JPH11252270A - Subscriber line interface and communication equipment using the subscriber line interface - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a circuit that detects a calling signal with less parts by parallelly connecting a calling signal pass filter to a switch that makes power supply fed from a subscriber line intermittent. SOLUTION: A subscriber line is connected to a power supply circuit 3 through a calling signal pass filter 1 and a station feeding control switch 2. The circuit 3 rectifies power supplied from an exchange via the subscriber line, adjusts voltage and supplies power supply to an interface 4. A loop current defined by prescribed impedance Z is caused to flow, notifying the exchange that it is in an off-hook state and makes a speech communication state by closing a switch 6 for DC closing. The arrival of a calling signal is notified to a microprocessor 5 as an interrupt. After the switch 2 is turned on after interrupt, the switch 2 is turned off to be in a waiting state when a calling signal is not detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a telephone subscriber line interface which operates with station power.

[0002]

2. Description of the Related Art In the telecommunications field, in order to protect network facilities having high publicity and to protect terminals, a high insulation property is required at a boundary between a network and a terminal (hereinafter referred to as a line interface). Small transformers for communication with high insulation properties have been used. However, with the spread and development of personal terminals, further miniaturization and weight reduction are required for portable terminals, and the improvement of materials and structures used for transformers has not been able to sufficiently meet the demand for miniaturization. Applications of isolators are being studied.

In applications such as measurement and medical treatment, it may be necessary to insulate a signal detection portion from a signal processing portion such as a sensor and a signal processing circuit. Also known as

[0004] Capacitive isolators have been developed for the purpose of reducing the size, increasing the reliability, and reducing the cost of the isolator. As a high withstand voltage capacitor technology as an individual component of the insulation barrier, a power or surge protection ceramic capacitor is known, and a signal transmission circuit block using the same is combined with a capacitive isolation amplifier or a capacitive isolation coupler. Called and used since the 1970s.

In Japanese Patent Application Laid-Open No. 62-260408, a pulse signal obtained by modulating an analog signal is transmitted to a secondary side which is insulated and separated by a capacitor, decoded, and the analog signal is reproduced to isolate the analog signal. Has been realized.

[0006] On the other hand, as represented by the term mobile computing, communication means such as a portable computer and a portable modem associated therewith have become widespread. Along with reducing the size and weight of these portable devices, reducing power consumption is a major technical issue. It goes without saying that realizing a device for realizing data communication by connecting to a telephone subscriber line using the above-described isolator will greatly contribute to a reduction in size and weight of a portable device. Further, if the circuit on the telephone subscriber line side of the isolator is operated using the power supplied from the exchange via the telephone subscriber line side (hereinafter referred to as office power supply), it greatly contributes to the reduction of power consumption. In addition, there is no need for an insulated power supply for supplying power to the circuit on the telephone subscriber line side, which greatly contributes to reduction in size and weight.

As described above, the prior art for operating the circuit on the telephone subscriber line side of the isolator by the power supply from the office (see “K930
G SILICON DAA FOR JAPAN APPLICATION ELECTRICAL
SPECIFICATIONS "Cripton, Kanematsu Semiconductor Corporation).

[0008]

What is described in the above documents is A / D, D / D for receiving / amplifying a signal from a signal line and performing D / A of a signal to be transmitted. The A converter is normally separated from the signal line by a switch. This switch is equivalent to a hook in a telephone. As described above, since the signal line is normally separated from the signal line, a bypass circuit is required to detect a call signal sent from the signal line. That is, a filter composed of a resistor and a diode is installed outside the A / D and D / A converters to detect a call signal.

However, such a configuration has a large circuit scale and is not suitable for miniaturization.

Accordingly, it is an object of the present invention to provide a circuit for detecting a call signal with fewer components.

[0011]

In order to achieve this object, the present invention provides a switch for interrupting power supplied from a subscriber line, and a switch for supplying power supplied from the subscriber line to an electronic circuit. In a subscriber line interface having a rectifier and a constant voltage circuit, a ringing signal pass filter is connected in parallel with the switch.

With this, even if the contact for controlling the power supply to the station is normally opened, if the call signal arrives, the signal passes through the call signal passing filter and is rectified by the power supply circuit thereafter, so that the isolator of the isolator is supplied by the power supply to the station. The circuit on the telephone subscriber line side can be operated.

Therefore, the ringing signal can be easily detected by the power-on detection circuit on the telephone subscriber line side of the isolator. Since the power-on detection is originally an indispensable circuit for the power-on reset, the call signal can be detected without any additional circuit.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a basic embodiment of the present invention. The subscriber line is connected to a power supply circuit 3 via a call signal passing filter 1 and a station power supply control switch 2. The power supply circuit 3 rectifies the power supplied from the exchange via the subscriber line, adjusts the voltage, and
Supply power to

FIG. 2 shows the waveform of the call signal. The ringing signal is a signal in which a 15 V AC component of 75 Vrms is applied to a 48 V DC component. Such a signal can be selectively passed by the ringing signal pass filter 1 shown in FIG. The capacitor C1 blocks a DC component and allows only an AC component to pass. Zener diodes ZD1, Z
D2 blocks small amplitude signals and passes only large amplitude signals. The signal used for normal communication is 0 dBm at most, that is, 2.2 Vp-p when the load impedance is 600 ohms.
Therefore, the signal is blocked by the ringing signal pass filter 1.

FIG. 4 shows an embodiment of the power supply circuit 3. The power supply circuit 3 includes a rectifier 31 and a constant voltage power supply (AVR) 32. The rectifier 31 operates a terminal such as a telephone irrespective of the polarity of a telephone subscriber line (bipolar power reception).
However, when a ringing signal is input, it operates as a rectifier that literally rectifies an AC component.

FIG. 5 shows an embodiment of the configuration inside the interface 4. A power ON detection circuit 41 is provided inside the interface 4, and when the power is turned ON, a power ON detection signal is output through the output interface 42 for a certain period of time. Originally, the power-on detection circuit 41 is an essential component of the power-on reset circuit for initializing the interface immediately after the power is turned on, and is not a circuit specially added for detecting a call signal.

FIG. 6 shows an embodiment of the internal structure of the interface 4 using the isolator 43. As shown in the figure, the subscriber line side of the power ON detection circuit 41 and the isolator 43 is operated by the power Vdd and the ground GND supplied by the station. The host side and the output interface 42 of the isolator 43 are operated by the power supply Vdd 'and the ground GND' supplied from the host side.

FIG. 7 shows an embodiment of the isolator 43.
The isolator 43 is obtained by coupling a differential driver 431 and a differential receiver 433 with a coupling capacitor 432.

FIG. 8 shows an embodiment in which a microprocessor 5 is provided on the host side. In this embodiment, the power ON detection signal 5
0 is connected to the interrupt input terminal INT of the microprocessor 5, and the station power supply control switch 2 is controlled by a signal from the microprocessor 5. The power-on detection signal 50 is notified to the microprocessor 5 by the arrival of the call signal, and the microprocessor 5 recognizes the arrival of the call signal as an interrupt. The microprocessor 5 recognizing the arrival of the call signal turns on the station power supply control switch 2 to activate the circuit on the subscriber line side of the interface by the station power supply, and sounds the ringer to notify the person.

Although not shown here, when a semiconductor switch is used as the station power supply control switch 2, it is necessary to insulate it from the microprocessor 5. Therefore, by passing through the isolator 48 in the interface 4 as shown in FIG. 9, the number of components for insulation is eliminated.

FIG. 10 shows an embodiment in which a signal receiving circuit 44 is added to the interface 4. The signal arriving via the subscriber line is received by the signal receiving circuit 44, and is received via the isolator 46 and the output interface 45.
Is output.

The received signal 47 is supplied to the power supply O as shown in FIG.
The microprocessor 5 recognizes the arrival of the call signal together with the N detection signal 40, and turns on the station power supply control switch 2 to activate the circuit on the subscriber line side of the interface by station power supply.

Note that the station power supply control switch 2 and the call signal passing filter 1 may be provided at a stage subsequent to the rectifier 31 as shown in FIG.

FIG. 13 shows an embodiment in which the microprocessor 6 controls the DC closing switch 6 as well. When the DC closing switch 6 is closed, a loop current determined by a predetermined impedance Z is passed to notify the exchange of the off-hook state, and the communication state is set.

FIG. 14 shows a processing flow of the microprocessor 5. First, the arrival of the call signal is notified to the microprocessor 5 as an interrupt 100. After the interruption, the station power supply control switch 2 is turned on (101), and if no call signal is detected, the station power supply control switch 2 is turned off (109) and the apparatus enters a waiting state (110). If there is an interruption 100 in the waiting state, the above processing is repeated again. Now, as a result of the judgment (102) as to whether or not the calling signal is detected, if the calling signal is detected, the received signal 47 is subsequently monitored and the Caller I
D is detected (103). When the detection of the Caller ID is detected, the Caller ID is displayed (104). Subsequently, the ringer is activated (105) to notify the person that the telephone is being called.

Further, when the off-hook is detected (106), the DC closing switch 6 is turned on to notify the exchange of the off-hook state, and the telephone is brought into the talking state (1).
07).

The processing flow for starting a normal call has been described above. However, the same flow can be realized when used as an interface for a fax or a modem.

The step (102) of monitoring the received signal 47 and determining whether or not a call signal has been detected is for preventing the false determination of the arrival of the call signal due to noise or the like, and is not always necessary processing.

[0031]

According to the present invention, it is possible to realize a subscriber line interface capable of detecting a call signal by using a station power supply with a small number of additional circuits, thereby reducing the size and weight of information terminals such as telephones and fax modems, reducing power consumption, The price can be reduced.

[Brief description of the drawings]

FIG. 1 shows a basic embodiment of the present invention.

FIG. 2 is a waveform of a call signal.

FIG. 3 shows an embodiment of the call signal pass filter 1;

FIG. 4 is an embodiment of a power supply circuit 3.

FIG. 5 is an embodiment of a configuration inside an interface 4;

FIG. 6 is an embodiment of an interface 4 using an isolator.

FIG. 7 shows an embodiment of an isolator 43.

FIG. 8 shows an embodiment using a microprocessor.

9 shows an embodiment using an isolator 48 in the interface 4. FIG.

FIG. 10 shows an embodiment in which a signal receiving circuit 44 is added to the interface 4.

FIG. 11 is an embodiment of a connection with a microprocessor for the embodiment of FIG.

FIG. 12 is an embodiment of a connection with a microprocessor for the embodiment of FIG. 10;

FIG. 13 shows an embodiment in which a DC closing switch 6 is controlled by a microprocessor 5;

FIG. 14 is a processing flow in a microprocessor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Call signal passing filter, 2 ... Station power supply control switch, 3 ... Power supply circuit, 4 ... Interface

Claims (8)

[Claims] 1. A subscriber line interface comprising: a switch for turning on and off power supplied from a subscriber line; a rectifier for supplying power supplied from the subscriber line to an electronic circuit; and a constant voltage circuit. A subscriber line interface, wherein a ringing signal pass filter is connected to the switch in parallel. 2. The subscriber line interface according to claim 1, wherein said call signal passing filter is a filter that passes only an AC component having a predetermined voltage or more. 3. The subscriber line interface according to claim 1, further comprising a circuit for detecting a rise of power supplied from the subscriber line, and a circuit for outputting a detection result of the detection circuit to the outside. A subscriber line interface. 4. The subscriber line interface according to claim 3, wherein the circuit for detecting the rise of the power supply and the circuit for outputting to the outside are electrically insulated from each other, and exchange information via an insulation isolator. Subscriber line interface. 5. The subscriber line interface according to claim 3, wherein an output signal of the circuit for outputting to the outside of the subscriber line interface is input to a microprocessor, and the switch is controlled by the microprocessor. A communication device using a subscriber line interface. 6. The subscriber line interface according to claim 1, wherein: a signal receiving circuit for receiving a signal applied to the subscriber line;
A subscriber line interface having a circuit for outputting the output of the detection signal receiving circuit to the outside. 7. The subscriber line interface according to claim 6, wherein said signal receiving circuit is electrically insulated from said external output circuit, and exchanges information via an insulating isolator. And the subscriber line interface. 8. A subscriber line interface according to claim 6, wherein an output signal of said circuit for outputting to the outside of said subscriber line interface is input to a microprocessor, and said switch is controlled by said microprocessor. A communication device using a subscriber line interface.