Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – With specific source of supply or bias voltage
Reexamination Certificate
1999-08-03
2001-05-15
Kim, Jung Ho (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
With specific source of supply or bias voltage
C323S313000
Reexamination Certificate
active
06232828
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to bandgap reference voltage generator circuits, and in particular, to bandgap-based reference voltage generator circuits with compensation for reducing the temperature coefficient.
2. Description of the Related Art
Electronic systems which require a precision reference voltage typically use a bandgap voltage reference circuit, which is advantageously capable of operating with a low power supply potential. As is well known, the basic principle of a bandgap voltage reference circuit is based upon the summation of the negative temperature drift of the base-emitter voltage (Vbe) of a bipolar junction transistor with an appropriate magnitude of a positive temperature drift of a thermal voltage (Vt) in order to achieve a net zero temperature drift sum.
Referring to
FIG. 1
, a conventional bandgap reference circuit includes two bipolar junction transistors Q
2
, Q
3
biased by a voltage divider circuit composed of resistors R
1
, R
2
, R
3
and a diode-connected transistor Q
1
and a current sinking circuit IS. The size of the emitter area of transistor Q
2
is ten times the size of the emitter area of transistor Q
3
. The collector currents of these transistors Q
2
, Q
3
are amplified differentially by a differential transconductance amplifier which produces the bandgap reference voltage Vbg (Vref), which, in turn, drives the voltage divider circuit. The diode-connected transistor Q
1
introduces a voltage into the voltage divider circuit which has a negative temperature coefficient. The difference between the base-emitter voltages Vbe of transistors Q
2
, Q
3
(&Dgr;Vbe=Vbe(Q
3
)−Vbe(Q
2
)) has a positive temperature coefficient. The value of the resulting bandgap voltage Vbg (Vref) can be determined in accordance with Equation 1:
Vref
=
Vbg
=
V
be
-
Q
1
+
(
1
+
R
1
+
R
3
R
2
)
Δ
V
be
Where
Δ
V
be
=
V
be
-
Q
3
-
V
be
-
Q
2
=
kT
q
ln
A
,
V
be
-
Q
1
=
kT
q
ln
IE1
IES
,
k
/
q
=
8.6167
×
10
-
5
I
ES
=
RT
m
ⅇ
-
qV
G0
kT
,
I
E1
=
Δ
V
be
R
2
1
Equation 1 can be rearranged and written as Equation 2:
Vbg
=
V
G0
+
kT
q
[
(
1
+
R
1
+
R
3
R
2
)
ln
A
+
ln
k
ln
A
qRR
2
-
(
m
-
1
)
ln
T
]
2
To establish a zero temperature coefficient (OTC) at the expected operating temperature (T
0
) Equation 2 is differentiated and set equal to zero. This produces Equations 3 and 4:
&AutoLeftMatch;
∂
Vbg
∂
T
&RightBracketingBar;
T
=
T
0
=
k
q
[
(
1
+
R
2
+
R
3
R
2
)
ln
A
+
ln
k
ln
A
qRR
2
-
(
m
-
1
)
ln
T
]
+
kT
q
&AutoLeftMatch;
[
m
-
1
T
]
&RightBracketingBar;
T
=
T
0
=
0
3
(
1
+
R
1
+
R
3
R
2
)
ln
A
=
(
m
-
1
)
-
ln
k
ln
A
qRR
2
T
m
-
1
4
Substituting Equation 4 into Equation 2 produces Equation 5 which defines the reference voltage Vref:
Vref
=
Vbg
=
V
G0
+
kT
q
(
m
-
1
)
-
kT
q
(
m
-
1
)
ln
T
T
0
5
Referring to
FIG. 2
, the reference voltage Vref with respect to temperature T is graphed in accordance with Equation 5. From this graph it can be seen that, assuming a bandgap energy voltage V
G0
=1.12 V, a constant m=5, an emitter-base junction constant of R=0.2818, an emitter area ratio A=10 and an operating temperature T
0
=20° C., the reference voltage Vref has a temperature coefficient of approximate 12.6 ppm/° C.
However, as the precision requirements for the operating characteristics of modem electronic systems increase, particular as the magnitude of the available power supply voltage decreases, temperature coefficients of such magnitude become increasingly unacceptable. Accordingly, it would be desirable to have a bandgap-based reference voltage generator circuit with compensation which provides for significantly reduced temperature coefficients. Additionally, it would be further desirable to be able to adjust such compensation and provide for such compensation using standard semiconductor processing techniques.
SUMMARY OF THE INVENTION
A bandgap-based reference voltage generator circuit in accordance with the present invention provides an increased output reference voltage and a reduced temperature coefficient. Such a circuit uses circuit components commonly available with standard semiconductor processing techniques. A temperature coefficient curvature correction voltage is generated based upon an IR (current times resistance) voltage drop. The resistance R exhibits a natural curvature over temperature and nonlinear cross products of the IR voltage drop provide for fine tuning of such curvature. This curvature correction voltage is provided as a separate and independent bias voltage that is introduced externally to a standard bandgap reference voltage generator circuit, thereby providing a simpler solution than those in which components with high temperature coefficients are integrated internally to the bandgap reference voltage generator circuit. This correction voltage can be turned off without adversely affecting standard bandgap circuit operation, and the first order temperature coefficient of the correction voltage curvature can be adjusted to be sufficiently minimized so as to not skew the temperature coefficient operation of the standard bandgap circuit. This is done by selecting the temperature coefficient of the current (TCI) to be the approximate inverse (−TCR) of the temperature coefficient for the resistor (TCR), thereby making the overall current-times-resistance (IR) temperature coefficient extremely low.
In accordance with one embodiment of the present invention, a bandgap-based reference voltage generator circuit with an increased output reference voltage and a reduced temperature coefficient includes a bandgap voltage generator circuit and a control voltage generator circuit. The bandgap voltage generator circuit is configured to receive a bandgap-based reference voltage and a curvature correction control voltage and in accordance therewith provide the bandgap-based reference voltage with a first arcuate voltage-versus-temperature characteristic having a first direction of incurvature. The control voltage generator circuit, coupled to the bandgap voltage generator circuit, is configured to provide the curvature correction control voltage with a second arcuate voltage-versus-temperature characteristic having a second direction of incurvature which is substantially opposite the first direction of incurvature.
In accordance with another embodiment of the present invention, a bandgap-based reference voltage generator circuit with an increased output reference voltage and a reduced temperature coefficient includes: a bias voltage generator circuit; a voltage divider circuit; first and second circuit branches; a differential amplifier circuit; a current source circuit; and a resistive circuit element. The bias voltage generator circuit is configured to receive a curvature correction control voltage and in accordance therewith provide a bias voltage, wherein a voltage difference between the curvature correction control voltage and the bias voltage has a negative temperature coefficient. The voltage divider circuit, coupled to the bias voltage generator circuit, is configured to receive the bias voltage and a bandgap-based reference voltage and in accordance therewith provide first and second intermediate voltages. The first and second circuit branches, coupled to the voltage divider circuit, are configured to receive the first and second intermediate voltages and in accordance therewith conduct first and second substantially equal branch currents at first and second substantially unequal current dens
Chen Yinming
Smith Gregory J.
Baker & McKenzie
Kim Jung Ho
National Semiconductor Corporation
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