JPH06284155A - Modulator and demodulator - Google Patents

Abstract

PURPOSE:To adopt a low power supply voltage for the MODEM and to improve the data transmission reception quality of the MODEM. CONSTITUTION:A data pump circuit 3 modulates/demodulates data. Modulation data outputted from a data pump circuit 3 are subjected to pulse density modulation by a 1-bit D/A converter provided to an output stage of the data pump circuit 3 and sent to a line 10 via a photocoupler 5. The pulse density modulation signal sent to the line 10 is converted into an analog transmission signal by an LPF 6 and the converted signal is sent to the telephone line 10. The analog reception signal received through the telephone line 10 is subjected to pulse density modulation by a 1-bit A/D converter 12 and sent to a terminal equipment via a photocoupler 14. The pulse density modulation signal sent to the terminal equipment is demodulated by the data pump circuit 3. A low power supply voltage is adopted and the data transmission quality is improved by using the photocouplers 5, 13, 14 as means isolating the line and the terminal equipment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a modulation / demodulation device for modulating / demodulating a signal transmitted / received between a communication line and a terminal device at the end of a communication line such as an analog telephone line, and particularly to the communication line and the terminal device. Regarding the insulation demarcation method between and.

[0002]

2. Description of the Related Art Conventionally, a device connected to a telephone line is required to meet various electrical conditions so as not to disturb the function of the network or to disturb other users or exchanges. It is said that this condition is specified by the Ordinance of the Ministry of Posts and Telecommunications. For this reason, in a modulation / demodulation device (modem) connected between the analog line and the data terminal device, it is necessary to somehow perform insulation demarcation between the line and the terminal.

In a conventional modulator / demodulator, a transformer having a simple structure and a low cost is used as a means for insulating and disassembling the line and the terminal. That is, the data output from the data terminal device is, for example, PSK modulated by the modulator / demodulator,
2 of the transformer through the transmission filter and mixing / distribution circuit
It is supplied to the secondary side and transmitted to the telephone line via the primary side of the transformer. Further, the analog reception signal received from the telephone line is transmitted from the primary side to the secondary side of the transformer, further PSK demodulated through the mixing / distribution circuit and the reception filter, and supplied to the data terminal device. In this way, the electrical condition described above can be satisfied by achieving insulation from the line via the transformer.

[0004]

However, in the above conventional modulator / demodulator, the primary side (line side) of the transformer is used.
To obtain sufficient amplitude characteristics, the secondary side (terminal side)
Therefore, the drive power commensurate with that is required, and the power for that must be supplied from the outside. In recent years, there is an increasing demand for lower power supply voltage in this type of device as well, but in the conventional device, it becomes impossible to drive the transformer with a sufficient amplitude when the power supply voltage is lowered. There is a problem that it is difficult to achieve. Also,
In the conventional device, there is a problem that the phase rotation of the modulation signal and the increase of the harmonic distortion cannot be avoided due to the analog transfer characteristic of the transformer, and the data error easily occurs.

The present invention has been made in order to solve such a problem, and aims at lowering the power supply voltage and downsizing of the device while achieving insulation demarcation between the line and the terminal, and at the same time, for transmitting / receiving data. An object of the present invention is to provide a modulator and a demodulator that can improve quality.

[0006]

A modulator according to the present invention is provided between a terminal device and a communication line, and an analog transmission signal for transmitting transmission data supplied from the terminal device on the communication line. In the modulation device for converting into, the modulation means for modulating the transmission data, the pulse modulation means for pulse-modulating the modulation signal obtained by the modulation means, and the pulse modulation signal obtained by the pulse modulation means by the analog transmission. It comprises a transmitting means for converting into a signal and transmitting it to the communication line, and an optical coupling means interposed between the pulse modulating means and the transmitting means for optically coupling and electrically insulating the both. It is characterized by

The demodulator according to the present invention is a demodulator provided between a communication line and a terminal device for converting an analog reception signal received from the communication line into reception data necessary for the terminal device. A pulse modulation means for pulse-modulating the analog reception signal, a demodulation means for converting the pulse-modulated signal obtained by the pulse modulation means into the reception data, and an interposition between the pulse modulation means and the demodulation means. And an optical coupling means for optically coupling the two and electrically insulating them.

[0008]

According to the modulator of the present invention, the modulation signal of the transmission data is further converted into the pulse modulation signal and the pulse modulation signal is transmitted to the line side through the optical coupling means. The terminal device and the communication line can be insulated and demarcated by means. In general, an optical coupling means such as a photocoupler has an insulation characteristic higher than that of a transformer, so that the electrical condition required for a modulator can be sufficiently satisfied. Furthermore, since the optical coupling means is smaller than the transformer, the device can be downsized. Further, according to the present invention, since the optical coupling means is used instead of the conventional transformer, the drive power on the secondary side can be significantly reduced as compared with the conventional one. Further, the power required on the primary side can effectively utilize the direct current for forming the reception monitoring signal of the line. Therefore, according to the present invention, it is possible to significantly reduce the power supply voltage of the device. Further, according to the present invention, since information is transmitted by a digital pulse modulation signal, there is no analog influence such as phase rotation or harmonic distortion. Therefore, the data transmission quality is also greatly improved.

Also in the demodulator of the present invention, the analog reception signal from the communication line is converted into a pulse modulation signal, and this pulse modulation signal is transmitted to the terminal device side via the optical coupling means. The communication line and the terminal device can be insulated and decoupled by the optical coupling means. Therefore, according to the present invention, it is possible to improve the data transmission quality as described above.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings. 1 is a block diagram showing the configuration of a modulation / demodulation apparatus according to an embodiment of the present invention. Transmission data Ds output from a terminal device such as a computer (not shown)
Are supplied to the transmission / reception controller 2 via the interface 1. The transmission / reception controller 2 transmits the transmission data Ds
Is subjected to speed adjustment by an internal buffer (not shown), data compression by Hoffman code or the like, addition of error check code, etc., and then data is supplied to the data pump circuit 3. The data pump circuit 3 converts the input data into P
After SK (Phase Shift Keying) modulation, this PSK
The modulated data is converted into a 1-bit pulse density modulated signal and output. This pulse density modulation signal drives the photodiode 5a on the input side of the photocoupler 5 via the amplifier 4. The pulse density modulation signal transmitted to the phototransistor 5b on the output side of the photocoupler 5 is demodulated into an analog modulation signal by the low pass filter 6, and is transmitted via the transmission filter 7, the mixing / distribution circuit 8 and the DP (dial pulse) relay 9. Are supplied to the telephone line 10.

On the other hand, the analog reception signal received from the telephone line 10 via the DP relay 9 is received by the reception filter 11.
Pulse density is modulated by the 1-bit A / D converter 12. In addition, A / in the 1-bit A / D converter 12
The clock for D conversion timing is given from the transmission / reception controller 2 to the 1-bit A / D converter 12 via the photo coupler 13. The pulse density modulation signal output from the 1-bit A / D converter 12 drives the photodiode 14 a on the input side of the photocoupler 14. The pulse density modulation signal transmitted to the phototransistor 14 b on the output side of the photocoupler 14 is demodulated into an analog modulation signal by the analog low pass filter 15 and supplied to the data pump circuit 3. The data pump circuit 3 A / D-converts the input analog modulation signal, PSK demodulates it, and supplies it to the transmission / reception controller 2. The transmission / reception controller 2 performs processing such as error check and data decompression from the received demodulated data, and outputs an retransmission request and the like to the telephone line 10 side when an error occurs, and also adjusts the data speed with an internal buffer to make the interface 1 The reception data Dr is supplied to the terminal device via the.

The sequence controller 16 controls the operations of the transmission / reception controller 2 and the data pump circuit 3 and exchanges control data with the terminal device via the interface 1 to drive the tone dialer 17 and the pulse dialer 18. . Tone dialer 17 is DTMF
A circuit for transmitting a (Dual Tone Multi Frequency) signal through the mixing / distribution circuit 8, a pulse dialer 18
Is a circuit for generating a dial pulse to drive the DP relay 9.

FIG. 2 is a block diagram showing details of the data pump circuit 3. Burst errors are dispersed in the transmission data supplied from the transmission / reception controller 2 by rearranging the data positions by the scrambler 21. The modulation circuit 22 outputs the output of the scrambler 21 to, for example, PSK.
Modulate. The obtained modulation data is multi-bit data, and the data is Δ-modulated by the 1-bit D / A converter 23 to become a 1-bit pulse density or pulse width modulated signal. On the other hand, the analog reception data is converted into digital data having a predetermined number of bits by the A / D converter 24, then demodulated by the demodulation circuit 25, for example, by PSK demodulation, and the order of the data is changed by the descrambler 26. This received data is supplied to the transmission / reception controller 2.

Next, the operation of the modulator / demodulator thus constructed will be described. (1) Modulation At the time of data transmission (at the time of modulation), as shown in FIG. 3, the multi-bit modulation data PSK output from the modulation circuit 22 is pulse density modulated by the 1-bit D / A 23, and further the LPF 6 Then, the data is transmitted to the line 10 after being converted back to the analog modulation signal. The signal is transmitted by the photocoupler 5 in the pulse density modulated signal form, so that the digitally processed primary side and the analogly processed secondary side in FIG. 1 are insulated and separated. . According to this method, the electric power required on the secondary side is the electric power for driving the photodiode 5a of the photocoupler 5, but this electric power may be much smaller than the electric power for driving the conventional transformer.

(2) At the time of demodulation At the time of data reception (at the time of demodulation), the analog reception signal output from the reception filter 11 is pulse density modulated by the 1-bit A / D converter 12, as shown in FIG. Further, after being converted into an analog reception signal by the analog LPF 15, it is supplied to the data pump circuit 3 and demodulated. And in this case also, in the form of pulse density modulated signal,
By the signal transmission by the photocoupler 14, the primary side (analog circuit) and the secondary side (digital circuit) in FIG. 1 are insulated and separated.

As described above, according to the modulation / demodulation apparatus of this embodiment, the means for insulating and demarcating the primary side and the secondary side are the photocouplers 5, 13 and 14, so that it is better than the case where a transformer is used. The device can be significantly downsized. The power supply for the circuit on the primary side is the telephone line 1 when off-hook.
Receive monitoring signal from the exchange that flows to 0 (DC current 20 mA
~ 120mA) can be used. Therefore, as the secondary power, the digital circuit or the photodiodes 5a, 1
Since only the power for driving 3a is sufficient, it is possible to reduce the power supply voltage of the device. According to this device,
Since the insulation demarcation point is transmitted by a digital pulse density modulation signal, there is no analog loss such as phase rotation or generation of harmonic distortion that occurs when a transformer is used. Therefore, the data transmission / reception quality can be improved.

FIG. 5 is a block diagram showing another configuration example of the data pump circuit 3. The data pump circuit 3 is different from that shown in FIG. 2 in that a 1-bit / multi-bit converter 31 is provided instead of the A / D converter 24 on the reception input side. This 1-bit / multi-bit converter 3
1 may be replaced by a digital low pass filter having a similar function. In this case, since the pulse modulation signal output from the photocoupler 14 can be directly input to the data pump circuit 24, the analog low-pass filter 15 in FIG. 1 becomes unnecessary. According to this embodiment, as shown in FIG. 6, at the time of data reception (at the time of demodulation)
The pulse-modulated signal from the 1-bit A / D converter 12 is converted into received data without passing through an analog signal.
That is, in this embodiment, the number of D / A conversions and A / D conversions is smaller than that of the previous embodiments by one time each, so that the quantization error and the like are reduced accordingly and more accurate information transmission is possible.

In the above embodiments, the photocoupler is used as the optical coupling means, but other optical coupling means using an optical integrated circuit or the like may be used. Further, the modulation / demodulation system is not limited to the PSK system, but may be FSK (Frequency Shift).
t Keying), QAM (Quadrature Amplitude Moduratio)
The present invention can also be applied to devices using other modulation / demodulation methods such as n). Further, in the above embodiment, the pulse density modulation method using the 1-bit A / D converter and the 1-bit D / A converter is used as the pulse modulation method. The pulse modulation method may be used. The modulation / demodulation device of the present invention may be incorporated in the terminal device as in the case of a facsimile or the like.

[0019]

As described above, according to the present invention,
Since the optical coupling means is used as the insulation demarcation means for the line and the terminal instead of the conventional transformer, the power supply voltage and the size of the device can be greatly reduced. Further, according to the present invention, since the insulation demarcation unit transmits information by a digital pulse modulation signal, there is no analog influence such as phase rotation or harmonic distortion, and the data transmission quality is significantly improved. There is an effect of improving.

[Brief description of drawings]

FIG. 1 is a block diagram of a modulation / demodulation device according to an embodiment of the present invention.

FIG. 2 is a block diagram of a data pump circuit in the device.

FIG. 3 is a diagram for explaining the operation of the apparatus during modulation.

FIG. 4 is a diagram for explaining an operation at the time of demodulation of the same device.

FIG. 5 is a block diagram of a data pump circuit according to another embodiment of the present invention.

FIG. 6 is a diagram for explaining an operation at the time of demodulation according to the same embodiment.

[Explanation of symbols]

1 ... Interface, 2 ... Transmission / reception controller, 3 ... Data pump circuit, 4 ... Amplifier, 5, 13, 14 ... Photo coupler, 6, 15 ... Low pass filter, 7 ... Transmission filter, 8 ... Mixing / distribution circuit, 9 ... DP Relay, 10 ... Telephone line, 11 ... Reception filter, 12 ... 1-bit A / D converter, 16 ... Sequence controller, 17 ... Tone dialer, 18 ... Pulse dialer, 21 ... Scrambler, 2
2 ... Modulation circuit, 23 ... 1-bit D / A converter, 24 ... A
/ D converter, 25 ... Demodulation circuit, 26 ... Descrambler,
31 ... 1-bit / multi-bit converter.

Claims (2)

[Claims] 1. A device provided between a terminal device and a communication line,
In a modulator for converting transmission data supplied from the terminal device into an analog transmission signal transmitted on the communication line, a modulation means for modulating the transmission data, and a modulation signal obtained by the modulation means for pulse modulation. Pulse modulating means, transmitting means for converting the pulse modulated signal obtained by the pulse modulating means into the analog transmission signal and transmitting the analog transmission signal to the communication line, and an interposing device between the pulse modulating means and the transmitting means. And a light coupling means for optically coupling the two and electrically insulating them. 2. Provided between the communication line and the terminal device,
In a demodulation device for converting an analog reception signal received from the communication line into reception data necessary for the terminal device, pulse modulation means for pulse-modulating the analog reception signal, and a pulse modulation signal obtained by the pulse modulation means And demodulating means for converting the received data into the received data, and an optical coupling means interposed between the pulse modulating means and the demodulating means for optically coupling the two and electrically insulating them. And a demodulator.