Active solid-state devices (e.g. – transistors – solid-state diode – Bipolar transistor structure
Reexamination Certificate
2001-03-14
2003-08-26
Thomas, Tom (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Bipolar transistor structure
C257S566000, C257S205000, C257S401000
Reexamination Certificate
active
06611043
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a bipolar transistor suitable for a reference voltage source circuit used as a power source circuit for integrated circuits and the like, and a semiconductor device having the same, and more specifically to a bipolar transistor designed to stabilize reference voltage output when applied in a reference voltage source circuit, and a semiconductor device having the same.
2. Description of the Related Art
It is necessary to raise the relative precision of the element and the absolute precision of the resistance, when providing a semiconductor device with a reference voltage source circuit. Therefore, conventionally, it has been common to manufacture the reference voltage source circuit by means of a bipolar process used very often and chiefly in analog circuits. This is because since an analog circuit was held to be necessary for the reference voltage source circuit, there was no choice but to use a bipolar process.
Recently, however, as circuits have become integrated, analog circuits have also started to be built into CMOS processes used in digital circuits. This has made it necessary to incorporate reference voltage source circuits into the CMOS process.
FIG. 1
is a circuit diagram showing a conventional reference voltage source circuit. The conventional reference voltage source circuit is provides with two PNP transistor groups GQ
31
and GQ
32
, whose collectors and bases are grounded. A resistor RE
33
and a resistor RE
32
are connected to the emitter of the PNP transistor group GQ
32
in series, in that order. Additionally, a resistor RE
31
is connected to the emitter of the PNP transistor group GQ
31
. Further, the input terminals of an amplifier AMP
31
are connected to the connection point of the emitter of the PNP transistor group GQ
31
and the resistor RE
31
, and to the connection point of the resistor RE
32
and the resistor RE
33
. The other end of the resistor RE
32
and the other end of the resistor RE
31
have a common connection, and this connection point is connected to the output terminal of the amplifier AMP
31
. Further, an output voltage terminal OUT
31
is connected to the output terminal of the amplifier AMP
31
. Note that the amplifier AMP
31
is composed of a CMOS transistor and the like.
Both of the PNP transistor groups GQ
31
and CQ
32
are composed of a plurality of PNP transistors.
FIG. 2
is a layout diagram showing a layout of PNP transistors making up the PNP transistor groups GQ
31
and GQ
32
. Below, the reference voltage source circuit described here in
FIG. 2
shall be called as a first prior art.
As shown in
FIG. 2
, the PNP transistor group GQ
31
comprises three PNP transistors Q
111
through Q
113
arrayed in a vertical column, and the PNP transistor group GQ
32
comprises nine PNP transistors Q
121
through Q
129
arrayed in three rows and three columns. In each of the PNP transistors Q
111
through Q
113
and Q
121
through Q
129
, an emitter electrode
106
is connected to the central portion of an emitter
103
. A base
102
is formed around the periphery of the emitter
103
, and within base
102
, base electrodes
107
are connected on either side of the emitter
103
, in the row direction as seen from the emitter
103
. A collector
101
is common to each of the PNP transistors, and collector electrodes
108
are connected on either side of the base
102
of each PNP transistor, in the row direction as seen from the base
102
. Note that each of the PNP transistors has the same emitter surface area. As the PNP transistor group GQ
32
includes the nine PNP transistors Q
121
through Q
129
while the PNP transistor group GQ
31
includes the three PNP transistors Q
111
through Q
113
, the total emitter area of the PNP transistor group GQ
32
is three times that of the PNP transistor group GQ
31
.
The reference voltage Vout output of a conventional reference voltage source circuit constructed in this way is shown in Formula 1 shown below, where the resistance of the resistor RE
31
and RE
32
is y, the resistance of the resistor RE
33
is x, the voltage between the emitter and base of the PNP transistor group GQ
31
is VEBGQ
31
, the total emitter surface area of the PNP transistor group GQ
31
is M, the total emitter surface area of the PNP transistor group GQ
32
is N, the Boltzmann's constant is k, the absolute operating temperature is T, the elementary electric charge is q.
Vout
=
VEBG31
+
y
x
·
k
·
T
q
·
log
e
(
N
M
)
[Formula 1]
Thus, reference voltage Vout fluctuates depending on the resistance ratio of the resistors (y/x), and the total emitter area ratio of the transistors (N/M). Consequently, even if the absolute values of the resistance x and y, and total emitter surface area N and M, change, as long as their respective ratios do not change, the reference voltage Vout will be stable. Under these circumstances, since, in the first prior art, the PNP transistor groups Q
31
and Q
32
are composed of a plurality of transistors, even if a number of these had low levels of precision, the impact on the overall relative precision would be slight. For this reason, as described above the reference voltage Vout is stable. Consequently, constructing a transistor group from a plurality of transistors facilitates the manufacture of a reference voltage source circuit with stable reference voltage.
Additionally, as the number of each electrode is kept down, the amount of space they take up on the chip is small. An array of the PNP transistors as shown in
FIG. 2
is described, for example, in the literature “A Precision Curvature-Compensated CMOS Bandgap Reference” (cited from: P634-643 IEEE JURNAL OF SOLID-STATE CIRCUITS, VOL. SC-18, No. 6, December 1983). The reference voltage source circuit described in this literature provides a separate external resistor in order to compensate from the gap from DC operation.
In another prior art from the literature, a reference voltage source circuit with a construction in which a plurality of transistors arrayed in a column have a collector in common is described in “A Precision CMOS Bandgap Reference” (cited from: IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL, SC-19, No. 6, December 1984 P1014-1021). The conventional reference voltage source circuit described below shall be called a second prior art.
FIG.3
shows a layout diagram of the reference voltage source circuit according to the second prior art.
Two transistor groups GQ
41
and GQ
42
are provided in the second prior art. The transistor group GQ
41
is made up of five transistors Q
131
through Q
135
forming a column, and the transistor group GQ
42
is made up of twenty-five transistors Q
141
through Q
165
forming five rows and five columns. Consequently, the total emitter surface area ratio of the transistor group GQ
41
to the transistor group GQ
42
is 1:5.
Note that while the above-mentioned reference in the literature does not describe the electrode arrangement and the like of each transistor in detail, it is thought that the five transistors forming a column have a collector
111
in common, and that a base electrode
117
and an emitter electrode
116
in a group of one row are alternately arrayed.
Additionally, Japanese Patent Laid-Open Publication No. Hei. 6-151705 discloses a bandgap generator circuit provided with a transistor group made up of a plurality of transistors in a square formation when seen from the plane. Below, this conventional bandgap generator circuit shall be called as a third prior art.
In the third prior art, the four transistors in a square formation are laid out in a square lattice formation. The four transistors have a collector and a base in common.
In the first prior art, however, since there is a large amount of parasitic resistance on the base and collector in each transistor, there is a problem in that the size of resistors RE
31
and RE
32
must be increased, and the current flowing through the transistor group GQ
31
and GQ
32
must be decreased, in order for the tr
Gebremariam Samuel A.
NEC Corporation
Thomas Tom
LandOfFree
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