Communication device

A circuit for generating dial pulses and a circuit for forming the direct current loop of a line have conventionally been made up of relays and a coil. In the present invention, these circuits are made up of components, such as capacitors and a semiconductor switching element, to render a network control unit smaller. A compensating circuit is provided for reducing the distortion (caused by the capacitor in the DC loop) of the waveforms of dial pulses and rise waveforms of a direct current when the direct current loop is formed.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a communication device and, more 
particularly, to a communication device having a Network Control Unit 
(NCU) for forming dial pulses and the DC loop of a communication line (the 
closure of a direct current). 
2. Description of the Related Art 
A conventional NCU utilizes relays to form dial pulses and coils for 
closure of a direct current. 
The conventional NCU will be described with reference to FIG. 7. As shown 
in this drawing, a P relay is turned on and off to generate dial pulses. 
However, the waveforms of the dial pulses are distorted because of the 
electromagnetic induction of a coil L for closure of the DC loop. To 
compensate for such distortion, an S relay is used, and is turned on only 
when the dial pulses are generated, at which time the direct current will 
not flow through the coil L. 
To closure the direct current, the DC loop between a telephone set and a 
switching system must be correctly formed when a relay switches the DC 
loop from the telephone set side to a facsimile device side. The coil L 
forms the DC loop made up of the telephone set and the switching system. 
However, the above conventional art utilizes relays and a coil, each of 
which is a relatively high-cost component and is larger than a 
semiconductor component, thus increasing the cost and size of the NCU. 
To solve such a problem, it is possible to construct an NCU using 
semiconductor elements. In such an NCU, however, the waveforms of the DC 
loop and dial pulses are distorted during an off-hook mode. 
SUMMARY OF THE INVENTION 
In view of the above problems, an object of the present invention is to 
provide an improved communication device. 
Another object of this invention is to provide a communication device in 
which the structure of a network control unit is simplified. 
A further object is to provide a communication device employing 
semiconductor elements to simplify the structure of a network control 
unit. A further object is to solve the problem of waveforms being 
distorted, which occurs when the semiconductor elements are employed. 
Other objects, features and advantages of this invention will become more 
fully apparent from the following detailed description of a preferred 
embodiment taken in connection with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The preferred embodiment of the present invention will be described below 
with reference to the drawings. 
Although this invention applies to and is described with respect to a 
facsimile type of communication device, it may equally be applied to other 
types of communication devices connected to telephone lines, such as telex 
and teletex devices. 
FIG. 1 is a view showing the structure of a facsimile device in accordance 
with this embodiment. 
A central processing unit (CPU) 1 is composed of, for example, a 
microprocessor, and controls the entire facsimile device in accordance 
with programs stored in a Read Only Memory (ROM) 2. 
A Random Access Memory (RAM) 3 stores binarized image data read by a 
reading unit 7 and analog waveforms in the form of binary data, etc. The 
waveforms are input through a telephone line 10 and a Network Control Unit 
(NCU) 9 and demodulated by a modem 8. 
A nonvolatile RAM 4 reliably stores data which must be retained, even when 
the facsimile device is turned off. 
A CG 5 is a ROM for storing font data in the form of character codes, such 
as Japanese Industrial Standards (JIS) codes and American Standard Code 
for Information Interchange (ASCII) codes. 
A recording unit 6 records data stored in the RAM 3 and outputs it in the 
form of hard copies. 
A reading unit 7 binarizes data which has been read by using a solid state 
imaging element (CCD), and successively transmits the binary data to the 
RAM 3. A manuscript sensor is capable of detecting the number of 
manuscripts placed on the reading unit 7, and a manuscript detecting 
signal is input to the CPU 1. 
The modem 8 modulates data stored in and transmitted from the RAM 3, on the 
basis of the control of the CPU 1, and outputs it to the telephone line 10 
via the NCU 9. It receives an analog signal transmitted through the 
telephone line 10 by way of the NCU 9, and demodulates it into binary data 
which is stored in the RAM 3. 
The NCU 9 switches the telephone line 10 to either the modem 8 or a 
telephone set 11, whereby the telephone line 10 is connected to one of 
such components. 
The telephone set 11 is made up of components, such as a handset, a dial 
and a speech network. 
An operating unit 12 is composed of a mode selection key, a key for 
starting to send or receive images, a ten-key pad for dialing, etc. The 
mode selection key is used for specifying operation modes when images are 
sent or received, such as a fine mode, a standard mode or an automatic 
reception mode. The CPU 1 detects whether any keys are depressed and, if 
so, which keys are depressed, and controls the above components in 
accordance with such detection. 
A displaying unit 13 is a liquid crystal display device capable of 
displaying, on the basis of the control of the CPU 1, representations like 
characters in 16 digits. 
This embodiment will now be described in more detail. 
FIG. 2 shows the circuitry of the NCU 9 which is formed of semiconductor 
components instead of the relays and coil employed conventionally. 
A signal transmitted from the CPU 1 turns a photocoupler 91 on and off, 
which turns transistors 94 and 93 on and off, whereby a dial pulse is 
formed. More specifically, when the signal from the CPU 1 has a low 
voltage of zero, an electric current flows toward the diode side of the 
photocoupler 91, thus turning the photocoupler 91 on, and the electric 
potential of point A falls to a ground level. The transistor 94 is turned 
off, thus stopping the electric current from flowing to resistors R1 and 
R2. The electric potential of point B becomes equal to the level of a 
voltage applied through the telephone line. In other words, the electric 
potential of point B is equal to that of point C. The transistor 93 is 
turned off, thus cutting off the DC loop. When the signal from the CPU 1 
has a high voltage of 5, the photocoupler 91 is turned off. The electric 
potential of point A becomes equal to the level of a voltage being applied 
to a resistor R4, thus turning the transistor 94 on. The electric 
potential of point B falls below that of point C. The transistor 93 is 
turned on, and the DC loop remains closed. FIG. 3 is a chart showing the 
timing for the operations mentioned above. The two transistors 93 and 94 
are utilized so as to smoothly control the electric current. (The 
transistor 94 serves to drive the base current of the transistor 93.) 
A transistor 95 in the circuitry shown in FIG. 2 is utilized in place of a 
coil for retaining the DC loop. When a direct current is closured, the 
electric current flows to resistors R5 and R6, thus charging a capacitor 
C2. The electric potential of a point D assumes a uniform value, and the 
transistor 95 remains on. The DC loop is thereby closed. The level of the 
electric current depends upon the resistance values of the resistors of 
the transistors 93 and 95, and a diode bridge 96 when these components are 
turned on. The resistance values of the resistors must be great enough to 
maintain the level of the electric current of the DC loop. 
As described previously, the rise waveform of the DC loop is distorted when 
the DC loop is formed, due to the effect of the capacitor C2. The resistor 
R5 shown in FIG. 2 has a significantly large capacitance to increase the 
impedance. Because of this capacitance, the speed at which the capacitor 
C2 is charged is slowed down, having an effect on the waveform of the 
direct current. A photocoupler 92 is employed to compensate for this 
trouble. The speed of charging the capacitor C2 is increased by turning 
the photocoupler 92 on. Thus, the capacitor C2 causes less distortion. 
(The capacitance of the resistor R5 is larger than that of a resistor R7.) 
If the photocoupler 92 is turned on immediately before the closure of the 
direct current, the rise waveform of the DC loop will not be distorted. 
After the DC loop has been closed and the capacitor C2 has been charged, 
the photocoupler 92 is turned off. If the photocoupler 92 remained on, the 
impedance on a primary side would decrease and would not match an 
impedance of 600 .OMEGA. on the secondary side. 
FIG. 4 is a chart showing the timing for the operations mentioned above. 
The amount of time t.sub.1 shown in FIG. 4 may be increased as much as 
possible as long as the photocoupler 92 is turned on before the closure of 
the direct current. Time t.sub.2 is the amount of time required to charge 
the capacitor C2 completely. FIG. 5 is a flowchart showing the control of 
shaping the rise waveform of the direct current in the DC loop during an 
off-hook mode. 
In step S1, a determination is made whether the off-hook mode is indicated 
by detecting a call signal or whether unillustrated keys of the operating 
unit 12 are depressed. Specifically, a determination is made whether the 
call signal transmitted through the line is detected or whether an 
off-hook key, a simplified dialing key or pushbutton digits are depressed. 
If the off-hook mode is indicated, the photocoupler 92 is turned on in 
step S2. In step S3, a determination is made whether time t.sub.1 has 
elapsed since the photocoupler 92 was turned on. If it has elapsed, in 
step S4 a CML relay 97 is switched from the side of the telephone set 11 
to the side of the facsimile device. In step S5, a determination is made 
whether time t.sub.2 has elapsed since the CML relay 97 was switched. If 
t.sub.2 has elapsed, the photocoupler 92 is turned off in step S6. 
When the DC loop is formed and then dialing (calling) is performed, as 
shown in the timing chart of FIG. 6, the CPU 1 first turns the 
photocoupler 92 on, and then turns the photocoupler 91 on and off in 
accordance with dial data. This is because when the dial pulse is 
generated, the capacitor C2 has an effect on the waveform of the dial 
pulse. Therefore, the photocoupler 92 compensates for such an effect. When 
all dial data have been completely transmitted, the photocoupler 92 is 
turned off, thus completing the call. 
As has been described above, in the conventional art, the portions of an 
NCU which are used for forming the DC loop and dial pulses are composed of 
relays and a coil. However, in the present invention, these portions are 
composed of semiconductor elements. This makes it possible to reduce the 
cost of the NCU circuitry and to render it smaller than the conventional 
NCU. With the NCU using the semiconductor elements, it is possible to 
decrease the distortion of the waveforms of the direct current and dial 
pulse by controlling a compensating circuit for wave distortion through 
software immediately before the direct current is closured and the dial 
pulse is generated. 
The present invention may be applied not only to facsimile devices but also 
to other types of communication devices, such as telephone sets and telex 
devices. 
This invention is not limited to the preferred embodiment described above, 
and various modifications can be made thereto.