JPH0327653A - Ring trip detection circuit - Google Patents

Abstract

PURPOSE:To decrease the delay in an off-hook detection time of a telephone set by eliminating an AC component through the in-phase input of the said component to both inputs of a comparator circuit detecting a DC change level so as to compare the substantial DC level. CONSTITUTION:Since the DC component is eliminated from a signal divided by a voltage division circuit 20 by a high pass filter 22, only an AC component for ringer exists at the output of the filter 22. A reference voltage for reference level setting for off-hook detection is added to the component by an adder 23 of the succeeding stage and the result is given to one input of a comparator circuit 24. On the other hand, an output of the circuit 20 is inputted as it is to other input of the comparator circuit 24. As a result, the Ac components of the same amplitude are fed to both inputs of the comparator circuit 24 and since the in-phase rejection ratio (CMRR) of the comparator 24 is normally as high as 100-dB or over, the in-phase AC component is rejected and only the reference voltage and a trip voltage are compared by the comparator 24. Since no low pass filter is included in the circuit, the time required for detecting a trip is considerably reduced.

Description

[Detailed description of the invention]

[8! Required] Regarding the ring trip circuit that detects when a telephone is off-hook, a high-pass filter that receives an input signal and passes only high-frequency components is used for the purpose of reducing the delay in the detection time for detecting that the telephone is off-hook. and an adder that adds a DC reference voltage to the output of the high-pass filter; the output of the adder is received at one input, the input signal is received at the other input, and the voltage of the input signal is set to the DC reference voltage. If it becomes larger than , the comparator treats it as off-hook and outputs a trip signal. INDUSTRIAL APPLICATION FIELD OF THE INVENTION The present invention relates to a ring trip circuit for detecting that a telephone is off-hook, and more particularly to an improvement in a ring trip circuit. In PCM primary group transmission devices and the like, a ring trip circuit is used that detects when a subscriber's telephone goes off-hook using a DC voltage that is proportional to the DC current flowing through the subscriber line when the subscriber's telephone is off-hook. In this case, the alternating current component (IOOV) of the calling signal is added to the direct current flowing during off-book.
(on the order of ) are superimposed, making the ring trip operation unstable. Therefore, it is necessary to perform the ring trip operation reliably. [Prior Art] FIG. 7 is a diagram showing a conventional system configuration of a PCM primary group transmission device. PCM between subscriber side terminal station 1 and exchange side terminal station 2
They are connected by signal line 3. The exchange side terminal station 2 and the exchange 4 are connected by a line 5. The subscriber side terminal station 1 includes a channel section (SC) 1a and a multiplexing/demultiplexing section (MUX) lb.
The exchange side terminal station 2 also includes a channel section 2a and a multiplexing/demultiplexing section 2b. A plurality of (for example, 30) telephones 6 are connected to the channel section 1a of the subscriber-side terminal station 1. In the system configured as described above, a signal originating from the telephone 6 is converted into a digital signal by the channel unit 1a, multiplexed by a PCM code in the multiplexing/demultiplexing unit 1b, and transmitted via the PCM signal line 3. and is sent to the terminal station 2 on the exchange side. The multiplexing/demultiplexing circuit 2b of the terminal station 2 on the exchange side separates signals as necessary, and
The signal is transmitted to the exchange 4 via a. Conversely, when a call is received from the exchange 4 side to the telephone set 6, the multiplexing/demultiplexing section 1b separates the PCM signal for each channel, converts it into an analog signal in the subsequent channel section 1a, and then sends the ringer to a predetermined telephone set 6. do. FIG. 8 is a diagram showing an example of the structure of a conventional ring trip circuit. The telephone 6 is powered by a ringer bell 6a, a capacitor CI connected in series with the ringer bell 6a, and a hook switch 6b connected to both ends of a signal line. When the calling signal sending relay (not shown) is driven,
Relay contacts rl and rflx operate to generate a ringer signal (for example, a frequency of 20Hz,
amplitude 100V) is resistor R1. Relay contact "1l, subscriber line B. The signal flows through the capacitor Cll bell 6a, the subscriber line A, the relay contact rfl2, and the resistor R2, causing the bell 6a to ring. Note that one end of the ringer oscillator 10 is connected to a ground potential, and the other end is connected to a resistor R1. One end of the resistor R2 is connected to the relay contact rlx, and the other end is connected to the potential Via (for example, -48V). At this time, since the DC signal is cut by the capacitor C, the voltage appearing across the resistor R2 is only an AC component. The voltage across the resistor R2 is input to one input of the comparator 12 after an AC component is removed by a low-pass filter (integrating circuit) 11 consisting of a resistor R and a capacitor C2. On the other hand, a reference voltage generated by a voltage dividing circuit 13 made up of resistors R4 and R connected between the ground potential and the potential vBB is applied to the other side of the comparator 12 via a buffer amplifier 14. When the telephone 6 is on-hook, the hook switch 6 shown in the figure
b is in an open state, and the telephone 6 is in high impedance. In this state, the output (ring trip voltage) V+ of the low-pass filter 11 is approximately 0, which is smaller than the reference voltage v2, and the comparator 12 does not operate. Here, when the subscriber responds to the ringer ringing, the hook switch 6b is turned on, and the ringer oscillator 10,
Resistor R1, relay contact 'g,, subscriber line B, capacitor c. , rM bell 5a, subscriber line A, relay contact rfJx, and resistor R2. As a result, a DC voltage is generated across the resistor R2, and this DC voltage enters the comparator 12 without being attenuated by the subsequent low-pass filter 11. As a result, the trip voltage V,
becomes larger than the reference voltage v2, and the comparator 12 operates. The operation signal from the comparator 12 turns off the calling signal sending relay A, disconnects the relay contact rIIerρ2 from the ringer circuit, and connects the subscriber lines A and B to the telephone set 6. [Problems to be Solved by the Invention] As mentioned above, in the conventional circuit, a low-pass filter 11 is used to remove AC components, but since phosphorus has a low frequency of 10-odd Hz, It is necessary to use a filter with a very large time constant. For this reason, a large resistance is applied to the resistor R2 and capacitor C2 that constitute the filter.
It was necessary to use a large capacity one. Furthermore, when off-hook, there is a problem in that the low-pass filter causes a delay in the response of ringer trip detection. FIG. 9 is a diagram showing operating waveforms of a conventional ring trip detector. (a) shows the case where the ringer signal is not superimposed, and (b) shows the case where the ringer signal is superimposed. In both cases, (a) is the input waveform (resistance R2
(b) is the output waveform (voltage appearing at both ends of comparator 1).
2 output) are shown respectively. Thus, in the conventional circuit, it took approximately 300 to 600 ms to reach the off-hook detection level L due to the time constant of the low-pass filter for removing the AC component. The present invention has been made in view of these problems, and an object of the present invention is to provide a ring trip detection circuit that can reduce the delay in detection time for detecting that a telephone is off-hook. [Means for Solving the Problems] FIG. 1 is a block diagram of the principle of the present invention. In the figure,
20 is a voltage dividing circuit that receives an input signal; 21 is the voltage dividing circuit 2;
22 is a high-pass filter that receives the output of the buffer amplifier 21 and passes only high-frequency components; 23 is an adder that adds a DC reference voltage to the output of the high-pass filter 22; , 24 connects the output of the adder 23 to one of its inputs,
This is a comparator which receives the output of the voltage dividing circuit 20 at its other input, and when the DC voltage output of the voltage dividing circuit 20 becomes larger than the DC reference voltage, it considers it to be off-hook and outputs a trip signal. Note that when the amplitude of the alternating current signal for ringer is small, the voltage dividing circuit 20 is not necessarily necessary. Further, when the output impedance of the voltage dividing circuit 20 is low, the buffer amplifier 21 is also not necessary.

[Effect]

Since the DC component of the signal voltage-divided by the voltage dividing circuit 20 is removed by the high-pass filter 22, the output of the high-pass filter 22 is only the AC component for the ringer. A subsequent adder 23 adds a reference voltage for setting a reference level for off-hook detection, and the resultant voltage is input to one input of a comparator 24 . On the other hand, the other input of the comparator 24 receives the output of the voltage dividing circuit 20 as it is. As a result, AC components of the same amplitude are applied to both inputs of the comparator 24, but
Normally, the common mode component rejection ratio (CMRR) of the comparator 24 is 10.
Since the voltage is as high as 0 dB or more, the in-phase AC component is removed and only the reference voltage and trip voltage are compared by the comparator 24. According to the present invention, since a low-pass filter is not included, the time required for trip detection is also significantly reduced. FIG. 2 is an explanatory diagram of the operation of the present invention, and is a diagram showing operation waveforms of the present invention. (a) shows the case where the ringer signal is not superimposed, and (b) shows the case where the ringer signal is superimposed. In both cases, (a) shows the human waveform (output voltage of the voltage dividing circuit 20), and (b) shows the output waveform (the output voltage of the comparator 24).
output) are shown respectively. In this way, in the present invention, since a low-pass filter for removing AC components is not included, the input signal is not dulled, and the time to reach the off-hook detection level L is about 30 ms, as shown in Figure W48. This is significantly shortened compared to the 600 ms arrival time of the conventional circuit shown in FIG. [Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings. FIG. 3 is a circuit diagram showing one embodiment of the present invention. Components that are the same as those in FIG. 1 are designated by the same reference numerals. The high-pass filter 22 includes a capacitor CIO and a resistor R.
It consists of a differential circuit consisting of 2o. The output of the high-pass filter 22 enters the adder 23 via a buffer amplifier 30 for impedance matching. The reference voltage is created by dividing the voltage from the connection point of resistors R21 and R22 connected between the ground potential and the power supply voltage VBB. The adder 23 has input resistors R2, . . . connected to the output of the buffer amplifier 30. Input resistance R24 for manually inputting the reference voltage,
It consists of an amplifier U, a feedback resistor R29 connected to the operational amplifier U, and a resistor R26 connected between one end of the resistor R2 and vBB. Adder 2
The output of comparator 24 enters one input of comparator 24, and the output of comparator 2
The other input of 4 contains the divided voltage of the voltage dividing circuit 20. The operation of the circuit configured as described above will be explained as follows. When off-hook, a DC voltage generated by off-hook and an AC voltage for phosphorus are applied to the voltage dividing circuit 20. From this voltage dividing circuit 20, signals obtained by dividing these voltages at a predetermined voltage dividing ratio enter a buffer amplifier 21 and a comparator 24. The output of the voltage divider circuit 20 is impedance matched by a buffer amplifier 21, and then passed through a high-pass filter 2.
Enter 2. The high-pass filter 22 includes a capacitor C, which is connected in series with the circuit. cuts the DC component and allows only the AC component to pass. As a result, the output of the high-pass filter 22 is only the ringer alternating current signal. The AC signal enters one of the adders 23. On the other hand, the other input of the adder 23 receives a reference voltage for providing an off-hook detection level from a voltage dividing circuit made up of R2, , R,2. Therefore, the output of the adder 23 is a DC voltage that provides a reference level and a ringer AC signal superimposed thereon. The output of this adder 23 enters one input of a comparator 24. On the other hand, the other input of the comparator 24 receives a signal in which the DC level caused by off-hook and a certain amount of AC for ringer are superimposed. FIG. 4 is a diagram showing operating waveforms of each part. (a) is a trip signal that directly enters the comparator 24 from the voltage dividing circuit 20, and (b) is the output of the adder 23. Now, at time t, if it is assumed that the trip signal is off-hook, the DC level VD is superimposed on only the AC signal up to that point, and the trip signal rises as shown in the figure. When this DC level VD becomes higher than the off-hook detection level L, the output (trip output) of the comparator 24 rises as shown in (c). In this case, the AC component enters both inputs of the comparator 24, but since the common mode component rejection ratio CMRR of the comparator 24 is extremely large, 100 dB or more, it is removed and does not appear in the output. According to the present invention, since the AC component is not removed using a low-pass filter, the DC component due to the off-hook quickly rises, and the trip output also quickly rises as shown in (c). Therefore, according to the present invention, it is possible to reduce the delay in the detection time for detecting that the telephone is off-hook. The circuit of the present invention shown in FIGS. 1 and 3 can also be used as it is in a loop detection circuit within a channel section of a loop system of a PCM primary group transmission device. The outline of this loop detection circuit is as shown in FIG. A switch SW is provided in the exchange 40 to connect and disconnect the loop, and current sources 11 and I2 are connected in series to the loop. A detection circuit 41 for detecting the loop is located at the K point of the loop.
is connected. Since the DC level at point K changes depending on when the loop is formed and when the loop is broken, the loop is detected by capturing this change in DC level. The conventional configuration of this detection circuit 41 is as shown in FIG. It looks like this. As is clear from the above, its basic structure is similar to the ring trip circuit shown in FIG. This circuit has the disadvantage that an AC signal from a commercial power supply or the like is generated by AC induction during the loop τ, and if the amplitude of this AC signal becomes the same level as the DC detection level, the detection circuit will malfunction. If the present invention shown in FIG. 1 is applied to this detection circuit 41 as well, it is possible to remove some of the alternating current generated by induction by applying the same phase to both the comparator's power, making it possible to compare only the direct current level. It can be done at high speed. In the above-described embodiment, a differentiating circuit including a capacitor and a resistor is used as a high-pass filter, but the present invention is not limited to this, and an active circuit using an operational amplifier may be used. Further, the voltage dividing circuit does not need to be a resistive voltage dividing method, and may be a voltage dividing method using another method. Furthermore, as mentioned above, when the amplitude of the AC signal used for phosphorus is small, the voltage divider circuit 20 is not necessary, and in this case, when the output impedance of the signal source or voltage divider circuit is small, the buffer amplifier 21 for impedance matching is also unnecessary. It is. [Effects of the Invention] As described above in detail, according to the present invention, the alternating current component is removed by manually applying the alternating current component in the same phase to both comparators that detect the change level of direct current, and the original direct current level is reduced. By configuring to perform the comparison, it is possible to avoid using a low-pass filter. Therefore, according to the present invention, the delay in detection time for detecting that the telephone is off-hook can be reduced. Further, according to the present invention, since a low-pass filter is not required, it is possible to improve the circuit margin and downsize the circuit.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the principle of the present invention, Fig. 2 is a diagram showing operating waveforms of the circuit of the invention, Fig. 3 is a circuit diagram showing an embodiment of the invention, and Fig. 4 is a diagram showing operating waveforms of each part. Figure 5 is a conceptual diagram of a loop detection circuit, Figure 6 is a conventional configuration diagram of a loop detection circuit, and Figure 7 is a PCM
Conventional system configuration diagram of primary transmission equipment! FIG. 128 is a diagram showing an example of the configuration of a conventional ring trip circuit, and FIG. 9 is a diagram showing operating waveforms of the conventional ring trip detection circuit. In FIG. 1, 20 is a voltage dividing circuit, 21 is a buffer amplifier, 22 is a high-pass filter, 23 is an adder, and 24 is a comparator.

Claims (1)

[Claims] A high-pass filter (22) that receives an input signal and passes only high-frequency components; an adder (23) that adds a DC reference voltage to the output of the high-pass filter (22); and the adder. A comparator (24) which receives the output of (23) at one input and the input signal at the other input, and when the voltage of the input signal becomes larger than the DC reference voltage, it is regarded as off-hook and outputs a trip signal. A ring trip circuit consisting of.