JPH1079962A - Subscriber circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a subscriber circuit which does not need a filter for inphase noise elimination in a loss switch and restrains the scale of the circuit by connecting a differential amplifier to eliminate inphase noise in parallel with a feeder circuit and connecting a direct current component eliminating device and the loss switch to its output in a subscriber circuit. SOLUTION: A direct current voltage component of a subscriber line 3 is directly inputted to a differential amplifier 5 by shifting a direct current component eliminating device that is provided on an input side of the amplifier 5 for signal synthesis to an output side of the amplifier 5, i.e., a codec part 8 in a subscriber circuit 1. Therefore, because the amplifier 5 gives an output signal to a loss switch circuit 6 after the amplifier 5 eliminates an inphase noise component that is superimposed on the line 3, the circuit 6 can detect line resistance of the line 3 based on direct current voltage in proportion to the line voltage of the line 3. As a result, a filter which eliminates inphase noise in the circuit 6 is not necessary to be installed.

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a subscriber circuit,
More particularly, the present invention relates to a subscriber circuit provided with a loss switch circuit for supplying a DC voltage from a power supply circuit to a subscriber line, determining a subscriber line resistance, and performing line loss control on a subscriber line signal.

FIG. 6 schematically shows a generally known subscriber circuit, in which a feeder circuit 2 is provided.
The subscriber terminal such as a telephone through is provided, TIP line constituting the subscriber line 3 to the power supply circuit 2 (ground electrode Gnd side line) and RING lines (-48V negative electrode V _BB side line) 4 are connected.

In a power supply circuit 2, transistors Q1 and Q2 are connected to a TIP line and a RING line via power supply resistors R1 and R2, respectively.
Line resistance RL1- subscriber terminal towards the Gnd side negative V _BB side transistors Q1- supply resistor R1-TIP line -
The line terminal RL2 of the RING line, the power supply resistor R2, and the transistor Q2 are connected in this order, and the subscriber terminal 4 is turned off.
When hooked, a direct current _IL flows from the positive electrode side to the negative electrode side as shown in the figure.

[0003] In the subscriber circuit 1 that supplies the subscriber terminal 4 with a 48 V DC power, an AC component such as an audio signal is superimposed on the DC I _L and flows.

On the other hand, in such a subscriber circuit 1, the level of the audio signal input to the subscriber line 3 changes greatly due to the variation of the line resistances RL1 and RL2 of the subscriber line 3.

For this reason, in the subscriber circuit 1, in order to prevent the level of the audio signal from largely fluctuating according to the value of the combined line resistance RL = RL1 + RL2 of the subscriber line 3, as shown in FIG. When it is found that the signal level is smaller than the predetermined value RL ', the audio signal level is reduced to increase the line loss. Conversely, when the subscriber line resistance RL is higher than the predetermined value RL', the line loss is suppressed without suppressing the audio signal level. A loss switch circuit for controlling the level fluctuation of the audio signal so as to reduce it is required.

[0006]

2. Description of the Related Art FIG. 8 shows a conventional subscriber circuit 1. In this subscriber circuit 1, a TIP line and a RING line of a subscriber line 3 shown in FIG. From the connection point of each capacitor 7 for removing the DC component
The differential amplifier 5 is connected via a and 7b.

The differential amplifier 5 has input resistors R51, R5
2, a bias resistor R53, a feedback resistor R54, and an operational amplifier A1. The DC component on the subscriber line 3 is cut by the capacitors 7a and 7b, and only the AC component is supplied to the differential amplifier 5. The differential amplifier 5 amplifies only this AC component and outputs it as an audio signal, which is supplied to an A / D converter 8a in a codec (CODEC) unit 8,
The A / D converter 8a converts the digital signal into a digital signal and performs digital processing in the codec unit 8.

Further, a loss switch circuit 60 is connected to the power supply circuit 2 in parallel with the differential amplifier 5, and the loss switch circuit 60 detects the subscriber line resistance RL, and as shown in FIG. The loss of the audio signal flowing through the subscriber line 3 is changed by a circuit (not shown) connected to the loss switch circuit 60 in accordance with the value of the subscriber line resistance RL, so that a constant level audio signal is always added. Terminal 4.

[0009]

In such a conventional subscriber circuit, the line voltage of the subscriber line 3 detected by the loss switch circuit 60 includes not only a DC component necessary for determining the subscriber line resistance but also an in-phase component. Therefore, in order to determine the subscriber line resistance, it is necessary to incorporate a filter or the like for removing these unnecessary noise components, which causes a problem that the scale of the loss switch circuit becomes large. there were.

Accordingly, the present invention relates to a subscriber circuit provided with a loss switch circuit for supplying a DC voltage from a power supply circuit to a subscriber line, determining a subscriber line resistance, and performing line loss control on the subscriber line signal. Another object of the present invention is to reduce the size of the loss switch circuit.

[0011]

In order to achieve the above object, a subscriber circuit according to the present invention connects a signal-combining differential amplifier for eliminating common-mode noise in parallel with a power supply circuit, and A DC component removing element and a loss switch circuit are connected to an output terminal of the differential amplifier, and the DC component removing element is further connected to a codec section, and the loss switch circuit converts a subscriber line resistance to an output voltage of the differential amplifier. It is characterized in that it includes a circuit for making a determination based on this.

That is, as shown in FIG. 1, the DC component removing element provided on the input side of the signal-combining differential amplifier 5 in the subscriber circuit 1 is replaced with the output side of the differential amplifier 5, that is, the codec section 8. , The DC voltage component of the subscriber line 3 is directly input to the differential amplifier 5.

Therefore, the differential amplifier 5 removes the in-phase noise component superimposed on the subscriber line 3 and then supplies the output signal to the loss switch circuit 6, so that the loss switch circuit 6 The line resistance of the subscriber line 3 can be detected based on the DC voltage proportional to the
Based on this, the loss switch circuit 6 can perform line loss control on the audio signal on the subscriber line 3.

On the other hand, the output signal of the differential amplifier 5 passes through the DC component removing element 7 so that only the audio signal is extracted and supplied to the codec section 8 (A / D converter 8a thereof) for digital processing. Will be

As a result, it is not necessary to newly provide a filter or the like for removing common-mode noise in the loss switch circuit 6, and the size of the loss switch circuit 6 can be reduced.

In the present invention, the loss switch circuit 6 includes a filter for removing an audio signal, and a comparison circuit for generating an on / off level output signal by comparing the output signal voltage of the filter with a threshold value. And can be composed of

Further, according to the present invention, the comparison circuit includes:
It may be configured to include a circuit that changes the threshold value in proportion to the supply voltage.

Further, in the present invention, the loss switch circuit 6
May be configured to include a clamp circuit for suppressing the output signal of the filter to a voltage range that can be input to the comparison circuit.

Further, in the present invention, the loss switch circuit 6
Alternatively, the output unit may be provided with a time guard circuit for preventing a malfunction due to a transient response of the subscriber line when the subscriber terminal 4 goes on / off hook.

[0020]

FIG. 2 shows an embodiment of the differential amplifier 5 and the loss switch circuit 6 in the subscriber circuit 1 according to the present invention shown in FIG. Is similar to the conventional example shown in FIG. 8, but in this embodiment, the loss switch circuit 6 is specifically shown.

That is, the loss switch circuit 6 is connected to the output terminal of the differential amplifier 5 and removes an audio signal. The filter 61 compares the output signal voltage of the filter 61 with a threshold value to turn on / off. It includes a comparison circuit 62 for generating an output signal of a level, and a clamp circuit 63 for suppressing the output signal of the filter 61 to a voltage range that can be input to the comparison circuit 62.

The filter 61 is a low-pass filter composed of a resistor R4 and a capacitor C1 connected to the output terminal of the differential amplifier 5, and extracts a filter output from a connection point between the resistor R4 and the capacitor C1. .

The comparison circuit 62 includes a resistor R3 connected between the output terminal of the filter 61 and the positive terminal (for example, +5 V) of the power source, and a positive terminal and a negative terminal (for example, 0 V) of the power source.
V) A resistor R that is connected between the terminals and divides the power supply voltage
5 and R6, and a non-inverting input terminal is connected to a connection point between the resistors R5 and R6 to input a threshold voltage and to connect the resistors R3 and R6.
4 is connected to an inverting input terminal, and the comparator CMP uses the filter output voltage as an input signal of the comparison circuit 62.
And a feedback resistor R7 for providing hysteresis connected between the output terminal of the comparator CMP and the non-inverting input terminal, and a pull-up resistor connected between the output terminal and the positive terminal of the comparator CMP. R8. It is connected via a resistor R3, and a connection point between the resistors R3 and R4 is given.

Further, the clamp circuit 63 includes resistors R1 and R2 connected in series between the power supply terminals, and a diode D1 connected in the forward direction between a connection point between the resistors R1 and R2 and the output terminal of the filter 61. It is composed of

In the operation of the embodiment shown in FIG. 2 when each resistor and capacitor use the values shown, the DC component of the line voltage of the subscriber line 3 constitutes the differential amplifier 5. When the resistance values of the resistors R51 and R52 are set to r1 in common and the resistance values of the resistors R53 and R54 are set to r2 in common, from the differential amplifier 5, the voltage between the subscriber lines × r2 / R1.

Since the differential amplifier 5 performs signal synthesis, the in-phase component of the AC component of the subscriber line 3 is removed, and the output AC component has a voltage of 2 × r2 / r1 times.

As described above, the differential amplifier 5 outputs the DC voltage with the AC component audio signal superimposed thereon,
Of these, the DC component is cut by the DC removing capacitor 7 and supplied to the A / D converter 8a of the codec unit 8.

On the other hand, when the output signal of the differential amplifier 5 is given to the loss switch circuit 6, the audio signal of the AC component is first removed in the filter 61 by the action of the low-pass filter constituted by the resistor R4 and the capacitor C1. Only the DC component is output in the form.

At this time, the output voltage of the filter 61 is divided by the resistors R3 and R4, and further divided by the resistors R1 and R2.
In addition, the clamp circuit including the diode D1 suppresses the input voltage of the comparator CMP to a voltage range in which the input can be performed.

That is, the output voltage of the differential amplifier 5 exhibits a power supply voltage range of, for example, 0 V to -48 V. If the output of the differential amplifier 5 is -48 V, the output of the resistors R3 and R4 The connection point, that is, the input voltage of the comparator CMP (the input voltage of the comparison circuit 62) is about −
It becomes 3.5V, but the resistance R1 in the clamp circuit 63
From the values of R2 and R2, the input voltage of the comparator CMP is about 1.
Because it is suppressed to 5V, it does not become -3.5V and +
It will be clamped to 1.5V.

In this case, since the inverting input terminal of the comparator CMP has a threshold of about 2.3 V due to the voltage division of the resistors R5 and R6, the clamp voltage +1.5 V from the clamp circuit 63 is applied to the inverting input terminal of the comparator CMP. Output, the output of the comparator CMP is at the ground potential (approximately 0
V), which indicates a logic L level.

On the other hand, when the output voltage of the differential amplifier 5 becomes 0 V, the voltage at the inverting input terminal of the comparator CMP becomes about +4.2 V due to the voltage division of the resistors R3 and R4. Since the voltage is higher than 1.5 V, the input voltage of the comparator CMP is +
4.2V is provided.

As a result, since the input voltage of the comparator CMP becomes higher than the threshold voltage, the output terminal of the comparator CMP generates an output of about 5 V as a logic H level.

The output voltage of the differential amplifier 5 is 0 to -4.
When outputting an intermediate value of 8V, the comparator CM
The output level of the loss switch circuit 6 becomes H level or L level with a threshold value given to the non-inverting input terminal of P as a boundary. This is the subscriber line resistance RL 'shown in FIG.
Is equivalent to performing line loss switching. Note that the value of the subscriber line resistance RL 'has a width in order to provide hysteresis so that the output is stabilized when the inverted input of the comparator CMP is near the threshold.

As described above, when the output voltage of the differential amplifier 5 is large and the output voltage of the loss switch circuit 6 is at the logic H level, it is determined that the subscriber line voltage is large and the loss is large, and the loss to the subscriber line signal is large. However, when the output voltage of the differential amplifier 5 is small and the output voltage of the loss switch circuit 6 is at the logical L level, the subscriber line-to-line voltage is small and the loss is small. Control is performed to increase the loss with respect to the line signal.

FIG. 3 shows a modification of the loss switch circuit 6 shown in FIG. In this embodiment, the resistors R5 and R6 for giving the threshold voltage at the non-inverting input terminal of the comparator CMP are connected between the positive power supply terminal (+ 5V) and the negative power terminal (V _BB = −48V) of the power supply circuit 2. The difference is that they are connected.

That is, the threshold value of the comparator CMP changes in proportion to the power supply voltage of the power supply circuit 2, and follows the fluctuation even when the power supply voltage of the power supply circuit 2 applied to the subscriber line 3 fluctuates. Thus, the threshold value can be changed, so that more accurate operation as a loss switch can be expected.

FIG. 4 shows still another modification of the loss switch circuit 6 shown in FIG. 2. In this modification, an on / off hook monitoring circuit 10 and a timer are provided at the output of the loss switch circuit 6. The circuit 11 is provided so that the timer circuit 11 operates by extending the output signal from the loss switch circuit 6 in response to the monitoring result of the monitoring circuit 10.

That is, the monitoring circuit 10 constantly monitors the subscriber line voltage (TIP line voltage (see FIG. 5 (1))), and when this subscriber line voltage changes as shown in the figure, the monitoring circuit Reference numeral 10 denotes a signal indicating the change from the on-hook state to the off-hook state to the timer circuit 11 (see FIG. 2B).

As a result, the output from the loss switch circuit 6 changes from on-hook to off-hook as shown in FIG.
Even if the transient response is caused by the change to the hook, the guard time GT by the timer circuit 11 is provided as shown in FIG. 4D, so that the output of the loss switch circuit 6 is suppressed from flapping. Output will be obtained.

[0041]

As described above, according to the subscriber circuit of the present invention, a differential amplifier for removing common-mode noise is connected in parallel with a power supply circuit, and a DC component is connected to an output terminal of the differential amplifier. Since the removing element and the loss switch circuit are connected, the DC component removing element is further connected to the codec section, and the loss switch circuit is configured to determine the subscriber line resistance based on the output voltage of the differential amplifier. A filter for removing common-mode noise is not required in the switch circuit, and the circuit scale can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing in principle the configuration of a subscriber circuit according to the present invention.

FIG. 2 is a block diagram showing an embodiment of a subscriber circuit according to the present invention.

FIG. 3 is a block diagram showing a modification (1) of the loss switch circuit used in the subscriber circuit according to the present invention.

FIG. 4 is a block diagram showing a modification (No. 2) of the loss switch circuit used in the subscriber circuit according to the present invention.

FIG. 5 is a time chart for explaining an operation of a modification of FIG. 4;

FIG. 6 is a diagram illustrating the concept of a general subscriber circuit.

FIG. 7 is a graph showing an example of a loss switch operation.

FIG. 8 is a block diagram showing a conventional subscriber circuit.

[Explanation of symbols]

 Reference Signs List 1 subscriber circuit 2 power supply circuit 3 subscriber line 4 subscriber terminal 5 differential amplifier 6 loss switch 7 DC component removing element (capacitor) 8 codec unit

Claims (5)

[Claims] 1. A subscriber circuit having a loss switch circuit for supplying a DC voltage from a power supply circuit to a subscriber line, determining a subscriber line resistance, and performing line loss control on a subscriber line signal. A differential amplifier for signal synthesis for removing common-mode noise is connected in parallel with the circuit, a DC component removing element and the loss switch circuit are connected to an output terminal of the differential amplifier, and the DC component removing element is further connected. A subscriber circuit connected to a codec unit, wherein the loss switch circuit includes a circuit for determining the subscriber line resistance based on an output voltage of the differential amplifier. 2. A filter according to claim 1, wherein said loss switch circuit includes a filter for removing an audio signal, and a comparator for comparing an output signal voltage of said filter with a threshold value to generate an on / off level output signal. A subscriber circuit characterized by comprising a circuit. 3. The subscriber circuit according to claim 1, wherein the comparison circuit includes a circuit that changes the threshold value in proportion to a power supply voltage from a power supply circuit. 4. The loss switch circuit according to claim 1, wherein the loss switch circuit includes a clamp circuit for suppressing an output signal of the filter to a voltage range that can be input to the comparison circuit. Subscriber circuit. 5. The time switch circuit according to claim 1, wherein the loss switch circuit includes a time guard circuit for preventing a malfunction caused by a transient response of the subscriber line when the subscriber terminal goes on / off hook. A subscriber circuit, which is provided in an output unit.