Reference current circuit and reference voltage circuit

Electricity: power supply or regulation systems – Self-regulating – Using a three or more terminal semiconductive device as the...

Reexamination Certificate

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C323S907000, C323S314000

Reexamination Certificate

active

06528979

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a reference current circuit and a reference voltage circuit. More particularly, the present invention relates to a bipolar or CMOS reference current circuit formed on a semiconductor integrated circuit, adapted to prevent an appearance of an effect of an early voltage, and operated from a low voltage to output a reference current having a positive temperature characteristic, alternatively to a bipolar or CMOS reference current circuit for outputting a reference current having an optional temperature characteristic. Furthermore, the present invention relates to a bipolar or CMOS reference voltage circuit operated from a low voltage to output a low reference voltage having no temperature characteristics.
2. Description of the Prior Art
First, description will be made of a conventional art regarding a reference current circuit. A reference current circuit has conventionally been available, which is adapted to prevent an appearance of an effect of such an early voltage, and output a reference current having a fixed temperature characteristic. Examples are a bipolar reference current circuit described in Japanese Patent Application Laid-Open No. 191629/1984, and a bipolar reference current circuit and a CMOS reference voltage circuit described in Japanese Patent Application Laid-Open No. 200086/1995.
Now, an operation of the conventional bipolar reference current circuit will be described.
FIG. 1
shows the bipolar reference current circuit described in Japanese Patent Application Laid-Open No. 191629/1984, which is generally called a proportional to absolute temperature (PTAT) current source circuit because it outputs a current proportional to a temperature. However, the PTAT current source circuit shown in
FIG. 1
is adapted to prevent an appearance of an effect of an early voltage. It is because collectors of respective transistors Q
5
and Q
6
are connected to bases of respective transistors Q
3
and Q
4
and, by setting currents flowing to the transistors Q
3
and Q
4
equal to each other, base baias voltages of the transistors Q
3
and Q
4
can be set equal to each other, and thus collector voltages of the transistors Q
5
and Q
6
are set equal to each other.
In
FIG. 1
, the transistors Q
2
and Q
3
are set as unit transistors, and an emitter area ratio of a transistor Q
1
is set to be K
1
times (K
1
>1) as large as that of the unit transistor. Here, if base width modulation is ignored, a relation between a collector current I
C
of the transistor and a voltage V
BE
between the base and an emitter is represented by the following equation (1):
I
C
=KI
S
exp(
V
BE
/V
T
)  (1)
In this case, I
S
denotes a saturation current of the unit transistor; and V
T
a thermal voltage, which is represented by V
T
=kT/q. Here, q denotes a unit electron charge; k Boltzmann constant; T absolute temperature; and K an emitter area ratio with respect to the unit transistor.
Assuming that a DC current amplification factor of the transistor is sufficiently near 1, by ignoring a base current, in the bipolar inverse Widlar current mirror circuit, from the equation (1), relations thus established are represented by the following equations:
V
BE1
=V
T
ln{
I
C1
/(
K
1
I
S
)}  (2)
V
BE2
=V
T
ln(
I
C2
/I
S
)  (3)
V
BE2
=V
BE1
+R
1
I
C1
  (4)
Now, by solving the equation (4) from the equation (1), a relation of an input/output current of the bipolar inverse Widlar current mirror circuit is obtained by the following equation (5):
I
C2
=(
I
C1
/K
1
)exp(
R
1
I
C1
/V
T
)  (5)
FIG. 2
shows an input/output characteristic of the bipolar inverse Widlar current mirror.
In this case, the transistor Q
3
drives the transistor Q
4
. The transistor Q
4
constitutes a current mirror circuit having a current mirror ratio of 1:1 with the transistors Q
5
and Q
6
. Since the transistors Q
1
and Q
2
are respectively driven by the transistors Q
5
and Q
6
, the bipolar self-biased inverse Widlar reference current circuit is provided, and a relation is represented by the following equation (6):
I
C2
=I
C1
  (6)
In the bipolar inverse Widlar current mirror circuit, a mirror current I
C2
is exponentially increased with respect to an increase of a reference current I
C1
. Thus, if an operation point is (I
p
=(V
T
/R
1
)ln K
1
=I
C1
=I
C2
), then I
C1
>I
C2
is established with I
p
>I
C1
, and I
C1
<I
C2
is established with I
p
<I
C1
. Accordingly, when Ip+&Dgr;I (&Dgr;I>0) is supplied to the transistors Q
4
to Q
6
, I
C4
=I
C6
=I
C1
=Ip+&Dgr;I is established. However, since I
C2
>I
C5
=Ip+&Dgr;I is established to cause a shortage of current supplied from the transistor Q
5
, the base current of the transistor Q
3
is pulled, and the transistor Q
3
turns off. Thus, a current flowing to the transistor Q
3
is reduced, and currents of the transistors Q
4
to Q
6
are also reduced to return to IP. Conversely, when I
p
−&Dgr;I (&Dgr;I>0) is supplied to the transistors Q
4
to Q
6
, I
C4
=I
C6
=I
C1
=I
p
−&Dgr;I is established. However, since I
C2
<I
C5
=Ip−&Dgr;I is established to cause a current supplied from the transistor Q
5
to be excessive, a current is pushed into the base of the transistor Q
3
, and the transistor Q
3
turns on. Accordingly, a current flowing to the transistor Q
3
is increased, and currents of the transistors Q
4
to Q
6
are also increased to return to I
p
. That is, a negative feedback current loop is constituted, an operation point is uniquely decided with I
C1
>0, realizing a stable operation.
In addition, since the following equation (7) is established,
Δ



V
BE
=


V
BE2
-
V
BE1
=
V
T

ln

(
I
Cl
/
I
S
)
-
V
T

ln

{
I
C2
/
(
K
1

I
S
)
=


V
T

ln

(
I
Cl
/
I
C2
)
=
V
T

ln

(
K
1
)
=
R
1

I
Cl
(
7
)
an equation (8) is obtained:
I
C1
=I
C2
=(
V
T
/R
1
)ln(
K
1
)  (8)
Here, K
1
denotes a constant having no temperature characteristics and, as described above, the thermal voltage V
T
is represented by V
T
=kT/q, exhibiting a temperature characteristic of 3333 ppm/° C. Accordingly, if a temperature characteristic of a resistor R
1
is smaller than that of the thermal voltage V
T
, exhibiting a primary characteristic with respect to a temperature, an output current I
0
of the reference current circuit outputted through the current mirror circuit is proportional to the temperature, realizing a PTAT current source circuit. In this case, since currents flowing to the transistors Q
1
to A
3
are all equal to one another, base bias voltages of the transistors Q
2
and Q
3
are also equal to each other. Thus, since collector voltages of the transistors Q
5
and Q
6
are fixed with these base bias voltages of the transistors Q
2
and Q
3
, and equally set, no effects of Early voltages of the transistors Q
1
and Q
2
appear. Since no changes occur in a desired current mirror ratio even if the collector voltages of the transistors Q
5
and Q
6
are changed to cause an appearance of effects of Early voltages, a highly accurate current output having only small changes with respect to fluctuation in a power supply voltage is obtained.
Next, a conventional art regarding a reference voltage circuit will be described. A reference voltage circuit having no temperature characteristics because of cancellation, and adapted to output a reference voltage of 1.2 V or lower has conventionally been available. An example is described in IEEE Journal of Solid-State Circuits, Vol. 32, No. 11, pp.1790 to 1806, November 1997.
First, an operation of this exemplary reference voltage circuit will be described.
FIG. 3
shows the reference voltage circuit described in IEEE Journal of Solid-State Circuits, Vol. 32, No. 11, pp. 1790 to 1806, November 1997. A c

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