Electricity: power supply or regulation systems – Self-regulating – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2001-07-12
2002-04-02
Riley, Shawn (Department: 2838)
Electricity: power supply or regulation systems
Self-regulating
Using a three or more terminal semiconductive device as the...
Reexamination Certificate
active
06366071
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an integrated circuit (IC), and more particularly to low voltage bandgap and sub-bandgap reference circuits.
2. Description of the Related Art
Usually the bandgap reference circuit provides a stable and zero temperature coefficient reference voltage by using PTAT voltage. The PTAT circuit uses delta VBE, i.e. the difference between two base-emitter voltages, VBE
1
and VBE
2
. Thus
&Dgr;VBE=VBE
1
−
VBE
2
=
VPTAT
(1)
Δ
VBE
=
kT
q
×
ln
(
J1
J2
)
(
2
)
where
k is Boltzmann's constant,
T is absolute temperature in degree Kelvin, q is electron charge,
J
1
and J
2
are current densities through the emitter of bipolar transistors T
1
and T
2
.
Reference is made to U.S. Pat. No. 6,016,051 (Can), filed Jan. 18, 2000, FIG. 2 and a description and explanation of that circuit therein. The circuit
200
of that FIG. 2 is reproduced herein as
FIG. 1
(prior art), circuit
100
. The circuit
100
is an example of using a PTAT circuit to generate a bandgap and sub-bandgap voltage. However, circuit
100
can hardly operate under a supply voltage VCC as low as 1 volt when used in the conventional process of 0.25 um or 0.18 um (um=micrometer) if the desired VREF≅|Vth|, where Vth is the threshold voltage of PMOS or NMOS transistors. The reason can be explained in
FIG. 2
(prior art), circuit
100
. This circuit substitutes generic current sources IPTAT and IBIAS with transistors M
1
and M
2
whose gates are driven by current source IBIAS. In
FIG. 2
the V
SD
of PMOS M
2
must be greater than
V
SG
−|V
th| of
M
2
.
Where V
SD
is the source-drain voltage of M
2
, and V
SG
is the source-gate voltage of M
2
. Thus
V
SD
≧V
SG
−|V
th|
where |Vth| is the threshold voltage of PMOS M
2
.
For circuit
100
to work, the following condition must be achieved.
V
SD,M2
+VBE+VREF<VCC
However, if the desired VREF≅0.5 volt, and VBE≅0.5 volt, then usually
V
SD,M2
+VBE+VREF>
1 volt
That is, circuit
100
cannot work at VCC as low as 1 volt.
Using this delta VBE, a correct circuit structure and an appropriate ratio between two resistors, not only a bandgap reference voltage but also a sub-bandgap reference voltage can be generated as will be demonstrated hereinafter. The bandgap reference circuit in accordance with one embodiment of the present invention can operate not only with CMOS technology but also under wide range of power supplies, even under low VCC of about 1V.
Other U.S. Patents, in addition to above referenced U.S. Pat. No. 6,016,051, which relate to the subject at hand are:
U.S. Pat. No. 5,818,292 (Slemmer), U.S. Pat. No. 5,132,556 (Cheng), and U.S. Pat. No. 4,808,908 (Lewis et al.) disclose bandgap reference circuits.
U.S. Pat. No. 5,646,518 (Lakshmikumar et al.), U.S. Pat. No.5,444,219 (Kelly), and U.S. Pat. No. 4,603,291 (Nelson) show patents otherwise related to the subject.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide circuits and methods to provide a bandgap and sup-bandgap reference voltage requiring a voltage supply no greater than the voltage drop of a transistor plus the generated bandgap reference voltage.
It is another object of the present invention to provide a bandgap reference voltage which produces a stable and zero temperature coefficient reference voltage.
It is another object of the present invention to utilize the ratio of two resistive circuits or resistive means to generate the bandgap and sup-bandgap reference voltage.
These and many other objects have been achieved by utilizing a new circuit structure where the sum of the PTAT current (IPTAT) and PTVBE current (IPTVBE) are summed in a resistive circuit or resistive means RX to generate the bandgap or sub-bandgap reference voltage. The IPTAT and IPTVBE currents are generated simultaneously in separate current source circuits and each of these currents is then used to gate a transistor, i.e., two transistor are used in the circuit of the preferred embodiment of the present invention. The current of these two transistors is then summed in RX, thus generating the bandgap or sub-bandgap reference voltage. The magnitude of the bandgap or sub-bandgap reference voltage is determined by the ratio of RX and a resistive circuit in the PTVBE current source.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments.
REFERENCES:
patent: 4603291 (1986-07-01), Nelson
patent: 4808908 (1989-02-01), Lewis et al.
patent: 5132556 (1992-07-01), Cheng
patent: 5444219 (1995-08-01), Kelly
patent: 5646518 (1997-07-01), Lakshmikumar et al.
patent: 5818292 (1998-10-01), Slemmer
patent: 6016051 (2000-01-01), Can
Ackerman Stephen B.
Riley Shawn
Saile George O.
Taiwan Semiconductor Manufacturing Company
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