JPH1023148A - Subscriber circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress and reduce the noises when a telephone set is hooked off and then the first dial pulse is transmitted by eliminating the quantization noises of in-band signals which are sent to an in-band ringer from a subscriber circuit. SOLUTION: The in-band signals of frequency fHz which are produced by a digital in-band signal oscillator 16 are converted into analog signals by a D/A converter 14 and sent to an in-band ringer via an interface circuit 19 of output impedance 600Ω. At the same time, the in-band ringer which received the analog signals from the converter 14 includes the quantization noises. The frequency component of the quantization noises is equal to an odd multiple compared with the greatest common divisor of in-band frequency fo Hz and sampling frequency 8KHz. The quantization noises contained in the analog in-band signals are eliminated by a filter circuit 17, and only the in-band signals containing no noises are outputted. Thus, a subscriber circuit can produce an in-band ringer that contains the reduced noises.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a subscriber circuit, and more particularly to a subscriber circuit having a built-in in-band signal generator and a detector facing an in-band ringer.

[0002]

2. Description of the Related Art As shown in FIG. 2, a conventional subscriber circuit of this type converts an in-band signal from an in-band ringer 1 of a terminal into a digital signal ("A / D converter"). 13), an in-band signal detector 15 for detecting an in-band signal converted to a digital signal, an in-band signal oscillator 16 for generating an in-band signal of a digital signal, and converting the digital signal into an analog signal. A digital / analog converter (referred to as "D / A converter") 14 for converting and sending an analog in-band signal to the in-band ringer 1 of the terminal.
And is provided. The details of a subscriber circuit incorporating a generator and a detector of an in-band signal facing the in-band ringer are described in, for example,
Reference is made to the description of the publication.

The subscriber circuit 10 includes an in-band ringer 1
Through to the telephone terminal 2. Further, the subscriber circuit 10 converts the in-band signal input to the subscriber through the terminal A from the in-band ringer 1 into digital, through test relays 11 and 12, which are drawn into a tester for testing the subscriber circuit. An A / D converter 13, an in-band signal detector 15 for detecting an in-band signal converted to a digital signal, an in-band signal oscillator 16 for generating an in-band signal of a digital signal, It has a D / A converter 14 for converting a signal into an analog in-band signal.

When the telephone 2 goes off-hook, normally, the in-band signal sent from the in-band signal generator 3 of the in-band ringer 1 to the subscriber circuit 10 is stopped, and the subscriber circuit 10 is activated. This is called the subscriber circuit 10
Is detected by the A / D converter 13 and the in-band signal detector 15, and the subscriber circuit 10 enters a state of receiving the dial signal from the telephone 2.

When the subscriber circuit 10 receives the first dial pulse, the in-band signal oscillator 1 of the subscriber circuit 10
6, the in-band signal sent from the in-band signal oscillator 16 to the in-band ringer 1 through the D / A converter 14 is stopped.

In the above-mentioned Japanese Patent Application Laid-Open No. 4-162882, an in-band signal generator and a detector are provided for diagnosis, and an in-band signal is output to the subscriber circuit under test to the line and the inside of the subscriber circuit. A diagnostic method has been proposed in which an in-band signal from inside a subscriber circuit is input to an in-band signal detector for diagnosis to improve diagnostic accuracy.

Japanese Patent Laid-Open Publication No. Sho 58-117760 discloses a ringer sending circuit of a subscriber circuit, which forms a phase from a call situation and a ringer signal, thereby turning the ringer on and off and sending the ringer to the telephone terminal. A paging signal transmission control system as described above has been proposed.

[0008]

The conventional subscriber circuit is:
There is a problem that noise can be heard until the telephone is off-hook and the first dial pulse is sent.

[0009] The reason is that the in-band signal of the subscriber circuit is generated from the digital in-band signal through the A / D converter. Because the signal containing the band signal and the quantization noise is applied to the in-band ringer, only the quantization noise is heard as noise by the telephone through the in-band signal filter of the in-band ringer.

[0010] Accordingly, the present invention has been made in view of the above circumstances, and an object of the present invention is to remove a quantization noise of an in-band signal sent from a subscriber circuit to an in-band ringer, thereby enabling a telephone. It is an object of the present invention to provide a subscriber circuit which suppresses and reduces noise during a period from off-hook to transmission of the first dial pulse.

[0011]

In order to achieve the above object, a subscriber circuit according to the present invention comprises a quantum circuit which is generated when an output of a digital in-band signal oscillator is converted into an analog signal by a D / A converter. And a filter for removing an activating noise component.

In the present invention, a quantization noise elimination filter is provided on the output side of the D / A converter.
The output signal of the digital in-band signal oscillator is D /
When converted to an analog in-band signal by the A converter,
The quantization noise component generated simultaneously with the in-band signal is removed, so that the noise becomes inaudible.

[0013]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the embodiment of the present invention.

Referring to FIG. 1, an embodiment of the present invention has an input impedance and an output impedance of 60.
An interface circuit A18 and an interface circuit B19 that look like 0Ω, an A / D conversion circuit 13, a D / A conversion circuit 14, an in-band detector 15 for digitally detecting an in-band signal, and an in-band signal oscillator 16. A filter 1 for cutting an in-band signal f ₀ and a frequency component that is an odd multiple of the greatest common divisor of a sampling frequency of 8 kHz.
7 are provided. The filter 17 is configured as a filter that allows the in-band signal to pass and blocks an in-band signal f ₀ in the band and a frequency component that is an odd multiple of the greatest common divisor of the sampling frequency of 8 KHz.

Next, the operation of the embodiment of the present invention will be described in detail with reference to FIG.

Referring to FIG. 1, an in-band signal having a frequency of fHz generated by a digital in-band signal oscillator 16 is converted into an analog signal by a D / A converter 14, and an interface whose output impedance appears to be 600Ω. In-band ringer (not shown) through circuit 19
Sent to

At this time, the in-band ringer of the analog signal output from the D / A converter 14 contains quantization noise.

This quantization noise has an in-band frequency f ₀
Hz and a frequency component that is an odd multiple of the greatest common divisor of the sampling frequency 8 KHz.

In the circuit according to the embodiment of the present invention, a filter 17 for removing the quantization noise contained in the analog in-band signal is inserted to output only the in-band signal from which the noise has been removed.

[0020]

As described above, according to the present invention,
By incorporating a filter that removes quantization noise included in the in-band signal, a subscriber circuit that can generate an in-band ringer with less noise can be realized.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a conventional in-band ringer subscriber circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 In-band ringer 2 Telephone 3 In-band signal generator 4 In-band signal removal filter 5 In-band signal detector 10 Subscriber circuit 11, 12 Test relay 13, 14 A / D, D / A converter 15 In-band signal Detector circuit 16 In-band signal oscillator 17 Filter 18, 19 Interface circuit A, B

Claims (2)

[Claims] 1. A digital in-band signal oscillator having a D / D
A subscriber circuit comprising a filter for removing a quantization noise component generated when the signal is converted into an analog signal by an A converter. 2. The subscriber circuit according to claim 1, wherein said filter is configured to block an in-band signal and a frequency component that is an odd multiple of the greatest common divisor of a sampling frequency.