JPH065846B2 - Ring trip circuit - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to ring trip circuits.

Background of the Technology In a telephone exchange system, a so-called subscriber circuit is provided between a subscriber telephone and a network (exchange switch). This subscriber circuit comprises a plurality of types of functional circuits, and the present invention refers to one of them, a ring trip circuit. This ring trip circuit sends a ringing signal to a telephone when it receives an incoming call and rings the bell. When the called party answers and goes off-hook, it detects this and stops sending the ringing signal. It has the function of outputting a ring trip signal. Although this ring trip circuit has an already established circuit configuration, various improvements are desired to meet new demands.

Prior Art and Problems FIG. 6 is a diagram showing an example of a general telephone exchange system. In the figure, 11 is a subscriber terminal, that is, a telephone, which is connected to a subscriber circuit (LC) 13 via a line 12. The subscriber circuit 13 is controlled by a central controller (CC) 15 via a scanning circuit (SCN) 16 and a signal distribution circuit (SD) 17. The central controller 15 is a network (NW) 1
4, that is, the switching switch is also controlled to comprehensively manage the switching connection processing with other subscriber terminals (not shown).
First, when the telephone 11 receives an incoming call from another subscriber, the central control unit 15 drives the relay (RL) 18 in the subscriber circuit 13 via the incoming call distribution circuit 17 to call the call signal CR.
(Continuous Ringing) is transmitted. This calling signal C
The R rings the bell in the telephone 11 and the subscriber answers off-hook. The central controller 15 detects, via the scanning circuit 16, the loop "closed" formed by this off-hook and subsequently proceeds with the switching connection procedure with the calling subscriber. After that, the conversation between the subscribers begins. The present invention mainly refers to the inside of the subscriber circuit 13 in the configuration of FIG.

FIG. 7 is a circuit diagram showing a conventional example of a ring trip circuit provided in the subscriber circuit 13 of FIG. In this figure, the same components as those in FIG. 6 are designated by the same reference numerals or symbols (this is the same in all the figures). In FIG. 7, among the subscriber circuits 13, a well-known power supply circuit 21, for example, a −48V DC power supply 22, the relay 1 is used.
The eight contacts r1 and the ring trip circuit 23 are shown. The power supply circuit 21 supplies power necessary for operating the handset and performs resistance power supply or constant current power supply.

When the telephone 11 receives an incoming call, the above-described relay 18 is driven, and its contact r1 is switched from the terminal t1 to t2. Then, the above-mentioned calling signal CR is transmitted to the telephone set 11. FIG. 8 is a waveform diagram of the calling signal CR. Call signal CR is an AC voltage _{V AC} (so-called ringer signal to a DC voltage _{V DC} (e.g., -48V) for example 95V
At a frequency of 20 Hz). GN
D is the ground level. Returning to FIG. 7, the signal CR
The AC component (V _AC ) of the signal passes through the capacitor 24, and drives the bell circuit (see 46 in FIG. 9) in the telephone 11 via the ringer sending resistor 25. The bell circuit rings the bell circuit, and when the subscriber goes off-hook, the bell circuit is not driven and a direct current loop is formed.
As a result, the capacitor 24 is charged with the polarity (+, −) shown by the DC voltage V _DC . When this charging voltage rises and exceeds the Zener voltage of the Zener diode 26, the photodiode in the photocoupler 27 is turned on and the paired phototransistors are turned on.
By this turning on, the voltage of the lower terminal of the resistor R3 in the figure drops to the ground level. This is the ring trip signal R
It becomes T. When this signal RT is detected by the scanning circuit 16 described above, the central controller 15 cuts off the transmission of the signal CR and starts the switching connection processing of the network 14. In FIG. 7, a resistor R1 is a discharge resistor of the capacitor 24, a resistor R2 is a protection resistor for the photodiode in the photocoupler 27, and a diode D is for protecting the photodiode from reverse bias.

A particular problem in the ring trip circuit 23 shown in FIG. 7 is the presence of the capacitor 24. If the capacitor 24 can be eliminated, the conventional problems can be solved at once. The first problem is that the capacitor 24 is usually 4
Since a large capacitance of 7 μF is required, the external dimensions of the ring trip circuit are increased, which is a disadvantage in mounting. This capacitor 24 is provided for each subscriber, and the number thereof is enormous. Therefore, it is preferable that its size is as small as possible.

The second problem is that the capacitor 24 must be charged before the ring trip signal RT is sent out,
That is, it takes a relatively long time to generate the ring trip signal RT. Since this time is proportional to the capacity (47 μF) of the capacitor 24, after all, it takes time from off-hook to exchange connection, and quick response cannot be performed.

A third problem is that the capacitor 24 cannot receive a call signal having specifications stricter than the call signal CR having specifications as shown in FIG. If the DC voltage _VDC forming the signal CR in FIG. 8 greatly exceeds -48V, the withstand voltage of the capacitor 24 must be further increased, or some protective means must be added to it. As a specific example, the message waiting service corresponds to this. This service is to display a call received while the subscriber is absent, that is, an incoming call by lighting a discharge lamp (neon tube). In this case, in order to turn on the neon tube, the DC voltage V
_{As DC} , -100V is used, which greatly exceeds -48V. FIG. 9 is a diagram showing an example of a conventional configuration in the telephone 11 shown in FIG. In the figure, 41 is a transmitter,
42 is a handset, which is driven by a normal telephone circuit 43. 46 is also a normal bell circuit, and has a DC blocking capacitor 47. When the receivers (41, 42) are picked up, the hook switch 45 is turned off (connected to the terminal t3 side). This is the hook switch 45 connects the neon tube 44, for notifying the incoming call was in away, DC for special service voltage V _{'DC (-100V)} is used as a call signal CR.

OBJECT OF THE INVENTION It is an object of the present invention to provide a ring trip circuit which can solve the above problems at the same time. Specifically, the function equivalent to that of the conventional ring trip circuit 23 is realized without using the capacitor 24 to reduce the outer dimensions, shorten the response time of the ring trip, and perform the message weighting described above. The purpose of the present invention is to provide a new ring trip circuit suitable for the special service of.

According to the present invention, in order to achieve the above-mentioned object, the conventional capacitor 24 is used as a ringer sending resistor, and a voltage change appearing at both ends of the ringer sending resistor is extracted by an operational amplifier to cause a ring trip. It is characterized by that.

First Embodiment of the Invention FIG. 1 is a circuit diagram showing a first embodiment of a ring trip circuit according to the present invention. First, the signal distribution circuit 17 (sixth
When a call is received from the telephone 11, the relay 18
(FIG. 6) is driven to connect the first contact point r1 to the terminal t2 side. At the same time, the call signal CR (Fig. 8) is sent to the telephone 1
Send to 1. This signal CR is transmitted to the first contact r1, the second contact r2, the ringer delivery resistor 25, and the first contact R1.
-Line 12 (lower side in the figure) -Phone 11-Line 12 (upper side in the figure) -Power supply circuit 21-Flows along the GND. This drives the bell circuit 46 (FIG. 9), which causes the bell to ring by the _AC voltage V _AC (FIG. 8) in the signal CR. In this case, since the telephone 11 is in the on-hook state, the contact of the hook switch 45 (Fig. 9) is connected to the terminal t4 side, and the signal CR passes only the bell circuit 46 (Fig. 9). The bell circuit 46 is normally represented equivalently as a series circuit of a coil, a capacitor and a resistor, and an AC voltage V of 20 Hz is applied.
_It exhibits a high impedance of 7 to 8 KΩ for _AC . Therefore, the second contact r2 and the ringer delivery resistor 2
5, the signal CR (AC signal) passing through the first contact point r1 is
For example, it is as small as 10 to 20 mA. Assuming that this AC signal is 10 mA, the ringer sending resistor 25 (for example, 820
The voltage appearing at both ends of Ω is 8.2V (10mA × 820)
Ω). I'm on hook now
The operational amplifier 52 must not be triggered by 8.2V. When the operational amplifier 52 is triggered, the output of the comparator 53 becomes "H" (high) level and the ring trip signal RT is sent out. Therefore,
In order to suppress the above-mentioned alternating current of 8.2 V during on-hook and prevent the operational amplifier 52 from being triggered, that is, in order not to transmit the ring trip signal RT, the operational amplifier 52 is provided with an alternating current component suppressor of the signal CR. This AC component suppressor is specifically a reduction filter and is realized by an integrating circuit. The resistor R4 and the capacitor C1 in FIG. 1 form this integrating circuit. If the resistance R4 is set to 100 KΩ, for example, the capacitor C1 may be about 3.3 μF. Here, the output V ₀ of the operational amplifier 52 is (However, Z _C1 is the AC component of the capacitor C1 (20 Hz)
And the above numerical example is used as R4 and C1, R4 = 100 KΩ, And V ₀ becomes about 0.2V. Thus, for the AC component of the calling signal CR, the above-mentioned voltage (= 8.2 V) generated at the input side of the operational amplifier 52 is 0.2 at its output.
It can be suppressed to V. After all, the ring trip circuit 51 of the present invention does not respond to the ringing signal CR being on-hook at all and does not output the ring trip signal RT. In order to balance the impedances of the inverting input (-) side and the non-inverting input (+) side of the operational amplifier 52, a resistor R5 and a capacitor C2 having the same configuration as the above-mentioned integrating circuit (R4, C1) are provided. Therefore, these values are also 100 KΩ and 3.3 μF, respectively.

Next, assume that the subscriber (called party) answers and goes off-hook. By this off-hook, the contact of the hook switch 45 shown in FIG. 9 is switched from the terminal t4 to the side t3. As a result, the bell circuit 46 is de-excited and the ringing of the bell is stopped. Also, at this time, the hook switch 45 'in the telephone circuit 43 is interlocked with the hook switch 45 to connect its contact to the terminal t3' side, so that a closed loop including the resistor 48 is formed. As a result, not only the _AC signal (VAC) of the calling signal CR but also the DC component ( _VDC ) of the signal CR starts to flow. In FIG. 1, the DC current due to this DC component produces a DC voltage across the ringer sending resistor 25, and this DC voltage appears in the output of the operational amplifier 52 as it is without being suppressed.
What appears as it is is that the DC voltage is the resistance R4 (= 1
1 (= 10KΩ) and resistor R6 (= 100KΩ)
This is because R6 / R4) is multiplied. In this case, the inverting input (−) side of the operational amplifier 52 has a higher potential than the non-inverting input (+) side, so that the output V ₀ of the operational amplifier 52 drops. However, since the above-mentioned capacitor C1 is inserted, the output V ₀ does not drop sharply, but gradually drops with a certain time constant. FIG. 2 is a waveform diagram showing the signal waveforms of the main parts in FIG. 1, and the above-mentioned gradually decreasing output V ₀ is shown in column (a) of this figure. The output V ₀ in column (a) is as a whole:
Gradually lower from the time T _{OFF when the} hook is off hook. When this output V ₀ is analyzed, it _{consists of} DC components v _dc and v _ac ,
v _ac is an AC signal of 20 Hz that constitutes the above-mentioned signal CR, and is superimposed on v _dc . Therefore, v _dc is the capacitor C1
Since it gradually drops by, v _ac also drops with it. It is clear from the circuit configuration of the telephone 11 shown in FIG. 9 that the amplitude of v _ac suddenly increases after the time T _OFF . Referring to FIG. 9, when the hook switch 45 is in the on-hook state, the AC signal (V _AC ) in the signal CR is all applied to the bell circuit 46 and its amplitude is small. This is because, as already mentioned, the impedance of the bell circuit 46, which is equivalently composed of a series circuit of a coil, a capacitor and a resistor, with respect to an AC signal (20 Hz) is usually 7 to 8K.
This is because it reaches Ω. However, when it goes off-hook (after T _{OFF in} FIG. 2), the hook switches 45 and 4
Each contact of 5'switches to terminals t3 and t3 ',
The impedance for the AC signal of 20 Hz is resistance 48
Because it will be only. The resistance value of this resistor 48 is usually 3
Since it is about 00Ω, it is much smaller than the above-mentioned AC impedance (7 to 8KΩ). This is the reason why the amplitude of the AC component v _{ac in} FIG. 2 becomes large after T _OFF . Since the DC component in the signal CR also increases significantly when the hook switches 45 and 45 'are turned on and off (the current also flows through the leak resistance in the telephone 11 when the hook switch is turned on), the output of the operational amplifier 52 is output. DC component in the V ₀ v _dc is as shown in FIG. 2, T _OFF after,
Gradually descend.

Returning to column (a) of FIG. 2, the falling output V ₀ crosses the threshold level V _TH at time T ₀ . This threshold level V _TH is a comparison reference input of the comparator 53 of FIG. 1 and is used for level comparison with V ₀ applied to the other input. As shown in FIG. 2 (b), V ₀ <V
_When it becomes _TH , the output of the comparator 53 is inverted to the “H” level. This "H" level output becomes the desired ring trip signal RT via the diode D1. The resistor R8 is a pull-down resistor. Thus, the ring trip circuit 51 of the present invention can output the ring trip signal RT without using the conventional capacitor 24 (FIG. 7). As a result, the above-mentioned first problem can be solved. However, new capacitors C1 and C2 (first
(Fig.) Is required, but each may be several μF and does not require a large capacitance of 47 μF as in the conventional capacitor 24. Furthermore, the ring trip circuit 51 of the present invention
Can shorten the time from off-hook to outputting the signal RT, and can solve the above-mentioned second problem.
This is obvious from the column (a) of FIG. 2, and although the DC component v _dc gradually decreases toward the threshold level V _TH , the AC component v _ac superimposed on this DC component v _dc is after the off-hook time T _OFF . Since its amplitude is increased, the time T
₀ (FIG. 2) has already crossed its level V _TH .
That is, the ring trip signal RT is output within a short time after T _OFF .

In the ring trip circuit of the present invention, the conventional capacitor 2
The elimination of 4 eliminates its inherent DC blocking function. Then, there is an unnecessary loss of DC power in the ring trip circuit. Therefore, the second
A contact point r2 (Fig. 1) is provided, and the contact point r2 is provided except when an incoming call is received.
Is preferably switched to the right terminal in the figure. This right terminal is set to ground level.

Next, a second embodiment relating to the above-mentioned third problem will be described.
FIG. 3 is a circuit diagram showing a second embodiment of the ring trip circuit according to the present invention. The ring trip circuit 71 can solve the third problem as well as the above-mentioned first and second problems. A ring trip circuit is provided here in the first embodiment (51 in FIG. 1) and the second embodiment (7 in FIG. 3).
The reason for dividing into 1) is that the special service such as the above-mentioned message weighting is not always required. Therefore, when it is installed in a hotel or the like that requires this special service, the ring trip circuit 71 of the second embodiment may be adopted. The second embodiment differs from the first embodiment in that a level suppressing means including a clamping resistor R9 and a clamping diode D2 is added.
The operating principle is basically the same as that of the first embodiment. That is,
In the normal case, the ring trip signal RT is output in response to the call signal CR shown in FIG. 8 and the signal change as shown in FIG. When the ring trip signal RT is not output, that is, when the called party is absent, the central control unit 15 (Fig. 6) instructs the message waiting service to be executed. That is, the neon tube 44 (9th
(Fig.) Keeps flashing to notify you that you have an incoming call while you were absent. Even if another call occurs during this period, the busy tone is sent back to the calling party, and as long as the called party is undergoing the message waiting service, the call cannot be answered.

In this message weighting service, a DC voltage _V'DC (-1 for special service) is used as a calling signal CR.
00V) is used, it is necessary to consider protection for the operational amplifier 52 and prevention of transmission of a false ring trip signal from the operational amplifier 52. This is because the input voltage of the operational amplifier is generally the power supply voltage (for example, +
5V and -24V), the output of the operational amplifier may become unstable or, in the worst case, may be destroyed. The erroneous sending of the ring trip signal is brought about by the indefiniteness of the above output, but the erroneous sending is caused by other factors (described later). Referring to Figure 3, first, direct current for special service voltage V _{'DC (=} -100V) is applied as a calling signal CR. Then, the bias potential _{V B} to provide a DC bias to the operational amplifier 52, for example -12V, through a more resistive R7 → the resistor R5 → relay contact r2, direct current flows in _{V 'DC.} Therefore, the resistance voltage division of R7 and R5 causes R7 and R5 to
A high voltage of -50 V, for example, is applied to the connection point of the two, that is, the non-inverting input (+) of the operational amplifier 52. On the other hand, the same applies to the inverting input (-) side of the operational amplifier 52, and the output of the operational amplifier 52 normally fluctuates within the range of the power supply voltage, but a request for special service occurs and the direct current voltage _V'DC (=- 100V)
When the output of the DC voltage is started, the DC bias (for example, -12V) is output, and the DC current passes through the resistor R6, the resistor R4, the resistor 25, and the Luray contact r2, and V '
It flows to _DC . Therefore, due to these resistance partial pressures, R6
A high voltage of, for example, -50 V is applied to the connection point between R4 and R4, that is, the inverting input (-) of the operational amplifier 52. When such a high voltage is applied to the input side of the operational amplifier 52, it exceeds the normal power supply voltage level of the operational amplifier 52. Therefore, the operational amplifier 52 is destroyed or, even if not destroyed, its output. Levels can be quite volatile. Therefore, first, the diode D2 is provided. It is, so to speak, a clamp diode. The anode of the diode D2 is connected to the clamping potential V _c , for example −22 V, and the cathode thereof is the emergency inverting input (+) of the operational amplifier 52.
Connected to. Thus the non-inverting input (+) is almost -22V
Clamped to. This −22V is also transmitted to the inverting input (−) of the operational amplifier 52 through the resistor R9, and if the voltage drop at R9 is 1V, the inverting input (−) is clamped to −23V, for example. This R9 is, so to speak, a clamp resistor. The resistance value of R9 is set to a value considerably smaller than the resistance value of R4 (for example, 100 KΩ). Thus, the input side of the operational amplifier 52 is protected from overvoltage, the operational amplifier 52 is protected from destruction, and its output level is not unstable.

The resistor R9 connected between the non-inverting input (+) and the inverting input (-) of the operational amplifier 52 also has a function of preventing an erroneous ring trip. It is, so to speak, a false trip prevention resistor. Wherein prior to sending the request for a special service to the V _{'DC (=} -100 V) is started, a DC blocking capacitor 47 to be connected to the bell circuit 46 of the telephone set 11 (FIG. 9) is fully charged, B line and A
Line A (-48V power supply side) of the subscriber line consisting of a pair of lines
Has a potential of -48V. Therefore, the relay contact r1
When but led to line A is connected to the terminal t1, the inverting input of the operational amplifier 52 (-) potential side i.e. A line side (-48V), the non-inverting input (+) side, i.e. V _'DC side (-
It becomes higher than 100 V), and the ring trip signal RT is output from the comparator 53. However, this ring trip is not the original ring trip based on the off-hook of the telephone set 11, but a false ring trip. Such false ring trips are also prevented by the resistor R9 and the diode D2. As described above, the anode of the diode D2 is connected to the clamping potential V _c (−22V), and the direct current is V ′ _DC (= −100) through the resistor R9 → the resistor R4 → the resistor R25 → the relay contact r2.
V). Therefore, the potentials of both ends of the resistor R9 are higher on the non-inverting input (+) side than on the inverting input (-) side. Thus, the above-described potential relationship between the non-inverting input (+) and the inverting input (-) of the operational amplifier 52 is reversed. That is, the non-inverting input (+) level of the operational amplifier 52 can be set higher than the inverting input (-) level,
Therefore, it is prevented that the ring trip erroneously immediately after the V _'DC delivery has started. 'After a few more advent of ms _DC, input of the operational amplifier 52 (+, -), since becomes almost the same potential by the so-called imaginary short, the voltage V' V after a lapse of several ms from the arrival of the _DC resistance R
It is equivalent to not having 9. That is, in the transition period immediately after the V _'DC arrives, the inverting input of the operational amplifier 52 (-) by and very inverted resistor connected between the input (+) R9, gain of the operational amplifier 52 is reduced. However, after the transient period passes and the output of the operational amplifier 52 becomes stable, the above-mentioned imaginary short circuit occurs between its inputs (-, +). If this imaginary short occurs, the voltage difference between these inputs (-, +) becomes almost 0 V, and the resistance R
The current flowing through 9 becomes extremely small, and the effect of the resistor R9 on the gain of the operational amplifier 52 can be virtually ignored. This transition period is several ms as described above. For example, if the capacitance of the feedback capacitor C1 of the operational amplifier 52 is 3.3 μF, the output voltage is 7.5 V, and the maximum drive current (constant current) is 10 mA, 2.48 ms (= 7.5V x 3.3
It becomes μF / 10mA. Since the time of 2.48 ms is a short time which is less than one cycle of the low-frequency AC voltage of 20 Hz shown in FIG. 2, it does not impair the original integration function of the operational amplifier 52. After all, the ring trip circuit 71 of the second embodiment can be used when performing services such as message weighting.

FIG. 4 is a circuit diagram showing an example of a relay drive circuit that cooperates with the ring trip circuit of the present invention. This relay drive circuit 81 drives the relay 18 shown in FIG. 6, and is applied to both the ring trip circuits 51 and 71 described above. The configuration and operation of this relay drive circuit 81
A description will be given with reference to the drawings and FIG. Note that FIG. 5 is a waveform diagram showing the waveform of the signal appearing in the main part of FIG.
First, when the calling party dials the number of the called party, the subscriber circuit (LC) to which the calling party is connected receives the dial pulse, and the central control unit 15 (Fig. 6) displays the called party's number. Give the number. This notification is sent by the calling party's connected scanning circuit (SCN).
Done by Therefore, the central controller 15 sends the signal sd from the signal distribution circuit (SD) 17 (FIG. 6) of the called party to the relay drive circuit 81. This appears in part b in FIG. 4 and has the waveform in column (b) of FIG. The signal sd is, for example, a repetition of 1 second on and 3 seconds off. This signal sd
Is applied to the reset input R of the flip-flop 82 composed of a NAND gate to generate the signal shown in the section (e) in the portion e, thereby turning the relay 18 on and off as shown in the section (f). In other words, the rectangular pulse portion in column (f) drives the bell circuit to call. In response to this call, time T
_{If you go off} hook with _OFF (see column (a) in Fig. 2),
The ring trip signal RT (see the column (c) of FIG. 2) shown in the column (a) appears at the time T ₀ in the portion a.
The inverter 83 inverts T, and the flip-flop 8
When applied to the second set input S, the signal having the waveform shown in the column (c) appears in the portion c and the signal having the waveform shown in the column (d) appears in the portion d. Here, the signal of the portion e which is the output of the flip-flop 82 is turned off as shown in the column (e), and the driving of the relay 18 is stopped. That is, the drive of the bell circuit is cut off. In the message waiting state, the neon tube 44 (FIG. 9) blinks at the timing shown in the column (f) to notify the called party of the incoming call which is absent.

EFFECTS OF THE INVENTION As described in detail above, according to the present invention, the above-mentioned 3
A ring trip circuit that can solve one of the above problems, that is, miniaturize the circuit, speed up the ring trip, and have high operation reliability is realized.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of a ring trip circuit according to the present invention, FIG. 2 is a waveform diagram showing signal waveforms of essential parts in FIG. 1, and FIG. 3 is a ring trip circuit according to the present invention. 2 is a circuit diagram showing a second embodiment of the present invention, FIG. 4 is a circuit diagram showing an example of a relay drive circuit which cooperates with the ring trip circuit of the present invention, and FIG. 5 is a waveform of a signal appearing in the main part of FIG. FIG. 6 is a waveform diagram, FIG. 6 is a diagram showing an example of a general telephone exchange system, FIG. 7 is a circuit diagram showing a conventional example of a ring trip circuit provided in the subscriber circuit 13 of FIG. 6, and FIG.
FIG. 9 is a waveform diagram of the call signal CR, and FIG. 9 is a diagram showing an example of a conventional configuration in the telephone 11 shown in FIG. 11 ... Telephone, 13 ... Subscriber circuit, 15 ... Central control unit, 16 ... Scan circuit, 17 ... Signal distribution circuit, 25 ... Ringer sending resistance, 45, 45 '... Hook switch, 46 ...
Bell circuit, 51 ... Ring trip circuit, 52 ... Operational amplifier, 53 ... Comparator, 71 ... Ring trip circuit, R
4 to R9 ... Resistance, C1, C2 ... Capacitor, D2 ... Diode, CR ... Ringing signal, RT ... Ring trip signal.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kenji Takato, 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa, within Fujitsu Limited (72) Inventor, Atsushi Ashikawa 1015, Kamiodanaka, Nakahara-ku, Kawasaki, Kanagawa Within Fujitsu Limited ( 56) References JP-A-58-88953 (JP, A) JP-A-55-100778 (P, A)

Claims (1)

[Claims] 1. A direct current component (V _DC ) to an alternating current component (V _AC ).
Supply the call signal (CR) that is superimposed on the telephone (11),
A bell circuit in the telephone (11) due to the _AC component (VAC)
A ringer sending resistor (25) for passing the ringing signal (CR) to drive the (46), detect the off-hook of the telephone (11) and send a ring trip signal (RT), and the ringer sending An operational amplifier (52) having a voltage appearing across the resistor (25) as an input, and a comparator (53) comparing the output level (V ₀ ) of the operational amplifier (52) with a threshold level (V _TH ).
And a inverting input (-) of the operational amplifier (52) is a first resistor (R).
4) connected to one end of the ringer delivery resistor (25), and the non-inverting input (+) of the operational amplifier (52) is connected to the ringer delivery resistor (25) via the third resistor (R5). ), The second resistor (R6) and the first capacitor (C) are connected between the output of the operational amplifier (52) and the inverting input (-).
1) is connected in parallel by a feedback circuit, and a fourth resistor (V) is provided between the non-inverting input (+) and the biasing potential (V _B ) for applying a DC bias to the operational amplifier (52). R7) and a second capacitor (C2) are connected in parallel, and the third resistor (R5), the fourth resistor (R7) and the second capacitor (C2) are respectively connected to the first resistor (R4). , The second resistor (R6) and the first capacitor (C1) have the same characteristics, and the comparator (53) is configured to output the threshold level (V _TH ) and the output level of the operational amplifier (52). (V ₀ )
The ring trip signal (RT) is output when a level inversion occurs between the operational amplifier (52) and the non-inverting input (+) of the operational amplifier (52). Fifth resistance (R
9), the anode input side to the clamping potential (V _C) for protection against overvoltages of the operational amplifier (52), and a diode (D2) whose cathode is connected to the non-inverting input (+) A ring trip circuit characterized by being provided.