JPS60197092A - Preventing circuit of intermittent noise of bell signal - Google Patents

Abstract

PURPOSE:To prevent completely the occurence of noises at the time of intermission of bells by connecting a serial circuit consisting of a capacitor and two terminal elements which exhibit the conductive condition only when a voltage more than the maximum voice level is impressed, between lines of subscribers. CONSTITUTION:A bell signal intermission noise pareventing circuit 53 in a subscriber circuit 3 consists of a serial circuit of a varister V2 and a capacitor C2. The varister V2 is made conductive due to a voltage more than the maximum value of a voice signal impressed between terminals L1 and L2, and the capacitor C2 exhibits a high reactance with respect to a bell signal of 16Hz. Even if noises at a high voltage level occur at the moment a connection of a relay 10 is switched from a point M to a point B, the capacitor C2 exhibits a low reactance with respect to noises, and the varister V2 is brought into the conductive condition; therefore a subscriber circuit is in the short-circuit condition in alternating current mode. As a result, the occurrence of noises at the time of intermission of a bell signal can be completely prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a circuit for preventing intermittent bell signal noise in a subscriber circuit used in a private branch exchange or the like.

[Technical background of the invention]

Generally, digital exchanges have a configuration as shown in FIG. That is, a subscriber circuit 3 that connects a subscriber telephone 1 with a subscriber line 2, a time division switch 4 that selectively connects a plurality of subscriber circuits 3 to form a PCM line, and this time division switch 4. The central office line trunk circuit 6 connects the central office line 5 to the central office line 5, and a common control device 7 controls all these circuits. The subscriber circuit 3 not only sends and receives audio signals to and from the subscriber telephone @1 through the subscriber line 2, but also has the function of sending out a bell signal for ringing the bell of the subscriber telephone 1. The bell signal is interrupted by a bell signal intermittent signal sent from the common control device 7 to the subscriber circuit 3 through the control line 8.

2 and 3 show a bell signal sending circuit in a conventional subscriber circuit 3, T is a hybrid transformer constituting a 2-wire 74-wire conversion circuit, and 2m11IIl of this hybrid transformer T is 148 volts. DC voltage is applied. 9 is a letter coil, and 10 is a relay having a switch circuit with two circuits and two contacts.When the switch circuit is switched to the contact B side, the subscriber line 2 is connected to the hybrid transformer T, and the switch circuit is switched to the contact M side. When the bell signal circuit 11 is connected to the subscriber line 2, the telephone 1
ring bell 12.

The bell signal generated from the bell signal circuit 11 is a 16 Hz signal of about 90 volts superimposed on -48 volts DC, and the bell 12 of the telephone 1 rings for 1 second and stops for 2 seconds. Intermittent by relay 1°. At this time, when the contact of the relay 10 is connected to point B, a direct current of 148 volts is supplied to the telephone 1. On the other hand, when the contact of relay 10 is connected to point M, a 16 Hz bell signal of about 90 pols) is sent to the bell circuit of the telephone.

In this case, as shown in FIG. 4(, ), when the contact of the relay 10 switches from point M to point B, the current of the bell signal changes rapidly, so the inductance of the bell 12 of the 4ml telephone As a result, a high voltage noise signal N as shown in FIG. 4(b) is generated for several seconds.

By the way, in the subscriber circuit 3, the internal wiring is usually formed as a printed pattern on an insulating substrate, and the 8 points of the relay IO and the terminals Ll and L2 are connected to each other.
When the above-mentioned high voltage noise signal N is generated on the pattern connecting the wiring pattern, this noise signal N is induced to other wiring patterns provided in the vicinity of the wiring pattern, and the noise signal N is induced to this. The wiring that was done! There is a risk that the circuit including the turn may malfunction, or if the wiring pattern is a telephone line, noise may be mixed into the telephone call.

For this reason, conventionally, as shown in FIG. 2, a noise prevention circuit 13 such as a series circuit of a resistor R and a capacitor C1 is connected between terminals L1 and L2, or as shown in FIG. A better noise prevention circuit 33 was connected to prevent noise by fC, .

[Problems with background technology]

In the case of the noise prevention circuit 13 shown in FIG. 2 described above, in order to obtain a sufficient noise prevention effect, it is necessary to select a sufficiently large value for the capacitance of the capacitor C1. Since the characteristics are adversely affected, the value of the resistance must be increased. However, when the value of the resistor R is increased, the noise prevention effect of the capacitor C1 is inhibited, and as a result, the noise prevention circuit 13 shown in FIG. 2 has the disadvantage that a sufficient noise prevention effect cannot be obtained.

In addition, in the case of the noise prevention circuit 33 using a varistor Vl as shown in FIG.
It is necessary to use a varistor of about 0.00 volts, and there is a problem that the desired noise prevention effect cannot be obtained. [Object of the Invention] The present invention eliminates the above drawbacks and achieves a sufficient noise prevention effect. An object of the present invention is to provide a circuit for preventing intermittent bell signal noise.

[Overview of the invention]

The present invention achieves the above object by using a noise prevention circuit comprising a series circuit of a two-terminal resistor and a capacitor that become conductive at a voltage higher than the maximum audio signal level.

[Embodiments of the invention]

FIG. 5 shows a ring signal sending circuit in the subscriber circuit 3 equipped with a bell signal intermittent noise prevention circuit 53 according to the present invention,
Portions corresponding to those in FIGS. 2 and 3 are designated by the same reference numerals, and detailed explanations of the common portions will be omitted. In the subscriber circuit 3 of FIG. 5, the bell signal intermittent noise prevention circuit 53
Fi is a series circuit of varistor v2 and capacitor C2. The varistor v2 in this embodiment has terminals L1. It has the property of being conductive at a voltage higher than the maximum voltage level of the audio signal applied between L2. Further, the capacitor C2 is selected to have a sufficiently large value within a range that exhibits a high reactance to a 16 Hz bell signal.

If the conduction voltage of varistor 2 and the capacitance of capacitor C2 constituting the bell signal intermittent noise prevention circuit 53 of the present invention are all selected to the above values, it is assumed that capacitor C2 exhibits a low reactance with respect to the audio signal. However, since the varistor V2 connected in series with the capacitor C2 is in a non-conducting state at the voltage level of the audio signal, there is no possibility that the audio signal will be adversely affected by the presence of the bell signal intermittent noise prevention circuit 53. Furthermore, even if the bell signal has a voltage higher than the maximum audio signal level, which is the conduction voltage of the lister V2, the capacitor C2, which exhibits a high actance at the frequency of the bell signal of 16 Hz, is in series with the risk v2. Since the bell signal is connected, there is no possibility that the presence of the bell signal intermittent noise prevention circuit 53 will affect the bell signal. Furthermore, even if a noise signal N of excessive voltage as shown in FIG. 4(b) occurs at the moment when the contact of the relay 11 switches from point M to point B, capacitor C2 is Since it exhibits a low reactance and the 4-lister V2 is in a conductive state, the subscriber lines are short-circuited in terms of alternating current. Therefore, the noise signal N when the bell signal is intermittent
can be completely prevented from occurring.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, it is possible to prevent noise that occurs when a bell signal is interrupted by a relay, without affecting the audio signal and the bell signal.

[Brief explanation of drawings]

Figure 1 is a block diagram of a digital exchange; Figures 2 and 3 are a bell signal sending circuit in a conventional subscriber circuit;
Figures 4(a) and (b) show the voltage waveforms generated between the subscriber lines when the relay is switched on and off, and Figure 5 shows the bell signal sending circuit in the subscriber circuit equipped with the bell signal intermittent noise prevention circuit according to the present invention. shows. 1...Subscriber telephone, 2...Subscriber line, 3...
Subscriber circuit, 4... Time division switch, 5... Office line,
6... Office line trunk circuit, 7... Common control device, 8
...Control line, 10...Relay, 11...Bell signal circuit, 12...Bell, 53...Bell signal intermittent noise prevention circuit. Representative Patent Attorney Takahisa Kimura Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] A voltage greater than or equal to the maximum voice signal level between the lines and terminals of a subscriber line drawn into a subscriber circuit configured to intermittently transmit a jiber signal via a relay to the subscriber telephone via the subscriber line. 1. A bell signal intermittent noise prevention circuit characterized by connecting a series circuit consisting of a two-terminal element and a capacitor that exhibit a conductive state only when .