JPS63311660A - Input/output circuit for electronic device - Google Patents

Abstract

PURPOSE:To cope with both 2-input connection and bridge connection by a simple circuit by switching an input impedance corresponding to each connecting state so as to share circuits even after an input circuit and succeeding circuits. CONSTITUTION:In turning off a changeover switch 13, two connection terminals 1, 2 are connected, a resistor R1 is disconnected fro a 1st connection terminal and a 2nd connection terminal 2 is disconnected from a 2nd input circuit 12. As a result, since a video signal inputted to the 1st connection terminal 1 is outputted as it is to the 2nd connection terminal 2, one is used as the input terminal and the other is used as an output terminal to cope with the bridge connection. The input impedance depends on the resistance R2 of the 1st input circuit 11. Thus, both the 2-input connection and the bridge connection are coped with by a simple circuit.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to input/output circuits for electronic devices having input/output terminals such as video terminals and audio terminals, and particularly relates to input/output circuits for electronic devices having input/output terminals such as video terminals and audio terminals. The present invention relates to input/output circuits for electronic devices capable of

[Summary of the Invention] The present invention provides an input/output circuit for an electronic device having input/output terminals such as a video terminal and an audio terminal. A first connection state is a two-person connection state in which the two connection terminals are operated as separate input terminals by switching control of the changeover switch; The connection terminal is shared by switching to the second connection state of the bridge connection state in which the input of the terminal is output to the other connection terminal, and the input impedance is switched corresponding to each connection state so that the input circuit and subsequent circuits are also shared. This makes it possible to support both two-person connection and bridge connection with a simple circuit.

[Prior Art] Conventionally, in video monitor televisions for security purposes, when displaying external video signals on a monitor, two video inputs are displayed in one system on one monitor television, and the other is in one system. In some cases, video signals were bridged to multiple monitor televisions and displayed simultaneously.

FIG. 4 is a conventional circuit diagram for two-person power connection in one system. This two-person power connection compatible circuit is configured by connecting the first connection terminal 1 to the first input circuit 3 and connecting the second connection terminal 2 to the second input circuit 4. These input circuits 3
．． The output terminals of 4 are connected and input to l-system buffer circuits 5. The first input circuit 3 consists of resistors R, , R and a capacitor CI, the resistor R1 is connected between the first connection terminal l and the ground, the resistor R1 and the capacitor C
I is connected in series, the l end is connected to the first connection terminal l, and the other end which is the output end is connected to the input point A of the buffer circuit 5. The second input circuit 4 includes resistors R, , R and a capacitor C2, and is configured in the same manner as described above, and its output terminal is connected to the input point A of the buffer circuit 5. In the above case, if signals are input from both the 1st and 2nd connection terminals, overlapping images and sounds can be obtained, but normally one of the two devices that manually inputs those signals is turned off. .

FIGS. 5(a) and 5(b) are circuit diagrams corresponding to conventional bridge connections. As shown in (a), in this bridge connection compatible circuit, the first connection terminal 6 and the second connection terminal 7 are connected,
These are configured to be input to a buffer circuit 9 via an input circuit 8.

1st. The input of the second connection terminal 6 is inputted to the input point B of the buffer circuit via the capacitor CIO of the input circuit 8,
Further, it is connected to ground via a 75Ω switch IO and a 75Ω resistor RIG connected in series for termination. In the above, the first connection terminal 6 is connected to a video signal output device as a video input terminal, and the second connection terminal 7 is connected to the first connection terminal of another monitor TV as a video output terminal, as shown in (b). is connected to the connection terminal 6' of
Thereafter, multiple monitor TVs are connected in a bridge manner in the same manner. At this time, since the input signal level is not attenuated, the input impedance of the input circuit of each television monitor must be large, and the input impedance of the video signal as a whole must be 75Ω. For this reason, each buffer circuit 9 employs an emitter follower with high input impedance, and a 75Ω switch is used only in the terminal TV monitor input circuit.
A high input impedance is provided by a 75Ω switch 10tl-OFFI, except when O is turned on and terminated by a 75Ω resistor R5.

Conventionally, the two-person connection and the bridge connection have been met by providing different input circuits.

[Problems to be solved by the invention] In the monitor television according to the above-mentioned conventional technology, there are two problems.
Since input circuits, buffer circuits, etc. are different between the manual connection and the bridge connection, it is difficult to combine them into one product and they are separate products. However, in recent years,
In order to appeal to users, there is a need for a low-cost monitor TV that can be used in any of these connection states.

In order to cope with the above, each TV monitor has two circuits, one for two-person connection shown in Figure 4 and the other for bridge connection shown in Figure 5 (a), and for example, the output C of one buffer circuit 5 and the other The output of the buffer circuit 9 can be changed over using a changeover switch and manually transmitted to the subsequent stage, but there is a problem in that the amount of connection terminals and circuits increases, which increases costs.

The present invention was devised in order to solve the above-mentioned problems, and an object thereof is to provide an input/output circuit for an electronic device that does not increase efficiency and is capable of supporting both two-person connection and bridge connection with a simple circuit. shall be.

[Means for Solving the Problems] The configuration of the input/output circuit of the electronic device of the present invention for achieving the above object includes a first connection terminal, a second connection terminal, and a changeover switch, The changeover switch is the first one. a first connection state in which the second connection terminals are respectively connected to separate input circuits;
The second connection terminal is connected to control switching between one of the input circuits and the connected second connection state, and the changeover switch changes the input impedance of the input circuit to the first and second connection terminals. It is characterized by switching in accordance with the second connection state.

[Function] The present invention provides a method for connecting two connection terminals to the first
The connection state is switched between the connection state of By switching the input circuit, the input circuit can be shared, and the subsequent buffer circuit can also be shared. By sharing the connection terminals and circuits, a simple input/output circuit corresponding to the first connection state and the second connection state can be realized without increasing costs.

[Example] Hereinafter, an example of the present invention will be described in detail based on the drawings.

FIG. 1 is an input/output circuit diagram showing one embodiment of the present invention.

This embodiment is applied to a video input/output circuit in a monitor television. Normally, a monitor television is equipped with an audio input/output circuit in addition to a video input/output circuit, but the same circuits can be used, with the only difference being the constants of some of the circuit elements. Since this input/output circuit is based on the conventional two-person connection circuit shown in FIG. 4, the same members will be described with the same reference numerals.

The video input/output circuit of this embodiment has a first connection terminal (VI
DEOIN)1 and the second connection terminal (VIDEOIN10
UT)2 and a first input circuit consisting of resistors R+, Rt and capacitor C1! 1, a second input circuit 12 consisting of resistors R3, R, and a capacitor C2, a changeover switch 13 for switching and controlling the connection state, and a buffer circuit 5.
Consists of etc.

Changeover switch! 3 has two circuit switching contacts T, ~Tll, and when it is slid to the ON side, only the contacts of TiT* and between the contacts of T and -T are turned on, and when it is slid to the OFF side, the 'rt- 'rs between contacts and T S
-T is turned on only between the contacts. This changeover switch 1
Each contact point of 3 is connected to each connection terminal 1.2 and input circuit 11.12 as follows to enable switching of the connection state and switching of impedance. Contact TI is resistor R
3, and the other end of the resistor R1 is connected to ground. A contact T is connected to a connection point between the first connection terminal l and one end of the capacitor CI. The contact T, together with the contact T4, is connected to the second connection terminal 2. Contact T is connected to a connection point between one end of resistor R3 and one end of capacitor C1.

In the first input circuit 11, the other end of the capacitor C1 is connected to one end of the resistor R1, and the other end of the resistor Rt is connected to the input point A of the buffer circuit 5. In the second input circuit, the other end of resistor R8 is connected to ground, and capacitor C
The other end of the resistor R4 is connected to one end of the resistor R4, and the other end of the resistor R6 is connected to the input point A of the buffer circuit 5 described above. Note that the resistor R2 and the capacitor CI may be arranged oppositely.

The same applies to resistor R4 and capacitor C2.

The buffer circuit 5 is composed of an npn type transistor Q1 and the like, and its emitter E serves as an input point A to which one ends of a resistor R6 and a Zener diode ZD are connected. The other ends of resistor R6 and Zener diode ZD are each connected to ground. The collector C of the transistor Q is connected to the +Vcc power supply via a resistor R6, and serves as an output point to the subsequent circuit. The base B of the transistor Q is connected to the connection point of resistors Rt and R* connected in series between the +Vcc'ti source and ground, and further connected to the other end of a capacitor C8 whose one end is connected to ground.

The operation of the embodiment with the above configuration will be described. When the selector switch 13 is turned ON in the input/output circuit shown in FIG. 1, the resistor R1 is connected to the connection point between the first connection terminal l and the capacitor C3,
The second connection terminal 2 is connected to the connection point between the resistor R3 and the capacitor C2 of the second input circuit I2, resulting in the same circuit configuration as the conventional two-person connection compatible circuit shown in FIG. Each connection terminal will be operated as an input terminal, but the input impedance Z of the first connection terminal I and the input impedance Zt of the second connection terminal 2 are different from each other when the input point A of the buffer circuit 5 is an AC input terminal. Since it is grounded when viewed from the ground, it can be determined from the formula.

Generally, in order to match signal reception and reception between devices, the value and range of human impedance are determined, for example, 75Ω for video signals, and 47Ω or more for audio signals. Therefore, to give an example in the embodiment, RI.

If R, = 91Ω and R1, R4 = 470Ω, an input impedance of 76.2Ω, which is close to 75Ω, is obtained. In addition, when applied to an audio signal input/output circuit, R,
, R3=470 and Ω, R, , R, -68, then
An input impedance of Ω or more is obtained at 47 (Ω at 59).

Next, when the selector switch 13 shown in Fig. 1 is set to the OFF side, the 2
At the same time when the two connecting terminals 1.2 are connected, the resistor R8 is disconnected from the first connecting terminal l, as shown in the equivalent circuit of FIG. 2, and the second connecting terminal 2 is connected to the second input circuit 12. be separated. As a result, the video signal input to the first connection terminal l is output as is to the second connection terminal 2, so by using one of them as an input terminal and the other as an output terminal, a bridge connection can be achieved. becomes possible. The human power impedance at this time is determined by the value of the resistor R2 of the first input circuit 11.

FIG. 3 shows an equivalent circuit of the bridge connection of the video input/output circuit. In this example, three video monitors are connected in a bridge manner, and the input impedance of the first and second video monitors is increased by setting the changeover switches of the first and second video monitors to the OFF side. In the example described above, the input impedance is 470Ω. The third monitor TV is at the end, so turn the selector switch on.
The input impedance for the N side is 75Ω (76.2Ω in the above example). In the case of bridge connection, each input impedance is connected in parallel, so the input impedance decreases depending on the number of connected devices. In order to increase the number of devices connected in this bridge connection, the input impedance of the monitor TV other than the terminal should be as large as possible. −
For example, in the circuit shown in Figure 1, Rt and R4 are I
It is also possible to use a combination such as increasing MΩ and setting R3 and Rs to 75Ω.

As described above, the changeover switch can also serve as a 75Ω switch. Alternatively, a changeover switch having four circuits of switching contacts may be used, two of which are used for the bidet output circuit, and the remaining two circuits are used for the audio input/output circuit.

Note that the input circuit and buffer circuit in the above embodiment are merely examples, and other circuits having equivalent functions can be used, and various types of changeover switches can also be used. As described above, the present invention can be applied and implemented in various ways in accordance with its gist.

[Effects of the Invention] As is clear from the above description, the input/output circuit of the electronic device of the present invention provides the following effects.

(1) By minimizing the number of connection terminals to two and sharing input circuits, buffer circuits, etc., it is possible to support both two-person connection and bridge connection with a simple circuit.

(2) One model can perform two-person connection and bridge connection, reducing the number of product types and making manufacturing and sales management easier.

[Brief explanation of drawings]

Fig. 1 is an input/output circuit diagram showing an embodiment of the present invention, Fig. 2 is an equivalent circuit diagram of the input/output circuit when the changeover switch is OFF, Fig. 3 is an equivalent circuit diagram of a bridge connection, and Fig. 4 is a conventional circuit diagram. Figures 5(a) and 5(b) are circuit diagrams for conventional bridge connections. ! ...First connection terminal, 2...Second connection terminal, 1
1.12... Input circuit, 13... Selector switch. Go 1 Shishi Itsu 7 OFF Gin's Output Circuit 0 Go 1 West Roo Genealogy (Switch 0 FF 1 [Switch OFF +
+ Zubutsu 7 ON) F) Hangeo C afternoon table 1 rib concave evening figure Figure 3 Conventional 2 people 77 losses 0 χ capital figure 4? (b) The 5th flash is much different from the conventional 7 diameter brush.

Claims (1)

[Scope of Claims] A first connection terminal, a second connection terminal, and a changeover switch, the changeover switch having a first connection terminal and a second connection terminal connected to separate input circuits, respectively. 1 connection state, and the first,
A second connection terminal is connected to a second connection state in which the input circuit is connected to one of the input circuits, and the changeover switch changes the input impedance of the input circuit to the first and second connection states. An input/output circuit for an electronic device characterized by adaptive switching.