JPH05145957A - Subscriber circuit - Google Patents

Abstract

PURPOSE:To eliminate the fluctuation of line resistance to be the threshold value of loop detection caused by the fluctuation of a power source for feeding. CONSTITUTION:When a telephone set 1 is off-hooked and a speaking current is supplied from a subscriber circuit 4 to the telephone set 1, a sum current detection circuit 7 detects the sum of currents flowing in a chip line 2 and a ring line 3. A comparator 9 compares this sum current detecting circuit output voltage V1 with a voltage V2 proportional to a power source VBB for feeding prepared by a reference voltage generating circuit 8, and the loop detection is judged. The value of the line resistance to be the threshold value of the loop detection can be set without depending on the power source VBB for feeding.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to subscriber circuits, and more particularly to loop detection circuits.

[0002]

2. Description of the Related Art A conventional loop detection circuit for a subscriber circuit is
The sum of the values of the currents flowing through the tip line and the ring line (hereinafter referred to as the sum current) is detected, and the loop detection is determined by whether the sum current exceeds a preset constant value.

[0003]

In the above-mentioned conventional loop detection circuit, since the loop detection is determined by whether the sum current exceeds a certain value, the loop detection is performed when the power supply for power supply changes. There is a drawback that the line resistance, which is the threshold value of, fluctuates.

An object of the present invention is to provide a subscriber circuit in which fluctuations in line resistance, which is a threshold for loop detection based on fluctuations in power supply for power supply, are eliminated.

[0005]

In order to achieve the above object, a subscriber circuit according to the present invention has a sum current detection circuit, a reference voltage generation circuit, and a comparator, and has a tip line and a ring line. A subscriber circuit for supplying a call current to a terminal device via a sum current detection circuit, which converts a sum of currents flowing in each of a tip line and a ring line into a voltage, detects the voltage, and outputs the voltage to a comparator. The reference voltage generation circuit is
It outputs to the comparator a voltage proportional to the value of the power supply, and the comparator compares the output voltage of the sum current detection circuit with the output voltage of the reference voltage generation circuit and outputs the result. ..

[0006]

When the telephone goes off-hook and the call current is supplied to the telephone from the subscriber circuit, the sum of the currents flowing through the tip line and the ring line is detected by the sum current detection circuit.
By comparing the output voltage V _{1 of the} sum current detection circuit and the voltage V ₂ proportional to the power supply V _BB for power supply generated by the reference voltage generation circuit by the comparator and determining the loop detection,
The value of the line resistance, which is the threshold for loop detection, is the power supply V _BB
It becomes possible to set it without depending on.

[0007]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a circuit diagram of an embodiment of the present invention. In the figure, a telephone 1 is connected to a subscriber circuit 4 via a tip line 2 and a ring line 3. The tip line 2 is grounded via the resistor R ₁ and the power supply circuit 5, and the ring line 3 is connected to the power supply V _BB via the resistor R ₂ and the power supply circuit 6. The power feeding circuit 5 has a resistor R ₉ and an inductance L ₁ , and the power feeding circuit 6 has a resistor R ₁₀ and an inductance L _2.
And a series circuit. Here, it is assumed that the resistors R ₁ and R ₂ and the resistors R ₉ and R _{10 have} the same resistance value.

Both terminals of the resistor R ₁ and the resistor R ₂ are connected to an operational amplifier OPA and resistors R ₃ , R ₄ , R ₅ , R ₆ , R ₇ and R _{8 respectively.}
Connect the sum current detection circuit 7 composed of a resistor and a current I _T flows from R ₁ to the chip line 2, a resistor R ₂ from the ring line 3
The voltage that is proportional to the sum of the current I _R flowing through the operational amplifier OPA is output from the operational amplifier OPA. Resistors R ₃ , R ₄ , R ₅ ,
R ₆ , R ₇ and R ₈ are all equal and resistors R ₁ and R _{2 are}
It is assumed that the resistance value is sufficiently large. The output terminal of the operational amplifier OPA is connected to the input terminal of the comparator 9.

In the reference voltage generating circuit 8, resistors R ₁₁ and R
The grounded terminal of R ₁₂ side of the series circuit of the _12, to the terminal of R ₁₁ side, the midpoint of the power supply source V _BB is connected and a resistor R ₁₁ and R ₁₂ are, via a rectifier circuit REC And is connected to the other input terminal of the comparator 9. The comparator 9 has a loop detection signal output terminal that outputs a loop detection signal when performing loop detection.

2A, 2B and 2C show a telephone 1
Shows the change with respect to the power supply V _BB of each unit when the call current is supplied from the subscriber circuit 4 to the telephone 1 by the above.

FIG. 2A shows a current I flowing through the chip line 2.
_The current I _R flowing through _T and the ring line 3 is shown in FIG.
Shows the output voltage V ₁ of the sum current detection circuit 7, and FIG.
(C) shows the output voltage V ₂ of the reference voltage generation circuit 8.

Next, the operation will be described. Phone 1 now
In the off-hook state, the telephone line 1 is supplied with the call current from the subscriber circuit 4, and the line resistance of the tip line and the ring line is _RL .

The current I _T flowing through the tip line and the ring line,
I _R is represented by the equation (1), where R ₁ + R ₉ = R ₂ + R ₁₀ = R _B. I _T = I _R = | V _BB | / (R _L + 2R _B ) (1)

The output voltage V ₁ of the sum current detection circuit is R ₁ +
When R ₂ = _RA , it is represented by the equation (2). _{V 1 = R A · (I} T + I R) = 2R A · | V BB | / (R L + 2R B) ... (2)

The output voltage V ₂ of the reference voltage generating circuit is
It is expressed by equation (3). V ₁ = R ₁₂ / (R ₁₁ + R ₁₂ ) · | V _BB | (3)

The condition of the threshold value for the loop detection judgment is expressed by the equation (4) because the output voltage V ₁ of the sum current detection circuit 7 and the output voltage of the reference voltage generation circuit 8 become equal. V ₁ = V ₂ (4)

From the equations (2), (3) and (4), the line resistance R _{1 which} is the threshold value for the loop detection determination is expressed by the equation (5). _{2R A · | V BB | /} (R L + 2R B) = R 12 · | V BB | / (R 12 + R 11) R L = 2 · R A · (R 12 + R 11) / R 12 -2R B ... (5)

From the equation (5), the line resistance _{RL, which} is the threshold value for the loop detection judgment, is determined by the resistors R ₁ , R ₂ , R ₉ , R ₁₀ ,
It is determined by the resistance values of R ₁₁ and R ₁₂ , and does not depend on the power supply V _BB for power supply.

[0019]

As described above, according to the present invention, by using a voltage proportional to the power supply for power supply as the threshold voltage that serves as a reference for loop detection, the line resistance that becomes the threshold for loop detection is used as the power supply for power supply. The effect is that it can be set independently.

[Brief description of drawings]

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

FIG. 2A shows a change in current flowing through a tip line and a ring line due to a power supply power supply, FIG. 2B shows a change in output voltage of a sum current detection circuit due to a power supply power supply, and FIG. ,
It is a figure which shows the change by the power supply for electric power feeding of the output voltage of a reference voltage generation circuit.

[Explanation of Codes] 1 Telephone 2 Chip line 3 Ring line 4 Subscriber circuit 5,6 Power supply circuit 7 Sum current detection circuit 8 Reference voltage generation circuit 9 Comparator REC rectifier circuit I _T Current flowing in chip line I _R Ring line Flowing currents R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ , R ₇ , R ₈ , R ₉ ,
R ₁₀ , R ₁₁ , R ₁₂ resistor OPA operational amplifier L ₁ , L ₂ coil V _BB power supply for power supply

Claims (1)

[Claims] 1. A subscriber circuit having a sum current detection circuit, a reference voltage generation circuit, and a comparator, which supplies a call current to a terminal device via a chip line and a ring line, the sum current detection circuit comprising: The circuit converts the sum of the currents flowing in each of the tip line and ring line into a voltage and detects it, and outputs it to a comparator.The reference voltage generation circuit outputs a voltage proportional to the value of the power supply A subscriber circuit, which outputs to a comparator, and the comparator compares the output voltage of the sum current detection circuit with the output voltage of the reference voltage generation circuit and outputs the result.