JPS62112462A - Silent reverse circuit - Google Patents

Abstract

PURPOSE:To prevent a silent reverse circuit from oscillation and to stabilize the circuit by arranging a silent reverse filter on the signal input side of a polarity inverting level shifting circuit and impressing a polarity inversion control signal and a reference voltage to the filter. CONSTITUTION:A two-wire (W) detector 11 detects a voltage V applied between chip rings and an AC cutting circuit 12 is driven to remove voice inputted from a telephone set 21 and to input only a DC component to a function generating circuit 13. A reference voltage Vref required for inverting the DC component inputted to the polarity inverting level shifting circuit 14 and a polarity inversion control signal PC are impressed to the silent reverse filter 15. Thereby, only a charging pulse of which polarity is gradually inverted is outputted from the shift circuit 14 and made to flow into a DC feedback course. Since the silent reverse filter is not included within the DC feedback loop, oscillation is not generated in the loop.

Description

[Detailed Description of the Invention] [Summary] This is a silent reverse circuit that attempts to maintain the stability of the circuit by preventing oscillation caused by a silent reverse filter.

[Industrial application field]

The present invention relates to a silent reverse circuit.

Generally, in a telephone communication network, DC power is supplied from an exchange to a terminal telephone. In such a power supply system,
Silent reverse circuits are used to eliminate the polarity reversal sound when the exchange sends billing pulses to public telephones.

That is, when money is put into a telephone box of a public telephone, the polarity or direction of the direct current is reversed and when the direction returns to the original, the money falls into the telephone box and you can talk to the other party.

However, if the direction of this direct current changes suddenly, the instantaneous sound becomes too loud, making the caller noisy and angry, making it difficult to make a call. For this reason, a silent reverse circuit is constructed to slowly reverse the polarity of the direct current and reduce the sound so as not to disturb the ears of the caller.

[Conventional technology]

A conventional silent reverse circuit composed of a power supply circuit and a DC feedback circuit has a silent reverse filter 15' inserted in the DC feedback path, as shown in FIG.

With this configuration, the voltage between the tip rings is detected by the 2W (wire) detector 11', the AC cut circuit 12' is operated to remove the sound, and the function generator circuit 13' causes a current corresponding to the voltage to flow. The DC characteristics are set as such, and the polarity inversion level shift circuit 14' inverts the polarity to generate a charge pulse whose direction changes, and the silent reverse filter 15' slowly inverts this polarity to reduce the inversion sound. Ta.

[Problems to be Solved by the Invention] According to the conventional circuit shown in FIG. 2, the polarity of the billing pulse changes rapidly when it is output from the polarity reversal level shift circuit 14', but the silent reversal filter 15' corrects this direction. That is, the polarity is slowly reversed.

However, there is a problem in that an oscillation phenomenon occurs in the DC feedback path in which the silent reverse filter 15' is inserted.

This is because the silent reverse filter 15' rotates the phase of low frequencies.

[Means for solving problems]

An object of the present invention is to solve the above-mentioned problems, prevent oscillation of the silent reverse circuit, and stabilize the circuit.

The means for this purpose is as shown in FIG. The current is applied to the silent reverse filter 15 which is removed from the DC feedback path.

[For production]

According to the present invention, the silent reversal filter 15 is provided on the signal input side of the polarity reversal level shift circuit 14, and the polarity reversal control signal pc and the reference voltage Vsef are applied to the silent reversal filter 15. The reference voltage Vsef itself gradually changes and is input to the polarity inversion level shift circuit 14, and only the billing pulse whose polarity is slowly inverted flows into the DC feedback path. According to this configuration, since phase rotation in the DC feedback path is reduced, oscillation can be prevented.

〔Example〕

Hereinafter, the present invention will be explained by way of examples with reference to the accompanying drawings.

FIG. 1 is a diagram showing an embodiment of the present invention, which is composed of a power supply circuit and a DC feedback circuit.

The power supply circuit includes a 2W (wire) detector 11, an AC cut circuit 12, a function generation circuit 13, and a polarity inversion level shift circuit 1.
4 and a silent reverse filter 15.

The 2W detector 11 is a device that detects the voltage between the chi and knob ring.

The AC cut circuit 12 is a circuit that removes the audio included in the output of the 2W detector 11.

The function generating circuit 13 is a circuit that sets DC characteristics in order to cause a DC current corresponding to the tip-ring voltage V to flow through 2W (wire).

The polarity inversion level shift circuit 14 is a circuit that shifts the level of the direct current generated in the preceding stage circuit 13 and inverts its polarity.

The silent reverse filter 15 is constituted by a low-pass filter, and gradually changes the reference voltage Vref and inputs it to the shift circuit 14.

On the other hand, the power supply circuit includes a telephone set 21, a first current source 2 and a second current source 2.
2, 26, the first and second hasha 2 connected to them
3, 25, and a buffer polarity inversion circuit 24.

The directions of the first current source 22 and the second current source 26 are mutually changed, so that when one source is draining current, the other is sinking the current.

The first and second buffers 23 and 25 are 2W (wire)
Shift the voltage to work.

The buffer polarity inversion circuit 24 is a circuit that inverts the input polarity of the buffers 23 and 25 in response to changes in the directions of the current sources 22 and 26.

The operation of the circuit shown in FIG. 1 having the above configuration will be explained below.

2W (wire) detector 11 detects the tip-ring voltage V
When detected, the AC cut circuit 12 operates to remove the voice input from the telephone 21, and only the DC component is input to the function generation circuit 13.

In the function generating circuit 13, a DC characteristic is set so that a direct current corresponding to the tip-to-ring voltage V flows, and unnecessary direct current does not flow.

The DC current output from the function generation circuit 13 is input to the polarity inversion level shift circuit 14.

On the other hand, a reference voltage Vref and its polarity inversion control signal PC necessary for inverting the DC input to the polarity inversion level shift circuit 14 are applied to the silent reverse filter 15. Therefore, Vref that has passed through the silent reverse filter 15 is input to the shift circuit 14 while being gradually changed by the control signal PC.

Therefore, in the shift circuit 14, only the billing pulse whose polarity is slowly reversed is outputted and flows into the DC feedback path. Therefore, since the silent bass filter is not included in the DC feedback loop, oscillation in the DC feedback loop as in the conventional case does not occur.

〔Effect of the invention〕

According to the present invention, the silent reversal filter is provided on the signal input side of the polarity reversal level shift circuit, and the polarity reversal control signal and the reference voltage are applied to the silent reversal filter, so that the reference voltage itself gradually changes. Only the charging pulse whose polarity was slowly reversed after being inputted to the polarity inversion level shift circuit flowed into the DC feedback path, and no oscillation occurred.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, and FIG. 2 is a diagram showing a conventional technique. ■... Chip, 2... Ring, 11... 2W detector, 12... AC cut circuit, 13... Function generation circuit, 14... Polarity inversion level shift circuit, 15... Silent reverse filter, 21... Telephone, 22... First current source, 23... First buffer, 24... Buffer polarity inversion circuit, 25... Second buffer, 26... Second 2 current sources.

Claims (1)

[Claims] In a silent reverse circuit that reduces the polarity reversal sound of a direct current in a power supply circuit connected to a tip ring (1, 2) including a telephone, a function is generated to output a current corresponding to the voltage of the tip ring. A silent reverse filter (15) is provided on the signal input side of a polarity inversion level shift circuit (14) that inverts the output polarity of the circuit (13). The reference voltage (Vsef) necessary to invert the polarity of the DC input of the shift circuit (14) and its polarity inversion control signal (
PC) and gradually change the reference voltage (Vsef), the polarity inversion level shift circuit (14
) is a silent reverse circuit.