JP2580770B2 - Switching circuit of signal coupling device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching circuit of a signal coupling device which converts a signal level of a signal transmission line for distribution automation and transfers it to a relay device.

[Prior Art] FIG. 1 shows an example of application of a signal coupling device.

In FIG. 1, a signal coupling device 1 is a device that is installed in a substation 2, converts a signal level input from a transmission line 3 for distribution, and transfers the signal level to a relay device 4 for transmission to a higher order.

In this case, the change width of the signal on the transmission line for distribution is largely different from the change width of the input to the relay device. Therefore, conventionally, a switching circuit is provided in the signal coupling device to perform level conversion.

FIG. 2 shows the configuration of a conventional switching circuit, and FIG. 3 shows its operation characteristics.

In FIG. 2, a signal input to an input terminal 5 passes through a band-pass filter 6 and is applied to a first switching circuit 7 and level detection circuits 13 and 14.

The detection level of the level detection circuit 13 is L ₁ , the level detection circuit
The detection level of 14 is L ₂ and L ₁ <L ₂ .

The outputs of the level detection circuits 13 and 14 are applied to a switching determination circuit 15, and the switching determination circuit 15 determines whether switching is necessary or not according to input conditions.

As a result, when it is determined that switching is necessary, a switching command is issued to the switching circuits 7 and 10.

By the operation of the switching circuits 7 and 10, the resistance attenuation circuit (L) 8
Is switched to the resistance attenuation circuit (H) 9.

The resistance decay circuit (H) 9 is higher than the resistance decay circuit (L) 8
It is assumed that the KdB attenuation is large.

The signal input to the switching circuit 7 passes through the resistance attenuation circuit (8 or 9) and the switching circuit 10 on the selected side and passes through the amplifier 11
Join.

 The output of the amplifier 11 is output to an output terminal 12.

 FIG. 3 shows the input / output characteristics of the switching circuit.

In FIG. 3, L ₀ is the level when there is no input signal, and is usually equal to the level of input noise.

The signal is an input level rises inputted, between L ₀ ~L _2, the input and output are in a proportional relationship.

It exceeds L ₂ the input signal is increased, the switching operation is performed, the resistance attenuation circuit the resistor attenuating circuit (L) 8 (H)
9 and the output drops by KdB.

As a result, the output and input between the input signals L ₂ ~L ₃ proportional relationship is maintained.

Furthermore, the end signal transmission, the signal of the level of the input signal is lower than L ₁ level detection circuit 13, the switching circuit 7 and 10 is restored switching determination circuit 15 is operated, a resistor attenuating circuit (H) 9 The mode is switched to the resistance attenuation circuit (L) 8.

The two levels L ₁ and L ₂ are provided to prevent the hunting operation near the switching by giving the switching characteristic a hysteresis characteristic.

[Problem to be Solved by the Invention] In the conventional method, only the level of the input signal is focused on as a condition for the switching determination. Therefore, when the level of the input signal fluctuates, the switching operation may be performed in the middle of the received information. there were.

When the switching operation is performed, the output signal suddenly drops by KdB, so that the demodulation circuit on the repeater side cannot respond,
In some cases, missing information bits occurred.

 FIG. 4 shows a demodulation circuit and operation waveforms on the relay device side.

In FIG. 4, the input terminal 16 receives the output signal of the signal combiner. The input signal passes through the reception filter 17, is demodulated by the demodulation circuit 18, and is output to the output terminal 19.

(A) shows an input waveform, which is a modulated signal. If the switching operation is performed in the middle of the signal, the level decreases by KdB.

(B) is a demodulated output signal, which is usually a pulse train of a binary code. When a sudden change occurs in the input signal due to the switching operation, bit loss may occur as shown in FIG.

The number of missing bits varies depending on the transmission speed, but the transmission speed (several hundred bits /
Seconds), the number of missing bits is within 1 bit.

As described above, when one information bit is lost, there is a case where the information bit is affected and a case where the information bit is not affected.

The effect of missing one information bit will be described with reference to FIG.

FIG. 5 shows a configuration example of the transmission format, which is divided into the following three parts.

First, the bit synchronization is information for synchronizing a sampling pulse for reading a demodulated signal. Even if one bit is missing, there is no problem in reading the information.

The frame synchronization is a signal for detecting the head of information. Usually, the first and last bits are 1 and the remaining bits are all 0.

Therefore, when one bit is lost, the frame synchronization information cannot be read normally.

Next, when one bit is lost in the data portion, it can be corrected by employing a CRC correction code or the like, but is added last.

If the parity bit is missing, information cannot be read normally.

In this way, the effect of the one bit loss depends on where in the information occurs.

Further, the 1-bit missing occurs, there signal level in the vicinity of the detection level L _2, for generating at the moment of exceeding the L _2, the degree of variation of the signal level, timing that occurs is quite random .

As described above, in the conventional method, since it is uncertain in which part of the information the switching operation occurs, there has been a drawback that the information cannot be read correctly depending on the timing of the occurrence.

"Means for Solving the Problems" The present invention has solved the drawbacks of the prior art by detecting not only the level detection condition but also the rising characteristic of an input signal as a condition for switching determination.

[Operation] As a result, the switching operation is always performed in the middle of the bit synchronization information, and even if one bit is lost, the information can always be read normally.

[Embodiment] FIG. 6 shows an embodiment of the switching circuit of the signal coupling device according to the present invention.

 FIG. 7 is a waveform diagram for explaining the operation.

6, the same numbers as those in the conventional method of FIG. 2 have the same functions.

 The newly added one is the sampling circuit 20.

In FIG. 7, the output of the reception filter 6 is applied to the level detection circuits 13 and 14, and the switching circuit 7.

The output of the level detection circuit 13 is supplied to the sampling circuit 20 and
It is added to the switching determination circuit 15.

When there is an input signal, the sampling circuit 20 generates a sampling pulse P after a predetermined time t.

The switching determination circuit 15 outputs a switching signal to the switching circuits 7 and 10 when there is an output of the level detection circuit 14 when the sampling pulse P is input.

When the input signal is lost and the output of the level detection circuit 13 is lost, the output of the switching determination circuit 15 is lost and the switching circuits 7 and 10 return.

The time t until the level detection circuit 13 operates and the sampling pulse P is generated is selected so as to be performed in the middle of the bit synchronization pulse.

[Effect of the Invention] By employing the switching circuit of the signal coupling device according to the present invention, the switching operation is always performed in the middle of the bit synchronization, so that even if one bit is lost, the reading of the information is not mistaken. .

Signal level rising portion of the always signal when sufficiently greater than L _2, that is, switching operation in the middle of the bit synchronization is performed.

Further, when the signal level is near L ₂ is the output conditions of the level detection circuit 14 at the sampling point,
Since the necessity of the switching operation is determined, the frame synchronization and the switching operation in the data portion are eliminated, and the information can be accurately read, and the reliability is greatly improved.

[Brief description of the drawings]

FIG. 1 shows an application example of a signal coupling device, and FIG. 2 is a diagram showing a switching circuit of a conventional signal coupling device. FIG. 3 is a diagram for explaining the operation of FIG. FIG. 4 is a diagram showing a configuration of a demodulation circuit and input / output waveforms of the relay device, and FIG. 5 is a diagram showing a transmission format of information. FIG. 6 shows an embodiment of the present invention, and FIG. 7 is a diagram for explaining the operation of FIG. 1 .... Signal coupling device, 2 .... Substation, 3 .... Distribution transmission line, 4 .... Signal relay device, 5 .... Input terminal, 6 .... Hand pass filter, 7.10. ... switching circuit, 8... the resistance attenuation circuit (L), 9... the resistance attenuation circuit (H), 11... amplifier, 12... output terminal, 13... the level detection circuit (L ₁₎ , 14 ........ Level detection circuit (L ₂ ), 15 ... Switching judgment circuit, 16 ... Input terminal, 17 ......... Reception filter, 1
8. Demodulation circuit, 19. Output terminal, 20 Sampling circuit.

Claims (1)

(57) [Claims] 1. A level L _{1 of} an input signal received from a transmission line and configured in the order of bit synchronization, frame synchronization, and data.
First and second level detecting circuits for detecting L ₂ (L ₁ <L ₂ ), detecting outputs of the first level detecting circuit, and generating a sampling pulse within a bit synchronization duration of an input signal. A sampling circuit, a switching determination circuit that receives the outputs of the sampling circuit and the first and second level detection circuits as inputs, two sets of attenuating circuits for attenuating the signal, and a switching circuit that selects one of the two sets of attenuating circuits In the signal coupling device, the AND condition of the output of the second level detection circuit and the output of the sampling circuit is detected by the switching determination circuit to operate the switching circuit, and the disappearance of the output of the second level detection circuit is determined by the switching determination circuit. A switching circuit for a signal coupling device, wherein the switching is detected and the switching circuit is restored.