JPH05268372A - Modem - Google Patents

Abstract

PURPOSE:To make the profile of the entire MODEM thin and to accommodate the MODEM into an IC card together with its transformer function. CONSTITUTION:The MODEM is provided with capacitors 3, 4 connecting respectively to two signal lines at a telephone line side, interrupting UC voltage and passing an AC signal, a differential amplifier circuit A 6 receiving a reception signal, and a differential amplifier circuit B 7 sending a transmission signal to a telephone line via the capacitors 3, 4. Then a reception analog signal is outputted to a data terminal equipment side by inputting a transmission signal of one of two signal lines at the telephone line side to a noninverting input terminal 10 of the differential amplifier circuit A 6 and the other transmission signal to an inverting input terminal 11 of the differential amplifier circuit A 6, an analog signal from the data terminal equipment is inputted to the differential amplifier circuit B 7, the analog signal inverted with respect to the input signal and the noninverting analog signal in the same polarity with the input signal are outputted to the capacitors 3, 4 respectively and then they are sent to the telephone line.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a modem device (hereinafter abbreviated as "modem") for transmitting and receiving data using a telephone line such as personal computer communication.

Miniaturization and thinning of portable personal computers, word processors and the like are being advanced. on the other hand,
It has become widespread to use a telephone line to connect computers to each other for data communication.

In such data communication, a modem for converting a digital signal into an analog signal and transmitting the analog signal to a telephone line and receiving an analog signal from the telephone line and converting it into a digital signal has a telephone line (hereinafter referred to as a computer). In order to ensure that it is separated from the power supply of the data terminal device (legally withstand voltage DC250V, insulation resistance 1MΩ
As described above, the line transformer is used in the modem to couple the telephone line and the data terminal device to the AC signal and separate them in terms of DC.

Since the line transformer is large, the conventional modem cannot be thinned, and a portable computer or I
It could not be built into a C card or the like.

[0005]

2. Description of the Related Art Prior to explaining the configuration of a conventional modem, the characteristics required of the modem will be described.

Since the modem is connected to the telephone line,
The following properties are needed: Requires a circuit that loops the DC current to capture the telephone line (5 at 20-120 mA DC)
0Ω-300Ω).

Between the telephone line and the modem circuit, it is necessary to insulate with high resistance against direct current (DC250V: 1
MΩ or more). AC signals need to be transmitted between the telephone line and the modem circuit.

While the AC signal on the telephone line side is a balanced signal, the computer side processes it as an unbalanced signal in order to facilitate IC integration, so it is necessary to make balanced / unbalanced matching.

Since in-phase noise is superimposed on the signal propagated through the telephone line in the middle of the transmission path, it is necessary to remove the in-phase noise. Since the above requirements can be easily satisfied by using the line transformer, the conventional modem mainly uses the line transformer as described above.

FIG. 3 shows the configuration of a conventional modem device. In the figure, 100 is an exchange, 101 is a telephone line, and 102
Is a ring detection circuit that detects a calling signal from the other party. Reference numerals 103 and 104 denote hook switches which respond to attachment / detachment of a receiver. 10
4 is a line transformer, the primary side of the line (telephone line side)
And the secondary side of the line (modem circuit side) are connected to an AC signal and are insulated in terms of DC. A modem circuit 105 converts an analog signal into a digital signal and a digital signal into an analog signal. 10
Reference numeral 6 denotes an interface on the modem side, which is a motem circuit 1
05 and the interface 107 of the data terminal device are connected. An interface 107 on the data terminal device side connects the data terminal device and the interface 106 of the modem. Reference numeral 108 is a data terminal device.

In the configuration shown in the figure, when a call signal is input from the exchange 100 via the telephone line 101,
The ring detection circuit 102 operates and the call signal is input to the modem circuit 105. When the modem circuit 105 detects the call signal, it closes the hook switches 103 and 104. Then, the AC signal on the primary side of the line sent from the telephone line is transmitted to the secondary side via the line transformer 104, the analog signal is converted into a digital signal in the modem circuit 105, and the signals are passed through the interfaces 106 and 107. And is input to the data terminal device 108.

On the other hand, when data is sent from the data terminal device 108 to the telephone line 101, the modem circuit 105
Closes the hook switches 103 and 104 and requests the other side to transmit data. And when the other party responds,
The modem circuit 105 converts the AC signal converted from the digital signal to the analog signal through the line transformer 104 to the line 1
Transmit to the next side. Then, the AC signal is transmitted to the other party via the telephone line 101.

FIG. 4 is an explanatory diagram of a transformer function in a conventional modem device. Figure (a) shows the case with a circuit transformer. The figure shows the line transformer in the modem, and other circuit parts are omitted.

When the line transformer 120 is used, all the above-mentioned requirements 1 to 4 for the modem are satisfied. That is, the DC loop is formed on the line 1 side. The insulation of the primary and secondary sides of the line from DC is satisfied because it is a transformer. The transmission of AC signal is also satisfied because it is a transformer. The matching of the balanced signal and the unbalanced signal of is also satisfied because it is a transformer. The noise removal of is satisfied for the following reasons. The noise superimposed on the telephone lines (L1, L2) in the middle of the transmission line is
Since they are sent as in-phase signals on the two lines, when they are input to the transformer, the magnetic fluxes cancel each other out, and noise components are not transmitted to the secondary side of the line transformer.

As described above, according to the line transformer, it is possible to easily meet the demand for the modem, but there is a drawback that the shape becomes large because the direct current required for line capture is passed.

Therefore, a loop for supplying a direct current is provided separately from the line transformer so that no direct current is supplied to the transformer, as shown in FIG. In the figure, reference numeral 130 is a repeater transformer which transmits only an AC component to the secondary side without passing a DC current to the primary side. Reference numeral 131 denotes a capacitor, which blocks a direct current component. Reference numeral 132 is a loop coil for flowing a direct current from the telephone lines (L1, L2).

In the configuration shown in the figure, the requirements (1) to (2) required via the modem are satisfied by the repeater transformer 130 as in the case of the line transformer (FIG. 1A).
The requirement for forming the DC current loop is satisfied by the loop coil 132.

Even when the repeater transformer shown in FIG. 3B is used, the loop coil 132 is required, and there is a limit to miniaturization. Therefore, the DC current loop is formed by active elements in Fig. (C).

FIG. 3C shows a pseudo inductance circuit.
In the figure, 140 is a pseudo-inductance and 141 is a diode bridge so that the polarity of the operating voltage of the pseudo-inductance can be kept constant even when the polarities of the telephone lines (L1, L2) are reversed. is there. 14
Reference numeral 2 is a repeater transformer, and C1 is a bypass capacitor for the AC component, which bypasses the AC component so that the bias voltage of the transistor 1 (TR1) and the transistor 2 (TR2) does not change due to the AC component. R
1 and R2 are voltage dividing resistors, which are transistor 1 (TR
1) and the bias voltage of the transistor 2 (TR2) are determined. Each of TR1 and TR2 is a transistor and forms a loop of direct current.
R3 is an emitter resistance, and is a transistor (TR
1) and the transistor 2 (TR2) form a direct current loop. C2 is a coupling capacitor for blocking the DC voltage and passing only the AC component.

In the structure shown in the figure, the transistor 1 (TR1) and the transistor 2 are biased by the DC voltage.
An almost constant DC current flows through (TR2) and the resistor R3 without being affected by the AC component. On the other hand, with respect to the repeater transformer 142, the DC voltage becomes
Is cut off by, and only the AC component flows through the coupling capacitor C2 to the primary side and is transmitted to the secondary side.

[0021]

As described above, the conventional modem requires the line transformer, the repeater transformer, the loop coil or the like, and since each of them is a large component, the modem including the transformer is included. It was impossible to put it in an IC card.

It is an object of the present invention to make the entire modem thinner so that it can be stored in an IC card or a thin portable computer.

[0023]

According to the present invention, instead of a line transformer, a circuit having the same function as that of the line transformer can be integrated into an IC by constructing a high withstand voltage capacitor and a differential circuit. I was able to fit in the card.

FIG. 1 shows the basic configuration of the present invention. In the figure, 1 is a modem device, 2 is a pseudo-inductance circuit (the same as the circuit in FIG. 4), 3 and 4 are capacitors C1 and C2, respectively, which cut off the DC current from the telephone line and only AC signals. It is to pass. 5
Is a transmission signal cutoff circuit that prevents the transmission signal of itself from being input to the reception circuit during transmission. A differential circuit A 6 is an analog unbalanced input by inputting one of the analog balanced received signals output from the pseudo-inductance circuit 2 to an inverting input terminal and the other to a non-inverting input terminal. It outputs the received signal. Reference numeral 7 denotes a differential circuit B, which inputs the analog unbalanced transmission signal converted by D / A, outputs a signal obtained by inverting the input signal from one output terminal, and outputs the same signal as the signal input from the other output terminal. It outputs a polarity signal. 8
Is a modulator / demodulator that demodulates an analog received signal into a digital signal and outputs it to the data terminal device side, modulates the digital signal of the data terminal device into an analog signal, and outputs it to the telephone line side.

Reference numerals 10 and 11 denote the non-inverting input terminal and the inverting input terminal of the differential circuit A (6), respectively, and 14 denotes the differential circuit A (6).
It is a reception signal output terminal of. Reference numerals 12 and 13 denote an inverting output terminal and a non-inverting output terminal of the differential circuit B (7), respectively, and a reference numeral 15 denotes a transmission signal input terminal of the differential amplifier circuit B (7).

Reference numeral 16 denotes an operational amplifier (OP1) in the differential circuit A (6), which is an example of the differential circuit A (6). Reference numerals 17 and 18 denote operational amplifiers (O of the differential circuit B (7)).
P2, OP3) and shows an example of the differential circuit B (7).

[0027]

The operation of the configuration shown in FIG. 1 will be described. In the configuration shown in the figure, the DC current from the telephone line is cut off by the capacitors C1 and C2 and is not input to the differential amplifier circuits A and B.

The case of receiving a signal and the case of transmitting a signal will be described separately. (1) When receiving. The AC signal component sent from the telephone line is the pseudo inductance circuit (2) and the capacitor C.
It is input to the differential circuit A (6) via the capacitor 1, and the capacitor C2. Since the received signal is substantially a balanced signal, the signal from the capacitor C1 is input to the non-inverting input terminal 10 of the differential circuit A (6). The signal from the capacitor C2 is input to the inverting input terminal 11 of the differential circuit A (6). The signal input to the inverting input terminal 11 is applied to the non-inverting input terminal 10
The input signal is used as a reference voltage, the polarity of which is inverted and the signal is output from the reception signal output terminal 14. Therefore, the differential circuit A
By (6), the input balanced signal can be output as an unbalanced signal.

(2) When sending. The unbalanced transmission signal converted from the digital signal of the data terminal device to the analog signal by the modulation / demodulation unit 8 is input to, for example, the inverting input terminal of the operational amplifier 17 (OP2) of the differential circuit B, and its polarity is inverted and inverted. It is output from the signal output terminal 12. The output of the operational amplifier 17 (OP2) is the operational amplifier 18 (OP2).
The non-inverting output terminal 13 outputs the signal having the same polarity as the signal input to the inverting input terminal 3), the polarity of which is inverted, and the signal input to the transmission signal input terminal 15. The outputs of the operational amplifiers 17 and 18 serve as balanced signals and are capacitors C1, C2, and pseudo inductance 2
Is output to the telephone line via.

In FIG. 1, the operational amplifier 16 (O
P1), operational amplifier 17 (OP2), operational amplifier 18
(OP3) is an example of the differential circuit A (6) and the differential circuit B (7), and the signal input / output method is also an example, and the present invention is not limited to this.

[0031]

FIG. 2 shows an embodiment of the present invention. In the figure,
L1 and L2 are telephone lines, 20 is a pseudo inductance circuit, 21 is a differential circuit A, 22 is a differential circuit B, 24, 2
5 and 26 are operational amplifiers (OP1, OP2, O, respectively)
P3). C1 and C2 are coupling capacitors that block direct current and pass alternating current. R1 is a resistor, and determines the reference voltage of the operational amplifier 24 (CP1) by the AC component input from L1 by the resistor R6. R2 is a resistor, and the operational amplifier 24 (OP1) for the AC component input from L2 by the resistor R7
It determines the amplification factor of. R3 and R4 are resistors that determine the impedance of the modem with respect to the AC component.

R5 is a resistor for preventing a transmission signal from being inputted to the differential circuit A (21) at the time of transmission so that the transmission signal of itself is not a recursive reception signal. R6 is a resistor that determines the reference voltage of the operational amplifier 24 (OP1) by the AC component input from L1 by the resistor R1. R7 is a negative feedback resistor of the operational amplifier 24, and determines the amplification factor with the resistor R2. R8 is a negative feedback resistor of the operational amplifier 25, and determines the amplification factor with the resistor R9. R9
Is a resistor, and the amplification factor is determined by the resistor R8. R10 is a resistor for stabilizing the operation of the operational amplifier 26. R11 is a negative feedback resistor, and the amplification factor is determined by the resistor R12. R12 is a resistor, and the amplification factor is determined by the negative feedback resistor R11.

The operation of the configuration shown in the figure will be described. (1) Operation during reception. It is considered that the transmission is substantially balanced in the telephone line. Therefore, for example, it is assumed that the transmission signal a is output from the capacitor C1 as illustrated and the signal b is output from the capacitor C2 as illustrated. The output signal of the operational amplifier 24 is a signal c.

The signal a is input to the non-inverting input terminal of the operational amplifier 24 and used as a reference voltage. Since the signal b is input to the inverting input terminal of the operational amplifier 24, its output is inverted and the signal c is output. A signal c is output by the balanced signal a and the signal b input to the operational amplifier 24.

(2) Operation during transmission It is assumed that the transmission signal is the signal d shown in the figure. The transmission signal d is input to the non-inverting input terminal of the operational amplifier 25. As a result, the operational amplifier 25 outputs the signal e in phase with the signal d. On the other hand, since the output signal e of the operational amplifier 25 is input to the inverting input terminal of the operational amplifier 26, the operational amplifier 2
A signal f is output from 6. Then, the signal e and the signal f
Is transmitted as a balanced signal to the telephone line via the capacitor C1, the capacitor C2 and the pseudo inductance circuit 20.

The transmission signal e is applied to the inverting input terminal of the operational amplifier 24 through the resistor R5 in an appropriate amount, so that the signal f applied to the inverting input terminal of the operational amplifier 24 through the resistors R4 and R2 and the resistance f. The signal e applied to the non-inverting input terminal of the operational amplifier 24 via R3 and R1 is canceled, and there is substantially no input of the transmission signal to the differential circuit A, and the transmission signal recurs as a reception signal. Input can be prevented.

[0037]

According to the present invention, the transformer function required for the modem and the function of the DC coil loop coil can be integrated into an IC by configuring them with an active circuit that does not include a transformer. It can be made thin. Therefore, the entire modem can be stored in the IC card.

[Brief description of drawings]

FIG. 1 is a diagram showing a basic configuration of the present invention.

FIG. 2 is a diagram showing a configuration of an embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of a conventional modem device.

FIG. 4 is an explanatory diagram of a transformer function in a conventional modem device.

[Explanation of symbols]

 1: modem device 2: pseudo-inductance circuit 3: capacitor C1 4: capacitor C2 5: transmission signal cutoff circuit 6: differential circuit A 7: differential circuit B 8: modulator / demodulator 10: non-inverting input terminal 11: inverting input terminal 12: Inverted output terminal 13: Non-inverted output terminal 14: Received signal output terminal 15: Transmitted signal input terminal 16: Operational amplifier (OP1) 17: Operational amplifier (OP2) 18: Operational amplifier (OP3)

Claims (6)

[Claims] 1. A modem device for performing data communication by connecting a data terminal device to a telephone line, each of which is connected to two signal lines on the telephone line side to cut off a direct current from the telephone line and to make an alternating current. Capacitors (3) and (4) that pass the signal, a differential circuit A (6) that inputs the received signal via the capacitors (3) and (4), and a transmission signal to the capacitor (3) and ( 4) via the differential circuit B (7) for outputting to the telephone line, and the received signal on one of the two signal lines on the telephone line side is connected to the non-inverting input terminal (10) of the differential circuit A (6). ), And the other received signal is connected to the inverting input terminal (11) of the differential circuit A (6), and the received analog signal is A / D converted by the modulator / demodulator and output to the data terminal device side. The digital signal from the data terminal device side is D
Input A / A converted analog signal to differential circuit B (7),
An analog signal whose polarity is inverted with respect to the input signal,
A modem device which outputs a non-inverted analog signal having the same polarity with respect to the input signal, inputs the non-inverted analog signal into the capacitors (3) and (4), respectively, and sends out to the telephone line. 2. The differential circuit A (6) according to claim 1, wherein a balanced signal is input and is output as an unbalanced signal, and the differential circuit B (7) is input with an unbalanced signal and balanced. A modem device characterized by being output as a signal. 3. The capacitor (3) according to claim 1,
, (4) and the differential circuit A (6) are connected to prevent the transmission signal output from the differential circuit B (7) from being input to the differential circuit A (6). A modem device comprising (5). 4. The differential circuit A according to claim 1, 2, or 3.
(6) is composed of operational amplifier (16), and differential circuit B (7)
Is an op amp (17) and an op amp (1
A modem device characterized by being constituted by 8). 5. A modem device according to claim 1, 2, 3, or 4, wherein a loop circuit for bypassing a direct current from the telephone line side is constituted by a pseudo inductance circuit (2) including active elements. 6. The modem device according to claim 1, 2, 3, 4 or 5, wherein the entire modem circuit is built in an IC card.