JPH07121139B2 - Subscriber circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a subscriber circuit in an electronic exchange, and more particularly to a subscriber for connecting a terminal such as an electronic telephone which generates a dial pulse by turning on / off a semiconductor switch. Related to the circuit.

[Conventional technology]

Conventionally, this kind of subscriber circuit has been constructed as shown in FIG. That is, the current flowing through the pair of subscriber lines 11a and 11b is detected by the current detecting means 13 via the power feeding resistors 12a and 12b, and the subscriber line state determining means 14 determines the subscriber based on the value of the detected current. The state of the line, that is, the presence or absence of a loop was determined. This determination is made by determining that the current value detected by the current detecting means 13 is off-hook when the current value is larger than the reference value, and is on-hook when the current value is smaller than the reference value.

Here, the operational amplifiers 15a and 15b are the feed resistance combination function generators.
The 16 output signals are input, and the output signals are output to the other ends of the feeding resistors 12a and 12b. Further, the operational amplifiers 15a and 15b are supplied with power from the power supply power supply 17.

[Problems to be Solved by the Invention]

However, since the conventional call current supply source for such a subscriber circuit has an output stage configuration using an operational amplifier,
The output stage cannot operate up to the power supply voltage of the operational amplifier, and is used in a range where the output voltage becomes smaller than the power supply voltage in order to operate the operational amplifier normally. Therefore, when operating at a low power supply voltage in order to save power, the voltage seen between the subscriber lines is lower than the power supply voltage. In the steady state, a loop current equal to or higher than a predetermined threshold value flows, so that loop detection can be correctly performed. However, in the electronic telephone, not a mechanical contact used in a conventional telephone, but a semiconductor switch having a certain transient characteristic until a transition from an off state to an on state is used. For this reason, the impedance is high immediately after the power is turned on, and the loop current is difficult to flow.Therefore, the current flowing from the subscriber circuit that is constant resistance power supply is small, and the time it takes for the current value to exceed the threshold value for loop detection. Becomes longer.
Therefore, the pulse width of the diamond pulse detected by the subscriber circuit is equivalently shortened. Since the opening and closing time width of the loop for identifying as a dial pulse is specified in advance, the time until the threshold for loop detection is exceeded becomes longer and the pulse width becomes shorter, so that the dial pulse is counted correctly. May not be possible.

[Means for Solving the Problems]

The present invention detects a current flowing through a subscriber line, and when the value of the current detected by the current detecting means is larger than a reference value, it is determined to be off-hook, and is smaller than the reference value. Subscriber line status determination means that determines that the line is on-hook at some time, and raises the voltage of the power supply when the state of this subscriber line changes from on-hook to off-hook, while it remains constant when it changes from off-hook to on-hook. And a power supply voltage control means for lowering the voltage of the power supply power supply after a lapse of time.

[Action]

As a result, a large amount of loop current flows when the dial pulse is sent, and the dial pulse can be reliably received.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

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

One end of each power feeding resistor 12a, 12b is connected to the pair of subscriber lines 11a, 11b connected to the telephone set 18, and each power feeding resistor 12a
The other ends of a and 12b are connected to the output ends of operational amplifiers 15a and 15b that realize a desired feeding impedance function from the voltages of the subscriber lines 11a and 11b. Further, a current detecting means 13 for extracting the voltage and detecting a current flowing therethrough is connected to both ends of the power feeding resistors 12a and 12b, and the current detecting means 13 serves as a reference for determining the output and the presence / absence of a loop. Subscriber line status determination means 14 for comparing

Based on the output, the subscriber line state determining means 14 supplies power to switch the output signal immediately when the signal changes from on-hook to off-hook, and when the signal changes from off-hook to on-hook after a certain period of time after the change. Voltage control means
19 is connected, and its output serves as the input of the power supply voltage switching signal of the power supply 17.

Now, when the subscriber picks up the handset of the telephone 18, the hook switch 20 is closed, and the loop current changes to the power feeding resistor 12a and the subscriber line 1
1a, hook switch 20, dial pulse sending switch
It flows to the power feeding line 17 through 21, the subscriber line 11b, and the power feeding resistor 12b. The current detection means 13 outputs an output corresponding to the voltage generated in the power feeding resistors 12a and 12b to the subscriber line state determination means 14, which compares the reference value with the reference value. If it exceeds, it outputs off-hook.

The power supply voltage control means 19 receives the output of the subscriber line state determination means 14 and detects that the power supply voltage is increased, detecting that the power supply voltage has been increased, and the power supply power supply 17 outputs the power supply voltage control means 19. To increase the power supply voltage. This causes the loop current to increase. For example, if the power supply voltage for power saving is 24 volts and the offset voltage for operating the operational amplifier normally is about 2 volts, the voltage seen on the subscriber line side will be 22 volts. In addition, the feedback function is set so that the power supply resistance of the subscriber circuit is 200 ohms, and the line resistance of the subscriber line is 300
It is assumed that the DC resistance of the ohms and telephones at steady state is 300 ohms. At this time, the current flowing through the loop current detection circuit is
It is expressed by the following equation.

(24-2) Volt / (200 x 2 +300 +300) ohm = 22 milliamps In the case of an electronic telephone where the transient DC resistance during dial pulse transmission looks like 700 ohms, the current flowing in the loop current detection circuit is expressed by the following equation. Be done.

(24-2) Volt / (200 x 2 +300 +700) ohm = 15.7 mA Normally, the loop detection threshold is set to about 12 mA, so the loop current in the transient state exceeds the loop detection threshold. The delay time up to is increased, and the determination time for a loop is shortened due to the break of the dial pulse.

Assuming that the power supply voltage is raised by about 4 volts by the power supply voltage control means, the loop current during transition is expressed by the following equation.

(24 + 4-2) volt / (200 × 2 + 300 + 700) ohm = 18.5 mA As described above, 18.5 mA flows, so the delay time until the loop detection threshold is exceeded is shortened, and the dial pulse is detected by the host device. It becomes possible to guarantee the pulse width necessary for

Next, when the subscriber dials, the dial pulse sending switch 21 is turned on and off. When turned off, no loop current flows, so the output of the current detection means 13 becomes zero. Then, the subscriber line state determination means 14 outputs on-hook because the loop current value does not exceed the reference value. The power supply voltage control means 19 detects the change from off-hook to on-hook, but does not lower the power supply voltage for a certain period of time, so the power supply voltage remains high. When the dial pulse sending switch 21 is turned on again, the loop current flows again, and the subscriber line status judging means 14 outputs off-hook by the output of the current detecting means 13. Therefore, the power supply voltage control means 19 continues to output the signal for raising the power supply voltage.

Here, by setting the fixed time of the above-mentioned power supply voltage control means 19 to be longer than the period of the dial pulse, the power supply voltage can be kept high during the dial pulse transmission.

〔The invention's effect〕

As described above, according to the present invention, based on the output of the subscriber line state determination circuit, the control signal is changed immediately when transitioning from the on-hook state to the off-hook state, and when the transition from the off-hook state to the on-hook state occurs, the dial pulse period is shorter than the dial pulse period. Since the control signal is changed for a long fixed time, it becomes possible to flow a large amount of loop current during dial pulse transmission. As a result, the transient DC resistance at the time of sending the dial pulse of the electronic telephone or the like can flow a large amount of current even to a terminal whose resistance is higher than the terminal resistance at the steady state, and the dial pulse can be normally received.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a block diagram showing a conventional example. 11a, 11b ... Subscriber line, 12a, 12b ... Feeding resistance, 13 ... Current detecting means, 14 ... Subscriber line status judging means, 15a, 15b ... Operational amplifier, 16 ... Feeding resistance composite function generation Power supply, 17 ... Feed resistance, 18 ... Telephone, 19 ... Feed voltage control means, 20 ... Hook switch, 21 ... Dial pulse sending switch.

Claims (1)

[Claims] 1. A transient DC resistance during dial pulse transmission is larger than that in a steady state in an off-hook state, and a line voltage of a pair of subscriber lines to which a subscriber unit is connected is detected and equivalent when viewed from the subscriber unit side. Calculated by converting the voltage for the constant resistance power supply to the detected line voltage by a predetermined feedback function, and adding this voltage through a specified resistor within the range of the power supply voltage being supplied. A power supply power supply applied to the power supply line, a power supply voltage source supplying a power supply voltage to the power supply power supply, a current detection means for detecting a current flowing through the predetermined resistance to which a voltage is applied by the power supply wire, and a current detection The magnitude of the current detected by the means is compared with a predetermined reference value, and when the detected current value is greater than or equal to the reference value, it is determined that the subscriber unit is in the off-hook state, and the detected current value is the reference value. Subscriber unit state determining means for determining that the subscriber unit is in the on-hook state when it is low, and when the subscriber unit state determining unit detects that the subscriber unit has changed from the on-hook state to the off-hook state Of the power supply voltage source so that the time required for the current value flowing through the resistor to exceed the reference value after the worker device changes from the on-hook state to the off-hook state is shorter than a predetermined time that causes a dial pulse detection error. The power supply voltage control means for increasing the output voltage and returning the output voltage of the power supply voltage source to the original voltage when this state continues for a certain period longer than the period of the dial pulse after the subscriber unit changes to the on-hook state. A subscriber circuit, comprising: