JPS6188670A - Input selector for information signal - Google Patents

Abstract

PURPOSE:To obtain an input selector for an information signal with high reliability by detecting purely electrically the presence or absence of an input of an external information signal so as to control automatically a switching means. CONSTITUTION:An input switching device 10 is provided to a receiver 1. A broadcast signal from an antenna 9 is fed to an internal information signal source 12 and its output video signals is fed to a video signal processing circuit 13 via a switching means 11. An internal information signal source 12 has a tuner and a video intermediate frequency amplifier circuit. A VTR2 is provided with a video signal source 51, which supplies a signal to an output terminal 53 via an impedance converting circuit 52. A control circuit 20 for input selection consists of a current source 30 and a comparator 40. When a coaxial cable 55 is not connected between the terminals 53 and 3, the relation of R4>>R2 exists and a terminal (b) of a switching means 11 is selected by a control voltage VC. When the coaxial cable 55 is connected between the terminals 53 and 3, the switching means 11 is thrown to the position (a).

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a television receiver -? The present invention relates to an information signal input selection device suitable for application to video equipment such as a VTR.

[Conventional technology]

In recent years, with the advancement of electronic technology, television receivers and VTRs
, a large number of video devices such as video cameras, video discs, and personal computers are on the market, but in order to enable the reception of video information signals between these video devices, each video device has an external information signal. The receiver is usually provided with an external input terminal.

For example, as shown in FIG. 2 or 3, an external input terminal (3) for external information signals is provided on the front panel of a television receiver (1) or VTR+2. In this case, it is necessary to switch between the external information signal and the internal information signal, and it is conceivable to provide a changeover switch (4) as shown in FIGS. 2 and 3 as the switching means.

However, when such a changeover switch (4) is turned on, the changeover switch (43'f
In addition to being on the open side, there are also problems such as forgetting the switching operation.

To eliminate these drawbacks, 1. For example, use an external manual terminal (3
) The human power signal source may be configured to be automatically switched in relation to a plug or connector for an external information signal inserted into the external information signal. For example, as shown in Fig. 4, if a changeover switch (8) is provided inside the jack into which the plug (6) is inserted, and this is controlled by the plug pin (6A), the input signal source can be automatically changed. Can be switched.

[Problem that the invention seeks to solve]

By the way, when providing 644-type detection means such as a changeover switch inside the jack (7) as the external input terminal (3), the shape of the jack (force) becomes thick (and the existing jack cannot be used). Furthermore, since it is a mechanical detection means, it has short lifespan and lacks reliability.

Furthermore, it is difficult to provide mechanical detection means in BNC type or multi-axis type connectors, and the number of connectors to be used tends to be limited.

This idea solves these conventional problems,
This paper proposes a long-life, highly reliable information signal input selection device that can use existing connectors, etc. as is, by automatically determining whether a human-powered signal source is wired or not. .

[Means for solving problems]

In order to solve the above-mentioned problems, in the present invention, as shown in FIG. A control circuit (2+11) is provided to control the switching means till depending on the presence or absence of an information signal.

A control circuit (2 (j) is a current source (311) that supplies an alternating current to an external input terminal, and a comparator (4 (# and The threshold value eb is ′#
The voltage prevailing across resistor R3 connected to the L current source is utilized.

[Effect]

When there is no external inn multiplied signal, the AC voltage ea applied to input terminal (3) K becomes the voltage of the resistor R20 + 41,
Let this voltage be eao. When the external information signal No. 1g is supplied, it is approximately determined by the current flowing through the resistors R1 and R2, and when s"1"=9R2, it becomes % of the AC voltage eao obtained when there is no external information signal. Let this voltage be eac. This AC voltage ea also appears at the connection point q, so the threshold value (comparison reference voltage) eb is expressed as eac < eb < 6ao...@(
Set to 1).

Therefore, the switching means aυ is switched to the terminal a side by the comparison output obtained when eb>esc, that is, the control output Vc.

〔Example〕

FIG. 1 shows an information signal input selection device (11) according to the present invention.
FIG. 2 is a connection diagram showing an example, in which a television receiver is used as a first video device, a VTR is shown as a second video device, and an input switching device according to the present invention is installed on the receiver (1) side. This shows the case where ul is provided.

Therefore, the broadcast signal fed from the antenna is supplied to the internal information signal source 11a, and the output video 11! The signal is connected to the video signal processing circuit (
13. The internal information signal source 113 is a tuner,
It has an optical intermediate frequency amplification circuit.

The VTR (2) is provided with a video signal source 6υ, and a reproduced video signal obtained from this is supplied to an impedance conversion circuit via a DC cut capacitor C1.

This impedance conversion circuit 521 has a transistor Ql for impedance conversion, and its output is a capacitor C2 for DC cut and an output.

Output terminal o via resistor R1 for impedance determination
, ll. The resistance value of resistor R1 is 75Ω.

This output terminal (531) and the external input terminal (3) provided on the receiver (1) are connected by a coaxial cable. The impedance conversion circuit 12υ is configured in the same manner as described above, and the emitter output of the transistor Q2 for determining impedance is supplied to the a terminal of the switching means (l117). Will be done.・
Note that the low-pass filter (221) provided in this impedance conversion circuit (211) allows only the reproduced video signal supplied to the input terminal (3) to pass through, and as will be described later, is used to detect the presence or absence of external input applied to point A. AC signal e
This is for bypassing A.

Control circuit for input selection (the edge is a current source (to) and a comparator (4)
The current source has a current mirror configuration as shown in the figure. The current source (to) has three transistors Q3 to Qs, the bases of which are connected in common, and the respective emitters of which are connected in common to the power source (3).
41. Transistor Q3 with diode function
AC voltage #Gυ, resistor 04, and power supply port are connected to the collector of . The frequency of the AC voltage source 6υ is selected to be an arbitrary frequency outside the frequency band of the video signal, for example 5.9 AdHz. In addition, the collector of the transistor Q4 is grounded via the resistor R3, and the AC voltage eb generated across the resistor R3 via the DC cut capacitor Cz 'a' is connected to the a terminal of the comparator (41). Supplied.

4fiK,) The collector of transistor Q5 is resistor R4.
It is grounded through the bandpass filter (3511) which allows only the AC signal e3 to pass through and is supplied to the b terminal of the comparator (40).The connection point q connected to the resistor R4 is connected to the capacitor C4. Input terminal (3) through
connected to.

This current mirror configuration of the current source (30) makes the collector currents 11 of the transistors Q4, Qs equal, and by providing the alternating voltage source Gl+, the collector current Il is modulated by its alternating frequency. Therefore, the collector current (1) becomes an alternating current signal. Furthermore, the AC component 11 of the collector current Il of the transistor Qli is passed through the terminating resistor (2) via the capacitor 04.
Therefore, a predetermined voltage ea is generated across the resistor R2.

Now, if the selection is made as follows, the input selection operation will be as follows.

First, if there is no connection between terminals 5 and 31 (like a coaxial cable), R4>>R2, so resistor R
The alternating current voltage obtained across the resistor R2, that is, the voltage obtained at the connection point q, is eaO, and eao ``''R2・'r''...(3) Also, the main alternating current voltage eb obtained across the resistor R3 is , the alternating current flowing through them is the same (because it is il, eb -= Ra ・it ・=・f4), and since R2>R3, eao > eb ..." f5)
becomes. The b terminal of the switching means 0υ is selected by the control output Vc of 'θ'' obtained at this time.

On the other hand, coaxial cable 0!Il between terminals M and (31)
When V T Ri2) is connected and V T Ri2) is in operation, the alternating current component 11 of the collector current line 1 of transistor Qs flows to resistor R2 and is connected to V T R (2) via the coaxial cable. Since the current also flows through the resistor R1, the parallel combined resistance value at point A becomes A, and as a result, the AC voltage eaC at point A becomes 2 eao.

Therefore, the AC voltage eao at the connection point is also Cao, and eac < eb (6
), the control output Vc is inverted to 1''.

As a result, the switching means tin is switched as shown, and the reproduced video signal, which is the external information signal, is automatically selected.

In addition, if the video signal is not supplied to the terminal (3) side even though the coaxial cable (G) is connected,
It is also possible that the switching means (1υ is switched to the terminal side, but in this case, the impedance conversion circuit 6 of the VTR12) is operating, so the above-mentioned AC component 11 is connected to the resistor Rt1itIIK17fE Therefore, the relationship in equation (6) always holds true.

Therefore, the control output Vc is not inverted again, and the switching means (old) maintains the switching state shown.

If the external information signal to be handled is not a composite color video signal as described above but a primary color signal of R, G, and H, three or more external input terminals are provided, so the present invention can be applied to such a device. In application, each input terminal is provided with the above-mentioned input selection device OI, or alternatively this input selection device OI is provided on the side of one input terminal, and the switching means 01 provided at the output of the three input terminals. should be controlled at the same time.

If an alternating current source is used instead of the alternating voltage source Gυ, the resistor 0) and the electric gap are not required.

The video equipment to which this invention can be applied is not limited to the video equipment of the embodiment.

〔Effect of the invention〕

As explained above, according to the present invention, the switching means (I
Since υ can be automatically controlled, the reliability of manual selection is high, and since no mechanical detection means are used, the lifespan is short.

Furthermore, since existing connectors can be used as external input terminals, the present invention can be applied to these connectors regardless of their types, providing a variety of effects that cannot be obtained with conventional methods, such as greater versatility. Obtainable.

Therefore, the present invention is extremely suitable for application to input selection devices for various video equipment as mentioned at the beginning.

[Brief explanation of drawings]

FIG. 1 is a connection diagram showing an example of an information signal input selection device according to the present invention, FIGS. 2 and 3 are diagrams showing an example of a video (#! device), and FIG. 4 is a configuration showing an example of a connector. It is a diagram. OI is an input selection device, (21j is a control circuit, circle is a current source, (4 (I is a comparator, +10 is a switching means, (3
) is external input terminal, - is coaxial cable, 6a, 12
1 is an impedance conversion circuit. bl col mouse ■... AJ =

Claims (1)

[Claims] an external input terminal to which a video information signal is supplied; a switching means for switching between the external information signal and the internal information signal supplied to the external input terminal; and controlling the switching means depending on the presence or absence of the external information signal. The control circuit includes a current source that supplies an alternating current to the external input terminal, and a comparator that compares the amplitude of the alternating current voltage generated by the alternating current with a predetermined threshold. An information signal input selection device configured such that the switching means is switched to the external information signal side by the output of the comparator obtained when the external information signal is supplied to the external input terminal.