JP2925409B2 - No-ringing terminal analog front end - Google Patents

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 remotely monitoring an instrument or the like using a telephone line, and more particularly to an erroneous trip on the exchange side when receiving a bell signal sent from the exchange. The present invention relates to a circuit configuration for prevention.

[0002]

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

FIG. 4 shows an output voltage V of the rectifier circuit 30 shown in FIG.
30 and a 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 FIG. In FIG. 3, when polarity inversion is performed on transmission lines L1 and L2 from a polarity inversion circuit (not shown) provided in exchange 10, polarity inversion detection circuit 40 in no-ringing terminal analog front end 20 detects this. , And outputs the detection result to its output terminal 43. Since this output drives the base of the transistor 63 to which the mirror capacitor 65 is added, the loop current required for communication is changed from a polarity inversion circuit (not shown) in the exchange 10 → the transmission line L1 → the input terminal 31 of the rectifier circuit 30 → Positive output terminal 33 of rectifier circuit 30 → DC loop current forming resistor 64 →
Transistor 63 → Negative output terminal 34 of rectifier circuit 30 →
Input terminal 32 of rectifier circuit 30 → transmission line L2 → switch 1
It flows smoothly through a polarity inversion circuit (not shown) within 0. The reason why the loop current flows while changing smoothly is due to the so-called Miller effect by the mirror 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. Therefore, the transformer 61 having a low impedance against a transient change is transiently provided by the resistor 64 for forming a DC loop current.
Since the current flows from the capacitor 62 to the capacitor 62, a large pulsating current instantaneously flows through the transmission lines L1 and L2, causing the switching apparatus 10 to malfunction (for example, erroneous call detection). Therefore, Miller capacitor 65 is an indispensable element. The communication state of the no-ringing terminal analog front end 20 is set as described above.

[0004]

However, in the circuit having the above-described structure, the normal communication (that is, the time when the telephone terminal is called) is performed.
When a bell signal is transmitted from the exchange 10 in the above, the bell signal current BI is converted into a bell signal source 16 → a ring trip detecting resistor 15 → a current limiting resistor 14 → a 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 (DC loop current forming resistor 64)
→ Capacitor 65 → Base of transistor 63 → Emitter of transistor 63 Simultaneously with turning on when transistor 63 exceeds an operation threshold, collector of transistor 63 → Emitter → Rectifier circuit 30
, The input terminal 31 of the rectifier circuit 30 → the transmission line L1 → the switch 11 in the exchange 10 → the current limiting resistor 12 → the battery V _BB → flows to the ground, and the capacitor 65
Causes the base of the transistor 63 to be temporarily driven. Therefore, the transistor 63 is turned on at a certain value of the waveform of the output voltage V30 of the rectifier circuit 30 (point P in FIG. 4), that is, the operation threshold of the circuit including the transistor 63, the capacitor 65, and the operation stabilizing resistor 66. (Point Q in FIG. 4), and a current of several tens of mA flows, so that an asymmetrical positive and negative bell signal current BI as shown in FIG. 4 flows.

[0005] Such asymmetrical bell signal current BI
Flows, the ring trip circuit 17 operates via the ring trip detecting resistor 15 in the exchange 10 even though the terminal is not responding, and it is considered that the terminal has responded, and the operation shifts to the switching operation. There was a problem. SUMMARY OF THE INVENTION The present invention relates to a non-ringing terminal analog front end in which an abnormal current flows when a bell signal is received in a circuit in the no ringing terminal analog front end and a false trip of an exchange occurs. Is provided.

[0006]

According to a first aspect of the present invention, there is provided a semiconductor device having first and second input terminals, a positive output terminal, and a negative output terminal. A rectifier circuit having a second input terminal connected to a pair of transmission lines extending from the exchange; a rectification circuit connected to the transmission line for detecting a polarity inversion 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 detects a bell signal from the transmission line;
A terminating circuit connected in parallel between a positive output terminal and a negative output terminal of the rectifier circuit, wherein the terminating circuit is connected to a control electrode by a first output terminal.
A ringing terminal having a switch element for turning on and off between the first and second electrodes to form a DC loop current required for no ringing communication, and a mirror capacitor connected between a control electrode of the switch element and a first electrode; At the front end, switch means is provided. The switch means is connected between the control electrode and the second electrode of the switch element, and has a function of turning on the switch element by turning on the output of the bell signal detection circuit. In a second aspect, the switch element according to the first aspect comprises a first transistor having a base as a control electrode, a collector as a first electrode, and an emitter as a second electrode. The switch means includes a second transistor having a collector and an emitter respectively connected between the base and the emitter of the first transistor, the base of which is controlled by the output of the bell signal detection circuit, and a base and an emitter of the second transistor. And an operation stabilizing resistor connected therebetween.

[0007]

According to the first and second aspects of the present invention, the analog front end of the no-ringing terminal is constructed as described above. When a bell signal is transmitted from the exchange via the transmission line, the bell signal is detected by the bell signal detection circuit. 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 occurrence of an erroneous trip can be prevented. Therefore, the above problem can be solved.

[0008]

FIG. 1 is a circuit diagram of an analog front end of a non-ringing terminal showing an embodiment of the present invention. Elements common to those in FIG. 3 are denoted by common reference numerals.

The no-ringing terminal analog front end 20A has a rectifier circuit 30, a polarity inversion detection circuit 40, a bell signal detection circuit 50, and a termination circuit 60 which are the same as those of the prior art.
The collector and the emitter of the switch means (for example, a 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. Further, the transistor 7
0, a resistor 71 for stabilizing operation is provided between the base and the emitter.
Is connected.

FIG. 2 shows an output voltage V30 of the rectifier circuit 30 and an output current I50 of the bell signal detection circuit 50 in FIG.
FIG. 11 is an operation waveform diagram of (ie, a base driving current of the transistor 70) and a bell signal current BI flowing through the transmission lines L1 and L2. The operation of FIG. 1 will be described with reference to FIG. In FIG. 1, when the polarity inversion circuit (not shown) provided in the exchange 10 inverts the polarity of the transmission lines L1 and L2, the polarity inversion in the analog front end 20A of the no-ringing terminal is detected as in the conventional case. Circuit 40
Detects this, and outputs the detection result to its output terminal 43. Since this output drives the base of the transistor 63 to which the mirror capacitor 65 is added, the loop current required for communication is changed from a polarity inversion circuit (not shown) in the exchange 10 → the transmission line L1 → the input terminal 31 of the rectifier circuit 30 → The positive output terminal 33 of the rectifier circuit 30 → the resistor 64 for forming a DC loop current → the transistor 63 → the negative output terminal 34 of the rectifier circuit 30 → the input terminal 32 of the rectifier circuit 30 → the transmission line L2 →
It flows along a route of a polarity inversion circuit (not shown) in the exchange 10 while smoothly changing.

The reason why the loop current flows while changing smoothly is due to the so-called Miller effect by the Miller capacitor 65 added between the collector and the base of the transistor 63, as described above. The communication state of the no-ringing terminal analog front end 20A is set as described above. Next, when a bell signal is transmitted from the exchange 10 during normal communication without polarity reversal from the exchange 10, the bell signal current BI becomes the bell signal source 16 in the exchange 10 → 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 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 → transistor 63 emitter → rectifier circuit 3
0 negative output terminal 34 → input terminal 31 of rectifier circuit 30 →
The transmission line L 1 → the switch 11 in the exchange 10 → the current limiting resistor 12 → the battery V _BB → the flow tends 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 to the output terminal 53 of the bell signal detection circuit 50 which 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 kept in the off state, and as shown in FIG. 2, a bell signal current BI substantially symmetric with positive and negative flows in the transmission lines L1 and L2.

As described above, in this embodiment, the bell signal current component from the mirror capacitor 65
, And the transistor 63 can be forcibly turned off without inputting to the base of the transistor 63. Therefore, abnormal current due to switching of the transistor 63 during reception of the bell signal can be prevented.
The waveform of the bell signal current BI flowing through the transmission lines L1 and L2 is substantially symmetric (that is, the DC component is eliminated), and the 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 constituted by other switch elements or switch 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, and the termination circuit 60 may have another circuit configuration.

[0014]

As described above in detail, according to the first aspect, the switch element having the mirror capacitor formed by smoothly switching the DC loop current of the termination circuit is added to the output of the bell signal detection circuit. Is turned on and off by the switch means driven in synchronization with the bell signal, so that the bell signal current component from the mirror capacitor is bypassed by the switch means and the switch element is forcibly turned off. it can. Therefore, abnormal current due to switching of the switch element during reception of the bell signal can be prevented, so that the bell signal current waveform flowing through the transmission line is substantially symmetrical (that is, the DC component is eliminated), and erroneous trip of the switch can be reliably prevented.

According to the second aspect of the present invention, the switch element and the switch means are respectively constituted by 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
The first transistor can be accurately turned off by the transistor, and the erroneous trip of the exchange can be more reliably prevented.

[Brief description of the 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.

FIG. 4 is an operation waveform diagram of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Exchange 20A No-ringing terminal analog front end 30 Rectifier circuit 31, 32 First and second input terminal 33 Positive output terminal 34 Negative 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)

(57) [Claims] A first input terminal, a positive output terminal,
A rectifier circuit having a first output terminal and a negative output terminal, wherein the first and second input terminals are connected to a pair of transmission lines extending from an exchange; A polarity inversion detection circuit for detecting, a bell signal detection circuit that is connected in parallel between a positive output terminal and a negative output terminal of the rectifier circuit, and detects a bell signal from the transmission line, and a positive output of the rectifier circuit. A terminating circuit connected in parallel between the terminal and a negative output terminal, wherein the terminating circuit controls on and off between the first and second electrodes by an output of the polarity inversion detecting circuit applied to a control electrode. Switching element for forming a DC loop current required for no ringing communication, and a non-ringing terminal analog front end having a mirror capacitor connected between a control electrode and a first electrode of the switching element 3. The ringing according to claim 1, further comprising a switch connected between the control electrode and the second electrode of the switch element and turned on by an 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. A second transistor having a collector and an emitter respectively connected between the base and the emitter, and having a base controlled by an output of the bell signal detection circuit; an operation stabilizing resistor connected between the base and the emitter of the second transistor; The no-ringing terminal analog front end according to claim 1, wherein: