Data processing: measuring – calibrating – or testing – Testing system – Of circuit
Reexamination Certificate
1998-01-22
2001-03-06
Shah, Kamini (Department: 2857)
Data processing: measuring, calibrating, or testing
Testing system
Of circuit
C365S225700, C365S230070
Reexamination Certificate
active
06199025
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to semiconductor devices, and particularly relates to a semiconductor device which allows a device type thereof to be switched.
2. Description of the Related Art
When semiconductor devices are manufactured, they are generally designed to be adaptable to various device types (different operational configurations), and one of the device types is selected and fixed before shipment of the semiconductor devices. For example, an input-output interface is designed such that the input-output interface can be switched between a 4-bit configuration, an 8-bit configuration, a 16-bit configuration, and a 32-bit configuration, thereby allowing a choice to be made at the time of shipment as to the input-output-interface configuration of the semiconductor device. Further, a memory device may be provided with a choice as to how many refresh commands should be input in order to refresh the whole memory cell array, and a desired configuration is selected at the time of shipment of the device.
Such a semiconductor device provided with a selectable device type conventionally uses pads for selecting a device type. This selection is made by bonding a selected pad to a power voltage VCC or a ground voltage VSS.
FIG. 1
is a circuit diagram of a device-type switching mechanism of the related art.
A device-type switching decoder of
FIG. 1
includes NAND circuits
201
through
204
, inverters
205
through
210
, and pads P
1
and P
2
. Depending on what combination of a HIGH (VCC) voltage and a LOW (VSS) voltage is applied to the pads P
1
and P
2
, one of the inverters
205
through
208
outputs a HIGH signal. The outputs of the inverters
205
through
208
correspond to a 4-bit configuration, an 8-bit configuration, a 16-bit configuration, and a 32-bit configuration of an input-output interface, respectively. Before the shipment of the semiconductor device, the semiconductor device needs to be sealed inside a package. During the sealing process, the pads P
1
and P
2
are bonded to the power voltage VCC or the ground voltage VSS. After this bonding, a selected one of the inverters
205
through
208
outputs a HIGH signal when the device is operated. The outputs of the inverters
205
through
208
are supplied to an internal circuit (including an input-output interface circuit) of the semiconductor device, so that the semiconductor device operates based on the selected input-output-interface configuration.
A pad occupies a large area. When pads are used for the switching of a device-type, chip size is bound to increase because of the incorporation of the ability to switch a device type. Within a limited chip size, it is difficult to secure a space for these pads, especially when the number of I/O signals is large.
Moreover, there is a need to examine output signals from a semiconductor device while providing various input signals to the semiconductor device in order to make a final check on operations after the bonding is put in place. When a device type is fixed to a 4-bit configuration by bonding pads, for example, the number of input-output-interface bits is one fourth of that of a 16-bit configuration. When the 4-bit configuration is selected, therefore, the check requires a test time four times as long as that of the 16-bit configuration.
Accordingly, there is a need for a semiconductor device which does not use pads for switching a device type.
There is another need for a semiconductor device which can switch a device type even after a device type is once fixed.
There is yet another need for a method of testing a semiconductor device which requires a relatively short time period when the semiconductor device described above is used.
SUMMARY OF THE INVENTION
Accordingly, it is a general object of the present invention to provide a semiconductor device and a test method which can satisfy the needs described above.
It is another and more specific object of the present invention to provide a semiconductor device which does not use pads for switching a device type.
It is yet another object of the present invention to provide a semiconductor device which can switch a device type even after a device type is once fixed.
In order to achieve the above objects, a semiconductor device according to the present invention includes a device-type switching circuit which determines selection signals based on fuse-cut conditions in a first mode, and determines selection signals based on control signals supplied thereto in a second mode, and an internal circuit having an operation thereof selected by selection signals from device-type switching circuit.
In the semiconductor device described above, an operation of the internal circuit is selected based on the fuse-cut conditions in the first mode, so that pad areas can be reduced compared to a case in which an operation is selected by bonding pads. Further, an operation of the internal circuit is selected based on the control signals in the second mode, so that the operation can be switched as it becomes necessary even after the fuses are cut.
According to one aspect of the present invention, the semiconductor device described above is such that the device-type switching circuit includes a fuse circuit which fixes at least one output thereof according to the fuse-cut conditions, and a device-type selecting circuit which receives the at least one output and the control signals, the device-type selecting circuit determining the selection signals based on the at least one output in the first mode and determining the selection signals based on the control signals in the second mode.
In the semiconductor device described above, the fuse circuit for fixing its output according to the fuse-cut conditions is provided, and, also, the devicetype selecting circuit for determining the selection signals based on the output of the fuse circuit or the control signals is provided. This configuration allows an operation of the device to be switched based on the control signals even after the fuses are cut.
According to another aspect of the present invention, the semiconductor device described above is such that the device-type switching circuit selects one of the first mode and the second mode based on the control signals.
In the semiconductor device described above, the control circuit is used for selecting one of the first mode and the second mode.
According to another aspect of the present invention, the semiconductor device described above is such that the internal circuit selects one of a plurality of input-output-interface configurations in accordance with the selection signals.
In the semiconductor device described above, the input-output-interface configurations of the internal circuit can be determined based on the fuse-cut conditions or the control signals.
According to another aspect of the present invention, the semiconductor device described above further includes a mode-check circuit checking whether an operation mode is a normal operation mode or a test operation mode, and a mode-decoder circuit which generates the control signals by decoding input signals supplied from an external source when the operation mode is the test operation mode, wherein the normal operation mode corresponds to the first mode, and the test operation mode corresponds to the second mode.
In the semiconductor device described above, operations in the normal operation mode are performed by using the input-output-interface configuration which is selected based on the fuse-cut conditions, while the input-output-interface configuration can be switched during the test operation mode in accordance with the externally provided input signals. This allows an input-output-interface configuration having a larger number of input-output bits to be used during the test operation mode, thereby reducing a time required for conducting the test.
It is still another object of the present invention to provide a method of testing a semiconductor device which requires a relatively short time period when the semicon
Fujii Atsushi
Okuda Masaki
Arent Fox Kintner Plotkin & Kahn, PLL
Fujitsu Limited
Shah Kamini
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