Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – Fusible link or intentional destruct circuit
Reexamination Certificate
2000-02-09
2001-05-15
Zweizig, Jeffrey (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
Fusible link or intentional destruct circuit
Reexamination Certificate
active
06232823
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a voltage setting circuit used for setting an arbitrary voltage, adjusted by trimming a fuse, in a semiconductor integrated circuit.
2. Description of Related Art
FIG. 11
is a constitutional view of a conventional voltage setting circuit.
As shown in
FIG. 11
, a conventional voltage setting circuit arranged in a semiconductor integrated circuit is composed of a resistor
2
of a resistance valuer r
2
, a resistor
3
of a resistance value r
3
, a resistor
4
of a resistance value r
4
and a resistor
5
of a resistance value r
5
arranged in series in that order, a trimming fuse
7
arranged in parallel to the resistor
2
, a trimming fuse
8
arranged in parallel to the resistor
5
, and an output terminal
9
for outputting an output voltage V
0
of a connection point between the resistors
3
and
4
. A first reference voltage
1
of a voltage value Vref
1
is applied to the resistor
2
, a second first reference voltage
6
of a voltage value Vref
2
is applied to the resistor
5
. The trimming fuses
7
and
8
respectively have a very small resistance value as compared with the resistance values r
2
to r
5
.
An operation of the voltage setting circuit is described. Because the resistance values of the trimming fuses
7
and
8
are very small, the output voltage value V
0
of the output terminal
9
is expressed as follows.
V
0
=(Vref
1
−Vref
2
)/(r
3
+r
4
)*r
4
+Vref
2
(1)
After a wafer process for manufacturing the voltage setting circuit is completed, the trimming fuse
7
or
8
is normally trimmed (or laser-cut) by using a laser beam to adjust the output voltage Vo of the output terminal
9
.
In cases where the trimming fuse
7
is trimmed, the output voltage V
0
is expressed as follows.
V
0
=(Vref
1
−Vref
2
)/(r
2
+r
3
+r
4
)*r
4
+Vref
2
(2)
Also, in cases where the trimming fuse
8
is trimmed, the output voltage value V
0
is expressed as follows.
V
0
=(Vref
1
−Vref
2
)/(r
3
+r
4
+r
5
)*(r
4
+r
5
)+Vref
2
(3)
Therefore, the output voltage V
0
at the output terminal
9
can be adjusted by appropriately trimming one of the trimming fuses
7
and
8
. In this case, the number of choices in the output voltage V
0
is 3 according to three equations (1), (2) and (3) by trimming one of the trimming fuses
7
and
8
in the voltage setting circuit using the four resistors
2
to
5
.
In general, in cases where the number of choices in the output voltage is increased, even though the resistors of the voltage setting circuit are not uniformly formed in the wafer process, the voltage setting circuit in which the output voltage V
0
is precisely set can be provided. Therefore, as shown in
FIG. 12
, in a second conventional voltage setting circuit, two resistors
11
and
12
of resistance values r
11
and r
12
are added, and two trimming fuses
13
and
14
having very small resistance values are added to be parallel to the resistors
11
and
12
. In this voltage setting circuit, the number of choices is 5. Also, in cases where a plurality of trimming fuses can be trimmed, the number of choices is increased to
16
. Therefore, because the number of choices in the output voltage V
0
is increased, even though the resistors are not uniformly formed, a voltage setting circuit in which an output voltage V
0
is precisely set can be provided.
However, in the above conventional voltage setting circuits, though the number of choices in the output voltage can be increased as the number of resistors is increased, an area occupied by the resistors is increased as the number of resistors is increased. Therefore, there is a drawback that a size of the semiconductor integrated circuit is increased.
Also, in cases where values of the output voltage V
0
are set at equal intervals, it is convenient to adjust the output voltage V
0
after the completion of the wafer process.
However, to set values of the output voltage V
0
at equal intervals, it is required to precisely set the resistance values r
2
to r
5
of the resistors
2
to
5
to different values in a design step, so that there is another drawback that the resistance value design for the voltage setting circuit is troublesome.
Also, to obtain the output voltage V
0
with a high precision, it is required to precisely set the resistance values of the resistors. Therefore, there is another drawback that it is difficult to obtain the output voltage V
0
with a high precision after the completion of the wafer process.
SUMMARY OF THE INVENTION
To solve the above drawbacks, a first object of the present invention is to provide a voltage setting circuit in which the number of choices in the output voltage is increased while suppressing the increase of an area occupied by resistors.
Also, a second object is to provide a voltage setting circuit in which a plurality of output voltage values obtainable are set at equal intervals or at almost equal intervals without setting resistance values of resistors to different values.
Also, a third object is to provide a voltage setting circuit in which an output voltage is easily obtained with a high precision after the completion of a wafer process.
To achieve the first object, a voltage setting circuit comprises
a first series element, made of a first trimming fuse and a first resistor, in which a first reference voltage is applied to a first end thereof;
a second series element, made of a second trimming fuse and a second resistor, in which a first end thereof is connected with a second end of the first series element and a second reference voltage is applied to a second end thereof;
a third series element, made of a third trimming fuse and a third resistor, in which a first end thereof is connected with the first end of the first series element;
a fourth series element, made of a fourth trimming fuse and a fourth resistor, in which a first end thereof is connected with a second end of the third series element and a second end thereof is connected with the second end of the second series element;
a first independent resistor in which a first end thereof is connected with the second end of the first series element and a second end thereof is connected with the second end of the third series element; and
a voltage output terminal for outputting a terminal voltage of the second end of the third series element.
In the above configuration, because the first, second, third and fourth series elements and the first independent resistors are arranged in the H shape, the number of choices in the voltage output from the voltage output terminal becomes 5 in the voltage setting circuit using five resistors. Therefore, the number of choices in the output voltage can be increased while suppressing the increase of an area occupied by the resistors.
To achieve the second object, it is preferred that the first resistor, the second resistor, the third resistor, the fourth resistor and the first independent resistor be set to the same resistance value.
In this invention, 5 types of output voltage values obtainable are set at equal intervals without setting resistance values of the resistors to different values. Therefore, the manufacturing of the voltage setting circuit can be simplified, and the output voltage can be easily adjusted.
Also, it is preferred that the voltage setting circuit further comprise voltage multiplying means for multiplying the first reference voltage or the second reference voltage to a multiplied reference voltage according to a terminal voltage applied to the second end of the first series element, wherein the multiplied reference voltage at the first end of the first series element or at the second end of the second series element is output from the voltage output terminal.
In this invention, because the voltage applied to the second end of the first series element is changed by trimming one of the trimming fuses, one voltage value can be selected from a plurality of values
Leydig , Voit & Mayer, Ltd.
Mitsubishi Denki & Kabushiki Kaisha
Zweizig Jeffrey
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