JPH0738886A - Cable characteristic compensating circuit - Google Patents

Abstract

PURPOSE:To compensate the attenuation quantity of a video signal of R, G, and B according to the length of a cable even when the cable is extended round long by switching ranges according to the length of the cable. CONSTITUTION:A D/A converter 52 outputs a 2-bit switching signal and supplies it to a decoder 6. The decoder 6 decodes the output and supplies a range switching signal to a low-frequency range switching circuit 7 and a high-frequency range switching circuit 8. The circuit 7 switches compensation characteristics of the frequency of nearly 8MHz of a frequency characteristic compensating circuit 9 according to the range of the cable length. The circuit 8 switches compensation characteristics of the frequency of about 20-50MHz of the circuit 9 according to the range of the cable length. The circuit 9 compensates frequency characteristics of the video signal of R, G, and B according to the switching of the circuits 7 and 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cable characteristic compensating circuit, and more particularly to a cable characteristic compensating circuit for compensating the attenuation amount of an RGB video signal attenuated by a signal cable and adjusting the frequency characteristic.

[0002]

2. Description of the Related Art In dealing systems of banks and communication companies, a large number of color monitors are arranged to display various information. In such a dealing system, as shown in FIG. 3, the signal source 1 includes the color monitors 21 to 24 and 3 respectively.
Often installed at a distance from 1-34,
In some cases, a coaxial cable of 200 m may be routed.

[0003]

As described above, when the coaxial cable is routed for 200 m, the attenuation amount of the RGB video signal becomes extremely large as shown in FIG. 4 (a).
As shown in FIG. 4B, the amount of amplitude attenuation increases in proportion to the length of the cable.

Further, in recent years, the resolution of color monitors used in dealing systems has been improved, and the frequency band of video signals is high, and there is a problem that the amount of attenuation increases when the cable is routed. .

Therefore, a main object of the present invention is to provide a cable characteristic compensating circuit capable of compensating the attenuation amount of RGB video signals according to the cable length even when a long cable is routed. That is.

[0006]

SUMMARY OF THE INVENTION The present invention is a cable characteristic compensating circuit for compensating an RGB signal attenuated by the length of a cable, and a range selector switch for switching the range according to the length of the cable. , For compensating the attenuation according to the length of the cable provided for each of the RGB signals, and for switching the high frequency characteristics of the compensating circuit according to the range switched by the range selector switch The high frequency characteristic switching circuit and the low frequency characteristic switching circuit for switching the low frequency characteristic of the compensation circuit according to the range switched by the range switch.

[0007]

In the cable characteristic compensating circuit according to the present invention, the range is switched according to the length of the cable, and the high frequency characteristic and the low frequency characteristic are switched according to the switched range to change the cable length. Compensate for the corresponding attenuation.

[0008]

1 is a block diagram of an embodiment of the present invention. In FIG. 1, a switch 4 is for switching the range according to the cable length, for example, range 1: 0 to 20 m, range 2:20 to 80 m, range 3:
The range of 80 to 140 m and range 4: 140 to 200 m can be switched, and the compensation amount can be selected according to the cable length. The control circuit 5 includes a microcomputer 51 and a D / A converter 52. In response to a command from the switch 4, the microcomputer 51 sends data so that the D / A converter 52 outputs a 2-bit switching signal corresponding to each range. The D / A converter 52 outputs a 2-bit switching signal and supplies it to the decoder 6. The decoder 6 decodes the output and gives a range switching signal to the low frequency range switching circuit 7 and the high frequency range switching circuit 8. The low frequency range switching circuit 7 is 8 MHz of the frequency characteristic correction circuit 9.
The compensation characteristics of the frequency around z (part on the screen, which looks like a sag or a tail) are switched according to the range of the cable length. The high frequency range switching circuit 8 switches the compensation characteristic of the frequency (the component relating to the rise and fall of one dot on the screen, especially in the vicinity of 20 to 50 MHz) of the frequency characteristic correction circuit 9 in accordance with the cable length range. The frequency characteristic correction circuit 9 compensates the input RGB video signal for the frequency characteristic according to the switching of the low frequency range switching circuit 7 and the high frequency range switching circuit 8.

FIG. 2 shows the frequency characteristic correction circuit 9 shown in FIG.
It is a concrete circuit diagram of. In FIG. 2, only the portion for compensating the R video signal is shown, but a similar circuit is provided for the G and B video signals.

In FIG. 2, transistors Tr1 and Tr
2 constitutes a frequency characteristic correction circuit 9 including an emitter peaking circuit, transistors Tr3 to Tr5 constitute a low frequency range switching circuit 7, and transistor Tr3
6 to Tr8 and Tr9 to Tr11 configure a high frequency range switching circuit 8. The CR circuit 10 is connected between the emitter of the transistor Tr1 and the ground, and the transistor Tr2 is connected.
By inserting the CR circuit 11 between the emitter of and the power source, it is possible to compensate for the attenuation amount in the high frequency range,
A capacitor C is connected between the emitter of the transistor Tr1 and the ground.
By inserting 1, it is possible to compensate for the attenuation in the low frequency range. Therefore, one end of the capacitor C1 is connected to the emitter of the transistor Tr1, and the other end of the capacitor C1 is connected to the collector of the transistor Tr3 and the resistor R1.
Through the collector of the transistor Tr4 and the resistor R4
Connected to the collector of the transistor Tr5 via
The emitters of the transistors Tr3 to Tr5 are grounded, and the switching signals s4 to s6 are given to the respective bases. Note that the resistance is selected as R4> R3, the switching signals s4 to s6 are not given in the range 1, the switching signal s4 becomes the “H” level in the range 2, and the transistor Tr3 becomes conductive.
The other end of the capacitor C1 is grounded. In the range 3, the switching signal s5 becomes the “H” level, the transistor Tr4 becomes conductive, the other end of the capacitor C1 is grounded through the resistor R3, and in the range 4, the switching signal s6 becomes the “H” level and the transistor Tr5. Are conducted, and the other end of the capacitor C1 is grounded via the resistor R4. The smaller the resistance value connected to the other end of the capacitor C1, the greater the compensation of the attenuation amount in the low frequency range.

On the other hand, in the high frequency range switching circuit 8,
By inserting resistors between the CR circuit 10 and the ground and between the CR circuit 11 and the power supply, the attenuation of high frequency is compensated. That is, the other end of the CR circuit 10 is connected to the collector of the transistor Tr6, the collector of the transistor Tr7 via the resistor R5, and the transistor T via the resistor R6.
connected to the collector of r8, these transistors T
The emitters of r6 to Tr8 are grounded. Transistor T
The switching signal s4 is applied to the base of r6, the switching signal s5 is applied to the base of the transistor Tr7, and the switching signal s6 is applied to the base of the transistor Tr8.
The resistance is selected such that R6> R5. Furthermore, CR
The circuit 11 includes a collector of the transistor Tr9 and a resistor R7.
Through the collector of the transistor Tr10 and the resistor R8
Is connected to the collector of the transistor Tr11 via. The emitters of these transistors Tr9 to Tr11 are connected to the power supply + V, the switching signal s1 is supplied to the base of the transistor Tr9, the switching signal s2 is supplied to the base of the transistor Tr10, and the transistor Tr1 is supplied.
The switching signal s3 is given to the base of 1. The resistor R8> R7 is selected.

The switching signals s1, s2 and s3 are inversion signals of the switching signals s4, s5 and s6.

In the cable compensating circuit configured as described above, when the range 1 is selected by the switch 4 shown in FIG. 1, the switching signals s1 to s3 all become "H" level and the switching signals s4 to s6. Becomes the "L" level. Therefore, none of the transistors Tr3 to Tr11 is conductive, the video signal of R is input to the base of the transistor Tr1 via the resistor R1, and the collector of the transistor Tr1 is further connected to the transistor T2 via the resistor R2.
It is input to the base of r2. And the transistor Tr
The R video signal is output from the second collector, and the frequency characteristic is not compensated.

Next, when the range 2 is selected, the switching signal s3 becomes "L" level and the switching signal s6 becomes "H" level. Therefore, the transistors Tr5, Tr8, and Tr11
Conducts. As a result, a series circuit of the capacitor C1 and the resistor R4 is inserted between the emitter of the transistor Tr1 and the ground, and the CR circuit 10 is grounded via the resistor R6. Further, the CR circuit 11 is connected between the transistor Tr2 and the power supply via the resistor R8. Capacitor C1
And the resistor R4 compensate for low frequency attenuation, and C
The R circuit 10 and the resistor R6 and the CR circuit 11 and the resistor R8 compensate the attenuation of the high frequency.

Next, when the range 3 is selected, the switching signal s2
Becomes "L" level, and the switching signal s5 becomes "H" level. Accordingly, the transistors Tr4, Tr7 and Tr10 are
Conducts. As a result, a series circuit of the capacitor C1 and the resistor R3 is inserted between the emitter of the transistor Tr1 and the ground, and the CR circuit 10 is grounded via the resistor R5.
The CR circuit 11 is connected to the power supply + V via the resistor R7. The resistors R3, R5 and R7 are respectively resistors R4, R6 and
Since the value is selected to be smaller than that of R8, the amount of compensation due to the attenuation of the low frequency and the high frequency is larger than that of range 2.

Further, when the range 4 is selected, the switching signal s1 becomes "L" level and the switching signal s4 becomes "H" level. Accordingly, the transistors Tr3, Tr6, and Tr
9 is conducted. As a result, the capacitor C1 is inserted between the emitter of the transistor Tr1 and the ground, the CR circuit 10 is grounded, and the CR circuit 11 is connected to the power supply + V. As described above, the capacitor C1 and the CR circuit 10 are directly grounded, and the CR circuit 11 is directly connected to the power source + V, so that the compensation amount of the attenuation of the low frequency and the high frequency becomes larger than that in the range 3. . Therefore, it is possible to adjust the attenuation amount of the low frequency and the high frequency according to the length of the cable.

[0017]

As described above, according to the present invention, the range is switched according to the length of the cable, and the high frequency characteristic and the low frequency characteristic of the compensation circuit are switched according to the range. Therefore, the attenuation of the RGB signals can be compensated according to the length of the cable.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is an electric circuit diagram of the frequency characteristic correction circuit shown in FIG.

FIG. 3 is a diagram showing an outline of a conventional dealing system.

FIG. 4 is a diagram showing frequency vs. amplitude attenuation and cable length vs. amplitude attenuation.

[Explanation of symbols]

 4 switch 5 control circuit 6 decoder 7 low frequency range switching circuit 8 high frequency range switching circuit 9 frequency characteristic correction circuit 10, 11 CR circuit 51 microcomputer 52 D / A converter R1 to R8 resistance C1 capacitor Tr1 to Tr11 transistor

Claims (1)

[Claims] 1. RGB that attenuates according to cable length
A cable characteristic compensating circuit for compensating a signal, comprising a range selector switch for switching a range according to the length of the cable, provided corresponding to each of the RGB signals, and depending on the length of the cable. A compensation circuit for compensating for the attenuation by means of a range switching switch, and a high frequency characteristic switching means for switching the high frequency characteristic of the compensation circuit according to the range switched by the range switching switch, and the range switching switch. A cable characteristic compensation circuit comprising a low frequency characteristic switching circuit for switching the low frequency characteristic of the compensation circuit according to the range.