JPH0685909A - No-ringing terminal analog front end - Google Patents

Abstract

PURPOSE:To prevent a mis-trip of an exchange by applying on/off control to a switch element with a mirror capacitor added thereto with a switch means driven synchronously with a bell signal by an output of a bell signal detection circuit. CONSTITUTION:A collector and an emitter of a 2nd transistor(TR) 70 are respectively connected between a base and an emitter of a 1st TR 63 and a base of the TR 70 is connected to an output terminal 53 of a bell signal detection circuit 50. Furthermore, a resistor 71 for operation stabilization is connected between the base and the emitter of the TR 70. Then a bell signal current component from a mirror capacitor 65 is bypassed by the TR 70 and not inputted to a base of the TR 63, which is forcibly turned off. Since an abnormal current due to switching of the TR 63 is prevented during the reception of the bell signal, a waveform of the bell signal current flowing to transmission lines L1, L2 is almost in symmetry and mis-trip of an exchange 10 is surely prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a no-ringing terminal analog front end for remote monitoring of instruments and the like by using a telephone line, and in particular, an erroneous trip on the side of the exchange when receiving a bell signal sent from the exchange. The present invention relates to a circuit configuration for preventing.

[0002]

2. Description of the Related Art FIG. 3 is a circuit diagram showing a configuration example of a conventional no-ringing terminal analog front end. A no-ringing terminal analog front end 20 is connected to the pair of transmission lines L1 and L2 extending from the exchange 10. The exchange 10 has a switch 11 connected to the transmission line L1, and the switch 11 is connected to, for example, a −48V battery V _BB via a current limiting resistor 12. The switch 13 is connected to the transmission line L2, to the switch 13, a current limiting resistor 14, and through the ring trip detection resistor 15, for example 16H _Z,
A bell signal source 16 of 75 Vr.ms is connected. The ring trip detection resistor 15 has a ring trip circuit 1
7 are connected in parallel. Although not shown, the exchange 10 is also provided with other circuits such as a polarity reversing circuit. The no-ringing terminal analog front end 20 includes a rectifier circuit 30, a polarity reversal detection circuit 40 that detects a polarity reversal state on the transmission lines L1 and L2, a bell signal detection circuit 50 that detects a bell signal from the exchange 10, and a termination circuit. 60 is provided. The first and second input terminals 31 and 32 of the rectifier circuit 30 and the input terminal 41 of the polarity inversion detection circuit 40,
42 is connected to the pair of transmission lines L1 and L2.
The input terminals 51 and 52 of the bell signal detection circuit 50 and the input terminal of the termination circuit 60 are connected in parallel between the positive output terminal 33 and the negative output terminal 34 of the rectifier circuit 30, respectively. The terminating circuit 60 includes a primary winding 61a of a transformer 61 for transmitting an AC signal and a capacitor 6 for blocking a DC current.
2, and a switch element (for example, a transistor) 63 for forming a DC loop, which are connected in series. Positive side output terminal 33 of rectifier circuit 30 and transistor 6
A resistor 64 of, for example, several KΩ to several tens KΩ for forming a DC loop current required at the time of no-ringing communication is connected between the third electrode and the collector serving as the first electrode. Between the collector / control electrode base of the transistor 63,
The mirror capacitor 65 is connected. A resistor 66 for stabilizing operation is connected between the base of the transistor 63 and the emitter as the second electrode, and the base of the resistor 66 is
It is connected to the output terminal 43 of the polarity inversion detection circuit 40. Further, output terminals 67 and 68 for AC signals are connected to the secondary winding 61b of the transformer 61, and the output terminal 6 thereof is
Transmission / reception with a modem or the like connected to the outside is performed via 7, 68.

FIG. 4 shows the output voltage V of the rectifier circuit 30 of FIG.
30 and the bell signal current BI flowing through the transmission lines L1 and L2
It is a figure which shows the waveform of. The operation of FIG. 3 will be described with reference to this figure. In FIG. 3, when polarity reversal is performed on the transmission lines L1 and L2 from a polarity reversal circuit (not shown) provided in the exchange 10, the polarity reversal detection circuit 40 in the no-ringing terminal analog front end 20 detects this. , And outputs the detection result to the output terminal 43. This output drives the base of the transistor 63 to which the mirror capacitor 65 is added, so that the loop current required for communication causes a polarity reversal circuit (not shown) in the exchange 10 → transmission line L1 → the input terminal 31 of the rectifier circuit 30 → Positive side output terminal 33 of rectifier circuit 30 → resistor 64 for forming DC loop current →
Transistor 63 → Negative output terminal 34 of rectifier circuit 30 →
Input terminal 32 of rectifier circuit 30 → transmission line L2 → switch 1
It flows to the route of the polarity inverting circuit (not shown) within 0 while changing smoothly. The flow of the loop current while changing smoothly is due to the so-called Miller effect due to the Miller capacitor 65 added between the collector and the base of the transistor 63. If the mirror capacitor 65 is not provided, the transistor 63 is rapidly turned on, so that the transformer 61 having a transient impedance lower than that of the resistor 64 for forming a DC loop current is transiently used.
Since a current flows from the capacitor 62 to the capacitor 62, a large pulsed current instantaneously flows through the transmission lines L1 and L2, causing the exchange 10 to malfunction (for example, to detect an erroneous call). Therefore, the mirror capacitor 65 is an indispensable element. As described above, the communication state of the no-ringing terminal analog front end 20 is set.

[0004]

However, in the circuit having the above configuration, during normal communication (that is, when calling a telephone terminal).
When a bell signal is sent from the exchange 10 at the bell switch, the bell signal current BI is the bell signal source 16 → the ring trip detection resistor 15 → the current limiting resistor 14 → the switch 13 →
Transmission line L2 → input terminal 32 of rectifier circuit 30 → positive output terminal 33 of rectifier circuit 30 → primary winding 61 of transformer 61
a → capacitor 62 (a resistor 64 for forming a DC loop current)
Shunt) → capacitor 65 → base of transistor 63 → emitter of transistor 63 and at the same time when transistor 63 exceeds the operating threshold, it is turned on temporarily, so collector of transistor 63 → emitter → rectifier circuit 30
Negative output terminal 34 → input terminal 31 of rectifier circuit 30 → transmission line L1 → switch 11 in exchange 10 → resistor 12 for current limiting → battery V _BB → ground and capacitor 65
Therefore, the base of the transistor 63 is temporarily driven. Therefore, the transistor 63 is turned on at a certain value (point P in FIG. 4) of the waveform of the output voltage V30 of the rectifier circuit 30, that is, at the operation threshold value of the circuit including the transistor 63, the capacitor 65, and the operation stabilization resistor 66. Since a current of several tens of mA flows (at point Q in FIG. 4), a positive / negative asymmetric bell signal current BI as shown in FIG. 4 flows.

Such a positive / negative asymmetric bell signal current BI
, The ring trip circuit 17 operates via the ring trip detection resistor 15 in the exchange 10 even if the terminal does not respond, and it is considered that the terminal has responded, and the exchange operation starts. There was a problem. SUMMARY OF THE INVENTION The present invention solves the problem that the prior art has with respect to the fact that an abnormal current flows at the time of receiving a bell signal in a circuit in a no-ringing terminal analog front end to cause an erroneous trip of a switchboard. Is provided.

[0006]

In order to solve the above-mentioned problems, a first invention has first and second input terminals, a positive side output terminal and a negative side output terminal. A rectifier circuit having a second input terminal connected to a pair of transmission lines extending from the exchange; a polarity reversal detection circuit connected to the transmission line for detecting a polarity reversal state on the transmission line; A bell signal detection circuit that is connected in parallel between the side output terminal and the negative side output terminal and that detects a bell signal from the transmission line,
A terminating circuit connected in parallel between the positive side output terminal and the negative side output terminal of the rectifier circuit, wherein the terminating circuit has a first output according to an output of the polarity reversal detection circuit applied to a control electrode.
A no-ringing terminal analog having a switch element for controlling on / off between a second electrode and a second electrode to form a DC loop current required for no-ringing communication, and a mirror capacitor connected between the control electrode of the switch element and the first electrode Switch means is provided at the front end. The switch means is connected between the control electrode and the second electrode of the switch element and has a function of being turned on by the output of the bell signal detection circuit to turn the switch element off. In the second invention, the switch element of the first invention is composed of the first transistor in which the control electrode is the base, the first electrode is the collector, and the second electrode is the emitter. The switch means includes a second transistor whose collector and emitter are respectively connected between the base and emitter of the first transistor and whose base is controlled by the output of the bell signal detection circuit, and a base and emitter of the second transistor. It is composed of an operation stabilizing resistor connected in between.

[0007]

According to the first and second aspects of the present invention, since the no-ringing terminal analog front end is configured as described above, when the bell signal is sent from the exchange through the transmission line, the bell signal detection circuit detects the bell signal. Is detected and the switch means is turned on in synchronization with the bell signal. As a result, the bell signal current input from the mirror capacitor to the control electrode of the switch element is bypassed by the switch means, the switch element is forcibly turned off, and an erroneous trip can be prevented. Therefore, the above problem can be solved.

[0008]

FIG. 1 is a circuit diagram of a no-ringing terminal analog front end showing an embodiment of the present invention, in which elements common to those in the conventional FIG. 3 are designated by common reference numerals.

The no-ringing terminal analog front end 20A has the same rectifier circuit 30, polarity reversal detection circuit 40, bell signal detection circuit 50, and termination circuit 60 as in the conventional case, and also the base of the first transistor 63.
The collector and the emitter of the switching means (for example, the second transistor) 70 are connected between the emitters, and the base of the transistor 70 is connected to the output terminal 53 of the bell signal detection circuit 50. In addition, transistor 7
A resistor 71 for stabilizing the operation is provided between the base and emitter of 0.
Are connected.

FIG. 2 shows the output voltage V30 of the rectifier circuit 30 and the output current I50 of the bell signal detection circuit 50 shown in FIG.
FIG. 10 is an operation waveform diagram of (that is, a base drive current of the transistor 70) and a bell signal current BI flowing in the transmission lines L1 and L2. The operation of FIG. 1 will be described with reference to this figure. In FIG. 1, when polarity reversal is performed on the transmission lines L1 and L2 from a polarity reversal circuit (not shown) provided in the exchange 10, polarity reversal detection in the no-ringing terminal analog front end 20A is performed as in the conventional example. Circuit 40
Detects this and outputs the detection result to its output terminal 43. This output drives the base of the transistor 63 to which the mirror capacitor 65 is added, so that the loop current required for communication causes a polarity reversal circuit (not shown) in the exchange 10 → transmission line L1 → the input terminal 31 of the rectifier circuit 30 → Positive side output terminal 33 of rectifier circuit 30 → DC loop current forming resistor 64 → Transistor 63 → Negative side output terminal 34 of rectifier circuit 30 → Input terminal 32 of rectifier circuit 30 → Transmission line L2 →
It flows to the route of a polarity reversing circuit (not shown) in the exchange 10 while changing smoothly.

The reason why the loop current flows while changing smoothly is the so-called Miller effect due to the Miller capacitor 65 added between the collector and the base of the transistor 63, as described above. As described above, the communication state of the no-ringing terminal analog front end 20A is set. Next, when a bell signal is transmitted from the exchange 10 during normal communication in which the polarity is not reversed from the exchange 10, the bell signal current BI changes from the bell signal source 16 in the exchange 10 to the resistance for ring trip detection. 15 → current limiting resistor 14 → switch 13 → transmission line L
2 → input terminal 32 of rectifier circuit 30 → positive side output terminal 33 of rectifier circuit 30 → primary winding 61a of transformer 61 in termination circuit 60 → capacitor 62 (shunt to resistor 64 for forming DC loop current) → Capacitor 65 → Transistor 63
Collector → emitter of transistor 63 → rectifier circuit 3
Negative output terminal 34 of 0 → input terminal 31 of rectifier circuit 30 →
The transmission line L1 → the switch 11 in the exchange 10 → the current limiting resistor 12 → the battery V _BB → tries to flow to the ground. However, the output voltage V3 of the rectifier circuit 30 as shown in FIG.
An output current I50 as shown in FIG. 2 flows through the output terminal 53 of the bell signal detection circuit 50 that operates by detecting 0, and this output current I50 drives the base of the transistor 70. Current is bypassed by the transistor 70 and does not enter the base of the transistor 63. Therefore, the transistor 63 can be maintained in the off state, and as shown in FIG. 2, the bell signal current BI, which is substantially positive-negative symmetrical, flows through the transmission lines L1 and L2.

As described above, in this embodiment, the bell signal current component from the mirror capacitor 65 is transferred to the transistor 70.
By bypassing, the transistor 63 can be forcibly turned off without inputting to the base of the transistor 63. Therefore, it is possible to prevent abnormal current due to switching of the transistor 63 during reception of the bell signal,
The waveform of the bell signal current BI flowing through the transmission lines L1 and L2 becomes substantially symmetrical (that is, the direct current component disappears), and erroneous trip of the exchange 10 can be reliably prevented.

The present invention is not limited to the above embodiment,
For example, the transistors 63 and 70 may be composed of other switching elements or switching means such as MOS transistors,
Alternatively, the transistor 70 and the operation stabilizing resistor 71
May be provided in the termination circuit 60 or the bell signal detection circuit 50, or the termination circuit 60 may have another circuit configuration.

[0014]

As described above in detail, according to the first aspect of the present invention, the switch element to which the mirror capacitor formed by smoothly switching the DC loop current of the termination circuit is added is used as the output of the bell signal detection circuit. Thus, since the switch means that is driven in synchronization with the bell signal is on / off controlled, the bell signal current component from the mirror capacitor is bypassed by the switch means, and the switch element can be forcibly turned off. it can. Therefore, the abnormal current due to the switching of the switch element can be prevented during the reception of the bell signal, so that the bell signal current waveform flowing through the transmission line is almost symmetrical (that is, the direct current component disappears), and the erroneous trip of the exchange can be reliably prevented.

According to the second aspect of the invention, since the switch element and the switch means are respectively composed of the first and second transistors, and the operation stabilizing resistor is connected between the base and the emitter of the second transistor, With a simple circuit configuration, the second
With this transistor, the first transistor can be turned off accurately, and erroneous trip of the exchange can be prevented more reliably.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a no-ringing terminal analog front end showing an embodiment of the present invention.

FIG. 2 is an operation waveform diagram of FIG.

FIG. 3 is a circuit diagram of a conventional no-ringing terminal analog front end.

4 is an operation waveform diagram of FIG.

[Explanation of symbols]

10 Exchanger 20A No-ringing terminal Analog front end 30 Rectifier circuit 31, 32 First and second input terminal 33 Positive side output terminal 34 Negative side output terminal 40 Polarity inversion detection circuit 50 Bell signal detection circuit 60 Termination circuit 61 Transformer 62 Capacitor 63 , 70 First and second transistors 64 DC loop current forming resistor 65 Miller capacitor 66, 71 Operation stabilizing resistor

Claims (2)

[Claims] 1. A first input terminal, a second input terminal, a positive output terminal,
And a rectifier circuit having negative side output terminals, the first and second input terminals being connected to a pair of transmission lines extending from the exchange, and a polarity inversion state on the transmission lines connected to the transmission line. A polarity reversal detection circuit for detecting, a bell signal detection circuit that is connected in parallel between the positive side output terminal and the negative side output terminal of the rectifier circuit, and detects a bell signal from the transmission line; and a positive side output of the rectifier circuit. A termination circuit connected in parallel between the terminal and the negative output terminal, wherein the termination circuit performs on / off control between the first and second electrodes by the output of the polarity reversal detection circuit applied to the control electrode. -Ringing terminal analog front end having a switch element for forming a DC loop current required for non-ringing communication and a mirror capacitor connected between the control electrode and the first electrode of the switch element In the non-ringing method, switch means is provided that is connected between the control electrode and the second electrode of the switch element and is turned on by the output of the bell signal detection circuit to turn the switch element off. Terminal analog front end. 2. The switch element comprises a first transistor having a control electrode as a base, a first electrode as a collector, and a second electrode as an emitter, and the switch means is provided with the first transistor. A second transistor having a collector and an emitter connected between the base and the emitter, the base of which is controlled by the output of the bell signal detection circuit; and an operation stabilizing resistor connected between the base and the emitter of the second transistor. 2. The no-ringing terminal analog front end according to claim 1, wherein