Bandgap reference circuit for improved start-up

Details Bandgap reference circuit for improved start-up Bandgap reference circuit for improved start-up

2002-12-02

2004-03-23

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

C327S513000, C323S313000

Reexamination Certificate

active

06710641

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a bandgap reference circuit that operates with low voltage.
BACKGROUND OF THE INVENTION
Bandgap reference voltage generators are used in DRAMs, flash memories and analog devices and are required to provide stable voltages over a wide range of voltage supplies and temperatures. Increasing demand for use of lower supply voltages will soon push the supply voltage below 1.25 Volts, the standard for which bandgap reference circuits are now designed. A conventional bandgap reference circuit includes three sections: a core where an input voltage is developed and conditioned, a bandgap generator, and a current generator. This circuit must operate with a supply voltage that is at least a few hundred millivolts (mV) above the desired bandgap voltage (≈1.25 Volts).
FIG. 1
illustrates a conventional bandgap reference circuit
10
having a core region
11
, a bandgap generator region
21
and a current generator region
31
. The core region
11
includes two PMOS transistors,
12
and
13
, connected at their sources to a voltage supply
14
and connected at their drains to negative and positive input terminals of a first operational amplifier
15
whose output terminal is connected to the gates of the first and second transistors,
12
and
13
. First and second matched bipolar transistors,
16
and
17
, have collectors and bases connected to ground. The emitters of the first and second bipolar transistors,
16
and
17
, are connected to the drain of the first PMOS transistor
12
and through a first resistor
18
to the drain of the second PMOS transistor
13
, respectively.
The bandgap voltage generator region
21
includes a third PMOS transistor
22
, with source connected to the voltage supply
14
and gate connected to the output terminal of the op amp
15
. The drain of the third PMOS transistor
22
is connected through a second resistor
23
to the emitter of a third bipolar transistor
24
, whose collector and base are grounded.
The current generator region
31
includes a fourth PMOS transistor
32
with sources connected to the voltage supply
14
and gate connected to an output terminal of a second op amp
34
. A negative input terminal of the second op amp
34
is connected to the drain of the third PMOS transistor. A positive input of the second op amp
34
and the drain of the fourth transistor
32
are connected through a third resistor
35
to ground. The fifth transistor
33
serves as a source for a current I
out
. This device requires two operational amplifiers, at least five PMOS transistors, and a supply voltage that is at least about 400 mV above a target bandgap reference voltage.
If the supply voltage is decreased to 1.2 V and below, the standard bandgap voltage of 1.25 V can no longer be maintained. What is needed is a bandgap reference circuit that allows operation with supply voltages as low as about 1 V, or preferably lower, and that has no more than one or two stable operating points.
SUMMARY OF THE INVENTION
These needs are met by the invention, which provides a bandgap reference circuit that operates with a supply voltage of about 1 V and that has one stable operating point, unless all currents in the system are substantially zero initially. The invention uses only one operational amplifier, four PMOS transistors and one additional current path to ground in one embodiment. The core includes a current generator embedded therein.


REFERENCES:
patent: 5512817 (1996-04-01), Nagaraj
patent: 5646518 (1997-07-01), Lakshmikumar et al.
Karel E. Kuijk, “A Precision Reference Voltage Source”, IEEE Journal of Solid-State Circuits, vol. SC-8, No. 3, (Jun. 1973) pp. 222-226.
Gerard C.M. Meijer, et al., “A New Curvature-Corrected Bandgap Reference”, IEEE Journal of Solid-State Circuits, vol. SC-17, No. 6, (Dec. 1982) pp. 1139-1143.
Ban-Sup Song, “A Precision Curvature-Compensated CMOS Bangap Reference”, IEEE Journal of Solid State Circuits, vol. SC-18, No. 6, (Dec. 1983) pp. 634-643.
Germano Nicollini, et al., “A CMOS Bandgap Reference for Differential Signal Processing”, IEEE Journal of Solid-State Circuits, vol. 26, No. 1, (Jan. 1991) pp. 41-50.
Ian A. Young, et al., “A PLL Clock Generator with 5 to 110 MHz of Lock Range for Microprocessors”, IEEE Journal of Solid-State Circuits, vol. 27, No. 11, (Nov. 1992) pp. 1599-1606.

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