Pulse or digital communications – Cable systems and components
Reexamination Certificate
2000-07-18
2004-08-24
Le, Amanda T. (Department: 2634)
Pulse or digital communications
Cable systems and components
C333S02400C, C333S172000
Reexamination Certificate
active
06782055
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a communication system that comprises a plurality of nodes connected in common to transmission lines.
2. Description of the Related Art
As shown in
FIG. 1
, in a prior-art communication system, two-wire transmission lines
1
,
2
are connected with transmission/reception circuits
3
1
through
3
n
as a plurality of nodes. All the transmission/reception circuits
3
1
through
3
n
comprise the same components. Positive potential Vcc (for example, 5V) is supplied to one end of the transmission line
1
via a terminal resistor
4
and positive potential Vcc is supplied to the other end via a terminal resistor
5
in the same way. Ground potential Vg (for example, 0V) is supplied to one end of the transmission line
2
via a terminal resistor
6
and ground potential Vg is supplied to the other end via a terminal resistor
7
in the same way.
In the transmission/reception circuit
3
1
a two-way I/O filter
11
is connected to the transmission lines
1
,
2
via a connector
12
. Connecting terminals A
1
, A
2
are provided for connecting the I/O filter
11
to the transmission lines
1
,
2
and connecting terminals B
1
, B
2
arranged as opposed to the connecting terminals A
1
, A
2
. A transmission signal is individually supplied to the connecting terminals B
1
, B
2
via a non-inverting amplifier circuit
13
and an inverting amplifier circuit
14
. In addition, bias circuits
17
,
18
are connected to the connecting terminals B
1
, B
2
of the filter
11
via AC coupling circuits
15
,
16
which comprise resistors
15
a
,
16
a
and capacitors
15
b
,
16
b
, respectively. Each of the signals provided by the bias circuits
17
,
18
serves as a reception signal via a comparator
19
comprising a differential amplifier.
Upon outputting the transmission signal, the signal is amplified by the non-inverting amplifier circuit
13
and amplified in an inverted manner by the inverting amplifier circuit
14
as well. Transmission signals having opposite phases to each other are supplied to the filter
11
from the non-inverting amplifier circuit
13
and the inverting amplifier circuit
14
. The filter
11
serves as a low-pass filter to allow the transmission signals to pass individually therethrough. An output transmission signal from the non-inverting amplifier circuit
13
passes through the filter
11
and is thereafter supplied to the transmission line
2
. An output transmission signal from the inverting amplifier circuit
14
passes through the filter
11
and is thereafter supplied to the transmission line
1
.
On the other hand, the information signals transmitted through each of the transmission lines
1
,
2
are supplied to the filter
11
. The filter
11
acts as a low-pass filter on each of these information signals to output signals to the AC coupling circuits
15
,
16
. Each of the AC coupling circuits
15
,
16
extracts AC components of the information signals and supplies the components to the bias circuits
17
,
18
, respectively.
For example, as shown in
FIG. 2A
, consider the case where a signal A transmitted through the transmission line
1
and a signal B transmitted through the transmission line
2
vary in phase opposite to each other. As shown in
FIG. 2B
, the bias circuit
17
applies a bias voltage to the information signal A to obtain a biased signal BIASA, while the bias circuit
18
applies a bias voltage to the information signal B to obtain a biased signal BIASB. As shown in
FIG. 2C
, the comparator
19
detects each of the output signals BIASA, BIASB from the bias circuits
17
,
18
as a reception signal.
When a break has occurred in the transmission line
1
, only the signal B is transmitted through the transmission line
2
. Accordingly, as shown in
FIG. 2D
, the biased signal BIASA remains constant, whereas the biased signal BIASB to the signal B, transmitted through the transmission line
2
, to which a bias voltage has been applied changes in the same way as the signal B. The comparator
19
compares the constant biased signal BIASA with the biased signal BIASB to obtain a reception signal as shown in FIG.
2
E. This holds true even when the transmission line
1
is grounded or when the transmission line
2
is broken or grounded.
Furthermore, no reception signals could be detected without the bias circuits
17
,
18
when a break occurred in the transmission line
1
since the signals A, B to be inputted into the comparator
19
would have the waveforms shown in FIG.
2
F.
Other transmission/reception circuits
3
2
through
3
n
also have the same configuration and operation as those of the transmission/reception circuit
3
1
. Furthermore, the aforementioned prior-art communication system is disclosed, for example, in Japanese Patent Laid-Open Publications No.Hei 3-171849. In addition, such a system as has the aforementioned AC coupling circuits
15
,
16
at the input stage of the receiver circuit is disclosed, for example, in Japanese Patent Laid-Open Publications No.Hei 1-317007 and No.Hei 1-261047.
As described above, the transmission/reception circuit is provided, at the input stage of the receiver circuit portion thereof, with the AC coupling circuits
15
,
16
to extract from an information signal transmitted only desired frequency components that include information regarding each of the bits given when transmitted. However, the AC coupling circuit comprises a time constant circuit with a resistor and a capacitor connected in series, so that the time constant given by the resistor and the capacitor exert an effect on the input information signal. That is, a large time-constant would cause the passing frequency bandwidth to become broad but the response to the input information signal to become slow. On the other hand, a small time-constant would cause the passing frequency bandwidth to become narrow but the response to the input information signal to become quick. As shown in FIG.
3
A and
FIG. 4A
, consider the case where the input information signal is a square wave of one bit, short in terms of time, and the time constant is large. In this case, the output signal waveform of the AC coupling circuit changes in a transient manner at the time of rising and falling as shown in
FIG. 3B
, so that a square wave cannot be obtained. On the other hand, if the time constant is small, the output signal waveform of the AC coupling circuit will be given a square wave with sharp rising and falling edges as shown in FIG.
4
B.
As shown in FIG.
5
A and
FIG. 6A
, consider the case where the input information signal is a square wave of a plurality of bits, long in terms of time and having a continuous high level, and the time constant is large. In this case, the output signal waveform of the AC coupling circuit changes in a transient manner at the time of rising and falling as shown in
FIG. 5B
, however, a square wave can be obtained since a constant level corresponding to the high level is sustained. On the other hand, if the time constant is small, the output signal waveform of the AC coupling circuit will be given a square wave with sharp rising and falling edges as shown in FIG.
6
B. However, since the level of the waveform is gradually reduced from the rising edge to the falling edge, a square wave cannot be obtained.
The information signal consists of a train of bits and the passing frequency bandwidth needs to be broadened in consideration of the bits having a continuous logic “1” level corresponding to the high level in the train of bits. Generally, the time constant of the AC coupling circuit is given a large value in accordance with the maximum number of bits that have a continuous logic “1” level in the train of bits. However, as can be seen from the foregoing, the passing frequency bandwith becomes broad but the response to the input information signal become slow when the time constant is large. Accordingly, the square wave portion formed only of a bit with logic “1” level in the information signal changes in a transient manner
Hashimoto Hiroshi
Iwamoto Kazuya
Nagatani Yuji
Honda Giken Kogyo Kabushiki Kaisha
Lahive & Cockfield LLP
Laurentano Anthony A.
Le Amanda T.
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