Low voltage bandgap reference circuit

Details Low voltage bandgap reference circuit Low voltage bandgap reference circuit

2000-08-18

2002-07-30

Cunningham, Terry D. (Department: 2816)

Miscellaneous active electrical nonlinear devices, circuits, and

Specific identifiable device, circuit, or system

With specific source of supply or bias voltage

C327S540000, C323S313000

Reexamination Certificate

active

06426669

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to semiconductor integrated circuits and, in particular, to a bandgap reference circuit that is capable of having output voltages below the nominal bandgap value and of being operated from very low supply voltages with a simple, one temperature trim procedure.
2. Discussion of the Related Art
In prior implementations of low voltage bandgap reference circuits, a proportional-to-absolute-temperature (PTAT) current is added to a current that is proportional to a base-emitter voltage V
BE
such that a constant current is applied to a resistor, thereby creating a constant voltage. Some designs of this type include a buffer amplifier.
The major disadvantages of this design approach lie in the Early voltage error in the current sources and in the difficulty of implementing a precision buffer amplifier for very low supply voltages. Another disadvantage of this prior art is the difficulty of trimming the ratio of the PTAT and V
BE
currents in an integrated circuit production environment. Two temperatures are usually required to obtain a low temperature coefficient.
SUMMARY OF THE INVENTION
The present invention provides a bandgap circuit capable of having an output voltage below a nominal bandgap value (1.206V) and of being operated from very low supply voltages.
In a bandgap voltage reference circuit in accordance with the present invention, the different-sized emitters of the two bipolar devices of a &Dgr;V
BE
stage return to ground (or other bias voltage) through separate resistors. The V
BE
term of the reference device is supplied by a V
BE
current source through a third resistor. The proportional-to-absolute-temperature (PTAT) term of the reference occurs as the difference of base-emitter voltages &Dgr;V
BE
between the larger and smaller emitters. An output voltage V
out
multiplier resistor feeds to the larger emitter through an inverting amplifier. In one embodiment of the invention, the output voltage V
out
trim at one temperature is obtained by trimming the base-emitter resistor of the “small emitter” device to compensate for the V
BE
process variation.


REFERENCES:
patent: 4887022 (1989-12-01), Gontowski
patent: 5068606 (1991-11-01), Kawate et al.
patent: 5424628 (1995-06-01), Nguyen
patent: 5488289 (1996-01-01), Yeung
patent: 5715532 (1998-02-01), Sagawa et al.
patent: 5926062 (1999-07-01), Kuroda
patent: 5945873 (1999-08-01), Antone et al.
patent: 6144250 (2000-11-01), Owen et al.
patent: 6278326 (2001-08-01), Murray et al.
A Curvature-Corrected Low-Voltage Bandgap Reference, Gunawan, et al., 1993.

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