenna input terminal A is transmitted to the TV output terminal D via the first transmission path 1.

Further, when selectively outputting the second high frequency signal of the RF modulator 22 to the TV output terminal D, a power supply voltage is applied to the control terminal E. Therefore, transistors Q1, Q2, Q3 and RF modulator 22
is turned on. The second from RF modulator 22
The high frequency signal is transmitted to the TV output terminal D via a low-pass filter and transistor Q3 (not shown). Further, among the second high-frequency signals, a signal that flows backward through the first transmission line 1 and is about to leak to the antenna input terminal A is attenuated by the ground fault between the transistors Q2 and Q1. Also, parallel resonant circuit 3
7 prevents its passage. Further, the high-order harmonic components of the second high-frequency signal are transmitted through transistors Q2 and Q1.
It is attenuated by conduction between the collector and emitter (ground fault). Furthermore, the first high frequency signal at the antenna input terminal is sufficiently attenuated by the ground fault between transistors Q1 and Q2.

Figure 2 shows the frequency characteristics. Figure 2 a is from antenna input terminal A when outputting the first high frequency signal selection.
This shows the frequency passing characteristics up to the TV output terminal D. a shows the characteristics of the circuit in FIG. 1, b shows the characteristics of the circuit in FIG. 7, and c shows the characteristics of the circuit in FIG. 6. Figure 2b shows the antenna input terminal A to the TV output terminal D when the second high-frequency signal is selected and output.
This shows the frequency passing characteristics (frequency blocking characteristics) up to. a, b, c are respectively Fig. 1, Fig. 7,
The characteristics shown in FIG. 6 are shown. In the present invention,
By providing the coil L15 and selecting the inductance, the combined impedance of the base-collector impedance of the transistor Q1 and the transistor Q2 and the coil L15,
The inductance is set to be constant in the stop band, and the coil L15 is configured to resonate with the capacitor C15. The impedance between the transistor Q1 and the transistor Q2 becomes large in the stop band, and at this time, the impedance between the base and emitter of the transistor Q1 and the transistor Q2 is quite low, so that the resonance effect is large.

Further, FIG. 3 shows a second embodiment of the present invention. Second
The figure shows an example in which one transistor is added to short-circuit the first transmission line 1 to the ground level compared to FIG. 1. Coils L20 and L21 are provided between the bases of transistors Q', Q', and Q'. Capacitors C20 and C21 form resonant circuits 37' and 37'' together with coils L20 and L21, improving blocking characteristics.

FIG. 4 shows a third embodiment of the present invention. In FIG. 4, the same parts as in FIGS. 1 and 6 are designated by the same reference numerals.

In the above circuit, a control voltage for turning on the double diode DD is applied from the terminals 22'V, 22'S of the RF modulator 22 via the resistors R1, R2 and the low-pass filter 32.

In the above circuit, when applying the power supply voltage to the control terminal E and outputting the second high frequency signal from the TV output terminal D, the terminal 22 of the RF modulator 22
A power supply voltage is applied to B, and this RF modulator 22 operates. And terminal 22'V, 2
2'S outputs audio/video high frequency signals, and also outputs DC voltage signals from terminals 22'V and 22'S. This DC voltage signal turns on the double diode DD via the second transmission line 2. Therefore, the second high frequency signal is selectively output from the television output terminal D.

The above circuit operates similarly to the circuit of FIG. This circuit describes the values of each component. The coil in the above circuit is an air-core coil, and its value (Henry value) varies depending on the frequency. Furthermore, the value of this air-core coil is adjusted by an adjustment jig. Therefore, the coil value is a reference value.

22...LA7055 manufactured by Sanyo Electric Co., Ltd., Q1, Q2...2SC2735 manufactured by Hitachi Ltd., Q4...Resistor-containing transistor RN2411 manufactured by Toshiba Corporation DD...1SS226 manufactured by Toshiba Corporation C10...0.01μF C9...0.01μF R1 …4.7KΩ R2 …1KΩ C12 …1200pF R3 …56Ω C3 …39pF L1 …198nH C4 …68pF L2 …201nH C5 …33pF C13 …39pF L18 …290nH L13 …145nH C14 …27pF L14 …150nH C1 5...22pF L15...155nH L16... 153nH C16...39pF R14...180Ω C17...4pF C18...100pF L17...276nH R7...390Ω In the above embodiment, terminals 22'S, 2
Double diode control voltage from 2'V
Although the voltage is applied to DD, it is also possible to insert a capacitor into the signal line of one terminal and turn on the double diode DD only with the control voltage of the other terminal.

(g) Effects of the Invention As described above, according to the present invention, a high-frequency signal selection output circuit with good pass characteristics when selectively outputting the first high-frequency signal [see a in FIG. 2a] can be realized with a simple configuration. It is useful.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a first embodiment of the present invention. FIG. 2 is a diagram showing frequency characteristics. FIG. 3 is a schematic diagram showing a second embodiment of the present invention. Fourth
The figure shows a third embodiment of the present invention. FIG. 5 is a diagram for explaining switching of high frequency signals.
FIG. 6 and FIG. 7 are diagrams showing conventional examples, respectively. 1stRF...First high frequency signal, A...Antenna input terminal (first input terminal), C...Input terminal (first
input terminal), D...TV output terminal (output terminal),
1...First transmission line, 22...RF modulator,
2ndRF...second high frequency signal, 2...second transmission line, 24...first switch means (switch means),
26...Second switch means (switch means), C
15, C20, C21...Capacitor (first electronic component), 36...High pass filter (filter means), Q1, Q2, Q', Q', Q'...Pair of transistors, L15, L20, L21... Coil (second electronic component), 37, 37', 37''...parallel resonant circuit.

Claims (1)

[Claims] 1. A first input terminal into which a first high frequency signal is input;
A first transmission line that transmits this first high frequency signal to the output terminal, a second transmission line that transmits the second high frequency signal output from the RF modulator to the output terminal, and the first and second high frequency signals are selected. a switch means provided on the first and second transmission lines for outputting the output to the output terminal, and a first electronic component inserted in series in the first transmission line; In a high-frequency signal selection output circuit comprising filter means for determining passage characteristics, the switching means constitutes the switching means, and a collector-emitter path is connected between both ends of the first electronic component and a reference potential point. a pair of transistors, a second electronic component connected between the bases of the pair of transistors, and a control means for applying a switching control voltage to the bases of the pair of transistors; Turn on the transistor to ground the first transmission line at a high frequency, and connect the second electronic component to the first electronic component in parallel to form a parallel resonant circuit to generate the same signal as the second high frequency signal. A high frequency signal selection output circuit characterized by blocking passage of band signals.