JPH0326090A - Dial pulse sending circuit - Google Patents

Abstract

PURPOSE:To minimize the false pulse of hit, etc., being observed after completing the sending of a dial pulse by rendering inductance equivalent characteristic just before the sending of the dial pulse immediately after the completion of the sending of the dial pulse. CONSTITUTION:During performing speech, a dial pulse circuit 12 is set at a low impedance state in DC fashion and a high impedance state in a sound area by making first and second contacts 8 and 7. When the dial pulse is sent, the first contact 8 is opened by breaking the second contact 7 just before sending the dial pulse, and the second contact 7 is made immediately after sending the dial pulse. Thereby, the dial pulse sending circuit can be set at the DC fashion, and at the high impedance state in the sound area, and also, the fluctuation of a bias voltage before and after sending the dial pulse can be suppressed, and the hit of a speech current after sending the dial pulse can be eliminated, and a false dial pulse can be prevented from occurring.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a dial pulse sending circuit that is applied to the trunk of a private branch exchange (PBX), and more specifically, a circuit that switches internal alternating current (voice band) inbegence when sending dial pulses. The present invention relates to a dial pulse sending circuit having a dial pulse sending circuit.

(Prior Art) An example of the structure of a PBXO office line trunk is shown in FIG. The dial pulse sending circuit 13 is connected in parallel to a subscriber line accommodated in the subscriber circuit of the opposing station.

Figure tX4 shows an example of a conventional dial pulse sending circuit.
j is a circuit diagram.

The configuration is as shown in Figure 4, with resistors R2, R3, and capacitor 01. The transistors Ql and k and the resistor R4 operate to equivalently exhibit inductance characteristics. That is, it has low impedance in terms of direct current, but high impedance in the voice band.

Therefore, by closing rB during a call, the evening DC holding function is realized. However, when sending dial pulses, the presence of inductance increases the distortion of the dial pulse waveform, so s'c'k is closed, and after bypassing the inductance component and forming a DC circuit with lower internal impedance, RA is opened and closed. In particular, it was sending out dial pulses.

(Problem to be Solved by the Invention) By the way, the dial pulse sending circuit shown in FIG. 4 completely bypasses the rc inductance component during exit of the dial pulse, so the current flowing to the transistor side becomes iL - O. .

Therefore. After releasing rc upon completion of pulse transmission.
The current iL has a certain time constant (T~
It can only be increased by R2/R3・01). In addition, the current also becomes O.

Therefore, the subscriber circuit of the opposing station is accommodated in the main office line trunk.
Depending on line conditions, the communication current I may be momentarily cut off.
There was a possibility of false dial pulses occurring.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks, and to provide a dial pulse sending circuit which can eliminate instantaneous interruptions in communication current after sending dial pulses and prevent generation of false dial pulses.

(Means for Solving the Problem) In order to achieve the above object, a dial pulse sending circuit according to the present invention is provided in a trunk circuit of an electronic exchange, and in the dial pulse sending circuit connected in parallel to subscriber lines, a transistor and a dial pulse sending circuit are provided. , an emitter resistor connected to the emitter of the transistor, first and second bias resistors supplying a bias current for operating the transistor in the active region, and bypassing an alternating current component applied to the base of the transistor. a first contact inserted in series with the dial pulse sending circuit, and an lM2i for disconnecting the capacitor in circuit terms.
During a call, the first and second contacts are set to make the dial pulse circuit low impedance in terms of NlIR and high impedance in the voice band, and when sending dial pulses, the dial pulse circuit Before, the second contact is set to break state and the first contact is opened and closed, and immediately after the dial pulse is sent, the #! 2 contacts are in the make state, and during dial pulse transmission, the dial pulse transmission circuit is made to have high impedance in the direct current and voice band, and is configured to suppress fluctuations in bias voltage before and after dial pulse transmission. It has been done.

(Example) Hereinafter, the present invention will be explained in more detail with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of a dial pulse sending circuit according to the present invention.

A positive feedback resistor (R4) 2 is connected to the emitter side of the transistor (Ql) 1. On the base side of transistor l, there is a resistor (R2) that determines the operating point of transistor l.
3, a resistor (R3) 4 and a capacitor (01) 6 are connected.

Relay contact (rc) 7 is connected in series with capacitor 6, and when relay contact 7 is opened and closed, capacitor OX is connected in parallel to resistor 4, and disconnected. Reference numeral 8 is inserted in the dial pulse sending circuit and the line, and the terminals a and b are connected to the subscriber line.

FIG. 2 is a diagram showing a pseudo-connection state of the dial pulse sending circuit used for the PBX c) central office line trunk in FIG. 1.

Figure 3 shows the contact (RA) 8s (
rc)7 is a timing diagram showing an example of the operation.

During a call on the central office trunk, contacts 8 and 7 are closed.

In such a state, this circuit has a low int''-/
It acts as a current holding circuit with high impedance and high impedance in terms of alternating current.

Resistors (R2) 3 and (R3) 4 are transistors (Ql).
)1, the value of KR2/R3 is generally selected to be sufficiently large with respect to the line impedance (for example, 6000, etc.).

The capacitor (01) 6 is selected such that z 0 1 - 1 011 (" is the angular frequency of the audio band) is sufficiently small with respect to the resistor (R2) 3.

This circuit is basically an emitter holo 7 circuit 9, terminal a
When a DC signal with an AC signal in the voice band is superimposed is applied from ,b, the current operating point depends on the characteristics of the resistors 2, 3.4> and the transistor 1, and depends on the applied DC voltage V. DC current flows.

However, in terms of AC, R2)) ZOI yo pV B turtle 0
, 1. Since the characteristics of the emitter follower are DVB to Vm0, alternating current does not flow into the transistor 1 and can be regarded as high impedance.

In other words, it is equivalent to the characteristics of inductance.

Next, a case will be described in which this circuit operates as a dial pulse sending circuit.

At the same time as the contact (RA) 8 is opened and closed under the desired dial pulse standard, the contact (RA) is opened and closed at the timing shown in Figure 3.
rc) 7 is also running.

Here, breaking Wl point 7 means transistor 1
The time constant R2 that operates as a pseudo inductance
●The waveform characteristics of the p-dial pulse can be improved by removing Ol.●While the contact 7 is broken, the voltage between the terminals of the capacitor 6 maintains the voltage before the dial pulse is sent out even when the dial pulse is being sent out. ing.

Strictly speaking, the leakage resistance of the three capacitors, the mounting board tlo
Although p gradually attenuates due to insulation resistance, etc., its time constant is sufficiently large compared to the dial pulse sending time.

Therefore, the transmission of the dial pulse is completed and the contact 7t-
Immediately after the transistor 1 is turned on, it resumes conduction without passing through the transient state, so there is no momentary interruption of the communication DC current, and the possibility of generating a false pulse is extremely small. .

In the above embodiment, the case where the contacts 7 and 81 are relay contacts has been described, but the scope of the present invention also includes a case where the switch is constructed of a semiconductor or the like.

(Effects of the Invention) As explained above, the present invention is configured to reproduce the inductance equivalent characteristics before the dial pulse transmission is completed immediately after the dial pulse transmission is completed. This has the effect of making pseudo pulses smaller.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of the dial pulse sending circuit according to the fIiIK of the present invention, Fig. 2 is a block diagram showing the connection state of the circuit shown in Fig. 1 to the PBXo office line trunk, and Fig. 3 is a block diagram showing the connection state of the circuit shown in Fig. Contact points ra. A timing chart showing an example of the operation of the rc, and FIG. 4 is a circuit diagram showing an example of a conventional dial pulse sending circuit. 1-}Transistor (Ql) 2... Resistor (R4) 3-... Resistor (R2) 4.
...Resistor (R3) 6...Capacitor (Ol) 7.-Relay contact (rc) 8..Relay contact (RA) 10.. Office line trunk 1 1-.. Call bidirectional amplifier 12.- Dial pulse sending circuit

Claims (1)

[Claims] A dial pulse sending circuit provided in a trunk circuit of an electronic exchange and connected in parallel to a subscriber line includes a transistor, an emitter resistor connected to the emitter of the transistor, and a bias current for operating the transistor in an active region. a capacitor for bypassing the alternating current component applied to the base of the transistor; a first contact inserted in series with the dial pulse sending circuit; During a call, the first and second contacts are set to make the dial pulse circuit low impedance in direct current and high impedance in the voice band, and the dial pulse is sent out. When the dial pulse is being sent, the second contact is set to a break state to open and close the first contact immediately before the dial pulse is sent, and the second contact is set to the make state immediately after the dial pulse is sent. Make the transmission circuit low impedance in direct current and voice band, and
A dial pulse sending circuit characterized in that it is configured to suppress fluctuations in bias voltage before and after dial pulse sending.