JP3880306B2 - Call signal detection circuit for trunk line of electronic exchange office line - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a call signal detection circuit provided in a trunk line interface of an electronic exchange.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, for example, a call signal detection circuit for detecting a call signal arriving from an opposite station is provided in a central line trunk interface of an electronic switch of a storage program system.
FIG. 6 is a circuit diagram showing an example of this type of call signal detection circuit, and FIG. 7 is a timing chart showing the operation of the call signal detection circuit of FIG.
6 includes a capacitor 102, a resistor 104, a Zener diode 106, a rectifier circuit 108, a smoothing circuit 110, a control circuit 112, and the like. The rectifier circuit 108 includes first and second half-wave rectifier circuits 114 and 116, and the first and second half-wave rectifier circuits 114 and 116 include first and second photocouplers 118 and 120, respectively. Has been. The photodiodes 122 of the first and second photocouplers 118 and 120 are connected in parallel with opposite polarities.
[0003]
The capacitor 102 is inserted in order to remove the direct current component included in the calling signal, and is connected in series with the photodiode 122 together with the resistor 104. The two Zener diodes 106 are connected in series with opposite polarities, and are connected in series to the photodiode 122. Since the Zener diode 106 is connected in this manner, a current flows through the photodiode 122 when the amplitude of the sinusoidal ringing signal generally exceeds a voltage determined by the Zener voltage of the Zener diode 106, and the photodiode 122 emits light. Then, the phototransistors 124 of the first and second photocouplers 118 and 120 are turned on.
[0004]
That is, as shown in FIG. 7, the photodiode 122 of the first photocoupler 118 emits light and the phototransistor 124 of the photocoupler is turned on in a period in which the calling signal 101 is positive and the absolute value of the amplitude is large to some extent. As a result, the output signal of the first half-wave rectifier circuit 114 becomes high level.
[0005]
On the other hand, the photodiode 122 of the second photocoupler 120 emits light and the phototransistor 124 of the second photocoupler 120 is turned on in a period in which the calling signal is negative and the absolute value of the amplitude is large to some extent, and the second half-wave rectifier circuit The output signal 116 becomes a high level.
[0006]
Since the output terminals of the first and second half-wave rectifier circuits 114 and 116 are wired OR as shown in FIG. 6, the input signal of the smoothing circuit 110 is shown in FIG. Thus, it becomes a kind of full-wave rectified waveform. The smoothing circuit 110 smoothes the input signal having such a waveform and outputs a detection signal that becomes a high level in a period corresponding to the duration of the calling signal. The control circuit 112 identifies the intermittent pattern of the calling signal based on this detection signal.
[0007]
[Problems to be solved by the invention]
By the way, as shown in FIG. 7, the call signal transmitted from the station does not immediately become zero even if transmission is stopped at timing T1, for example, and the amplitude is maintained for a certain period t. There is a case. This phenomenon is also called voltage residual, and if the amplitude of the calling signal 101 is maintained abnormally long due to voltage residual, in the example of FIG. 7, the output signal of the first half-wave rectifier circuit 114 becomes high level. The period becomes abnormally long after the timing T1, and as a result, the input signal of the smoothing circuit 110, and thus the output signal of the smoothing circuit 110, originally becomes a low level at the timing T1, but maintains a high level until the timing T2. . Therefore, if the duration of the call signal 101 is determined based on the output signal of the smoothing circuit 110, the duration is longer than the actual duration.
[0008]
In recent years, a technique of switching and providing various communication services according to the pattern of intermittent time of a call signal has been used. For example, in the number display service provided by a group company of Nippon Telegraph and Telephone Corporation, the first call signal is intermittently sent from the station at a specific cycle corresponding to the service, and the incoming call from a caller registered in advance Even in the case of a service that changes the ringing tone repetition period in this case, the service is specified by the intermittent pattern of the calling signal.
[0009]
In such a service, since the service is switched according to the intermittent pattern of the call signal, it is necessary to accurately detect the duration of the call signal. However, if the duration of the call signal cannot be accurately detected due to the voltage remaining as described above, the pattern of the call signal interruption time cannot be accurately identified, and therefore it is difficult to switch the service correctly.
[0010]
The present invention has been made to solve such problems, and an object thereof is to provide a call signal detection circuit for an electronic switching center line trunk which can accurately detect the duration of the call signal.
[0011]
[Means for Solving the Problems]
  In order to achieve the above object, the present invention provides a rectifier circuit that rectifies and binarizes a call signal when an absolute value of the call signal exceeds a predetermined level when a call signal arriving from an opposite station is input, and the rectifier circuit. A call signal detection circuit including a smoothing circuit that smoothes the output signal of the output signal, including a waveform shaping circuit that performs waveform shaping of the output signal of the rectifier circuit and supplies the waveform shaping circuit, and the waveform shaping circuit includes: A binary signal that takes the first or second logic level is output, and when the logic level of the output signal of the rectifier circuit changes, the logic level of the signal that it outputs becomes the first logic level, and then When the logic level of the output signal of the rectifier circuit returns to the original logic level or when a certain time has elapsed, the logic level of the signal output by itself is set to the second logic level.The waveform shaping circuit includes a counter that starts counting a clock signal having a fixed period when the logic level of the output signal of the rectifier circuit changes, and a arrival signal when the count value of the counter reaches a reference value. When the logic level of the determination circuit to output and the output signal of the rectifier circuit changes and the counter starts counting, the first logic level signal is output, and then the logic level of the output signal of the rectifier circuit is An output control circuit that outputs a signal of a second logic level when the determination circuit outputs the arrival signal, or returns to the original logic level, and the waveform shaping circuit includes the determination circuit A clock signal is supplied to a counter when the circuit does not output an arrival signal, and the counter of the clock signal when the determination circuit outputs the arrival signal And further comprising a clock control circuit for stopping the supply ofIt is characterized by that.
  The present invention also provides a rectifier circuit that rectifies and binarizes a call signal when an absolute value of the signal exceeds a predetermined level when a call signal arriving from an opposite station is input, and an output signal of the rectifier circuit. A call signal detection circuit including a smoothing circuit that performs smoothing, and includes a waveform shaping circuit that performs waveform shaping of an output signal of the rectifier circuit and supplies the waveform to the smoothing circuit, wherein the waveform shaping circuit is a first or second waveform shaping circuit. A binary signal having a logic level of 2 is output, and when the logic level of the output signal of the rectifier circuit changes, the logic level of the signal output by itself is set to the first logic level, and then the output of the rectifier circuit When the logic level of the signal returns to the original logic level or when a certain time has elapsed, the logic level of the signal output by itself is set to the second logic level, and the waveform shaping circuit A time determination step for determining whether or not a fixed time has passed after the logic level of the output signal of the rectifier circuit has changed, the waveform shaping program comprising a microcomputer that operates based on the output circuit; And a first output control step for causing the output circuit to output a signal of the first logic level when the logic level of the output signal of the rectifier circuit changes, and the logic level of the output signal of the rectifier circuit has changed. Thereafter, when the logic level of the output signal of the rectifier circuit returns to the original logic level or when it is determined in the time determination step that a certain time has elapsed, the signal of the second logic level is output to the output circuit. And a second output control step.
  The present invention also provides a rectifier circuit that rectifies and binarizes a call signal when an absolute value of the signal exceeds a predetermined level when a call signal arriving from an opposite station is input, and an output signal of the rectifier circuit. A call signal detection circuit including a smoothing circuit that performs smoothing, and includes a waveform shaping circuit that performs waveform shaping of an output signal of the rectifier circuit and supplies the waveform to the smoothing circuit, wherein the waveform shaping circuit is a first or second waveform shaping circuit. A binary signal having a logic level of 2 is output, and when the logic level of the output signal of the rectifier circuit changes, the logic level of the signal output by itself is set to the first logic level, and then the output of the rectifier circuit When the logic level of the signal returns to the original logic level or when a certain period of time has elapsed, the logic level of the signal output by itself is set to the second logic level. The first photocoupler includes a phototransistor including a phototransistor. When the calling signal has a first polarity, a current flows through the photodiode when the call signal has a first polarity, the photodiode emits light, and the phototransistor is turned on. In the second photocoupler, when the calling signal has a second polarity opposite to the first polarity, a current flows through the photodiode, the photodiode emits light, the phototransistor is turned on, and the rectifier circuit The first and second photocouplers The output signal of the rectifier circuit is generated based on the ON / OFF state of the transistor, and is output to the waveform shaping circuit.
[0012]
In the call signal detection circuit of the present invention, the waveform shaping circuit sets the logic level of the signal output from the waveform shaping circuit to the first logic level when the logic level of the output signal of the rectifier circuit changes, and then the output signal of the rectifier circuit. When the logic level of the signal returns to the original logic level or when a predetermined time has elapsed, the logic level of the signal output by itself is set as the second logic level.
Therefore, even if the calling signal is actually stopped, the waveform shaping circuit output signal returns to the second logic level after a certain period of time even if the amplitude is maintained for a certain period of time. The output signal of the smoothing circuit also returns to the signal level corresponding to the second logic level at a timing close to the actual stop timing of the calling signal. As a result, it is possible to detect the duration of the calling signal with high accuracy.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
1 is a circuit diagram showing an example of a call signal detection circuit for an electronic switching center line trunk according to the present invention, FIG. 2 is a circuit diagram showing an example of a waveform shaping circuit constituting the call signal detection circuit of FIG. 1, and FIG. FIG. 4 is a timing chart showing the operation of the waveform shaping circuit of FIG. In FIG. 1, the same elements as those of FIG. 6 are denoted by the same reference numerals, and detailed description thereof will be omitted here.
[0014]
The call signal detection circuit 1 of the embodiment shown in FIG. 1 is particularly different from the call signal detection circuit shown in FIG. 6 in that the first and second half-wave rectifier circuits 114 and 116, the smoothing circuit 110, A waveform shaping circuit 6 including first and second waveform shaping circuits 2 and 4 is provided between the two.
The first and second waveform shaping circuits 2 and 4 each output a binary signal having a high level or a low level, and when the output signals of the first and second half-wave rectifier circuits 114 and 116 become a high level. The logic level of the signal output by itself is set to the high level, and then the output signals of the first and second half-wave rectifier circuits 114 and 116 return to the low level or are shorter than the half cycle of the calling signal. When elapses, the signal output by itself is set to low level.
[0015]
More specifically, as shown in FIG. 2, each of the first and second waveform shaping circuits 2 and 4 includes a counter 8 (binary counter), a determination circuit 10, an output control circuit 12, a registration circuit 14, and clock control. A circuit 16 is included.
The reset terminal 18 of the counter 8 is supplied with the output signal of the first or second waveform shaping circuit 114, 116 control circuit. When the output signal of the rectifier circuit is high level, the reset is canceled and the counter 8 Counts a clock signal 22 of a fixed period input to the clock terminal 20 and outputs the value of each binary bit representing the counting result to the determination circuit 10.
[0016]
The determination circuit 10 is supplied with the count result of the counter 8 and the reference value from the registration circuit 14, and the determination circuit 10 outputs an arrival signal when the count value of the counter 8 reaches the reference value. The reference value is registered in advance in the registration circuit 14, and the registration circuit 14 outputs the registered reference value to the counter 8.
[0017]
The output control circuit 12 is a circuit for generating the output signals of the first and second waveform shaping circuits 2 and 4, and the output signals of the first and second half-wave rectifier circuits 114 and 116 become high level. When changed, a high level signal is output. After that, when the output signals of the first and second half-wave rectifier circuits 114 and 116 return to a low level, or when the determination circuit 10 outputs an arrival signal, the low level signal is output. Output a signal. The outputs of the output control circuits 12 of the first and second waveform shaping circuits 2 and 4 are wired-or connected as shown in FIG. 1 and connected to the input of the smoothing circuit 10.
The clock control circuit 16 supplies the clock signal 22 to the counter 8 when the determination circuit 10 does not output the arrival signal, and the counter 8 of the clock signal 22 when the determination circuit 10 outputs the arrival signal when the determination circuit 10 outputs the arrival signal. Stop supplying to
[0018]
Next, the operation of the call signal detection circuit configured as described above will be described.
The operations of the first stage of the first and second waveform shaping circuits 2 and 4 and the operation of the smoothing circuit 110 are the same as those of the conventional call signal detection circuit described with reference to FIGS. The operation of the newly provided waveform shaping circuit 6 will be mainly described.
Even when the output of the calling signal 101 is stopped at the timing T1, the amplitude of the calling signal is maintained at a certain value for a period t as shown in FIG. The output signal of the first half-wave rectifier circuit 114 constituting the half-wave rectifier circuit 114 is at a high level for a longer time than originally intended. As a result, when the waveform shaping circuit 6 is not provided, the input signal of the smoothing circuit 110 becomes abnormally long during the last high level period as shown by the dotted line in FIG.
[0019]
However, in the present embodiment, the first and second waveform shaping circuits 2 and 4 have a high level when the output signals of the first and second half-wave rectifier circuits 114 and 116 become high level. The signal is output, and then the low-level signal is output when the output signal of the first and second half-wave rectifier circuits 114 and 116 returns to the low level or when a certain time shorter than the half cycle of the calling signal has elapsed. To do. Therefore, even when the call signal maintains the amplitude after the actual stop time T1 and the output signal of the first half-wave rectifier circuit 114 becomes high until timing T3, the waveform shaping circuit at timing T4. 6 (the input signal of the smoothing circuit 110) is at the low level, and as a result, the output signal of the smoothing circuit 110 is also at the low level at the timing T4.
[0020]
The operation of the first and second waveform shaping circuits 2 and 4 will be described in more detail with reference to FIG. Since the operations of the first and second waveform shaping circuits are basically the same, the operation will be described here by taking the first waveform shaping circuit as an example.
As shown in FIG. 4, the counter 8 is in the reset state during the period up to the timing T <b> 0 when the output signal of the first half-wave rectifier circuit 114 is at the low level, and therefore the count operation is not performed. When the output signal of the first half-wave rectifier circuit 114 becomes high level at timing T0, the counter 8 starts counting the clock signal 22. When the counter 8 is in the reset state, the count value is zero and does not match the reference value, so that the determination circuit 10 does not output a reaching signal and the output of the determination circuit 10 is at a low level. Therefore, the clock control circuit 16 is in a state of supplying the clock signal 22 to the counter 8.
[0021]
Further, when the output signal of the first half-wave rectifier circuit 114 becomes high level at the timing T0, the output control circuit 12 changes its output signal to high level, so that the output signal of the waveform shaping circuit 6 becomes high level. Become.
After the timing T0, the calling signal is stopped from being sent out at the sending side at the timing T1 (see FIG. 3), but the amplitude of the calling signal does not immediately become zero as described above, and as a result, the first half-wave rectification is performed. The output signal of the circuit 114 remains high until timing T3.
[0022]
During this time, the counter 8 performs a counting operation and outputs the value of each binary bit representing the counting result to the determination circuit 10 through each bit line 24, 25 or the like. When the count value reaches the reference value at timing T5, the determination circuit 10 outputs a high level signal as the arrival signal. As a result, the output control circuit 12 changes the output signal to a low level. Further, since the determination circuit 10 outputs the arrival signal, the clock control circuit 16 stops supplying the clock signal 22 to the counter 8, and thus the counter 8 stops the counting operation. As a result, the counter 8 holds the count value that matches the reference value as it is, and the determination circuit 10 continues to output the arrival signal until the timing T3.
[0023]
Thereafter, when the output signal of the first half-wave rectifier circuit 114 becomes low level at timing T3, the counter 8 is reset, and the determination circuit 10 also stops outputting the arrival signal. As a result, the clock signal 22 is supplied to the counter 8 again, but the counter 8 is reset, so that the counting operation is not performed.
[0024]
Thus, in the call signal detection circuit 1 according to the present embodiment, the amplitude that continues for an abnormally long time even though the call signal 101 supplied to the call signal detection circuit 1 is actually stopped. Even when the signal is maintained, the output signals of the first and second waveform shaping circuits 2 and 4 return to the low level when a certain time elapses and the count value of the counter 8 reaches the reference value. Therefore, the output signal of the smoothing circuit 110 also becomes a low level at the timing T5 close to the original stop timing of the calling signal 101, and the duration of the calling signal can be detected with high accuracy.
As a result, when the communication service is switched and provided according to the pattern of the call signal intermittent time, the pattern of the call signal intermittent time can be accurately specified, and various services can be reliably executed. .
[0025]
Here, an example has been described in which the output signal of the first half-wave rectifier circuit 114 is maintained at a high level for a longer time than the original time when the call signal is stopped. However, depending on the timing of the call signal stop, In some cases, the output signal of the half-wave rectifier circuit 116 maintains an abnormally long high level. In that case, the second waveform shaping circuit 4 operates in the same manner as the first waveform shaping circuit 2, and the waveform shaping signal that remains at the high level for a time close to the duration of the actual call signal is supplied to the smoothing circuit 110. It is possible to correctly detect the duration of the call signal.
[0026]
In the present embodiment, the waveform shaping circuit 6 is configured by an electronic circuit. However, the first and second waveform control circuits are each configured by, for example, a microcomputer and an output circuit (not shown), and the output control circuit 12 is configured. Instead of being controlled by the determination circuit 10 as described above, the output circuit corresponding to can be controlled by a microcomputer. In that case, for example, a waveform shaping program is stored in a ROM (read only memory) that constitutes the microcomputer, and the CPU that constitutes the microcomputer is operated based on the program, so that it is the same as the waveform control circuit. Can be realized.
[0027]
FIG. 5 is a flowchart showing a processing procedure based on the waveform shaping program. Since the first and second waveform shaping circuits have the same configuration, here, the case of the first waveform shaping circuit will be described as an example.
The microcomputer receives the output signal of the first half-wave rectifier circuit 114 and monitors the signal, and when the output signal of the first half-wave rectifier circuit 114 becomes high level as shown in FIG. In step S1, the timer by software is started (step S2), and a high level signal is output from the output circuit (step S3). Then, it is determined whether or not the output signal of the waveform shaping circuit 114 continues to be at a high level (step S4). If the determination result is positive (Yes in step S4), it is determined whether or not the software timer has timed out. (Step S5). If the determination result is NO, the process returns to step S4 and repeats steps S4 and S5. When the determination result becomes positive, the process proceeds to step S6, where the software timer is stopped and the output signal is set to the low level. Switching is performed (step S7).
[0028]
On the other hand, if the determination result in step S3 is negative, the output signal of the first half-wave rectifier circuit 114 is normal and the output signal of the first half-wave rectifier circuit 114 is low before the timer expires. At this time, the timer is stopped (step S8), and the output signal of the output circuit is switched to the low level (step S7).
[0029]
The steps S2 and S5 constitute a time determination step according to the present invention, the steps S1 and S3 are the first output control steps according to the present invention, and the steps S4, S7 and S8 are the second time control steps according to the present invention. The output control step is configured.
[0030]
In the call signal detection circuit 1 of the above embodiment, the first and second waveform shaping circuits 2 and 4 are individually provided for the first and second half-wave rectifier circuits 114 and 116, respectively. For example, a single waveform shaping circuit having the configuration shown in FIG. 2 may be provided for the rectifier circuit 108 to achieve the same effect. In that case, for example, the outputs of the first and second half-wave rectifier circuits 114 and 116 may be supplied to the waveform rectifier circuit of FIG.
[0031]
【Example】
After the output signals of the first and second half-wave rectifier circuits 114 and 116 become high level, the time until the determination circuit 10 outputs the arrival signal is the clock signal period and the registration circuit 14 determines the determination circuit 10. Determined by the reference value to be supplied.
In Japan, the frequency of the call signal sent from the public network to the terminal is 15 Hz or more and 20 Hz or less. For this reason, the period during which the output signals of the first and second half-wave rectifier circuits 114 and 116 are at a high level does not exceed 34 ms.
Accordingly, if the period of the clock signal 22 supplied to the counter 8 is 4 ms as an example, the reference value registered in the registration circuit 14 is set to 9 as an example, and the determination circuit 10 reaches when the counter 8 counts 9 clocks. Since the signal is output, even when the amplitude does not quickly return to zero after the call signal is stopped, the period during which the output signal of the waveform shaping circuit 6 is at the high level can be limited to 36 ms at the maximum.
[0032]
【The invention's effect】
As described above, in the call signal detection circuit of the present invention, when the logic level of the output signal of the rectifier circuit changes, the waveform shaping circuit sets the logic level of the signal output by itself as the first logic level, and then When the logic level of the output signal of the rectifier circuit returns to the original logic level or when a certain time has elapsed, the logic level of the signal output by itself is set as the second logic level.
Therefore, even if the calling signal is actually stopped, the waveform shaping circuit output signal returns to the second logic level after a certain period of time even if the amplitude is maintained for a certain period of time. The output signal of the smoothing circuit also returns to the signal level corresponding to the second logic level at a timing close to the actual stop timing of the calling signal. As a result, it is possible to detect the duration of the calling signal with high accuracy.
As a result, for example, when a communication service is switched and provided according to the pattern of the call signal intermittent time, the pattern of the call signal intermittent time can be specified accurately, and various services can be executed reliably. Become.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing an example of a call signal detection circuit for an electronic switching center line trunk according to the present invention.
FIG. 2 is a circuit diagram showing an example of a waveform shaping circuit constituting the call signal detection circuit of FIG. 1;
FIG. 3 is a timing chart showing an operation of the call signal detection circuit of FIG. 1;
4 is a timing chart showing the operation of the waveform shaping circuit of FIG.
FIG. 5 is a flowchart showing a processing procedure based on a waveform shaping program.
FIG. 6 is a circuit diagram showing an example of a conventional call signal detection circuit.
7 is a timing chart showing the operation of the call signal detection circuit of FIG. 6;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Call signal detection circuit, 2 ... 1st waveform shaping circuit, 4 ... 2nd waveform shaping circuit, 6 ... Waveform shaping circuit, 8 ... Counter, 10 ... Judgment circuit, 12 ... Output Control circuit 14... Registration circuit 16... Clock control circuit 18... Reset terminal 20. Clock terminal 22. Clock signal 24 24 Bit line 100 Call signal detection circuit 102. ...... Capacitor 104... Resistor 106. Zener diode 108. Rectifier circuit 110. Smooth circuit 112. Control circuit 114. First half-wave rectifier circuit 116. Wave rectifier circuit 118... First photocoupler 120. Second photocoupler 122... Photodiode 124.

Claims (5)

A rectifier circuit that rectifies and binarizes the call signal when an absolute value of the call signal that has arrived from the opposite station exceeds a predetermined level; and a smoothing circuit that smoothes the output signal of the rectifier circuit; A call signal detection circuit including:
Including a waveform shaping circuit that shapes the waveform of the output signal of the rectifier circuit and supplies the waveform to the smoothing circuit;
The waveform shaping circuit outputs a binary signal having a first or second logic level, and when the logic level of the output signal of the rectifier circuit changes, the logic level of the signal output by itself is changed to a first logic level. After that, when the logic level of the output signal of the rectifier circuit returns to the original logic level or when a certain time has elapsed, the logic level of the signal output by itself is set as the second logic level ,
The waveform shaping circuit outputs a arrival signal when a count value of the counter reaches a reference value, and a counter that starts counting a clock signal with a fixed period when the logic level of the output signal of the rectifier circuit changes. When the logic level of the output signal of the determination circuit and the rectifier circuit changes and the counter starts counting, a signal of the first logic level is output, and then the logic level of the output signal of the rectifier circuit is the original An output control circuit that returns to a logic level or outputs a signal of a second logic level when the determination circuit outputs the arrival signal,
The waveform shaping circuit supplies a clock signal to the counter when the determination circuit does not output an arrival signal, and stops supplying the clock signal to the counter when the determination circuit outputs the arrival signal A clock control circuit that further includes:
A call signal detection circuit for an electronic switching center line trunk. The waveform shaping circuit, call signal detecting circuit according to claim 1 electronic exchange office line trunk, wherein that further include a register circuit for supplying the reference value to the decision circuit. A rectifier circuit that rectifies and binarizes the call signal when an absolute value of the call signal that has arrived from the opposite station exceeds a predetermined level; and a smoothing circuit that smoothes the output signal of the rectifier circuit; A call signal detection circuit including:
Including a waveform shaping circuit that shapes the waveform of the output signal of the rectifier circuit and supplies the waveform to the smoothing circuit;
The waveform shaping circuit outputs a binary signal having a first or second logic level, and when the logic level of the output signal of the rectifier circuit changes, the logic level of the signal output by itself is changed to a first logic level. After that, when the logic level of the output signal of the rectifier circuit returns to the original logic level or when a certain time has elapsed, the logic level of the signal output by itself is set as the second logic level,
The waveform shaping circuit includes a microcomputer that operates based on a waveform shaping program and an output circuit, and the waveform shaping program has passed a certain time after the logic level of the output signal of the rectifier circuit has changed. A time determination step for determining whether or not, a first output control step for causing the output circuit to output a signal of the first logic level when the logic level of the output signal of the rectifier circuit changes, and the rectifier circuit When the logic level of the output signal of the rectifier circuit is changed to the original logic level after the change of the logic level of the output signal, or when it is determined in the time determination step that a certain time has elapsed, the output circuit A second output control step for outputting a signal of a second logic level ,
Call signal detection circuit you wherein electronic exchange station trunk that. A rectifier circuit that rectifies and binarizes the call signal when an absolute value of the call signal that has arrived from the opposite station exceeds a predetermined level; and a smoothing circuit that smoothes the output signal of the rectifier circuit; A call signal detection circuit including:
Including a waveform shaping circuit that shapes the waveform of the output signal of the rectifier circuit and supplies the waveform to the smoothing circuit;
The waveform shaping circuit outputs a binary signal having a first or second logic level, and when the logic level of the output signal of the rectifier circuit changes, the logic level of the signal output by itself is changed to a first logic level. After that, when the logic level of the output signal of the rectifier circuit returns to the original logic level or when a certain time has elapsed, the logic level of the signal output by itself is set as the second logic level,
The rectifier circuit includes first and second photocouplers each including a photodiode and a phototransistor. In the first photocoupler, a current flows through the photodiode when the calling signal has a first polarity, and the photodiode Is emitted and the phototransistor is turned on. When the calling signal has a second polarity opposite to the first polarity in the second photocoupler, a current flows through the photodiode, the photodiode emits light, and the phototransistor The rectifier circuit is turned on, and the rectifier circuit generates the output signal of the rectifier circuit based on the on / off states of the phototransistors of the first and second photocouplers, and outputs the output signal to the waveform shaping circuit .
Call signal detection circuit you wherein electronic exchange station trunk that. The waveform shaping circuit is provided for each of the first and second photocouplers, and each waveform shaping circuit receives the output signal generated based on the on / off state of the phototransistor of each photocoupler. 5. The ringing signal detection circuit for an electronic switching center line trunk according to claim 4, wherein:

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