JPH0339958Y2 - - Google Patents

Description

[Detailed Description of the Invention] "Industrial Application Field" This invention relates to improvement of an antenna input distribution circuit for a VTR (video tape recorder).

``Prior art'' Generally, a VTR divides the input signal supplied from an antenna into two parts, one of which is sent to the tuner of the VTR, and the other is sent to the VTR tuner.
An antenna input distribution circuit is used to supply the other signal to the television receiver via a high frequency signal switching circuit. Figure 3 shows a conventional antenna input distribution circuit, in which a television signal received by an antenna (not shown) is input to the antenna input terminal IN.
is applied to the base of the transistor 3 via the DC blocking capacitor 2. Its emitter is grounded via a resistor 4, and its collector is connected via a resistor 5 to a power supply terminal E _B.
The base of the transistor 3 is connected to the power supply terminal E _B via a resistor 6 and grounded via a resistor 7 in order to receive a bias current.
The collector is connected to the middle point of the distribution transformer 10 via the DC blocking capacitor 8, and one end of the distribution transformer 10 is connected to the first output terminal OUT ₁ .
The other end is connected to the base of a transistor 13 via a DC blocking capacitor 12. The emitter of the transistor 13 is grounded through a parallel circuit of a resistor 14 and a bypass capacitor 15, and its collector is connected through a resistor 16 to a power supply terminal E _B. The base of the transistor 13 is connected to the power supply terminal E _B via a resistor 17 and grounded via a resistor 18 in order to receive a bias current. The collector of the transistor 13 is connected to the output terminal via a DC blocking capacitor 19.
Connected to OUT ₂ . A circuit 20 consisting of elements indicated by numerals 2 to 8 and surrounded by a dotted line and a circuit 21 consisting of elements indicated by numerals 12 to 19 and surrounded by a dotted line each constitute an amplifier. The amplifiers 20 and 21 and the distribution transformer 10 constitute an antenna input distribution circuit.

The television signal applied to the antenna input terminal IN is amplified by the amplifier 20 and supplied to the distribution transformer 10, where it is divided into two parts, and one of the divided outputs is sent to the tuner of the VTR via the first output terminal OUT ₁ . the other distributed output is amplifier 2
1, is amplified there, and is output to the second output terminal.
VTR high frequency signal switching circuit 22 via OUT ₂
is supplied to one input terminal of Note that the other input terminal and output terminal of the high frequency signal switching circuit 22 are connected to the RF modulator 23 of the VTR and the television receiver, respectively. When the VTR is put into play mode (depending on the model, when the VTR's TV/video switch is switched to the video side), the high frequency signal switching circuit 22 is controlled and transmission from one input terminal to the output terminal is blocked. The RF signal supplied to the other input terminal is supplied to the television receiver via the output terminal. When the VTR is not playing (depending on the model, the VTR
(when the television/video changeover switch is switched to the television side), the input from the antenna applied to one of the input terminals is applied to the television receiver from the output terminal. (At this time, since the VTR is not in the playback state, there is no RF signal from the RF modulator 23.) Even if noise voltage is applied to the first output terminal OUT ₁ from the tuner side of the VTR for some reason,
The distribution transformer 10 prevents the signal from flowing around to the amplifier 21 side, thereby preventing it from adversely affecting the television receiver side.

``Problems that the invention attempts to solve'' In order to make VTRs smaller, more stable, and more economical,
Efforts are being made to integrate the various subcircuits that make up a VTR, and the antenna input distribution circuit is no exception. However, since it is difficult to integrate the distribution transformer, in the case of integration, the circuits other than this must be integrated and the distribution transformer must be externally attached to the circuit. In this case, since the largest distribution transformer cannot be integrated, the effect of miniaturization through integration is halved.

The purpose of this invention is to improve the antenna input distribution circuit so that it does not require a distribution transformer, which hinders integration.

"Means for Solving the Problem" According to this invention, there is provided a control terminal connected to an antenna input terminal, a first terminal capable of obtaining an output having a polarity opposite to that of the antenna input signal applied to the control terminal, and the above-mentioned antenna. A distribution transistor is used that has a second terminal that provides an output with the same polarity as the input signal. An amplifier is connected to the second terminal, and its output is supplied to the television receiver. Further, the output of the first terminal is supplied to the tuner of the VTR.

"Embodiment" An embodiment of this invention is shown in FIG. 1, with the same reference numerals attached to the parts corresponding to those in FIG. 3, and repeated explanation will be omitted. As is clear from FIG. 1, the conventional distribution transformer is removed, and the collector (first terminal) of the transistor 3 is directly connected to the first output terminal OUT ₁ via the capacitor 8, and the emitter (second
terminal) is connected to the input side of the amplifier 21. An output having a polarity opposite to that of the antenna input signal applied to the base (control terminal) is obtained from the collector, and this output is supplied to the tuner of the VTR via the first output terminal. An output having the same polarity as the antenna input signal is obtained from the emitter, and this output is supplied to the amplifier 21. That is, the transistor 3 constitutes a distribution transistor.

Even if noise voltage is applied to the first output terminal OUT ₁ from the tuner side of the VTR for some reason,
Amplifier 20 seen from the collector side of transistor 3
Since the output impedance of is generally quite high,
Noise current cannot flow from the collector side, and therefore, the noise current is prevented from flowing from the emitter side to the input side of the amplifier 21 via the transistor 3, thereby adversely affecting the television receiver. There's no fear. On the other hand, the noise voltage from the high frequency signal switching circuit 22 side is output to the second output terminal OUT _2.
Even if the signal is applied to the amplifier 21, the transmission to its own input side is blocked by the amplifier 21. Therefore, there is no risk that the signal will leak to the first output terminal OUT ₁ side via the transistor 3 and adversely affect the tuner side.

In FIG. 1, the base of transistor 13 is separated from the emitter of transistor 3 by capacitor 12 in terms of direct current. However, it can also be constructed as a direct amplifier. An example of this is shown in FIG. Resistors 17 and 1 of FIG. 1 were used to supply bias current to the base of transistor 13.
8 can be reduced together with the capacitor 12.

Although the transistors 3 and 13 have been described as bipolar transistors in FIGS. 1 and 2, it is easy to understand that the present invention is not limited thereto and that field effect transistors (FETs) may be used.

"Effects of the invention" As described above, according to this invention, it is possible to construct an antenna input distribution circuit without using a distribution transformer, which has traditionally been an obstacle to integration. It becomes easier, and it is possible to make it more compact and economical in the future.

Furthermore, even if integration is not performed, the distribution transformer, which is the largest in size and is expensive, can be eliminated, so it goes without saying that this can similarly contribute to miniaturization and economicalization of the circuit.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the VTR antenna input distribution circuit of this invention, Fig. 2 is a circuit diagram showing another embodiment of this invention, and Fig. 3 is a circuit diagram of a conventional VTR antenna input distribution circuit.
FIG. 2 is a circuit diagram of an antenna input distribution circuit for a VTR.

Claims (1)

[Claims for Utility Model Registration] A control terminal connected to an antenna input terminal, a first terminal capable of obtaining an output of opposite polarity to the antenna input signal applied to the control terminal, and an output having the same polarity as the antenna input signal. and an amplifier connected to the second terminal to supply the output to the television receiver, and the output of the first terminal to be supplied to the tuner of the VTR. VTR antenna input distribution circuit.