Miscellaneous active electrical nonlinear devices – circuits – and – Specific signal discriminating without subsequent control – By amplitude
Reexamination Certificate
1999-06-21
2001-05-01
Nelms, David (Department: 2818)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific signal discriminating without subsequent control
By amplitude
C365S200000
Reexamination Certificate
active
06225836
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor integrated circuit device, and more particularly to a semiconductor integrated circuit device having a function to alter the operating mode.
2. Description of the Background Art
At present, in general, in semiconductor integrated circuit devices produced, an operating mode is set in which one of two alternatives is selected where the representative examples of such selection include the selection between +5V and +3.3V for the operating power supply voltage, and the selection between the Fast Page mode (hereinafter referred to as the FP mode) and the Hyper Page mode (or the Extend Data Output mode, hereinafter referred to as the EDO mode).
When shipped, a semiconductor integrated circuit device has one of the two alternatives of an operating mode set according to the product specifications. It is desirable, however, to allow alteration of the operating mode with flexibility according to the state of production or the trend of market demands.
As an example of a technique that allows the switching of the operating mode of a semiconductor integrated circuit device according to changes in the state of production or the trend of market demands, a mode switching circuit is disclosed in the Japanese Patent Laying-Open No. 4-199541.
FIG. 17
is a circuit diagram of a prior art mode switching circuit
500
.
As shown in
FIG. 17
, a mode switching circuit
500
includes an external input terminal
201
to which a voltage is applied externally for switching the mode, an external input pad
202
connected to external input terminal
201
, a node
220
for outputting a control signal to switch the mode, a power supply line
204
for supplying a power supply voltage Vcc, a ground line
205
for supplying a ground potential Vss, an electric fuse
210
and resistive element
206
connected in series between power supply line
204
and node
220
, and a resistive element
207
connected between ground line
205
and node
220
.
Mode switching circuit
500
further includes an N-channel MOS transistor
203
having a gate connected to node
220
for connecting external input pad
202
with node
220
.
In mode switching circuit
500
, normally the resistance value ratio of resistive element
206
to resistive element
207
is determined such that the potential of node
220
is at the logic high or “H” level (Vcc). Here, N-channel MOS transistor
203
is designed to have a threshold voltage which allows the off state to be maintained even when external input terminal
201
is at the Vss level. Thus, under normal circumstances, external input terminal
201
and external input pad
202
are disconnected from node
220
.
When switching the mode, a potential having a sufficient potential difference from the Vcc level is applied to external input terminal
201
to blow electric fuse
210
. By blowing electric fuse
210
, the potential of node
220
can be made to attain the logic low or “L” level (Vss) by resistive element
207
, and thus the mode is switched.
Mode switching circuit
500
allows switching of the mode by having a voltage applied from outside to the memory device and having the electric fuse blown after the completion of the manufacturing process.
Thus, in a semiconductor integrated circuit device having a prior art mode switching circuit
500
, it is possible to switch the mode by an operation performed from outside even after the manufacturing process is completed.
While the prior art mode switching circuit
500
allows switching of the operating mode after the completion of the manufacturing process, since an additional step of fuse blowing is required for the switching of the operating mode, alteration at a later time of an operating mode once determined at the stage of circuit design prior to the start of the manufacturing process may affect productivity, when, for instance, a great number of products must be subjected to such an alteration.
In addition, in the prior art mode switching circuit
500
, since an electric fuse is blown by a current that flows through an MOS transistor and since the potential applied from outside to blow the fuse is also supplied to a node for generating a control signal, the internal circuit may be adversely affected, a successful fuse blow may not be ensured, and problems regarding performance reliability may arise.
Further, as to the above-mentioned MOS transistor, an MOS transistor having different characteristics from those of the other transistors in the semiconductor integrated circuit may be required to maintain the off state under normal conditions and to allow the passage of the fuse blow current when switching the mode. In such a case, the degree of freedom in layout designs could be limited.
SUMMARY OF THE INVENTION
One object of the present invention is to provide a semiconductor integrated circuit device which allows setting of the operating mode with certainty and flexibility by an external electrical input even after the device is encapsulated in a product package.
In brief, the present invention provides a semiconductor integrated circuit device including an internal circuit and an operating condition setting circuit, wherein
the internal circuit operates according to either one of the two operating conditions according to an operating condition setting signal,
the operating condition setting circuit generates an operating condition setting signal, and
the operating condition setting circuit includes a first external input terminal, an internal control signal generating circuit for generating an operating condition setting signal that selects either one of the two operating conditions depending on whether the first external input terminal is coupled to a prescribed potential, and an operating condition alteration circuit which allows the alteration of the operating condition to be set selectively and in a non-volatile manner, independent of the potential level of the first external input terminal by an electrical signal provided externally.
According to another aspect of the present invention, the present invention provides a semiconductor integrated circuit device including an internal circuit and an operating condition setting circuit, wherein
the internal circuit operates according to either one of the two operating conditions according to an operating condition setting signal,
the internal circuit includes a memory cell array having a plurality of memory cells arranged in a matrix of rows and columns, an address signal terminal for receiving a plurality of address signals for selecting the row and the column of the memory cells, and a control signal terminal for receiving a plurality of control signals for controlling the operation of the semiconductor integrated circuit device,
the operating condition setting circuit generates an operating condition setting signal, and
the operating condition setting circuit includes an external input terminal, an internal control signal generating circuit for generating an operating condition setting signal that selects one of the two operating conditions depending on whether the external input terminal is coupled to a prescribed potential, and a test operating condition setting circuit selectively allowing the alteration of the operating condition to be set, independent of the potential level of the external input terminal, by the combination of a plurality of control signals and a plurality of address signals provided externally.
Thus, the principal advantage of the present invention is the improved freedom with which an operating mode of the semiconductor integrated circuit device is set and the increased certainty with which a fuse is blown, owing to the fact that the operating mode, once selected depending on the presence/absence of coupling between an external input terminal and a prescribed potential, can be altered by blowing a fuse element provided independent of the circuit for generating the operating condition setting signal.
Furthermore, circuit evaluation and analysis can b
McDermott & Will & Emery
Mitsubishi Denki & Kabushiki Kaisha
Nelms David
Tran M.
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