Electronic digital logic circuitry – Signal sensitivity or transmission integrity – Bus or line termination
Reexamination Certificate
2001-05-09
2002-07-30
Le, Don Phu (Department: 2819)
Electronic digital logic circuitry
Signal sensitivity or transmission integrity
Bus or line termination
C326S090000
Reexamination Certificate
active
06426646
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an emitter coupled logic (ECL) terminating circuit which terminates an output end of an ECL outputting circuit or a pseudo emitter coupled logic (PECL) outputting circuit that is used at digital telecommunication.
DESCRIPTION OF THE RELATED ART
At digital telecommunication equipment using an ECL outputting circuit or a PECL outputting circuit, its supply voltage has been lowered, consequently, it has been difficult to secure a desirable amplitude of a signal outputted from the ECL outputting circuit or the PECL outputting circuit in, and also to secure good wiring of a signal transmission line for the outputted signal.
FIG. 1
is a block diagram showing a structure of a conventional ECL terminating circuit. Referring to
FIG. 1
, the structure of the conventional ECL terminating circuit is explained.
Generally, when a high speed PECL signal is transmitted through a transmission line, at the case that the distance of the transmission line becomes long, it is necessary that a terminal resistance of 50 &OHgr; is loaded. As shown in
FIG. 1
, this conventional ECL terminating circuit consists of a PECL outputting circuit
51
, a resistor
52
, a transmission line
53
, and a load circuit
54
. And the output end of an NPN transistor
511
in the PECL outputting circuit
51
is connected to one end of the resistor
52
and one end of the transmission line
53
, and the other end of the transmission line
53
is connected to the load circuit
54
whose input impedance is 50 &OHgr;.
Consequently, the load impedance for the PECL outputting circuit
51
becomes a resistance value that the resistance value of the resistor
52
and the input impedance 50 &OHgr; of the load circuit
54
are added in parallel. As a result, the load impedance for the PECL outputting circuit
51
becomes lower than 50 &OHgr;, and there is a problem that the amplitude of the output signal from the PECL circuit
51
becomes small.
And it is possible that the load impedance for the PECL outputting circuit
51
is made to be almost equal to 50 &OHgr; by that the resistance value of the resistor
52
is made to be large. However, when the resistance value of the resistor
52
is made to be large, the output current from the NPN transistor
511
becomes small, and the desirable amplitude of the output signal from the PECL outputting circuit
51
can not be secured. Further, recently, the supply voltage for the circuit has been lowered, and the resistance value of the resistor
52
must be lowered, if not, the output current from the NPN transistor becomes small. And when the resistance value of the resistor
52
is made to be large, as mentioned above, the desirable amplitude of the output signal from the PECL outputting circuit
51
can not be secured.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an ECL terminating circuit, in which it is prevented that the amplitude of an output signal from an ECL outputting circuit or a PECL outputting circuit is lowered caused by that the supply voltage for the circuit has been lowered, and also it is prevented that the waveform of the output signal is deteriorated caused by that the distance of a transmission line where the output signal being high speed is transmitted is made to be long.
According to a first aspect of the present invention, there is provided an ECL terminating circuit, which terminates the output end of an ECL outputting circuit or a PECL outputting circuit using at digital telecommunication. And the ECL terminating circuit provides a terminating means that is connected in series to a resistor connecting to the output end of the ECL outputting circuit or the PECL outputting circuit, and a resistance value of the terminating means becomes about 0 &OHgr; at a direct current (DC) and the resistance value of the terminating means becomes large at an alternating current (AC).
According to a second aspect of the present invention, in the first aspect, the terminating means is an inductor.
According to a third aspect of the present invention, in the first aspect, the terminating means is composed of that an inductor and a resistor are connected in parallel.
According to a fourth aspect of the present invention, in the third aspect, the terminating means is an impedance element having an equivalent function to that an inductor and a resistor are connected in parallel.
According to a fifth aspect of the present invention, there is provided an ECL terminating circuit, which terminates the output end of an ECL outputting circuit or a PECL outputting circuit using at digital telecommunication. And the ECL terminating circuit provides a first resistor whose one end is connected to the output end of the ECL outputting circuit or the PECL outputting circuit that is used, a 50 &OHgr; transmission line whose one end is connected to the output end of the ECL outputting circuit or the PECL outputting circuit that is used, a terminal element whose one end is connected to the other end of the first resistor and whose the other end is connected to ground, and whose resistance value is about 0 &OHgr; at a DC and becomes large at an AC, and a load circuit that is connected to the other end of the 50 &OHgr; transmission line and whose input impedance is about 50 &OHgr;.
According to a sixth aspect of the present invention, in the fifth aspect, the terminal element is an inductor whose one end is connected to the the other end of the first resistor and the other end is connected to ground.
According to a seventh aspect of the present invention, in the fifth aspect, the terminal element is composed of an inductor and a second resistor, and the inductor and the second resistor are connected in parallel, and one end of the terminal element is connected to the other end of the first resistor and the other end of the terminal element is connected to ground.
According to an eighth aspect of the present invention, in the fifth aspect, the terminal element is an impedance element having an equivalent function to that an inductor and a resistor are connected in parallel, and one end of the impedance element is connected to the other end of the first resistor and the other end of the impedance element is connected to ground.
REFERENCES:
patent: 6064248 (2000-05-01), Seki
patent: 6208161 (2001-03-01), Suda
patent: 6212586 (2001-04-01), Mros et al.
Tachigori Masashi
Yoshizawa Munetoshi
Le Don Phu
NEC Corporation
Young & Thompson
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