Electricity: power supply or regulation systems – Self-regulating – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2000-06-28
2001-11-27
Berhane, Adolf Deneke (Department: 2838)
Electricity: power supply or regulation systems
Self-regulating
Using a three or more terminal semiconductive device as the...
C363S073000
Reexamination Certificate
active
06323630
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a reference voltage generation circuit and reference current generation circuit in a semiconductor device, and more particularly to a reference voltage generation circuit and reference current generation circuit constituted by MOS transistors in a semiconductor device using, for example, a reference voltage lower than the power supply voltage.
A band gap reference (BGR) circuit has been known as a less temperature-dependent, less power-supply-voltage-dependent reference voltage generation circuit. The name of the circuit has come from generating a reference voltage almost equal to the silicon's bandgap value of 1.205V. The circuit is often used to obtain highly-accurate reference voltages.
With a BGR circuit constituted by conventional bipolar transistors in a semiconductor device, the forward voltage (with a negative temperature coefficient) at a p-n junction diode or the p-n junction (hereinafter, referred to as the diode) between the base and emitter of a transistor whose collector and base are connected to each other is added to a voltage several times as high as the voltage difference (having a positive temperature coefficient) of the forward voltages of the diodes differing in current density in order to output a voltage of about 1.25V with a temperature coefficient of nearly zero.
At present, the voltage on which semiconductor devices operate is getting lower. When the output voltage of a BGR circuit was about 1.25V, the lower limit of the power supply voltage was 1.25V+&agr;. Consequently, however small &agr; may be made, the semiconductor device could not be operated on the power supply voltage of 1.25V or lower.
The reason for this will be explained in detail.
FIG. 1
shows the basic configuration of a first conventional BGR circuit constituted by n-p-n transistors.
In
FIG. 1
, Q
1
, Q
2
, and Q
3
indicate n-p-n transistors, R
1
, R
2
, and R
3
resistance elements, and I a current source. Furthermore, V
BE1
, V
BE2
, and V
BE3
represent the base-emitter voltages of the transistors Q
1
, Q
2
, and Q
3
respectively, and V
ref
the output voltage (reference voltage).
When the transistors Q
1
, Q
2
have the same characteristics, the emitter voltage V
2
of the transistor Q
2
is:
V
2
=V
BE1
-V
BE2
=V
T
·ln(I
1
/I
2
) (1)
This gives:
V
ref
=V
BE3
+(R
3
/R
2
)V
2
=V
BE3
+(R
3
/R
2
)V
T
·ln(I
1
/I
2
) (2)
The first term in equation (2) has a temperature coefficient of about −2 mV/° C. In the second term in equation (2), the thermal voltage V
T
is:
V
T
=k·T/q (3)
Thus, the temperature coefficient is expressed as:
(R
3
/R
2
)(k/q)ln(I
1
/I
2
) (4)
To find the condition for making the temperature coefficient of V
ref
zero, substituting
k=1.38×10
−23
J/K (5)
q=1.6×10
−19
C (6)
This gives:
(R
3
/R
2
)ln(I
1
/I
2
)=23.2 (7)
In equation (2), if V
BE3
=0.65V at 23° C.,
then V
ref
=0.65+0.6=1.25V (8)
This value is almost equal to the bandgap value (1.205) of silicon.
The BGR circuit of
FIG. 1
has disadvantages in that its output voltage is fixed at 1.25V and its power supply voltage cannot be made lower than 1.25V.
FIG. 2
shows the basic configuration of a second conventional BGR circuit using no bipolar transistor.
The BGR circuit is constituted by a diode D
1
, an N number of diodes D
2
, resistance elements R
1
, R
2
, R
3
, a differential amplifier circuit DA
1
constituted by CMOS transistors, and a PMOS transistor T
p
.
The voltage V
A
at one end of the diode D
1
is supplied to the—side input of the differential amplifier circuit DA
1
and the voltage V
B
at one end of the diode D
2
is supplied to the +side input of the circuit DA
1
, so that feedback control is performed such that V
A
is equal to V
B
(the voltages at both ends of R
1
is equal to those of R
2
).
Thus, I
1
/I
2
=R
2
/R
1
(9)
The characteristics of the diode are expressed by the following equations:
I=Is{e
(q·V
F
/k·T)
−1} (10)
V
F
>>q/k·T=26 mV (11)
where Is is the (reverse) saturation current and V
F
is the forward voltage.
From equation (11), −1 in equation (10) can be ignored. This gives:
V
F
=V
T
·ln(I/Is) (12)
The voltage across the resistance element R
3
is:
dV
F
=V
F1
-V
F2
=V
T
·ln(N·I
1
/I
2
)
=V
T
·ln(N·R
2
/R
1
) (13)
The thermal voltage V
T
has a positive temperature coefficient k/q=0.086 mV/° C. and the forward voltage V
F1
of the diode D
1
has a negative temperature coefficient of about −2 mV/° C.
Then, under the following conditions:
V
ref
=V
F1
+(R
2
/R
3
)dV
F
(14)
V
ref
/
T=0 (15)
the resistance values of the resistance elements R
1
, R
2
, and R
3
are set.
As an example, if N=10, R
1
=R
2
=600 k&OHgr;, and R
3
=60 k&OHgr;, dV
F
will be the voltage difference between diode D
1
and diode D
2
whose current ratio is 1:10. This will give:
V
ref
=V
F1
+10·dV
F
=1.25V (16)
Like the first conventional circuit, the second conventional circuit has disadvantages in that its output voltage is fixed at 1.25V (or invariable) and the power supply voltage used cannot be made lower than 1.25V.
As described above, conventional BGR circuits that generate a less temperature-dependent, less power-supply-voltage-dependent reference voltage have disadvantages in that their output voltage is fixed at about 1.25V and they cannot be operated on a power supply voltage lower than about 1.25V.
BRIEF SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention is to provide a reference voltage generation circuit capable of generating a less temperature-dependent, less power-supply-voltage-dependent reference voltage at a given low voltage in the range of a supplied power-supply voltage and further operating on a voltage lower than 1.25V.
It is anther object of the present invention to provide a reference current generation circuit capable of generating a less temperature-dependent, less power-supply-voltage-dependent reference current.
According to one aspect of the present invention, there is provided a reference voltage generation circuit comprising a first current conversion circuit for converting a forward voltage of a p-n junction into a first current proportional to the forward voltage; a second current conversion circuit for converting a voltage difference between forward voltages of p-n junctions differing in current density into a second current proportional to the voltage difference; and a current-to-voltage conversion circuit for converting a third current obtained by adding the first current from the first current conversion circuit to the second current from the second current conversion circuit into a voltage, wherein MIS transistors are used as active elements other than the p-n junctions.
According to another aspect of the present invention, there is provided a reference current generation circuit comprising a first current conversion circuit for converting a forward voltage of a p-n junction into a first current proportional to the forward voltage; a second current conversion circuit for converting the voltage difference between forward voltages of p-n junctions differing in current density into a second current proportional to the voltage difference; and a current add circuit for adding the first current from the first current conversion circuit to the second current from the second current conversion circuit, wherein MIS transistors are used as active elements other than the p-n junctions.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the in
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