Output circuit, input circuit and input/output circuit

Details Output circuit, input circuit and input/output circuit Output circuit, input circuit and input/output circuit

2002-04-19

2003-02-25

Cunningham, Terry D. (Department: 2816)

Miscellaneous active electrical nonlinear devices, circuits, and

Signal converting, shaping, or generating

Current driver

C327S537000

Reexamination Certificate

active

06525576

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to output circuits, input circuits and input/output circuits which can be built-in in an integrated circuit or an IC. More specifically, this invention relates to a plurality of improvements developed for providing three independent groups of circuits which are allowed to be built-in in an IC.
The circuits belonging to the first group of this invention are output circuits each of which acts as an interface employable for outputting a voltage signal to an external circuit which works under a power supply of which the voltage is e.g. 5V which is higher than the voltage e.g. 3V which is the voltage of a power supply under which the output circuit works. The ultimate purpose of this invention is to provide output circuits which are possible to output such voltage signals quickly with a higher speed without consuming a large amount of electric power. More precisely, the output circuits belong to the first group of this invention are output circuits which are possible to increase the potential level of such an output signal at least to the level of the voltage e.g. 3V which is the voltage of a power supply employed in the output circuits, very quickly, without consuming a large amount of electric power.
The circuits belonging to the second group of this invention are input circuits each of which acts as an interface employable for receiving a voltage signal from an external circuit which works under a power supply of which the voltage is e.g. 5V which is higher than the voltage e.g. 3V which is the voltage of a power supply under which the input circuit works. The ultimate purpose of this invention is to provide input circuits which are possible to receive voltage signals of which the potential is higher than the voltage of a power supply employed in the input circuit and forward the voltage signals toward the next stage circuit in a voltage corresponding to the full amount of the voltage of a power supply employed in the input circuit. More precisely, the input circuits belonging to the second group of this invention are input circuits which are possible to forward a voltage signal having a sufficient potential level, with respect to the VIH rule, to the next stage circuit. More specifically, the input circuits belonging to the second group of this invention are input circuits which receive a voltage signal from a circuit which works under a power supply of which the voltage is higher than the voltage of a power supply under which the input circuits work and forward the voltage signal having a voltage of the full amount of the voltage of a power supply under which the input circuits work or V
DD
, rather than (V
DD
−V
th
) to the next stage circuit.
The circuits belonging to the third group of this invention are input/output circuits each of which is convertible between an output circuit having an advantage referred to above and an input circuit having an advantage referred to above.
BACKGROUND OF THE INVENTION
An output circuit allowable to be built-in in an integrated circuit and which is available in the prior art and an input circuit allowable to be built-in in an integrated circuit and which is available in the prior art will be described below, referring to drawings.
Referring to
FIGS. 1 and 2
, an output circuit allowable to be built-in in an integrated circuit and which is available in the prior art has an open drain circuit consisting of an n channel normally on type field effect transistor (N
1
O
1
) connected a pull-up resister (R
1
) through a “PAD” of the IC in which the output circuit is built-in. The pull-up resister (R
1
) is arranged outside the IC and works under a power supply Vcc of e.g. 5V, despite the output circuit works under a power supply of e.g. 3V. The n channel normally on type field effect transistor (N
101
) has a function to reduce the voltage applied between the source and the drain of the n channel normally on type field effect transistor (N
102
).
FIG. 2
shows that the voltage of the output signal very slowly increases up to the voltage of Vcc or 4V in this example, in excess of the voltage level of the voltage signal which is outputted from this output circuit and which is shown by (IN). It is noted that a very long time is required for transmission of a voltage signal having a potential level of e.g. 3V to an external circuit which works under a power supply of a higher voltage of e.g. 5V. Incidentally, it is noted the output circuit can be employed as the output circuit of an IC having a less amount of dielectric strength.
Referring to
FIGS. 3 and 4
, an input circuit allowable to be built-in in an integrated circuit and which is available in the prior art has an n channel normally on type field effect transistor (N
100
) which has a function to reduce the voltage of an input signal which is inputted through a “PAD” of the IC and which has a voltage range of zero through 5V to a voltage range ranging from zero to the voltage difference between the V
DD
voltage or the power supply voltage of circuit and the threshold voltage of the n channel normally on type field effect transistor (N
100
), before forwarding the input signal to the next stage circuit produced the IC. Therefore, the input circuit can be employed for an integrated circuit having a less amount of dielectric strength. The threshold voltage of the IC is designed to be less than that of the ordinary input circuit. In the drawing, “PAD” means the bonding pad for the input circuit.
FIG. 4
shows the voltage of an input signal received at an input terminal (IN) is reduced to the potential level of the node (Y), before being applied to an amplifier and forwarded to the next stage circuit.
In the first place, referring to
FIG. 2
, the output signal outputted from the output circuit illustrated in
FIG. 1
increases at a rate determined by a time constant which is further determined by the amount of the pull-up resister (R
1
). This means that if a high operation speed is required, a less amount of the pull-up resister (R
1
) is required. If the amount of the pull-up resister (R
1
) is made less, the power consumption increases accordingly, vice versa.
This is a drawback inevitably involved with the foregoing output circuit available in the prior art, described referring to
FIGS. 1 and 2
.
In the second place, supposing the power supply voltage of the input circuit illustrated in
FIG. 3
or the V
DD
is 3V, an input signal of 5V inputted into the input circuit through the “PAD” is reduced to a value which is V
DD
less the threshold voltage of the n channel normally on type field effect transistor (N
100
), (V
DD
−V
th
) or approximately 2.3V, before being applied to the node (Y). Accordingly, it is not easy for such an input circuit to satisfy the requirement of VIH, which is a regulation inspecting whether or not an “H” level voltage issued by an input circuit has a sufficient amount of margin with respect to the threshold value of the internal circuit of the input circuit.
This is a drawback inevitably involved with the foregoing input circuit available in the prior art, described referring to
FIGS. 3 and 4
.
OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, an object of this invention is to provide output circuits which are allowed to be built-in in an integrated circuit and which can output voltage signals into an external circuit which works under a power supply of which the voltage is higher than the voltage of a power supply under which the output circuits work, with a higher operation rate and without consuming a large amount of electric power.
Another object of this invention is to provide input circuits which are allowed to be built-in in an integrated circuit and which can receive input voltage signals from an external circuit which works under a power supply of which the voltage is higher than the voltage of a power supply under which the input circuits work, and to forward the input signals to the next stage circuit, in the voltage corresponding to the full amount of the voltage of a power supply under which

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