Semiconductor integrated circuit

Details Semiconductor integrated circuit Semiconductor integrated circuit

2000-05-24

2002-04-30

Smith, Matthew (Department: 2825)

Miscellaneous active electrical nonlinear devices, circuits, and

Gating

Utilizing three or more electrode solid-state device

C327S544000

Reexamination Certificate

active

06380795

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor integrated circuit.
This application is a counterpart application of Japanese application Serial Number 285898/1999, filed Oct. 6, 1999, the subject matter of which is incorporated herein by reference.
2. Description of Related Art
In the development of semiconductor integrated circuits, part of a circuit is sometimes common to different types of integrated circuits. Development costs can be reduced and development time shortened by having parts of the circuits in common.
In the case where part of an integrated circuit is made common, unused pads are sometimes formed within the integrated circuits.
For example, we will consider the case of two types of integrated circuits A and B, where three types of control signals S
1
, S
2
, and S
3
must be input from outside to the integrated circuit A, but only control signals S
1
and S
2
need be input from outside to the integrated circuit B and the control signal S
3
is not used thereby.
In such a case, when these integrated circuits A and B have common portions, pads P
1
, P
2
, and P
3
for inputting control signals S
1
, S
2
, and S
3
are formed in each integrated circuit A and B. Pads P
1
, P
2
, and P
3
are all used in integrated circuit A, but only pads P
1
and P
2
are used in integrated circuit B and pad P
3
is not used thereby.
When unused input pads are present in a conventional semiconductor integrated circuit, these unused input pads must be set to a prescribed potential. In a conventional semiconductor integrated circuit, wires or the like are therefore bonded to unused input pads as well as to used pads and potentials such as V
CC
and V
SS
are supplied thereto. The potential must be fixed because, when the potential of unused input pads is not fixed, the varying potential of the input pads due to minority carriers or the like may be handled within the integrated circuit as an input signal and cause erroneous operation of the integrated circuit.
Moreover, it is desirable that the number of pads to be bonded be reduced in view of reducing manufacturing costs for semiconductor devices and improving yields.
From this perspective, a technique for eliminating the need for the bonding of unused input pads is desirable.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a semiconductor integrated circuit that does not require the potential of unused input pads to be held at an externally supplied potential.
In order to achieve this object, the semiconductor integrated circuit relating to the present invention is provided the unique constitution described below. Specifically, the semiconductor integrated circuit relating to the present invention is provided an input circuit between an input pad and first stage input gate. In the present invention, this input circuit comprises a determining portion to determine the presence of bonding at an input pad according to the potential of that input pad, and a switching portion to output a first level potential to the first stage input gate when the determining portion determines that “there is no bonding” and to connect the input pad to the first stage input gate when the determining portion determines that “there is bonding”.
In a semiconductor integrated circuit relating to the present invention, the determining portion checks for bonding and the switching portion sets the potential level of the first stage input gate in the case there is no bonding. Consequently, it is not necessary to perform bonding because it is not necessary to fix the potential of the unused input pads with an externally supplied potential.


REFERENCES:
patent: 4945267 (1990-07-01), Galbraith
patent: 5412333 (1995-05-01), Okunaga
patent: 5621348 (1997-04-01), Furutani et al.
patent: 5920227 (1999-07-01), An
patent: 5942809 (1999-08-01), Hashimoto
patent: 6028474 (2000-02-01), Ito

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