JPH0272745A - Waveform arranging circuit - Google Patents

Abstract

PURPOSE:To set a fall time shorter than a rise time by changing the time constant of a waveform arranging circuit at the time of letting fall a sending pulse differently from that at the time of rising the pulse. CONSTITUTION:When the level of an input pulse goes to L, the base potential of a Q1 goes to an L level, and the Q1 is turned on, and a Q2 is turned off, and a Q4 is turned on, and next, a Q5 is turned on, then, a signal pulse is sent out to a digital line. At this time, delay in the rise time is decided by the time constant tau=C1.R5. Next, when the base of the Q1 goes to an H level, the Q2 is turned on, and the Q4 and the Q5 are turned off, however, since an electric charge in a C1 is discharged via a time constant circuit, the base potential of the Q4 is not decreased instantly, and a pulse waveform falls with a delay time. However, the fall time is remarkably shortened when only a change-over switch S2 is connected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] This invention relates to a waveform shaping circuit used in a digital signal sending device in a digital subscriber line transmission system.

Provides a waveform shaping circuit that can prevent an increase in waveform distortion by setting the fall time of a pulse waveform to be shorter than the rise time when a capacitive load is inserted on the line side of a digital signal transmission device. The purpose is to.

A digital signal transmitting device that transmits a pulse signal to a digital subscriber line includes a pulse input circuit, a time constant circuit consisting of a capacitor and a plurality of resistors, and a pulse input circuit that receives waveform falling information from the pulse input circuit and receives waveform falling information when the waveform falls. a time constant switching circuit that switches the time constant of the time constant circuit to form a time constant different from that at the time of rising; and a time constant selection information receiving circuit that receives time constant selection information and instructs the time constant switching circuit to switch. and a pulse sending circuit which sends the signal pulses sent through one time constant circuit to the digital subscriber line as waveform-shaped pulses.

[Industrial application field]

The present invention relates to a waveform shaping circuit used in a digital signal sending device in a digital subscriber line transmission system.

FIG. 3 shows the main configuration of a digital subscriber line transmission system to which the present invention is applied. A digital signal transmission device is used in combination with a digital exchange, receives a unipolar signal as an input signal, performs waveform shaping, etc., and then transmits a bipolar signal to a digital subscriber line consisting of a two-wire metallic transmission line. It has the function of sending out a (bipolar) signal as a digital signal.

In the figure, the digital signal sending device receives a unipolar signal as an input signal, converts it into a bipolar signal in a unipolar/bipolar converter 1, and sends two bipolar signal pulses to pulse signal sending sections 2a and 2b one side at a time.

In the pulse signal sending sections 2a and 2b, the pulse rises steeply.

In order to prevent the signal pulse from leaking to other lines due to the falling edge, waveform shaping is performed to delay the rising and falling times of the waveform, and then it is passed through the signal transmission pulse transformer 3 and sent to the digital subscriber line as a bipolar signal. Send. The transmitted signal is received by a pulse signal receiving section on the subscriber terminal side and undergoes necessary processing.

If a capacitive load such as a line protection circuit (surge arrester, etc.) is inserted on the line side of such a digital signal transmission device, the rise and fall times of the pulse waveform will further increase, causing waveform distortion to exceed the standard value. There is a possibility that the signal transmission characteristics will be deteriorated. For this reason.

A correction means is required that can shorten both or either one of the rise and fall times of the pulse waveform depending on line conditions.

[Conventional technology]

FIG. 4 is a principle configuration diagram of a waveform shaping circuit in a pulse signal sending section of a conventional digital signal sending device. As shown in the figure, the conventional waveform shaping circuit has a pulse input circuit (1
), and time constant circuits (2) and 9 having only − pairs of time constants.
It consists of a pulse sending circuit (3) that sends the signal pulse sent through the time constant circuit (2) to the digital subscriber line as a waveform-shaped pulse, and the rising and falling times of the waveform are the same. Waveform shaping is performed using constants.

FIG. 5 is an example of a waveform shaping circuit in a pulse signal sending section of a conventional digital signal sending device.

This figure shows the pulse sending section for one side of the bipolar signal in FIG. 3, but the other side is exactly the same.

In the same figure, Ql to Q5 are transistors, R1 to R7
is a resistor, CI is a capacitor, and T is a pulse transformer. The capacitor C1 and the resistor R5 constitute a set of time constant circuits that are part of a waveform shaping circuit.

Now, when the level of the input pulse becomes L, the base potential of Ql becomes L level, Ql turns ON, C2 turns OFF, the base current of C4 flows through the Vc-R2-R5 route, and C4 turns ON. , then C5 turns ON and Vc-T-
A current flows through the C5 route, and a pulsed current is sent to the digital line. At this time.

Time constant τ where charging current for C1 is determined from 01 and R5
= C1・R5, so the base potential of C4 does not rise immediately (but gradually becomes higher as C1 charges). When the same potential reaches a value, the base current and collector current of C4 increase. The current begins to flow and gradually increases according to the charging curve of ct.Since the current of C5 also follows the current increasing curve of C4, the pulse current sent to the two lines does not rise suddenly.

Next, when the base of Ql becomes H level, Ql turns OFF,
C2 turns ON, C4 and C5 turn OFF,
This is because the charge on CI is discharged through the R5-C2 route.

The base potential of C4 does not drop immediately, but with the same time constant as when the waveform rises. Therefore, C4, C
The current No. 5 also does not turn off immediately, and the pulse current falls with the same delay time as when it rises. As described above, by delaying the rise and fall times of the waveform, waveform shaping is performed and signal leakage to two adjacent lines can be reduced.

FIG. 6 shows a conceptual diagram of the waveform of the signal pulse sent to the line. A in the same figure shows an ideal waveform when no waveform shaping is performed.9 shows a waveform after waveform shaping.

After waveform shaping, the waveform will rise and fall with a delay time as shown in the figure.

When such a waveform is sent to a digital subscriber line, a capacitive load CL as shown in FIG. 5 is inserted on the line side of the digital signal sending device.

The rise time and fall time of the pulse are further delayed as shown in FIG. 6C, and there is a possibility that the waveform distortion will exceed the permissible limit. However, this is because the conventional technology does not assume an increase in capacitive load.

The time constant circuit is fixed, and no measures are taken to shorten either the rise or fall times.

[Problem to be solved by the invention]

As mentioned above, in the conventional waveform shaping circuit.

Due to the capacitive load inserted on the line side of the digital signal transmission device, the rise time and fall time are longer than necessary (even if delayed).

Since neither the rise time nor the fall time can be shortened, the waveform distortion exceeds the allowable limit.

There is a problem that signal transmission characteristics may be deteriorated.

The present invention provides a waveform that can prevent an increase in waveform distortion by setting the fall time of the pulse waveform to be shorter than the rise time when a capacitive load is inserted on the line side of a digital signal transmission device. The purpose is to provide a shaping circuit.

[Means to solve the problem]

FIG. 1 is a diagram showing the principle configuration of the present invention. The figure shows a pulse signal sending section of a digital signal sending device.

l is a pulse input circuit that receives pulses from the exchange.

2 is a time constant circuit consisting of a capacitor and multiple resistors.

Reference numeral 3 denotes a time constant switching circuit which receives waveform falling information from the pulse input circuit 1 and switches the time constant of the time constant circuit 2 so as to form a different time constant at the falling edge of the waveform than at the rising edge. Further, 4 is a time constant setting information receiving circuit which receives time constant setting information from the control section of the exchange and sends switching information to the time constant switching circuit 3, and 5 is a waveform of the signal pulse sent through the time constant circuit 2. This is a pulse sending circuit that sends shaped pulses to digital subscriber lines.

In the same figure, the input pulse is transmitted to the pulse input circuit 1.
The signal is then transmitted to the time constant circuit 2, where it is shaped into a waveform and sent from the pulse sending circuit 5 to the digital subscriber line via a pulse transformer.However, when the waveform rises, the total resistance value of the capacitor and multiple resistors in the time constant circuit 2 is The rise time of the waveform is delayed by the time constant determined by , and waveform shaping is performed. Time constant switching information to be set at the falling edge of the waveform is sent in advance to the time constant setting information receiving circuit 4 from the control unit of the exchange (not shown).
However, when the waveform rises, the time constant switching circuit 3 does not operate because the pulse input circuit 1 does not send waveform fall information.

When the waveform falls, information indicating the fall of the waveform is transmitted from the pulse input circuit 1 to the time constant switching circuit 3, and the time constant switching circuit operates so that the time constant is set according to the above time constant setting information. .

Specifically, in the time constant circuit 2, a time constant circuit is formed by the capacitor and some of the plurality of resistors. That is,
By setting a time constant smaller than that at the rising edge, the delay time at the falling edge of the waveform is made shorter than at the rising edge.

This is because the setting of the time constant in the time constant switching circuit 3 can be instructed in advance to the time constant selection information receiving section 4 by the control section of the exchange using hardware or software (program control) means.

It is easily possible to selectively shorten the fall time of the pulse waveform relative to the rise time.

[Effect]

In the present invention, as described above, by changing the time constant of the waveform shaping circuit at the falling edge of the sending pulse from that at the rising edge, the falling time can be set to be shorter than the rising time.

In addition, since the time constant at the time of falling can take multiple values as mentioned above, if a capacitive load is inserted on the line side of the digital signal transmission device to delay the rise and fall times of the pulse waveform, By selecting and setting an appropriate value depending on the degree of waveform distortion, it becomes possible to compensate for deterioration in signal transmission characteristics.

〔Example〕

FIG. 2 is a circuit diagram of one embodiment of the present invention. In the figure, 1~
Reference numeral 5 indicates the same component as in FIG. Also, Ql ~Q
7 is a transistor, R1 to R4, R5a.

R5b, R5c, R6, and R7 are resistors, C1 is a capacitor, and T is a pulse transformer. capacitor ci
and resistors R5a, R5b, and R5c constitute a time constant circuit that is part of the waveform shaping circuit.

Now, when the level of the input pulse becomes L, the base potential of Ql becomes L level, Ql is 0IJL, and C2 is OFF.
becomes. By turning off C2, Vc -R2-(R
The base current of C4 flows through the route of 5a+R5b+R5c), C4 turns on, then C5 turns on, and Vc-T
A current flows through the -C5 route and a signal pulse is sent out to the digital line. At this time, since a charging current flows to C1, the base potential of C4 does not rise immediately, but +
If R5a'' R5b +R5c = R5, the rise time delay follows the same time constant τ-C1·R5 as in the conventional system.

Next, when the base of Ql becomes H level, C2 turns ON,
C4 and C5 are turned off, but since the charge of CI is discharged through the time constant circuit, the base potential of C4 does not drop immediately, and the pulse waveform falls with a delay time. However, in the case of falling, depending on the setting conditions of the changeover switches of Sl and S2, C2 is turned on at the same time as C2 is turned on.
Since either or both of C6 and C7, which have the same base potential as , is turned on, the charge of ci is (R5a+
In addition to the route R5b+R5c)-C2, (R5b
+R5c) -Discharge occurs via either or both of C6 and R5cmQ7 routes. Now, if only 32 is connected and R5c is set to an extremely small value, the discharge time of C1 is almost equal to R5.
Since it is determined by the route C-C7, the fall time is extremely short. As described above, it is possible to selectively shorten the fall time rather than the rise time.

In FIG. 2, C6 and C7 are set, but it is of course possible to use only one of them or to increase the number of similar circuits, and for example, the resistance value of R5c can be changed to C1.
That is, it is also possible to short-circuit. The falling time can be easily selected and set by determining a plurality of resistance values of the time constant circuit 1 and setting the changeover switches Sl and 32 of the time constant switching circuit 2. The changeover switch can be set by receiving the time constant setting information from the exchange in the time constant setting information receiving circuit 4, decoding it, and sending it to the time constant switching circuit 2 to operate the corresponding changeover switch.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to set the fall time of the waveform to be shorter than the rise time, so that when a capacitive load is inserted on the line side of the digital signal transmission device, This makes it possible to prevent an increase in waveform distortion, which greatly contributes to improving the signal transmission characteristics of such a digital signal transmitting device.

[Brief explanation of the drawing]

FIG. 1 is a basic configuration diagram of the present invention, FIG. 2 is a circuit diagram of an embodiment of the present invention, and FIG. 3 is a main configuration diagram of a digital subscriber line transmission system to which the present invention is applied. FIG. 4 is a basic configuration diagram of the prior art, FIG. 5 is a circuit diagram of an embodiment of the prior art, and FIG. 6 is a conceptual diagram of a signal pulse waveform sent to a digital line. The symbols in the figure indicate the following. Q1-Q7...Transistor C1...Capacitor R1-R7...Resistor T...Pulse transformer S1. , S2...Selector switch CL...Capacitive load

Claims (1)

[Claims] A digital signal transmitting device that transmits a pulse signal to a digital subscriber line includes a pulse input circuit (1), a time constant circuit (2) consisting of a capacitor and a plurality of resistors, and a waveform falling from the pulse input circuit (1). a time constant switching circuit (3) that receives information and switches the time constant of the time constant circuit (2) so as to form a different time constant at the falling edge of the waveform than at the rising edge; A time constant setting information receiving circuit (4) that instructs the constant switching circuit (3) to switch, and a signal pulse sent through the time constant circuit (2) is sent to the digital subscriber line as a waveform-shaped pulse. A waveform shaping circuit comprising a pulse sending circuit (5).