Pulse or digital communications – Cable systems and components – Transformer coupling
Reexamination Certificate
1999-02-05
2002-10-15
Pham, Chi (Department: 2631)
Pulse or digital communications
Cable systems and components
Transformer coupling
C375S288000, C375S289000, C375S291000, C333S025000, C307S007000, C307S083000, C307S087000, C307S127000, C307S129000, C307S138000, C363S089000, C363S097000
Reexamination Certificate
active
06466627
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a pulse signal transmitting circuit and, more particularly, to a pulse signal transmitting circuit used for a line build out (LBO) type balanced line drive circuit which generates a pulse voltage signal to be transmitted through a transmission cable. The LBO type balanced line drive circuit using the pulse signal transmitting circuit according to the present invention is suitable for a subscriber's line terminal apparatus.
2. Description of the Related Art
FIG. 1
is a circuit diagram of a conventional pulse signal transmitting circuit. The pulse signal transmitting circuit shown in
FIG.1
comprises data input terminals
1
and
2
, switching transistors
3
and
4
, a transformer
5
(N
1
:N
2
=1:1.3) and a filter circuit
6
. A secondary side of the transformer
5
is connected to an ABAM cable (shieldless pair line)
7
so as to transmit an output of the pulse signal transmitting circuit to a load circuit
8
.
The switching transistors
3
and
4
are push-pull connected to each other, and are connected to the transformer
5
as a load circuit. A power source (+5V) is connected to a middle point of a primary winding of the transformer
5
.
The ABAM cable
7
has a frequency characteristic as shown in a graph of FIG.
1
-(
e
). That is, a cable loss increases as a frequency of the signal transmitted through the ABAM cable
7
increases. Such a frequency characteristic is compensated for by pre-distorting a pulse signal to be transmitted through the ABAM cable on the transmitter side.
FIG. 2
shows an example of a pulse template recommended for a North America DS-1 apparatus specified by the Bell specification with respect to a transmission cable such as the ABAM cable
7
. The pulse template shown in
FIG. 2
is characterized in that an overshoot
31
and an undershoot
32
of a pulse signal are allowed. In order to conform to the specification, the pulse signal transmitting circuit shown in
FIG. 1
is provided with the filter circuit
6
. The filter circuit
6
is connected in series to the power source of the pulse signal transmitting circuit.
When a positive pulse signal (FIG.
1
-(
a
)) is input to the data input terminal
1
, the positive pulse signal is provided to a base of the transistor
3
. Accordingly, the transistor
3
is turned on, and a current flows in a primary winding of the transformer
5
in a direction D
1
. At this time, the filter circuit
6
connected to the power source attenuates a low-frequency component of the positive pulse signal. As a result, a high-frequency component of the current flowing in the direction D
1
is enhanced. Accordingly, a positive pulse signal is generated in a secondary winding of the transformer
5
. Similarly, when a positive pulse signal (FIG.
1
-(
b
)) is input to the data input terminal
2
, the positive pulse signal is provided to a base of the transistor
4
. Accordingly, the transistor
4
is turned on, and a current flows in the primary winding of the transformer
5
in a direction D
2
which is opposite to the direction D
1
. Similar to the current flowing in the direction D
1
, a high-frequency component of the current flowing in the direction D
2
is enhanced by the filter circuit
6
, and a negative pulse signal is generated in the secondary winding of the transformer
5
.
Accordingly, when the positive pulse signal (FIG.
1
-(
a
)) is input to the data input terminal
1
and the positive pulse signal (FIG.
1
-(
b
)) is input to the data input terminal
2
, a bipolar pulse signal shown in FIG.
1
-(
c
) is generated in the secondary winding of the transformer
5
which bipolar pulse signal has an enhanced high-frequency component. The bipolar pulse signal generated in the transformer
5
is transmitted to the load circuit
8
through the ABAM cable
7
. While the pulse signal is transmitted through the ABAM cable
7
, the high-frequency component of the pulse signal is attenuated and a pulse signal shown in FIG.
1
-(
d
) is obtained at the load circuit
8
.
As mentioned above, the conventional circuit is provided with the filter circuit
6
so as to obtain the pulse signal having an enhanced high-frequency component as shown in FIG.
1
-(
c
). However, there is a problem in that a power loss occurs in the filter circuit
6
since the filter circuit
6
attenuates a low-frequency component of the current input to the transformer
5
.
SUMMARY OF THE INVENTION
It is a general object of the present invention to provide an improved and useful pulse signal transmitting circuit in which the above-mentioned problem is eliminated.
A more specific object of the present invention is to provide a pulse signal transmitting circuit which can generate a pulse signal having an enhanced high-frequency component with a reduced power loss.
In order to achieve the above-mentioned object, there is provided according to the present invention a pulse signal transmitting circuit, comprising:
a transformer having a primary winding and a secondary winding, the secondary winding being connected to a transmission cable;
first and second switching elements connected to the primary winding of the transformer, a voltage output from an external power source being input to the primary winding of the transformer when at least one of the first and second switching elements is closed so that a pulse voltage signal is input to the transformer; and
a booster power supply circuit provided between the external power source and a middle point of the primary winding of the transformer, the booster power supply circuit superimposing a boost voltage onto the voltage input to the primary winding of the transformer so that a high-frequency component of the pulse voltage signal input to the primary winding of the transformer is enhanced.
According to the above-mentioned invention, the booster power supply source generates a boost voltage and superimposes or adds the boost voltage to a voltage supplied from the power source. Accordingly, when one of the first and second switching elements is closed and the voltage of the power source is supplied to the transformer, the boost voltage is superimposed or added onto the voltage supplied to the transformer. Since the boost voltage is generated so as to enhance a high-frequency component of the pulse voltage signal to be input to the primary winding of the transformer, a pulse voltage signal generated in the secondary winding of the transformer also has an enhanced high-frequency component. Thus, the pulse signal transmitting circuit according to the present invention can generate a pulse voltage signal having an enhanced high-frequency component without causing power loss whereas the conventional apparatus generates a pulse voltage signal having an enhanced high-frequency component by cutting off a low-frequency component.
In the above-mentioned invention, the booster power supply circuit may store energy when the first and second switching elements are opened, the booster power supply circuit discharging the stored energy when at least one of the first and second switching elements is closed so as to enhance the high-frequency component of the pulse voltage signal supplied to the primary winding of the transformer.
According to this invention, the booster power supply circuit stores energy during a period in which the voltage of the power source is not supplied to either the first switching element or the second switching element. Thus, energy of the power source can be efficiently used.
In one embodiment of the present invention, the booster power supply circuit may comprise a coil having a predetermined inductance. The coil generates a reverse electromotive force when the pulse voltage signal is input to the transformer, and a voltage caused by the reverse electromotive force is superimposed onto the voltage supplied to the transformer.
Additionally, the pulse signal transmitting circuit according to the present invention may further comprise a third switching element connected in series with
Katten Muchin Zavis & Rosenman
Pham Chi
Tran Khanh Cong
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