Electricity: power supply or regulation systems – Self-regulating – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2000-06-22
2001-05-01
Wong, Peter S. (Department: 2838)
Electricity: power supply or regulation systems
Self-regulating
Using a three or more terminal semiconductive device as the...
Reexamination Certificate
active
06225796
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to electronic circuits and specifically to a zero temperature coefficient bandgap reference circuit and method.
BACKGROUND OF THE INVENTION
Many electronic circuits require a stable and accurate reference voltage for effective operation. Reference voltages, however, may be unstable due to temperature variations caused during circuit operation. To compensate for the temperature dependence of reference voltages, bandgap circuits have been designed to minimize the effect of temperature on the reference voltage. These conventional bandgap circuits compensate for the first order temperature coefficient of a transistor's base to emitter voltage without completely eliminating the temperature dependent characteristics of the circuit. Thus, the base to emitter voltage remains dependent on changing operating and process characteristics.
FIG. 1
a
illustrates a typical bandgap circuit
10
. The current source
12
is designed to increase with temperature using the same type of resistivity as resistor
14
. In other words, as the temperature goes up, the current will also go up and, as a result, the voltage across resistor
14
will go up. The diode
16
, on the other hand, has a negative temperature coefficient. In this case, as the temperature goes up, the voltage across diode
16
will go down. With proper trimming, the circuit
10
can be designed to provide a constant, to the first order, bandgap voltage V
BG
across both resistor
14
and diode
16
.
As illustrated in
FIG. 1
b
, the bandgap voltage V
BG
as function of temperature will not be constant to higher orders. In typical applications, the circuit will be tuned such that it has a zero temperature coefficient at some predetermined temperature T
0
, typically room temperature (e.g., 25° C.). In some applications, this variation creates issues and therefore it is desirable to correct the higher order effects.
Most techniques used in the past to correct the curvature of the bandgap reference usually vary too much with process and introduce extra errors which are not trimmed out. These techniques limit the performance of the bandgap reference at the best of ±1% specification over the full military (e.g., −50° C. to 150° C.) temperature range.
SUMMARY OF THE INVENTION
In one aspect, the present invention provides a new and improved technique to correct the curvature by breaking the temperature range in smaller ranges and optimizing only the first order temperature in each range successively. The curvature shape becomes, after trimming the first order temperature coefficient, a series of much smaller curvatures connected one after another. A temperature detection circuit provides as many break points in temperature as necessary to minimize the temperature variation of the bandgap reference.
In a first aspect, the present invention provides a method of generating a substantially constant voltage. A bandgap reference circuit is trimmed such that a voltage output V
BG
from the bandgap reference circuit is at its peak value when an operating temperature is at its minimum value within a specified operating temperature range. A plurality of additional current sources are also provided with the bandgap reference circuit. Each current source is designed to successively provide additional current as the operating temperature increases within the specified operating temperature range.
As a first exemplary embodiment, a bandgap reference circuit includes a first current source, possibly including a current mirror. A first element has a positive voltage temperature coefficient and a second element has a negative voltage temperature coefficient. These first and second elements are coupled in series such that current provided by the current source flows through the first and second elements. The circuit also includes a plurality of additional current sources and a plurality of switches, each switch including a current path between a respective one of the additional current sources and the first and second elements. The switches are controlled by a temperature detection circuit.
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Brady III Wade James
Laxton Gary L.
Moore J. Dennis
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
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