JPS6361596A - Hook-on detection circuit - Google Patents

Abstract

PURPOSE:To simplify a circuit and to improve the reliability of the circuit by substituting the two switchers of the titled circuit with a R-S flip-flop and an inverter. CONSTITUTION:If a current through the line has an amplitude equal to or higher than a detection threshold value, a line current detector 1 turns a line current detecting signal (a) to a High level, and a hook off detecting signal (e) is converted to a High level by the R-S flip-flop circuit 5, and the hook-off detecting signal is outputted from an output terminal 6. When the line current is interrupted for a time longer than a Low level guard time after said state in which a hook-off is detected, a Low level guard signal (c) comes in a Low level, and the hook-off detecting signal (e), too, goes to a Low level, and the state turns to be one in which no hook-off is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a hook-off detection circuit, and more particularly to a simplified hook-off detection circuit.

[Conventional technology]

Conventionally, a hook-off detection circuit has a line current detection circuit 1, a high level guard device 2, and a low level guard circuit, as shown in FIG.
A hook-off detection signal was created using the W level guard device 3 and two switches, a first switch and a second switch.

The line current detector 1 detects the current of the telephone line and outputs a line current detection signal a when the current is above a certain threshold value. The high level guard device 2 inputs the line current detection signal a and changes the line current detection signal a from Low level to High level.
A constant high level with a high level when changing to a high level
The output goes high when it lasts for the gh level guard time.
The h reperno node signal a is changed from low level to high level, and the change in line current detection signal a from high level to low level is transmitted as is. The low level guard device 3 changes the output low level guard signal C from high level to low level when the low level lasts for a certain low level guard time when the line current detection signal a changes from high level to low level.
w level, and the line current detection circuit a changes from Low level to High level. , to convey.

The first switch 4 is switched when the output of the second switch 5 is at High0 level. Now, when line current is detected, H
The level guard signal becomes L (level) and the signal switches the second switch 5. At this time, the @H level signal is applied to the second switch 5. A signal is output from the terminal 6 as a hook-off detection signal.The output also switches the first switch 4 to the guard device 3 side.Next, when i!J[R is no longer detected, , the first switch 4 is restored and the second switch 5 outputs an L level signal as the signal becomes Low+L+ level.

[Problem that the invention seeks to solve]

As explained above, the conventional hook-off detection circuit has the disadvantage that the circuit is complicated because it requires two switching devices.

[Means for solving problems]

The hook-off detection circuit of the present invention has an inverter and an S-S flip-flop circuit instead of two switches.

〔Example〕

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

FIG. 1 shows an embodiment of the present invention. A line current detector 1 detects the current of the telephone line and outputs a line current detection signal a when the current exceeds a certain threshold value. 2 is High
h level 4 guard device, which inputs the line current detection signal a and outputs a certain High level when the line current detection signal a changes from Low level to High level.
The output goes High when it lasts for the h level guard time.
The level guard signal a is changed from low level to high level, and the change in line current detection signal a from high level to low level is transmitted as is. 3 is Low
It is a level guard device, and the line current detection signal a is High.
When changing from a level to a low level, if the low level lasts for a certain low level guard time, the output low level level is changed from level to low, and the line current detection signal a is changed from low level to low level.
A change from w level to high level is transmitted as is.

4 is an inverter which inverts the logic of the high level guard signal d and outputs an inverted signal d. 5 is an R-8 flip-flop circuit, and the Low level guard signal C is High.
h level and the inverted signal d goes to the low level, the hook-off detection signal e goes to the high level, and the inverted signal d goes to the high level and the low level guard signal C goes to the low level.
When the hook-off detection signal e reaches the w level, the hook-off detection signal e is set to the low level. 6 is an output terminal which outputs a hook-off detection signal e to an external circuit (not shown).

Next, the operation of the device will be explained step by step.

When the line current has an amplitude equal to or greater than the detection threshold, the line current detector 1 sets the line current detection signal a to High level 1.
,, If the High level state continues for the High level guard time or longer, the inverted signal d, which is the output of the High level guard device 2, becomes Low level. At this time, Lo
w Since the low level guard signal output from the level guard device 3 is at a high level, the shift off detection signal e is set to high level by the 几S flip-flop circuit 5.
At the high level, the hook-off detection detection band is output from the output terminal 61c. If the line current is interrupted by the dial pulse signal in this state, if the Low level guard time is set larger than the repetition period of the dial pulse of the telephone, the output Low of the Low level guard device 3 will be reduced.
Since the level guard signal C does not change to Low level, the hook-off detection signal e is kept at High level.Next, if the line current is longer than the Low level guard time from the state where hook-off is being detected, When the low level guard signal read signal is at low level, the inverted signal d is at high level, so the hook-off detection signal e becomes low level, and the hook-off is not detected.This hook-off is detected. When the ringer signal from the line is not activated and a repeating signal of IIGB level and Low level is output to the circuit current detection signal a), the High level guard time is set to the line current detection signal by the ringer signal. By setting the high level level of signal a to be larger than the level repetition period w, the high level guard signal from the high level guard device remains at a low level and does not change, so the inverted signal d remains at a high level. , the hook-off detection signal e does not change and hook-off is not detected.

〔Effect of the invention〕

As explained above, the present invention provides two hook-off detection circuits.
By replacing the two switches with an S-S flip-flop and an inverter, the circuit can be simplified and its reliability can be improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional hook-off detection circuit. 1...Line current detector, 2...High
h level guard device, 3...Low level guard device, 4...inverter, 5...1%-S flip-flop circuit, 6...output Terminal, a...
...Line current detection signal, b...High level guard signal, C...Low level guard signal, d...Inverted signal, e... Hook-off detection signal.

Claims (2)

[Claims] (1) A line current detector that detects the current in the telephone line and outputs a line current detection signal when the current in the telephone line exceeds a certain threshold, and a line current detection signal from the line current detector as input. The line current detection signal is low
When the level changes from high level to high level and the high level lasts for a certain high level guard time, the output high level guard signal changes from low to high level, and the change from high level to low level is transmitted as is. High level guard device and
When the line current detection signal changes from high level to low level and the low level continues for a certain low level guard time, the output low level guard signal is changed from high to low level and from low to high.
A low level guard device that transmits the change to high level as is, and a high level guard device that transmits the change to high level as is.
an inverter that inputs an h-level guard signal, inverts the logic of the input signal, and outputs the same; and an R-S flip-flop circuit that outputs a hook-off detection signal according to the inverted signal from the inverter and the low-level guard signal. A hook-off detection circuit having a hook-off detection circuit. (2) The R-S flip-flop circuit outputs a hook-off detection signal when the line current has an amplitude greater than or equal to the detection threshold and continues for more than a high level guard time, and in a state where no hook-off is detected. If the given line current is in the form of a pulse with an amplitude greater than the detection threshold and a period less than the High level guard time, the hook-off detection signal is not output, and the line current is output while hook-off is being detected. To maintain the output of the hook-off detection signal even if the line current is intermittent at a cycle shorter than the Low level guard time, and to stop outputting the hook-off detection signal if the line current is intermittent for the Low level guard time or longer while hook-off is being detected. A hook-off detection circuit according to claim (1), characterized in that: