JPS631292A - Loop detection system - Google Patents

Abstract

PURPOSE:To prevent the malfunction by storing the output voltage of a differential amplifier corresponding to a loop current in a sampling and holding circuit and generating a threshold voltage proportional to an off-hook current value on a basis of said stored voltage by a circuit which generates the threshold voltage for the loop current. CONSTITUTION:A loop detecting circuit 2 is provided in the output side of a differential amplifier OPA which converts the current flowing to an electronic inductor to a voltage. An output voltage V0 of the differential amplifier OPA corresponding to the loop current is stored in a sampling and holding circuit 23, and threshold voltages VtL and VtG proportional to the output voltage V0 are generated by circuits 24 and 25, which generate threshold voltages for the loop current and a ground key, on a basis of the stored output voltage and are inputted to comparators 21 and 22. The loop current and a ground key depression current are detected on a basis of variable threshold voltages VtL and VtG. Consequently, the malfunction is prevented even if noise is superposed on the output voltage V0 of the differential amplifier, and the loop current is accurately detected.

Description

[Detailed Description of the Invention] [Summary] This is a loop detection method that attempts to prevent malfunctions by obtaining a threshold voltage proportional to the off-footer current value.

[Industrial application field]

The present invention relates to a loop detection method applied to a loop monitoring circuit of a telephone.

[Conventional technology]

Conventional loop detection methods include firstly the A relay method (FIG. 4) and secondly the electronic method (FIG. 5).

The above-mentioned first prior art (Fig. 4) is provided with A relays a'1 and a'2 in the loop monitoring circuit connected to the audio circuit 1', and when the subscriber picks up the handset, the hook switch H3W By closing, a loop current flows between the A line and the B line.

The A relay "l+aZ has high impedance in terms of AC, and when the handset is lifted to enter the off-footer state, a DC loop current flows, which activates and notifies the control device that the off-footer state is present.

However, since this first conventional technique is not suitable for high density, a second conventional technique shown in FIG. 5 was proposed. Fourth
a'1 in the figure. a′2 are a′, , a″2 in Fig. 5, respectively.
It corresponds to

In this second prior art, when an off-footer state occurs, the voltage across the resistor R generated by the off-hook current flowing through the loop monitoring circuit is amplified by a differential amplifier OPA, and the obtained voltage (2) is obtained. is compared with the threshold voltage ■ in the comparator COMP.

■. If it is larger than , it is judged that the loop current is flowing, and if it is smaller, it is judged that it is not flowing, and this is notified to the control device via the photocoupler PHC.

The ground key GND is used for business purposes, such as emergency calls, and is used to call the other party when the other party accidentally hangs up during a call.If the GND is closed, the loop current becomes zero. Therefore, we can create a similar circuit by B
Detection is done using an additional circuit on the wire.

[Problem that the invention seeks to solve]

In the second prior art shown in FIG. 5, the threshold voltage Vth is a fixed value (FIG. 6).

However, a large amount of off-footer current flows when the distance is short;
In the case of long distances, there is less flow. That is, operational amplifier OPA
The output voltage of is VO3 corresponding to the short-distance current, and Vat corresponding to the long-distance current (FIG. 6).

Therefore, for a fixed V, the margin M of V is ■
. , is smaller than the margin M5 of .

In such a situation, the second prior art (Fig. 5) uses transistors Q + and Q 2 because it is electronic, but transient phenomena caused by the on/off operation of the hook switch H3W and the dial pulse contact can be avoided. Therefore, these transistors ql and Qz may become saturated or the operational amplifier OPA
Noise n may be superimposed on Vol due to the saturation characteristics of Vol (FIG. 6).

Further, since the OPA is a differential amplification, AC induced noise components should originally be removed, but due to variations in parts, etc., this AC bone may appear as noise n.

In the second prior art, since the threshold voltage VLk is fixed at a low level for long distance use, the off-hook current flowing due to such noise n cannot be detected by the comparator COMP, and the output There is a problem with malfunctions such as turning on and off.

Furthermore, there is a problem in that the detection of the ground key GND requires a circuit of the same size and separate from that for loop detection.

[Means for solving problems]

An object of the present invention is to solve the above-mentioned problems and to stabilize the operation of loop current detection while also enabling ground key detection.Means for this purpose are as shown in FIG.
A loop detection circuit 2 is provided on the output side of the differential amplifier OPA that converts the current flowing into the electronic inductor into voltage, and the loop detection circuit 2 is connected to a loop current comparator 21, a ground key comparator 22,
The output voltage of the differential amplifier OPA corresponds to the loop current. is stored in the sample and hold circuit 23, and based on this, the loop current and ground key variable threshold voltage generating circuits 24, 25 generate threshold voltages VLL, V1(,
The present invention is characterized in that both the loop current and the ground key pressing current can be detected using the variable threshold voltage v LL + v tc as a reference by generating and inputting it manually to both the comparators 21 and 22. This is a loop detection method.

[For production]

As described above, according to the present invention, the variable threshold voltage vtt is proportional to the loop current and the ground key pressing current.
,, VtG can be obtained (Figure 3 (A), (
B)).

Therefore, even if the noise n is superimposed on the output voltage (i) of the differential amplifier (FIG. 3(A)), the loop current can be accurately detected without malfunction.

Furthermore, since the ground key can also be detected at the same time using the same detection circuit 2 (FIG. 3(B)), there is no need to provide a separate circuit.

〔Example〕

The invention will now be explained by way of example with reference to the accompanying drawings.

FIG. 2 is a diagram showing an embodiment of the present invention.

The embodiment in FIG. 2 is a detailed diagram of the loop detection circuit 2 connected to the output side of the differential amplifier OPA (FIG. 1), including a loop current comparator 21, a ground key comparator 22, and a sample hold circuit 23. , a loop current variable threshold generation circuit 24, a ground key variable threshold generation circuit 25, and photocouplers 26 and 27.

The loop current comparator 21 detects whether a current flows through the loop in the off-footer state, and the ground key comparator 22
detects whether the ground key is pressed.

The sample hold circuit 23 includes switches 231 and 23
2, resistor 233, capacitor 234, differential amplifier 235
and the output voltage V of the differential amplifier OPA.

Save up.

The loop current variable threshold voltage generation circuit 24 includes:
Consisting of resistors 241 and 242, sample and hold circuit 2
A variable threshold voltage (2) for detecting the L-loop current is generated by multiplying (k<1) the output voltage (1) by (k<1).

The ground key variable threshold voltage generation circuit 25 consists of a differential amplifier 251 and resistors 252 and 253, and further multiplies the output voltage VLL of the loop current variable threshold voltage generation circuit 24 by m (m>-), and generates the ground key by multiplying the output voltage VLL by m (m>-). Generates a variable threshold voltage VLG for detection.

Photocouplers 26 and 27 inform the control device of the output results of the comparators 21 and 22.

Hereinafter, the operation of the embodiment shown in FIG. 2 having the above configuration will be explained as follows.
This will be explained based on the diagram.

When the subscriber is idle, that is, when the subscriber is not picking up the handset, the control device opens the switch 23Hsw,) and closes the switch 232 (SW2) (FIG. 3(A)). At this time, reference voltage Vr is applied to capacitor 234. This Vr is set equal to Vo, which corresponds to the loop current during the longest loop, that is, during a long distance. 1=1. When a subscriber picks up the phone, a loop current flows,
At this time, vo rises and the comparator 21 outputs Vtt=kVr.
When compared to
SWz) (Figure 3 (A)).

Therefore, the capacitor 234 is charged by this rising Vo. 1=12 and the switch 231 (S
W,) also opens and becomes V,=Vo.

After that, the variable output voltage V1 of the sample hold circuit 23
A variable threshold voltage VLL=k V + correspondingly multiplied by (k<1) is input to the comparator 21 so that from 1=13 to t4 by the dial pulse and 1=1 . In the following, for other reasons, the loop state can be detected accurately even with noise n (see Fig. 3).
A)).

On the other hand, since the above-mentioned V L L is input to the ground key variable threshold voltage generation circuit 25, it is amplified by the amplification degree determined by the resistors 252 and 253.
c=mVLt (m>-) is output.

[At = t0, when the ground key detection is pressed, a current larger than the normal loop current flows through the loop monitoring circuit, so the input voltage V0 to the comparison r&22 also becomes large after 1=10 (see Figure 3). B)).

The comparator 22 compares this increased voltage Vo with the variable threshold voltage V L G = m V L L, and the photocoupler 26 notifies the control device.

(Effects of the Invention) As described above, according to the present invention, the loop detection circuit of an electronic inductor is configured by a sample hold circuit, a variable threshold voltage generation circuit for loop current, and a variable threshold voltage generation circuit for ground key. , the threshold voltage can be made variable, making the operation more stable than before. Also, this variable threshold voltage includes that for ground key detection, so ground key detection can also be done separately. without the need for a circuit.
Now you can do it.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the principle of the present invention, FIG. 2 is a diagram showing an embodiment of the present invention, FIG. 3 is a diagram explaining the operation of the present invention, FIG. 4 is a configuration diagram of the first prior art, and FIG. 5 is a diagram showing an embodiment of the present invention. 2nd conventional technology configuration diagram, 6th
The figure is an explanatory diagram of the operation of the second prior art. DESCRIPTION OF SYMBOLS 1... Audio circuit, a,, ag... Electronic inductor, 2... Loop detection circuit, 21... Comparator for loop current, 22... Comparator for ground key, 23... Sample and hold circuit, 24... Variable threshold voltage generation circuit for loop current, 25... Variable threshold voltage generation circuit for ground key, 26.27... Photo coupler.

Claims (1)

[Claims] 1. A loop detection circuit is provided on the output side of a differential amplifier that converts the current flowing into the electronic inductor into a voltage, and the loop detection circuit is connected to a loop current comparator, a sample hold circuit, and a loop current comparator. The output voltage of the differential amplifier corresponding to the loop current is stored in the sample and hold circuit, and based on this, the output voltage of the differential amplifier corresponding to the loop current is proportional to the sample and hold voltage by the variable threshold voltage generation circuit for the loop current. A loop detection method characterized in that a loop current can be detected using a variable threshold voltage as a reference by generating a threshold voltage and inputting it to the comparator. 2. A loop detection circuit is provided on the output side of the differential amplifier that converts the current flowing into the electronic inductor into voltage, and the loop detection circuit is connected to a loop current comparator, a ground key comparator, a sample hold circuit, and a loop current comparator. The output voltage of the differential amplifier corresponding to the loop current is stored in the sample and hold circuit, and based on this, the sample and hold is generated by the variable threshold voltage generation circuit for the loop current and ground key. A loop characterized in that by generating a threshold voltage proportional to the voltage and inputting it to both of the comparators, both the loop current and the ground key pressing current can be detected using the variable threshold voltage as a reference. Detection method.