JPS59112730A - Alternating current branching circuit - Google Patents

Abstract

PURPOSE:To perform the stable AC branching of a two-wire circuit even when a large gain is provided by allowing a switch to connects an amplifier output in the direction of a circuit whose input is detected first and cuts off the output of an amplifier in the other direction. CONSTITUTION:When there is an input to a circuit M, a comparator CMP circuit 4a generates an output and a control circuit 6 registers its state in its internal memory and also turns on the switch SW5a to send out the output of an amplifier 2a to circuits S1 and S2. At this time, it is informed that a CMP circuit 4b also generates an output, but the circuit M is judged to be first, so an SW5b is not turned on to disconnect the path including an amplifier 2b; and there is no stray input to a hybrid circuit 1a, so that no oscillation occurs even when the gain of the amplifier 2a is large. The contents of the memory registered by the circuit 6 are reset when the input to the circuit M is ceased and input from a new circuit is held in readiness.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an AC branch circuit, and particularly to an AC branch circuit that can suppress unstable phenomena such as oscillation caused by providing a gain for line loss compensation. It is.

[Prior art]

AC branch circuits are used to condense multiple lines into one line, and there are three types of AC branch circuits: those that use a transformer itself, those that use resistance division, and those that use amplifiers. In the first two of these, the output is branched from the input via the passive element, so the energy only decreases and oscillation does not occur.

On the other hand, in the case of a two-wire type, oscillation occurs due to input from the hybrid depending on how the gain is determined in a type with an amplifier. For this reason, methods have been taken such as lowering the gain of the amplifier or adjusting the hybrid to reduce the interference. Furthermore, if a sufficient gain is provided, oscillation is likely to occur even if the hybrid is adjusted, which makes it difficult to significantly compensate for line loss in a two-wire system.
1 is a block diagram of a conventional AC branch circuit for a two-wire line, and FIG. 2 is a block diagram of a hybrid circuit used in FIG. 1.

In FIG. 1, N 1 a+ 1 b+ l c is a hybrid circuit, 2a and 2b are amplifiers, and the convex portion is an adder circuit T.

be. The input from the line M of the AC branch circuit is amplified by the amplifier 2a from the hybrid circuit 1a, passes through the hybrid circuit 1 b r 1 c, and is output to the circuit iS 1.82. On the other hand, the input from the MSI is the hybrid circuit 1
After passing through b, the signal is added to the input of line S2 by addition circuit 3, enters amplifier 2b, is amplified here, and is output to line M through hybrid circuit 1a. Here, the ideal operation of the hybrid circuit 1a is to transmit the output of the amplifier 2b only to the line M and not to the amplifier 2a, but in reality, leakage to the amplifier 2& side occurs. I end up.

For this reason, conventionally, as shown in Fig. 2, the driving voltage EBND is set by using the relationship between the turns ratio T, , T, , T8 of the transformer of the hybrid circuit and the terminated resistors R11R21R8, R4. Transmitted only to R0 side・Resistance R8
An attempt is made to suppress the voltage ERCV appearing on the side. In this case, for example, if the value of the resistor R1 corresponding to the line side impedance changes, the balance is immediately broken and the loop voltage ERov increases.

It is a sex curve diagram. In Fig. 3, the horizontal axis shows the value of the resistance R of the line side impedance, in Fig. 4, the horizontal axis shows the signal frequency, and the vertical axis shows the ratio of sneak voltage EROV in both Figs. /E[I am taking 111D.

Ryo shown in FIG. 3 is a normal line impedance and is designed to provide the best attenuation. That is, even if the value RH increases or decreases from this value, the reduction in the loop voltage will be small. In other words, the rotation becomes larger. Also, since this hybrid circuit uses a transformer, it has frequency characteristics, and as shown in Figure 4, it shows good characteristics in the specified band (line frequency band), but attenuates in the low and high frequencies. becomes smaller and goes around 1
The pain gets bigger. Therefore, depending on the gain and frequency characteristics of the amplifier, low-frequency oscillations such as high frequency oscillation and motor boating are likely to occur. Conventionally, the method to prevent such oscillations has been to reduce the gain of the amplifier, as mentioned above, which is a passive solution in which the AC branch does not have any gain to compensate for line loss. There was only one.

[Purpose of the invention]

The purpose of the present invention is to eliminate such conventional drawbacks by realizing a stable AC branch of a two-wire line even with a sufficiently large gain, extending the communication distance, and improving the system configuration. An object of the present invention is to provide an AC branch circuit that reduces the above restrictions.

[Summary of the invention]

The AC branch circuit of the present invention is a detection circuit that detects the presence or absence of an input from the main line in an AC branch circuit equipped with a terminal for single output to the main line and terminals for input/output to two or more secondary lines. , a detection circuit that detects the presence or absence of input from the secondary line, a logic circuit that determines which of the above inputs is detected first, a memory circuit that stores the result of the above judgment, and an amplified output based on the result of the above judgment. It is characterized by having an intermittent switch circuit.

(Embodiment of the Invention) FIG. 5 is a pull-out diagram of an AC branch circuit showing an embodiment of the invention, and FIG. 6 is an operation timing chart in FIG. 5.

The present invention provides a two-wire AC branch, which is difficult to provide a large gain, with a sufficiently large gain on the condition of half-duplex communication. In the case of half-duplex communication, a two-wire communication line, which is originally bidirectional, is used alternately as one-way communication whose direction changes over time. Using this half-duplex communication, the input line is temporally sampled to determine one direction of amplification. In other words, the present invention detects the line where the input was first received, performs amplification toward other lines, and prohibits input from other lines, thereby cutting off input from the hybrid circuit. Performs direction amplification.

As shown in FIG. 5, the AC branch circuit of the present invention includes, in addition to the conventional AC branch circuit shown in FIG. 1, a comparator circuit 4a+4b and a switch circuit 5a.

5b is provided.

First, when there is an input on the line M, an output appears on the comparator circuit 4a as indicated by the arrow in FIG. The control circuit 6 checks the presence or absence of input to other lines and determines the line that received the input earliest. 6, the comparator circuit 4b is connected to the line S1. Although it is provided in common with line s1.S2, it is provided separately and switch 5b also connects line s1. s
If the signals are separated every 2, the S/N will be even better.

At time point 0 in FIG. 0, it is determined that there is an input to the line M earliest, so the control circuit 6 registers the state in an internal memory circuit (not shown), and also registers the state in the switch 5.
A is turned on, and the output of amplifier 2a is sent to lines Sl and S2. At this time, the comparator circuit 4b also notifies that there is an output, but it has already been determined that the line M is the first one.

Switch 5b is never turned on. That is, since the path passing through the amplifier 2b is cut off by the switch 5b, there is no loop input to the hybrid circuit 1a, and even if the gain of the amplifier 2a is large, the circuit does not form a loop, so oscillation will not occur. doesn't happen. Here, the memory registered in the control circuit 6.

The contents are a set that eliminates the input to the iM.

and waits for input from the new line.

Next, when there is an input from the line S1 or S2 at time t2 or t8 in the Chikushi diagram, the comparator circuit 4b notifies that there is an output, so it is determined that there is an input before the others, so that the internal The state is registered in the memory circuit, and at the same time the switch 5b is turned on. The comparator circuit 4a notifies the existence of an input by the input of the hybrid circuit 1a, but the switch 5a is not turned on while the switch 5b is turned on. Line 31.
0: When the input registered as S2 disappears, the memory contents of the control circuit 6 are reset, and waits for notification of input from a new line. In this way, the outputs of the amplifiers 2a+21) are controlled by the switches 5a+5b so that only one of them is enabled (-1). That is, in the present invention, full-duplex lines are used, but since bidirectional communication is not performed at the same time, it is possible to provide sufficient gain to the amplifier by cutting off the harmful loop voltage of the hybrid circuit. can. In other words, since the signal is amplified alternately in one direction by dividing the time, there is no wraparound and no oscillation occurs even if the gain is increased.

〔Effect of the invention〕

As described above, according to the present invention, since it is used only for half-duplex communication, it is possible to realize an AC branch of a two-wire line that operates stably even if it has a sufficiently large gain. As a result, when the output of an external line and the output of the own station are combined and sent to another line, the communicable distance can be extended, and restrictions on system configuration can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional AC branch circuit, Fig. 2 is a configuration diagram of a hybrid circuit used in Fig. 1, Fig. 3,
FIG. 4 is a characteristic curve diagram of the hybrid circuit, FIG. 5 is a block diagram of a half-duplex communication/reliable AC branch circuit showing an embodiment of the present invention, and FIG. 6 is an operation time chart according to FIG. la, lb, lc: hybrid circuit, 2a. 2b: Amplifier fp=w, 3: Adder, 4a, 4b: +amparator circuit, 5a, 5b: Switch, 6: 1 control circuit. Patent applicant: Hitachi, Ltd. No. 1 Figure 1c Figure 2 ROV Figure 3 Figure 4 □ Frequency

Claims (1)

[Claims] 1. In an AC branch circuit equipped with an input/output terminal to the main line and an input/output terminal to two or more secondary lines, a means for detecting the presence or absence of input from the main line, and a means for detecting the presence or absence of input from the secondary line. It is characterized by having a means for detecting, a means for determining which of the above inputs is detected first, a memory for storing the result of the determination, and a switch for turning on/off the amplified output according to the result of the determination. AC branch circuit.