JP2752053B2 - Modem device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a modem device using line power.

[0002]

2. Description of the Related Art In recent years, a data communication system in which a data terminal device (DTE) such as a personal computer is connected via a telephone line and data is transmitted and received between the data terminal devices has rapidly spread. In order to perform these data communications, generally, as shown in FIG.
0A, 100B and the telephone line 200 between the modem device (M
ODEM) 10 is required. The modem device 10 is a device that modulates a signal from a data terminal device into a signal corresponding to a line, and demodulates a signal received from the line into a signal corresponding to the data terminal device. Plays a role. Note that, in the figure, reference numeral 210 denotes an RS232C cable.

As shown in FIG. 5, a conventional modem device 10 includes a modem circuit 12, a network control unit (NCU) 14, and a two-wire four-wire circuit (TFC) 16. The modulation / demodulation circuit 12 modulates a digital signal from the data terminal device 100 into a line signal and sends it to the line 200, and also demodulates a line signal received from the line 200 into a digital signal and sends it to the data terminal device 100. It is. The network control unit 14 controls the connection between the modem circuit 12 and the telephone line 200. The two-wire / four-wire circuit 16 separates a telephone line into a transmission side circuit and a reception side circuit of the modem circuit 12.

[0004]

However, the conventional modem device requires a dedicated power supply to drive the modem device, which makes it difficult to reduce the size of the modem device. The residual current after sending the signal to the two-wire four-wire circuit 16 was wasted in the network control unit 14.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks, and has as its object to provide a downsized modem device by effectively utilizing a surplus line current.

[0006]

In order to achieve the above-mentioned object, a modem device according to the present invention modulates a signal input from a data terminal device, transmits the modulated signal to a telephone line, and outputs a signal input from the telephone line. A modulation / demodulation circuit for demodulating the data and sending it to the data terminal device; a network control unit connected to the telephone line;
In a modem device having a two-wire / four-wire circuit interposed between the network control unit and the modulation / demodulation circuit for separating transmission and reception of a signal, the network control unit receives a direct current from an off-hook current input from a telephone line. A constant current circuit for separating components and a smoothing circuit for smoothing the constant current output; and a power conversion circuit connected to the smoothing circuit for converting the output to power of a predetermined voltage level. The circuit is connected to a modulation / demodulation circuit and a two-wire / four-wire circuit to supply power.

[0007]

With this configuration, the power of the off-hook current, which has been wasted by the conventional network control unit, can be converted into a predetermined power by the power conversion circuit and used as the driving power of the entire modem device. That is, the power required by the modulation / demodulation circuit or the two-wire / four-wire circuit at the time of off-hook is obtained from the telephone line. The constant current circuit provided in the network control unit is
The DC component obtained from the off-hook current is supplied to the power conversion circuit as a constant current, and the amount of current separated from the off-hook current is limited by appropriately determining the input impedance of the constant current circuit. . Further, the smoothing circuit stabilizes the power supplied to the power conversion circuit and removes noise, and the smoothing action causes an off-hook current flowing through the telephone line due to the operation of the power conversion circuit. To fluctuate.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an example of the modem device of the present invention. 1 to 3, the same parts as those of the conventional example shown in FIGS. 4 and 5 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In FIG. 1, a modem device 20 is connected to an RS2.
It is connected to the data terminal device 100 via a 32C cable 210 and to a telephone line (200 in FIG. 4) via terminals L1 and L2. The modem device 20 includes a modem circuit 12, a network control unit (NCU) 14, a two-wire four-wire circuit (T
FC) 16 and a power conversion circuit 18.

The network control unit 14 sends the signal current superimposed on the off-hook current input from the terminals L 1 and L 2 to the two-wire four-wire circuit 16, and converts the remaining current of the off-hook current, that is, the DC current component, into a power conversion circuit. To 18.

The power conversion circuit 18 is composed of a DC-DC converter circuit for converting the power of the off-hook current, and inputs the DC component of the off-hook current input to the network control unit 14 from the terminals L1 and L2. Then, the power conversion circuit 18 converts the off-hook current to a predetermined voltage level and supplies it to the two-wire four-wire circuit 16 and the modulation / demodulation circuit 12 as drive power.

The battery 19 supplies power to the modulation / demodulation circuit 12 only when the line goes on-hook. That is, the battery 19 is connected to the modulation / demodulation circuit 12 via the diode 22 and the power conversion circuit 1
8 is connected to the modulation / demodulation circuit 12 via a diode 24. The diode 22 prevents the current from the power conversion circuit 18 from flowing to the battery 19 when the battery is in an off-hook state, and the diode 24 prevents the current from flowing from the power conversion circuit 18 to the power conversion circuit 18 when the current from the battery 19 is in an on-hook state. ing. The voltage supplied from the power conversion circuit 18 is higher than the voltage of the battery 19.

Therefore, the modem device 20 does not need to provide a dedicated power supply separately, and can use the off-hook current, which is a line current, as a drive power source by converting the off-hook current into power.

Next, the configurations of the network control unit 14 and the power conversion circuit 18 will be described in detail with reference to FIG.

As shown in FIG. 1, when the modem device is in a communication state, that is, in an off-hook state, the photocoupler PH1 in the network control unit 14 is turned on.
The transistors Tr1 and Tr2 are turned on, and rectified line current flows from the terminals L1 and L2 connected to the telephone line via the diode bridge D1. The current from the telephone line at this time is the off-hook current, the signal current is output to the two-wire four-wire circuit 16, and the remaining current is used as power.

The network control unit 14 includes a constant current circuit 30, a shunt regulator circuit 32, and a smoothing circuit 34. The constant current circuit 30 includes a transistor Tr3,
It comprises a resistor R3 and a capacitor C1. Resistance R3
And the capacitor C1 determine the base current of the transistor Tr3. In this case, the resistance value of the resistor R3 is set to a large value in order to reduce the passage of the signal current of the off-hook current. That is, in the off-hook state to increase the impedance on the collector side of the transistor motor Tr3. Accordingly, the two-wire four-wire circuit 1 connected to the collector of the transistor Tr1
6, a signal can be transmitted to the modulation / demodulation circuit 12 (not shown) as before. Since the capacitor C1 allows the alternating current component to flow to the ground, the base voltage of the transistor Tr3 is constant, and as a result, a constant current is obtained from the emitter.

Further, the shunt regulator circuit 32
The power conversion circuit 18 is composed of a Zener diode ZD1 and resistors R4 and R5, and operates normally when the off-hook current is almost over.

The smoothing circuit 34 is a smoothing circuit or a filter circuit comprising a choke coil L1 and a capacitor C2, and is a circuit for smoothing the input current of the power conversion circuit 18. This circuit of choke coil L1 and capacitor C2 prevents fluctuations in the output current of shunt regulator 32, which fluctuate due to the operation of DC-DC converter 18, from causing fluctuations in the off-hook current of the telephone line.

FIG. 3 shows a two-wire four-wire circuit 16. The DC component of the off-hook current, which is the output of the transistor Tr1, is removed by the capacitor C8, and the signal current of the off-hook current is supplied to the two-wire four-wire circuit 16. The operational amplifier Ic1-1 sends the signal input from the telephone line to the modulation / demodulation circuit 12 (not shown) via the photocoupler PH2, while the operational amplifier Ic1-2 transmits the signal input to the
The signal from the modulation / demodulation circuit received at H3 is transmitted to the telephone line. On the telephone line side, use photocouplers PH2 and PH3, respectively.
Is insulated from the modulation / demodulation circuit 12 (not shown).

Accordingly, the network control unit 14 according to the present embodiment device
Supplies the signal current input from the telephone line to the two-wire / four-wire circuit 16 in the off-hook state and the power conversion circuit 1
8 can be supplied with the remaining off-hook current.

Next, the power conversion circuit 18 comprises a self-excited converter. The output terminal of this self-excited converter is a GND (ground) terminal, a positive terminal V for a two-wire four-wire circuit.
cc1 and a negative terminal VEE1, and a terminal Vcc2 for the modulation / demodulation circuit 12.
Consists of Then, signals of the same voltage level with the ground terminal as a zero point are output to the positive and negative terminals of the two-wire four-wire circuit. Since the self-excited converter circuit is a conventionally well-known circuit, its details are omitted, but its configuration and operation will be briefly described below.

The transistor Tr4 has a base terminal connected to the positive terminal of the smoothing circuit 34 via a resistor R6, and an emitter terminal connected to a ground terminal. The collector terminal of the transistor Tr4 is connected to the positive terminal of the smoothing circuit 34 via the winding n2 of the transformer T1.

The transformer T1 further has a primary winding n1, which is wound in the same polarity and in series with the primary winding n2, and the other end of which is connected to the cathode of a diode D2. The anode of D2 is connected to the ground terminal. The other end of the primary winding n1 is connected to a capacitor C3.
Is connected to the base terminal of the transistor Tr4.

In the self-contained converter according to the embodiment, a self-excited oscillator is formed by the primary circuit of the transformer, and its oscillating operation will be briefly described.

When a predetermined voltage is applied from the positive electrode of the smoothing circuit 34, a base current is supplied to the transistor Tr4 via the resistor R6, whereby the transistor Tr4 is turned on to supply a collector current to the primary winding n2. I do.

At the same time, a charging current is supplied from the positive terminal of the smoothing circuit 34 to the capacitor C3 via the primary winding n1, and this charging current acts in a direction to increase the conductivity of the transistor Tr4. Tr4 increases its collector current.

However, the current flowing through the primary winding n1 tends to disappear in a relatively short time due to the small capacity of the capacitor C3. As a result, the base current catches up with the increase in the collector current of the transistor Tr4. When the collector current Ic is equal to the base current Ic as shown in the above equation,
When the required amplification collector current based on B is exceeded, the transistor Tr4 is rapidly turned off. Note that hf
e is the current amplification factor.

In the off state of the transistor, the energy stored in the operating state of the transistor Tr4 flows from the primary winding n1 toward the capacitor C2 of the smoothing circuit 34.
Is kept off. When the release of the stored energy is completed, the base current of the transistor Tr4 is supplied again via the resistor R6, and the circuit continues the self-excited oscillation. The self-excited oscillation frequency is a frequency determined by a circuit constant and a load.

By the self-excited oscillation described above, the secondary coil n
3, n4 , and n5, a current flows through the diode D3.
, D4 and D5 charge capacitors C4, C5 and C6. Accordingly, the same level of positive and negative voltages can be output to the bipolar terminals Vcc1 and VEE1 when the illustrated ground terminal is set to the zero point, and power is supplied to the two-wire four-wire circuit 16.
Further, a predetermined voltage level is also output to the terminal Vcc2 and supplied to the modulation / demodulation circuit.

As described above, according to the self-excited converter used in the present embodiment, the DC-DC converter circuit outputs a positive / negative signal according to an off-hook current signal, for example, a 48V signal input from the telephone line in the off-hook state. 5-
A voltage of 10 V can be obtained.

In the above embodiment, the shunt regulator circuit can be omitted. Also, the smoothing circuit 3
4 may be a smoothing circuit using a transformer.

[0032]

As described above, according to the modem device of the present invention, in the off-hook state, of the off-hook current supplied from the telephone line to the network control unit, it is conventionally wastefully consumed in the network control unit. The used line power can be effectively used as drive power for a modulation / demodulation circuit or the like. In addition, since a constant current circuit that separates a DC component from an off-hook current is provided in the network control unit, a current output of a constant current amount is obtained, and a current amount of a current that is separated from the off-hook current is limited. The signal current to be supplied can be secured,
Further, there is an effect that the off-hook current can be maintained within the range of the allowable current amount specified for the telephone line. Further, the smoothing circuit in the network control unit supplies a smoothed current to the power conversion circuit, and has an effect of preventing the off-hook current from fluctuating due to the influence of the operation of the power conversion circuit by the smoothing action. Furthermore, since the power for the modulation / demodulation circuit and the like is generated inside the modem device, a specially-designed power supply circuit is not required, and a miniaturized modem device can be obtained. Therefore, it is most suitable for a card-type modem device in which the mounting density of electronic components is increased.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a modem device according to the present invention.

FIG. 2 is a partial connection diagram of a circuit showing an embodiment of the modem device of the present invention.

FIG. 3 is a connection diagram of a two-wire four-wire circuit used in the modem device of the present invention.

FIG. 4 is an explanatory diagram of a data communication system.

FIG. 5 is a schematic configuration diagram of a conventional modem device.

[Explanation of symbols]

10, 20: Modem device 12: Modulation / demodulation circuit 14: Network control unit (NCU) 16: Two-wire four-wire circuit 18: Power conversion circuit 19: Battery 22, 24,. Diode 30 Constant current circuit 32 Shunt regulator 34 Smoothing circuit 40 Self-excited DC-DC converter 100, 100A, 100B Data terminal device (D
TE)

 ────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-62-86947 (JP, A) JP-A-58-42356 (JP, A) JP-A-55-149564 (JP, A)

Claims (2)

(57) [Claims] 1. A modulation / demodulation circuit for modulating a signal input from a data terminal device and transmitting the modulated signal to a telephone line, demodulating a signal input from the telephone line and transmitting the signal to the data terminal device, and a modulation / demodulation circuit connected to the telephone line. A network control unit, and a two-wire four-wire circuit interposed between the network control unit and the modulation / demodulation circuit to separate transmission and reception of the signal. A constant current circuit for separating a DC component from an off-hook current input from a line and a smoothing circuit for smoothing the constant current output, and an electric power connected to the smoothing circuit for converting the output to electric power of a predetermined voltage level A modem device comprising: a conversion circuit; and connecting the power conversion circuit to the modulation / demodulation circuit and the two-wire / four-wire circuit to supply power. 2. The modem device according to claim 1, wherein a shunt regulator circuit is connected between said constant current circuit and said smoothing circuit.