Electricity: power supply or regulation systems – Self-regulating – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2002-04-29
2003-09-02
Riley, Shawn (Department: 2838)
Electricity: power supply or regulation systems
Self-regulating
Using a three or more terminal semiconductive device as the...
C327S513000, C327S539000
Reexamination Certificate
active
06614209
ABSTRACT:
BACKGROUND OF THE INVENTION
1. The Field of the Invention
The present invention relates to the field of bandgap voltage reference circuits. In particular, the present invention relates to circuits and methods for providing a bandgap voltage reference less dependent on or independent of a resistor ratio.
2. The Prior State of the Art
The accuracy of circuits often depends on access to a stable bandgap voltage reference. Accordingly, numerous bandgap voltage reference circuits have been developed. Bandgap voltage reference circuits will also be referred to herein as “bandgap references.” A traditional bandgap reference generates a bandgap voltage reference that is stable with temperature by summing a relatively small Proportional To Absolute Temperature (PTAT) voltage (V
PTAT
) with a base-emitter voltage (V
BE
) of a bipolar transistor to generate a bandgap reference voltage that is stable with temperature.
FIG. 1
schematically illustrates a conventional bandgap reference
100
in accordance with the prior art. The bandgap reference
100
includes a PTAT voltage generator
101
that generates the PTAT voltage V
PTAT
. The PTAT voltage generator
101
is coupled to a bipolar transistor, which is in turn coupled to a current bias
103
as illustrated. The result is an output voltage V
OUT
that is equal to the sum of V
PTAT
and V
BE
. The positive temperature drift of V
PTAT
largely compensates for the negative temperature drift of V
BE
thus resulting in the output voltage V
OUT
being relatively stable with temperature.
FIG. 2
illustrates a conventional PTAT voltage generator
200
, which may be the PTAT voltage generator
101
of FIG.
1
. The PTAT voltage generator
200
includes four equivalently-sized bipolar transistors
201
through
204
coupled together as shown, and having an emitter terminal coupled to a corresponding current source
211
through
214
. The current sources
211
and
212
are “M” times the magnitude of the current sources
213
and
214
. The emitter terminals of the bipolar transistors
202
and
203
are each coupled to an input of an operational amplifier
224
. The output of the amplifier
224
is coupled to ground via a series of elements that includes a resistor
222
having a resistance R
2
, a resistor
221
having a resistance R
1
, and a bipolar transistor
223
, as shown.
In the illustrated configuration, the voltage across the resistor
221
, which will be referred to as V
1
, is defined by the following Equation (1).
V
1
=2
U
T
ln
(
M
) (1)
where,
M is equal to the current ratio between current sources
211
and
212
and current sources
213
and
214
; and
U
T
is often referred to as the “thermal voltage” and is equal to
kT
q
.
Note that k is Boltzmann's constant (1.38×10
−23
Joules(J)/Kelvin(K) or 8.62×10
−5
electron volts (eV)/K), T is temperature in degrees Kelvin, and q is the magnitude of charge of an electron (1.60×10−19 Coulombs(C)). In addition, the voltage across both,resistors
221
and
222
, which will be referred to as V
PTAT
, is defined by the following Equation (2).
V
PTAT
=
(
1
+
R
1
R
2
)
2
U
T
ln
(
M
)
(
2
)
In order to compensate for the negative temperature drift of the bipolar transistor
102
, the PTAT voltage generator
101
needs a PTAT voltage V
PTAT
of approximately 33ln(2)U
T
. The resistor ratio R
1
/R
2
of the PTAT voltage generator
200
may thus be adjusted so that the PTAT voltage V
PTAT
approximates 33ln(2)U
T
. In the case of the design in
FIG. 2
with the density ratio M being 100, the resistor ratio R
1/R
2
would be approximately 1.48. Although there are a variety of circuits for providing a PTAT voltage, such circuits typically employ a resistor ratio in order to provide the needed level of positive temperature shift.
Resistors can often take up significant chip space. With integrated circuits becoming increasing compact and complex, there is an effort to reduce the size of circuitry where possible. Accordingly, what is desired are circuits and methods for providing a bandgap voltage reference in a more compact fashion.
SUMMARY OF THE INVENTION
The foregoing problems in the prior state of the art have been successfully overcome by the present invention, which is directed to circuits for providing a bandgap voltage reference that is less dependent on a resistor ratio. By reducing the dependency on the resistor ratio, the resistor ratio may be lowered thereby reducing the size of the resistors that generate the resistor ratio. In one embodiment, the dependency on a resistor ratio is eliminated completely, in which case there is not need for a resistor ratio at all.
Conventional bandgap voltage references use a single Proportional To Absolute Temperate (PTAT) source to generate a small PTAT voltage. That voltage is then added to a base-emitter voltage of a bipolar transistor to generate an accurate bandgap voltage. Conventional PTAT sources typically use a resistor ratio to generate the PTAT voltage. However, contrary to conventional technology, the principles of the present invention use more than one PTAT source coupled in series. The PTAT voltage generated by all previous PTAT sources in the series are added to the supplemental PTAT voltage generated by the next PTAT source in the series, and so forth, until the final PTAT voltage has been generated by the terminating PTAT source in the series.
One might think that the addition of supplemental PTAT sources might increase the size of the overall bandgap generation circuit. However, in many applications, the bandgap voltage references in accordance with the present invention may be made smaller when factoring in that the resistor ratio dependency is reduced or even eliminated.
Additional features 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 the practice of the invention. The features and advantages of the invention may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. These and other features and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.
REFERENCES:
patent: 4636710 (1987-01-01), Stanojevic
patent: 5325045 (1994-06-01), Sundby
patent: 6121824 (2000-09-01), Opris
patent: 6137341 (2000-10-01), Friedman et al.
patent: 6259307 (2001-07-01), Aram
A CMOS Temperature-Compensated Current Reference, Willy M. Sansen, Frank Opt Eynde and Michiel Steyaert, IEEE Journal of Solid-State Circuits, vol. 23, No. 3, Jun. 1988, pp. 821-824.
A CMOS Voltage Reference, Yannis P. Tsividis and Richard W. Ulmer, IEEE Journal of Solid-State Circuits, vol. SC-13, No. 6, Dec., 1978, pp. 774-8.
AMI Semiconductor Inc.
Riley Shawn
Workman & Nydegger & Seeley
LandOfFree
Multi stage circuits for providing a bandgap voltage... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Multi stage circuits for providing a bandgap voltage..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Multi stage circuits for providing a bandgap voltage... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3001602