JPH0432580B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ringing signal detection circuit that prevents problems such as resonance between telephones.

In the parent device of tone-ringer calling type telephones and wireless telephones, a ring signal detection circuit detects the arrival of a ring signal from an exchange, and the detection output drives a separate ring circuit to generate a ring tone from a speaker, etc. I try to do that. FIG. 1 shows an example of the calling signal detection circuit. In other words, the detection circuit guides a ringing signal appearing on a pair of telephone line terminals to a bridge rectifier circuit D via capacitors C ₁ and C ₂ , and smoothes the signal rectified by this rectifier circuit D by a circuit including a capacitor C ₃ . Then, the level after smoothing is determined by a gate circuit G to obtain a detection output.

However, when this type of ringing signal detection circuit is applied to a case where multiple telephones are connected in parallel to a telephone line terminal, the ringing signal detection circuit simply rectifies and smoothes the input signal to determine its level. , a dial impulse generated during a dial operation may be erroneously detected as a ringing signal, causing so-called resonance with other telephones. In the case of wireless telephone devices, there is not only a problem of resonance but also a problem of unnecessary transmission of radio waves. This is because the dial impulse is very similar to the ringing signal in voltage and generation form.

Conventionally, attention has been paid to the fact that the call signal is a sine wave and the dial impulse is basically a pulse, and resonance has been prevented by determining the forms of these waveforms. However, since exchanges and telephone lines have complex impedances, dial impulses often have waveform distortion due to transient responses and are no longer rectangular waves. For this reason, dial impulses are still sometimes erroneously detected as calling signals, and it has not been possible to completely prevent resonance.

The present invention has been made in view of the above-mentioned circumstances, and its object is to provide a ringing signal detection circuit that reliably prevents erroneous detection of dial impulses and does not cause resonance.

First, the principle of the present invention will be explained with reference to FIG. Figure a shows the voltage waveform between the telephone line terminals when making a call, and b shows the voltage waveform between the telephone line terminals when receiving a call.

That is, the voltage between the telephone line terminals is, for example, -48V with one terminal as a reference during standby. When the telephone connected to the above telephone line terminal is taken off-hook in this state, the voltage between the telephone line terminals is approximately -10V due to the direct current termination between the same terminals with several tens of ohms, as shown after time _t1 . The voltage will be as follows. Next, when dialing (t ₂ ), a dial impulse appears between the terminals as shown in ○A in the figure, and the other subscriber responds to the call made by the exchange and goes off-hook. When the exchange completes the connection, the dial impulse appears between the terminals. As shown after t ₃ , the voltage between the terminals becomes a positive voltage. Then, when the calling side goes on-hook to end the call, the terminals are opened and the voltage becomes +48V as shown after time _t4 in the figure.When the exchange detects this on-hook and performs the call end processing,
As shown after time _t5 , the voltage between the telephone line terminals returns to -48V, and the line enters the standby state from then on.

On the other hand, when a call is received from the exchange in standby mode, the voltage across the telephone line terminals increases as shown in the figure (time
t ₆ ) The voltage changes from -48V to +48V, and then the calling signal ○○○ is sent out. This calling signal is generally
It sends out a sine wave with a minimum of 45Vrms at 16Hz for 1 second and repeats a 2-second break. When the call is answered by going off-hook and the line is in a talking state, the voltage between the terminals is approximately -10V or less as shown from time t ₇ to time t ₈ because the terminals are terminated with a DC voltage of several tens of ohms. becomes voltage. However, when the on-hook is turned on, the voltage between the terminals becomes -
The voltage returns to 48V and the line goes into standby mode.

Note that the polarity of the voltage waveform shown above will be reversed if the telephone line wiring to the exchange is reversed.
Essentially nothing has changed.

By the way, if you compare the voltage between each terminal when making a call and when receiving a call, the absolute value of the DC voltage at the time of receiving a call is always 48V, whereas the absolute value of the DC voltage just before the dial impulse arrives is approximately 48V. The voltage will be 10V or less. Therefore, if each of these voltage values is detected and the detected voltage value is equal to or higher than a preset judgment value (for example, an intermediate value between 10V and 48V), the detected voltage value at this time is the one at the time of incoming call. If the detection voltage value is less than the judgment value, the detection voltage at this time is the one immediately before the dial pulse arrives. It may be configured to take this into account and prohibit generation of the paging detection signal. The above is the basic principle of the present invention.

A first embodiment of the present invention will be described below with reference to the drawings. FIG. 3 is a block diagram of the calling signal detection circuit according to the same embodiment, in which L ₁ and L ₂ indicate the respective terminals of the telephone line, and 1 indicates the 16 Hz signal detection circuit.
This 16Hz signal detection circuit 1 has telephone line terminals L ₁ ,
It detects a calling signal appearing between _L2 and is made of, for example, the circuit shown in FIG. Therefore, this circuit 1 may detect a dial impulse as a calling signal.

Now, the signal appearing between the telephone line terminals L ₁ and L ₂ is also led to the rectifier circuit 2 . This rectifier circuit 2 is composed of a diode bridge circuit, and detects the absolute value of the voltage (potential difference) between the telephone line terminals L ₁ and L ₂ . Therefore, no matter what direction the telephone line terminals are connected to the exchange, the voltage across the terminals can be reliably detected. On the other hand, the DC voltage detection circuit 3 shown at 3 in the figure monitors the level of the rectified output and determines whether the signal arriving at the telephone line terminals L ₁ and L ₂ is a calling signal or a dial impulse. be. Then, when the level of the rectified output falls to a value corresponding to the voltage between terminals L1 and L2 (absolute value 10V or less) in the off-hook state immediately before the arrival of the dial impulse, the detection output is turned off.

FIG. 4 is a circuit diagram showing the configuration of this DC voltage detection circuit 3. The detection circuit guides the rectified output of the rectifier circuit 2 to the light emitting diode 32 via the current limiting resistor 31, and causes the light emitting diode 32 to emit light. At this time, the resistance value of the current limiting resistor 31 is such that the DC resistance value of the telephone terminal is the standard value when the DC loop of the subscriber line is open.
It is set to be 1MΩ or more. Therefore, the impedance seen from the exchange side is maintained at a sufficiently large value. Then, the light emitting output of this light emitting diode 32 is received by a phototransistor 33 and converted into a voltage with a gain determined by a resistor 34. This voltage is averaged by an integrating circuit 35 and introduced into a comparator 36, and is input to a reference power source 37. It is compared with the output voltage of Then, the phototransistor 33
When the average output level exceeds the reference voltage level, it is regarded as an off-hook state immediately before the dial impulse arrives, and the generation of the detection output is stopped. Note that the time constant of the integrating circuit 35 is the second
During the off-hook period immediately before the arrival of the dial impulse shown in Figure a, the telephone line terminals L1 and L at this time
The voltage corresponding to the DC voltage (less than +10 V) between the two is set to a relatively small value so that an integrated output voltage exceeding the reference voltage level is output from the integrating circuit 35.

Furthermore, the gate of the AND gate circuit 4 shown in FIG.
The detection signal output from the signal detection circuit 4 is output to a ring tone generation circuit (not shown) as a detection output of a ring signal.

With such a configuration, the telephone line terminal L ₁ ,
When a calling signal arrives at _L2 , a detection signal is generated from the 16Hz signal detection circuit 1, and since the absolute value of the DC level is as large as approximately 48V, a detection output is also generated from the DC voltage detection circuit 3. Therefore, from the AND gate circuit 4, the above 16Hz signal detection circuit 1
The detection signal passes through as is, and as a result, a ringing tone generating circuit (not shown) is driven and a ringing tone is generated from the speaker.

On the other hand, when a dial impulse arrives at the telephone line terminals L ₁ and L ₂ , even if the dial impulse is erroneously detected by the 16Hz signal detection circuit 1, the voltage between the terminals L ₁ and L ₂ at the time of the arrival of the dial impulse Since the level is relatively small, below 10V, as shown in FIG. 2, no detection output is generated from the DC voltage detection circuit 3. Therefore, the AND gate circuit 4 becomes non-conductive, and the detection signal of the 16Hz signal detection circuit 1 does not pass through.As a result, the ringing tone generation circuit does not operate and no ringing tone is generated. Also, at this time, the level judgment by the DC voltage detection circuit 3 is made during the off-hook period (between t ₁ and t ₂ in FIG. 2) before the dial impulse actually arrives, so 16
The AND gate circuit 4 is surely rendered non-conductive before the Hz signal generating circuit 1 generates the detection signal by the dial impulse. Therefore, resonance due to dial impulses is reliably prevented.

In this way, according to this embodiment, the telephone line terminal
Since the DC voltage appearing at L ₁ and L ₂ is rectified and the rectified output level is judged by the DC voltage detection circuit 3, and the AND gate circuit 4 is gate-controlled by this judgment output, false detection due to dial impulse is avoided. Even if a signal is generated, it can be reliably cut off, and as a result, resonance can be reliably prevented. In addition, since it is only necessary to determine the DC voltage level appearing at the telephone line terminals _L1 and _L2 , it has the advantage of being extremely simple compared to systems that compare the waveforms of the dial impulse and the ringing signal. be.

FIG. 5 is a circuit diagram showing a DC voltage detection circuit according to a second embodiment of the present invention, in which the same parts as in FIG. 4 are given the same reference numerals. In the figure, the difference in configuration from the previous embodiment (Figure 4) is that a constant voltage element 38 is connected in series with the light emitting diode 32, so that the rectified output of the rectifier circuit 2 is adjusted to the level immediately before the arrival of the dial impulse. The light emitting diode 32 is turned off when the voltage drops below the level in the off-hook state (for example, 10V),
Further, the turning off of the light emitting diode 32 is detected as an increase in the integrated output voltage by the phototransistor 33 and the integrating circuit 35, and this detection result is outputted by the inverter circuit 39 as a change from the "H" level to the "L" level. This is the point.
In the circuit of this embodiment as well, the time constant of the integrating circuit 35 is set such that the DC voltage between the telephone line terminals L1 and L2 at this time is set within the off-hook period immediately before the arrival of the dial impulse, as in the above embodiment. (less than +10V), inverter circuit 39
The integrated output voltage input to the output voltage is set so that it has a voltage value corresponding to the "H" level.

With such a circuit, when the rectified output of the dial impulse is introduced, its level is smaller than that of the ringing signal and does not exceed the conduction voltage of the constant voltage element 38, so that the light emitting diode 32 and phototransistor 33 doesn't work. Therefore, the detection output of the inverter circuit 39 becomes "L" level, and as a result, the AND gate circuit 4 becomes non-conductive and does not allow the detection signal from the 16 Hz signal detection circuit 1 to pass through.

Therefore, according to this embodiment, resonance due to dial impulses can be reliably prevented as in the previous embodiment. Further, by using the constant voltage element 38, there is an advantage that the circuit configuration can be simplified compared to the one using the comparator 36 of the above embodiment.

On the other hand, FIG. 6 is a circuit diagram of a DC voltage detection circuit according to a third embodiment of the present invention, in which the same parts as in FIG. 5 are given the same reference numerals. The detection circuit converts the DC output obtained by the constant voltage element 38, the light emitting diode 32, and the phototransistor 33 into, for example, a TTL level using an inverter circuit 40. And with this conversion output AS, the gate circuit 4
The gate circuit 43 is gate-controlled by the above-mentioned conversion output which is logically inverted by the inverter circuit 42, and the clock signals BS and CS from the clock oscillator 44, which have been pass-controlled, are sent to the first and second counter circuits 45, 46 respectively. These first and second counter circuits 45 and 46 count the clock signals BS and CS that have passed through each of the gate circuits 41 and 43, and output an output every time the counted value reaches a predetermined number. Then, the flip-flop circuit 47 is set and reset by each of these outputs, and its output DS
is directly output to the AND gate circuit 4 of FIG. 3 as a detection output.

With this configuration, the H level conversion output AS is always output in the standby state, so
The first counter circuit 45 performs a repetitive counting operation, and as a result, the flip-flop circuit 47
holds the set state and outputs an H level detection output.

Now, in this state, a calling signal arrives at time t6, and the conversion output AS is shown in FIG. When the level is temporarily set to "L" as shown in a, the gate circuit 43 replaces the gate circuit 41 and enters the gate open state, and as a result, the clock signal CS is supplied to the second counter circuit 46, and the clock signal CS is supplied to the second counter circuit 46. 46
starts counting operation. In addition, the above clock signal
The count value of the first counter circuit 45 is reset by CS. However, the repetition counting time of the second counter circuit 46 is set longer than the L level period of the conversion output AS. Therefore, the second counter circuit 46 does not output an output until the conversion output AS returns to the H level, and the flip-flop circuit 47 is not reset. Therefore, the detection output DS is kept at H level.
Thereafter, even if the conversion output AS is turned on and off according to the cycle of the calling signal, the detection output DS maintains the H level. Therefore, AND gate circuit 4 in FIG.
maintains a conductive state, and the detection signal of the 16Hz signal detection circuit 1 is supplied as is to the ringing tone generating circuit, and as a result, a ringing is performed.

On the other hand, when a dial operation is performed on another telephone, the conversion output AS becomes "L" level as shown in Figure 7b due to the off-hook operation at that time, and this state occurs when the caller does not perform a dial operation. Continues until started. Therefore, the second counter circuit 46 starts counting operation instead of the first counter circuit 45. Here, the period from off-hook to the start of dial operation is generally as long as about 1 second.
Therefore, here, the second counter circuit 46
If the counting period is set to be always shorter than the above-mentioned period, the second counter circuit 46 will output an output within the above-mentioned L level period before the dial operation is started. Therefore, the flip-flop circuit 47 is reset, and the detection output DS becomes the value shown in FIG. 7b.
It becomes L level as shown in FIG. After that, the dial impulse arrives, which causes the conversion output AS to change to the seventh
Even if it changes between H level and L level as shown in Figure b, the counting period of the first counter circuit 45 is set longer than the H level period due to the dial impulse of the conversion output AS. Counter circuit 45 does not produce an output. Therefore, the flip-flop circuit 47 maintains the reset state,
Hold the detection output DS at L level. Therefore, generation of a ringing tone due to the dial impulse is prevented.

In this way, in this embodiment, the low level period due to the off-hook state immediately before the arrival of the dial impulse is detected and the AND gate circuit 4 is set to the non-conductive state, so that Definitely AND gate circuit 4
As a result, malfunctions caused by dial impulses can be almost completely prevented. In addition, the DC voltage obtained by the light emitting diode 32, phototransistor 33, etc. is converted to a TTL level by the inverter circuit 40, and the signal judgment is performed using this conversion output.
Most of the circuit can be configured with digital circuits, making circuit design easier and integration easier.

Further, FIG. 8 is a block configuration diagram of a calling signal detection circuit in a fourth embodiment of the present invention. In this figure, the same parts as those in FIG. 3 are given the same reference numerals and detailed explanations will be omitted.

This embodiment circuit eliminates unnecessary circuits during normal operation in order to reduce the power consumption of the circuit during normal operation and to prevent the DC voltage detection circuit 3 from reducing the DC resistance seen from the telephone line terminals L ₁ and L ₂ . This is to put it in a non-operating state.

That is, a first switch 5 is provided between the rectifier circuit 2 and the DC voltage detection circuit 3, and a second switch 6 is provided in the power supply path to the DC voltage detection circuit 3. 6 is turned on by the starting circuit 7. This starting circuit 7 detects when the DC voltage between the telephone line terminals L ₁ and L ₂ is lower than the normal state, that is, when an off-hook is performed, and activates each of the switches 5 and 6.
It generates a signal that causes the switch to be turned on. On the other hand, timer 8 is connected to DC voltage detection circuit 3.
A signal is generated after a certain period of time has elapsed since the detection output of the switch changes from L level to H level, and this signal is applied to each of the switches 5 and 6 to open the switches. Moreover, the preset circuit 9 is
This is for setting the AND gate circuit 4 in a conductive state by giving an H level signal to the AND gate circuit 4 when the DC voltage detection circuit 3 is not operating, and generates the above signal when there is no output from the starting circuit 7. .

Incidentally, FIG. 9 is a diagram showing an example of the circuit configuration of the starting circuit 7. As shown in FIG. In the same figure, capacitor 7
1 and resistor 72 constitute a differentiating circuit, and this differentiating circuit detects the falling edge of the voltage between terminals L ₁ and L ₂ . This falling edge is then supplied to a flip-flop circuit 75 via a photocoupler consisting of a light emitting diode 73 and a phototransistor 74, and sets the flip-flop circuit 75. This flip-flop circuit 75 generates its set output as an activation signal. Further, the set state of the flip-flop circuit 75 is reset by the output of the timer 8.

With this configuration, during standby, that is, during normal operation, each of the first and second switches 5 and 6 is in an open state, so that the telephone line terminal
L ₁ , L ₂ and the DC voltage detection circuit 3 are disconnected,
Further, the power supply to the DC voltage detection circuit 3 is cut off. Therefore, in this state, the DC voltage detection circuit 3 is inactive and does not consume power, nor does the DC resistance as seen from the telephone line terminals L ₁ and L ₂ decrease.

Now, in this state, when the voltage between telephone line terminals L ₁ and L ₂ drops due to off-hook, this is detected by the starting circuit 7 and a signal is output.
Then, the second switches 5 and 6 are turned on. Therefore, the DC voltage detection circuit 3 enters the operating state, and thereafter inputs the rectified output of the rectifier circuit 2, determines its level, and outputs an L-level detection output.
As a result, the preset circuit 9 is reset, and the AND gate circuit 4 becomes non-conductive, thereby blocking the passage of an erroneous detection signal caused by the dial impulse from the 16 Hz signal detection circuit 1 even if it is generated. Therefore, generation of ringing tone due to dial impulse is prevented.

On the other hand, telephone line terminals L ₁ and L ₂ are connected by on-hook.
When the DC voltage between the two returns to a high level and the detection output of the DC voltage detection circuit 3 becomes H level, the timer 8
starts the counting operation and generates an output after a certain period of time has elapsed. As a result, the switches 5 and 6 are opened, thereby cutting off the power supply to the DC voltage detection circuit 3 and disconnecting the rectifier circuit 2 and the DC voltage detection circuit 3. At the same time, the output of the starting circuit 7 is cut off, so that the preset circuit 9
is preset, and as a result, AND gate circuit 4
is maintained in a conductive state.

Note that when a calling signal arrives, the telephone line terminals L ₁ ,
Since the voltage between _L2 continues at a high level, the startup circuit 7 does not operate.

In this way, in this embodiment, the DC voltage detection circuit 3 is activated only when the dial is operated, and the connection between the rectifier circuit 2 and the DC voltage detection circuit 3 is maintained, so that during normal operation The DC voltage detection circuit 3 is made inactive, and the telephone line terminal L ₁ ,
Can be disconnected from _L2 . Therefore,
It is possible to reduce power consumption and prevent a decrease in DC resistance, and it is possible to realize a more practical circuit.

As described in detail above, the present invention makes it possible to perform a substantial detection operation only when there is a possibility that a calling signal will arrive by determining the DC potential difference between the telephone line terminals. In other words, when there is no possibility that a paging signal will arrive, the detection operation is substantially prohibited.

Therefore, it is possible to provide a calling signal detection circuit that can reliably prevent erroneous detection of dial impulses and can prevent resonance from occurring with high accuracy.

Although a gate circuit is used in the example,
The output of the DC voltage detection circuit may control the operation of the 16Hz signal detection circuit itself, or may control the opening/closing of the signal input path to the 16Hz signal detection circuit.

[Brief explanation of drawings]

Figure 1 is a circuit configuration diagram of a 16Hz signal detection circuit used as a conventional calling signal detection circuit, Figure 2a,
b is a signal waveform diagram of a telephone line used to explain the principle of the present invention, FIG. 3 is a block diagram of a ring signal detection circuit in the first embodiment of the present invention, and FIG. 4 is a main part of the circuit. 5 is a circuit diagram showing a main part of the second embodiment of the present invention, FIG. 6 is a circuit diagram of a main part showing a third embodiment of the present invention, and FIGS. A signal waveform diagram used to explain the operation of the circuit, FIG. 8 is a block configuration diagram of a calling signal detection circuit in a fourth embodiment of the present invention, and FIG. 9 is a circuit configuration diagram showing the main parts of the circuit. be. 1... 16Hz signal detection circuit, 2... Rectifier circuit, 3
...DC voltage detection circuit, 4...AND gate circuit, 5...first switch, 6...second switch, 7...starting circuit, 8...timer, 9...preset circuit, L ₁ , L ₂ ...Telephone line terminal.

Claims (1)

[Scope of Claims] 1. In a ringing signal detection circuit provided in at least one telephone among a plurality of telephones mutually connected in parallel to a telephone line terminal, a detection circuit for detecting a ringing signal from a signal arriving at the telephone line terminal. a circuit body and the detection circuit body are provided in parallel with the telephone line terminal, and detect a DC voltage between the telephone line terminals in this state within a period immediately before the arrival of a signal arriving at the telephone line terminal; a DC voltage detection circuit that generates a detection signal indicating whether the detected value is within a preset range; and a DC voltage detection circuit that generates a detection signal indicating whether or not the detected value is within a preset range; When it indicates that the detection signal is within the predetermined range, the gate is closed and the output of the detection signal generated from the detection circuit body is prohibited.On the other hand, when it indicates that it is not within the predetermined range, the gate is closed. 1. A calling signal detection circuit comprising: a gate circuit that enables output of a detection signal generated from the detection circuit main body when the detection circuit main body enters a state.