Low voltage bandgap reference circuit

Details Low voltage bandgap reference circuit Low voltage bandgap reference circuit

2001-11-08

2003-03-11

Riley, Shawn (Department: 2838)

Electricity: power supply or regulation systems

Self-regulating

Using a three or more terminal semiconductive device as the...

C327S538000

Reexamination Certificate

active

06531857

ABSTRACT:

BACKGROUND OF THE INVENTION
As CMOS technologies continue to migrate into deep submicron region, the power supply voltage will likewise scale to below 1.5 V for reliable operation of devices. In various hand-held and/or wireless devices it is advantageous for the supply voltage to be reduced even further to keep power consumption and weight low. As an essential and integral part of more and more very large scale integration circuit systems, a temperature-compensated (or commonly called bandgap) reference circuit that works with supply voltages below 1.5 V is desired.
FIG. 1
shows a simplified diagram of a conventional CMOS bandgap reference circuit. The closed loop of on operational amplifier A
0
forces the voltages at nodes PT and Q
2
E to be equal, resulting in a bandgap reference voltage
V
REF
=
R
0
R
PT
⁢
ln
⁡
(
a
E
⁢
m
2
)
⁢
V
T
+
V
EB2
,
where a
E
is the ratio of emitter areas of Q
1
over Q
2
, and M
2
is the current ratio, I
2
/I
1
. V
&tgr;
=kT/q, the thermal voltage, has a positive temperature coefficient and V
EB
has a negative temperature coefficient of about −2MV/°C. Satisfying the condition dV
REF
/dT=0 for T=T
0
usually results in V
RFF
≈1.2 V with a
E
=8, M
2
=1. Allowing some voltage drop across the current sources M
1
and M
2
, the minimum supply voltage will typically be V
DD
≧1.5 V.
The minimum supply voltage required to properly operate this circuit is V
DD
≧V
REF
+V
SD
since V
REF
>V
EB2
. A common technique to lower the minimum V
DD
is to generate a Proportional To Absolute Temperature (“PTAT”) current and a current proportional to V
EB
, and then sum the two currents into a resistor to generate a bandgap voltage that may contain only a fraction of a V
EB
instead of a whole V
EB
voltage. This is commonly referred as a fractional V
EB
bandgap reference.
Bandgap a reference circuits with minimum supply voltages of V
DD
≧0.9 V have been achieved. A first technique results in a bandgap reference voltage V
REF
>V
EB
, which limits the supply voltage to V
DD
≧0.9 V. A second technique predicted a lowering of supply voltage to V
DD
≧0.85 V, but achieves only V
DD
≧2.1 V due to technology limitations. The second technique requires that two resistors be connected across the emitter-base terminals of two separate PNP transistors to generate a whole V
EB
current and sum it with a PTAT current. It then forces the resultant current through a third resistor to produce an appropriate bandgap reference voltage. For a given voltage drop, V
0
, across a resistor having a current, I
0
, flowing through, the resistance of the resistor is R
0
=V
EB
/I
0
. Therefore, the total resistance of the two resistors connected across the emitter-base terminals of two separate PNP transistors is
R
t
=
2
⁢
V
EB
I
0
,
whee I
0
is the current flowing through each resistor. For example, I
0
=1 &mgr;A (10
−6
A) and V
EB
=0.7 V results in R
1
=1,400,000&OHgr;. In integrated circuit technologies, chip area needed to implement a resistor is directly proportional to the total resistance of the resistor. Therefore, additional resistors or resistances requires additional chip area.
SUMMARY OF THE INVENTION
Embodiments of the invention provide a bandgap reference circuit that may use reduced substrate area compared to prior art bandgap reference circuits, while requiring relatively low voltage. A first embodiment of the invention includes a bipolar transistor with a resistor electrically connected across the emitter-base of the bipolar transistor. The resistor sums a first current with a second current and also generates a fractional V
EB
.
In an illustrative embodiment of the invention the bandgap reference circuit has a first current is proportional to V
EB
, and a second current proportional to a PTAT current.
In a further embodiment of the invention the bandgap reference circuit has an impedance booster.
The present invention also includes a method of regulating a voltage level using embodiments of the bandgap reference circuit.


REFERENCES:
patent: 5087831 (1992-02-01), Ten Eyck
patent: 6016051 (2000-01-01), Can
patent: 6037832 (2000-03-01), Kaminishi
Anne-Johan Annema, Low-Power Bandgap References Featuring DTMOST's ,IEEE Journal of Solid-State Circuits, vol. 34, No. 7, pp. 949-955, Jul. 1999.
Hironori Banba, et al., “A CMOS Bandgap Reference Circuit with Sub-1-V Operation”,IEEE Journal of Solid-State Circuits, vol. 34, No. 5, pp. 670-673, May 1999.
Harry Neuteboom et al., “A DSP-Based Hearing Instrument IC”,IEEE Journal of Solid Circuits, vol. 32, No. 11, pp. 1790-1806., Nov. 1997.
Klaas Bult, et al., “A Fast-Settling CMOS Op Amp for SC Circuits with 90-dB DC Gain”,IEEE Journal of Solid State Circuits, vol. 25, No. 6, pp. 1379-1384, Dec. 1990.

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