Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Amplitude control
Reexamination Certificate
1998-11-27
2001-05-22
Nu Ton, My-Trang (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Amplitude control
C327S108000
Reexamination Certificate
active
06236255
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an output circuit, and more particularly, to a high-speed output circuit for matching impedance.
Referring to
FIG. 7
, a conventional output circuit of this type includes a PMOS transistor
106
and an NMOS transistor
206
. The output circuit is connected to a transmission line. In general, it is important to match impedance between the transmission line and a load (the output circuit). MOS transistors
106
and
206
have resistor components, however, since it is difficult to match the impedance by using only the resistor component of the MOS transistor itself, a resistor is built in the LSI or added to the exterior of the LSI to match the impedance. Thus, the output circuit is provided with a termination resistor
308
for matching the impedance between the transmission line and the output circuit. The output circuit inputs an input signal from an input terminal
508
and outputs an output signal to a output terminal
506
via resistor
308
.
However, in this embodiment, since the resistance value of the MOS transistors is influenced by variations in temperature or power voltage or a manufacturing process, rather than that by the resistor
308
, it is necessary to increase the resistance of resistor
308
. At the same time, the resistance component of the MOS transistors should be decreased. As a result, the gate widths of the MOS transistors
106
and
206
are increased. Thus, a problem arises because the size of the MOS transistor increases. In general, since a LSI has a plurality of output circuits, the size of the LSI also increases. Furthermore, as the size of the MOS transistor increases, another problem is produced because noise and power consumption increases due to an increase of the through-current of MOS transistors
106
and
206
.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a high-speed output circuit.
Another object of the present invention is to provide a small output circuit.
Another object of the present invention is to provide an output circuit which reduces noises and power.
According to one aspect of the present invention, there is provided: an output circuit which comprises an output terminal; a first circuit having a first input terminal, to which a first input signal is input, connected to a first power supply source, wherein the first circuit forms a first current path between the first power supply source and the output terminal in accordance with the first input signal; a second circuit having a second input terminal, to which a second input signal is input, connected to a second power supply source, wherein the second circuit forms a second current path between the second power supply source and the output terminal in accordance with the second input signal; a third circuit which provides the first input signal to the first input terminal and makes current flowing on the first current path constant or substantially constant; and a fourth circuit which provides the second input signal to the second input terminal and makes current flowing on the second current path constant or substantially constant.
According to another aspect of the present invention, there is provided an output circuit which comprises a buffer circuit connected to a power supply source and a output terminal, wherein the buffer circuit forms a current path between the power supply source and the output terminal, and a control circuit which makes current flowing on the current path constant or substantially constant.
REFERENCES:
patent: 4006423 (1977-02-01), Kuniyoshi et al.
patent: 4742247 (1988-05-01), Venkatesh
patent: 5315186 (1994-05-01), Baker
patent: 5929668 (1999-07-01), Kim
patent: 5955893 (1999-09-01), Chang et al.
patent: H8-195669 (1996-07-01), None
NEC Corporation
Nu Ton My-Trang
Sughrue Mion Zinn Macpeak & Seas, PLLC
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