JPS62231572A - Television monitor device - Google Patents

Abstract

PURPOSE:To easily switch from a broadcast radio wave to a monitor signal and vice versa by permitting a monitor modulation circuit to modulate the monitor signal according to a set channel even if a television channel is positioned at any place. CONSTITUTION:A comparator 44 compares the output of a detection circuit 42 with a reference value. When the frequency of a difference signal being the output of a mixing circuit 38 becomes a fixed value, 58.75 mHz, said signal is supplied to a variable carrier oscillator circuit 28 to fix the frequency. The output of the comparator 44 is supplied to a changeover switch 14, and an input terminal is switched to an input terminal 14b for monitor from an input terminal 14a for a broadcast radio wave. Through the said switching operation the monitor signal from an external video source 16 is video-modnlated by a decided carrier frequency and supplied to a video receiving circuit 10. Therefore it can receive the monitor signal on a currently selected channel as it is.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a television monitor, particularly to an improvement in a receiving circuit for video modulating a monitor signal.

[Prior Art] Television receivers are normally used to receive broadcast waves, but as video sources in each building have diversified in recent years, television receivers have become used not only for receiving broadcast waves (111) but also as monitors. There has been a marked increase in the number of cases in which it is used as a

The video source may be, for example, a video tape recorder,
Television cameras, cable televisions, video game consoles, and the like are known, and a general home television receiver must selectively receive monitor signals from these diversified video sources to ensure reliable reception.

[Problems to be Solved by the Invention] As is well known, since television receivers mainly receive broadcast waves, their input section handles signals modulated with high-frequency carrier waves. Monitor signals other than broadcast radio waves are also once modulated at a predetermined carrier frequency and then supplied to the monitor input terminal of the television receiver.

The frequency of the carrier wave of the broadcast radio wave is set to a different value for each broadcasting station, and this is divided by a designated desennel.

Therefore, in the past, when a television receiver was used as a monitor device, the monitor signal from the outside was received using an empty channel that was not used in normal broadcast radio waves, and as a result, the monitor signal was transmitted to the -H video modulation circuit. For example, depending on the region, the signal is modulated using the carrier frequency of a two-channel or one-channel tunnel, which is an empty channel.

However, in such conventional devices, the television signal supplied from the outside is only received on a predetermined empty channel, and as a result, the television receiver is not able to receive normal broadcast waves. In order to switch to monitor reception, it was necessary to switch the TV channel to the set monitor channel.

Therefore, in the conventional device J3, this channel switching is troublesome and an unpleasant llg image appears on the screen each time the channel is switched, which is inconvenient to handle.

In addition, in recent years, monitoring devices have been incorporated into home or business security systems, and systems have been put into practical use that use a television camera to positively image visitors at the entrance and display this image on a television screen each time they visit. In such a case,
Each time there is a visitor, the user has to take the trouble of switching the TV channel to the one for monitoring.

The present invention was made in view of the above-mentioned conventional problems, and an object of the present invention is to automatically convert monitor signals supplied from the outside without requiring channel switching when a television receiver is used as a monitor device. An object of the present invention is to provide an improved television monitor device that displays images on a television receiver.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides that when television reception is switched from normal broadcast wave reception or a non-reception state to monitor reception, the currently selected detects the channel and modulates the externally supplied monitor signal on the carrier frequency corresponding to this channel, thereby allowing the television to be tuned to whatever channel is selected without the need for one channel at a time. This allows the receiver to be used for monitoring.

In the present invention, the selection of the carrier frequency is achieved by detecting the local oscillation frequency of the television receiver using leakage No. 18 of the high frequency receiving system, and on the other hand, incorporating a variable frequency oscillation circuit that sequentially changes the frequency and outputs it as a carrier wave signal. However, this carrier wave frequency and the frequency of the leakage signal are compared, and when the difference frequency becomes a constant value, the frequency of the carrier wave is selected.

[Function] Therefore, according to the present invention, the user can receive the external monitor signal on the current television receiver by simply switching the desired video source for each television reception, regardless of the output channel. This makes it possible to eliminate the trouble of the conventional troublesome or unpleasant dial switch IJ.

[Embodiments] Hereinafter, preferred embodiments of the present invention will be described based on the drawings.

In FIG. 1, a portion of the television receiver is shown as a television reception circuit 10. As shown in FIG.

Normally, broadcast waves from an antenna 12 are input to the television receiving circuit 10, but in the embodiment J3, an antenna changeover switch 14 is provided at the input section of the television receiving circuit 10.
A broadcast radio wave signal from the antenna 12 is supplied to an input terminal 14a, and an input from an external video source, which will be described later, is supplied to a monitor input terminal 1/Ib.

Broadcast radio waves inputted from the antenna 12 through the terminal 14a have a carrier frequency fO determined for each broadcasting station, while the television receiving circuit 10 has a carrier frequency fO.
A local oscillation circuit is provided to obtain a constant carrier frequency (interlayer wave number) in the receiving circuit for each channel by mixing the It is determined in correspondence with the frequency from .

As is well known, in the current standard television broadcasting system, the difference between the carrier frequency from the broadcasting station and the local oscillation frequency in the television receiving circuit 10 selected for each channel fσ is a constant value for any channel. , that is, 58
．． It is set to 75811Z.

In the present invention, focusing on the fact that the difference between the local oscillation frequency and the carrier frequency of the broadcasting station is a constant value for each channel, the video modulation frequency of the television monitor device is adjusted within the currently set television receiving circuit 10. As a result, the carrier frequency in the television monitor device corresponds correctly to the local oscillation frequency in the television receiving circuit 1o, and the currently set data The monitor signal can be accurately received on the t/channel.

Furthermore, a feature of the present invention is that the local oscillation frequency set in the television receiving circuit 10 is detected from the leakage signal of the high frequency receiving system for each television reception.

In the present invention, the external video source 16 may include, for example, a security system television camera 18, a videotape recorder 20, or a television game 22, in combination or alone; A video signal and an audio signal are being extracted.

A monitor signal output from the external video source 16 is modulated by a monitor modulation circuit 24 in the same manner as a broadcast signal from a television station, and is supplied to the input terminal 14b of the changeover switch 14.

The monitor modulation circuit 24 includes a video modulation circuit 26 that video modulates the monitor signal according to a desired carrier frequency, and the frequency of the carrier wave is determined by the variable carrier oscillation circuit 2 in the embodiment.
8.

In the present invention, the variable carrier wave oscillation circuit 28 outputs the carrier frequency of the broadcasting station set in the A channel of the television receiving circuit 10, but for this frequency selection, the excavation circuit 28 outputs the carrier frequency of the broadcasting station set in the A channel of the television receiving circuit 10. A signal is output while sequentially selecting or continuously changing the frequency, and the output frequency fn is determined by a carrier wave selection circuit, which will be described later.

This carrier signal is passed through an amplifier circuit 30 to a video modulation circuit 2.
The video modulation circuit 24 can modulate the monitor signal at the carrier frequency determined in the present invention.

The carrier frequency 1'n of the variable carrier wave oscillation circuit 28 described above
In order to select a predetermined value, the present invention is provided with a carrier wave selection circuit 32, which determines the frequency of the variable carrier wave based on the local oscillation frequency leakage signal detected from each television reception.

In the embodiment, the carrier wave selection circuit 32 receives the local oscillation frequency f from the high frequency receiving system of the television receiver as its input signal.
In the example, antenna 1
The branch outputs from each branch 34 connected to 2 are input.

This branch output contains the local oscillation frequency f[ of the television receiving circuit 10 as a leakage signal, and the carrier wave selection circuit 3
2 amplifies the voltage level of the leakage signal to a processable level by a bandpass amplifier circuit 36 provided at its input section.

The leakage signal is further mixed with the carrier wave signal fn of the variable carrier wave oscillation circuit 28 in the monitor modulation circuit 24 by a mixing circuit 38, and in the embodiment, this mixing circuit 38 outputs a difference signal obtained by calculating the difference between the frequencies of both signals. do.

Therefore, the output signal frequency of the mixing circuit 38 is the difference frequency between the output frequency fn of the variable carrier oscillation circuit 28 and the local oscillation frequency fL set in the television receiving circuit 10 detected as a leakage signal, and at this time, When the frequency fn of the carrier wave signal matches the television broadcasting frequency of the channel selected by the television receiving circuit 10''c, the frequency of the difference signal can be a constant value, that is, 58.75 HIIz. it is obvious.

Therefore, in the present invention, when the frequency of the difference signal reaches the constant value, if the output frequency of the variable carrier oscillation circuit 28 is fixed to the frequency at the time of coincidence, the modulation frequency of the monitor modulation circuit 24 is changed to the current frequency. It is understood that this corresponds correctly to the channel set within the television receiving circuit 10.

The carrier selection circuit 32 passes the difference signal through the filter 40 as a signal near the predetermined intermediate frequency, and the detection circuit 42 converts it into a DC signal.

The output of the detection circuit 42 is compared with a reference value by a comparator 44, and when the frequency of the difference signal that is the output of the mixing circuit 38 reaches a constant value, that is, 58.75H1lz, a signal is sent to the variable carrier oscillation circuit 28. Fix this frequency by supplying Further, the output of the comparator 44 is supplied to the changeover switch 14, and the input terminals are changed from the broadcast wave input terminal 14a to the monitor input terminal 14b.
Switch to

Therefore, by this switching operation, the monitor signal from the external video source 16 is video-modulated by the carrier frequency determined as before, and is supplied to the video receiving circuit 10, so that the currently selected monitor signal in the television receiving circuit 10 is It becomes possible to receive the monitor signal as it is by using the channel II.

In an embodiment, the monitor modulation circuit 24 and carrier selection circuit 32 are normally powered off, and the external video source 1
For this purpose, the output of the external video source 16 is supplied to the monitor signal detection circuit 46, and only when the external video source 16 is activated is the power supplied to the external video source 16. 24. Put 32 into operation.

Therefore, according to this embodiment, even when the external video source 16 is used as a security television camera 18, etc.
The TV input signal can be automatically switched to the required degree.

The aforementioned variable carrier wave oscillation circuit 28 is a carrier wave selection circuit 32.
The output frequency is sequentially switched until the output frequency fn is fixed, and this variable frequency circuit can be assembled arbitrarily, but as shown in Figure 2, the frequency corresponding to each channel is sequentially switched and output. An example of a variable carrier wave oscillation circuit 28 is shown.

The variable oscillation circuit 50 uses a coil 52 . to determine the oscillation frequency. Capacitor 54.56. It has a resonant circuit including a variable capacitance diode 58, and its output is output from a capacitor 60 via an amplifier circuit 62 as a carrier wave 8 (frequency fn).

Therefore, in this embodiment, the tta transmission frequency corresponding to each desired channel can be selected depending on the voltage supplied to the variable capacitance diode 58.

The voltage applied to the variable length diode 58 is as shown in the example J.
3 are provided for each V channel and are determined by variable resistors 64-1 to 64-12 having different resistances, and the output of each variable resistor 64 is connected to contacts 66-1 to 66-6, respectively.
6-12 to the variable capacity diode 58.

The contacts 66 each have a corresponding relay driver 68-
1 to 68-12, and a shift register 70 is provided in the embodiment to cyclically drive this relay driver 68.

The shift register 70 is set by the initial reset circuit 72 so that cyclic selection is initiated from the relay driver 68-1 for the first channel 11,
Further, by supplying the signal of the clock circuit 73 from the AND gate 74, the driving signals for each of the relay drivers 68 can be sequentially shifted.

The other input of the AND gate 74 is supplied with a signal from the comparator 44 shown in FIG. 1j+L, the AND gate 74 is turned off.
Then, the shift of the shift register 70 is stopped, and the output of the variable oscillation circuit 50 selected at this time is fixed.

In the present invention, the variable carrier wave oscillation circuit 2
8 can also be arbitrarily configured by other components such as a phase-locked loop circuit.

As explained above, according to the present invention, the television receiver circuit 1
No matter what channel the 0 tunnel is, the monitor modulation circuit 24 performs the desired modulation action according to this preset channel, making it possible to switch between broadcast radio waves and monitor signals without any channel switching. shall be.

[Effects of the Invention] As described above, according to the present invention, even if the TV channel is in an arbitrary order, the monitor modulation circuit modulates the monitor signal according to the set chitunnel. Broadcast radio waves and monitor signals can be pasted together without the need for switching at all, and the troublesome switching process that results from using empty channels as in the past can be eliminated.

[Brief explanation of drawings]

FIG. 1 is a main block circuit diagram showing a preferred embodiment of a television monitor device according to the present invention, and FIG. 2 is a circuit diagram showing a preferred embodiment of the variable carrier oscillation circuit in FIG. 1. 10... Television receiver/multiplier circuit 14... Antenna selection switch 16... External video source 24... Monitor modulation circuit 26... Bit'0; A modulation circuit 28... Variable carrier wave oscillation circuit 32 ... Carrier wave selection circuit.

Claims (1)

[Claims] (1) In a television monitor device capable of switching between a broadcast wave input terminal and a monitor input terminal, a video modulation circuit modulates a monitor signal and supplies it to the monitor input terminal, and a video modulation circuit modulates a carrier wave signal of a selected frequency. A monitor modulation circuit having a variable carrier oscillation circuit that supplies a variable carrier wave to a carrier wave selection circuit that selects the carrier wave signal in which the difference frequency of .