Regulated low-voltage generation circuit

Details Regulated low-voltage generation circuit Regulated low-voltage generation circuit

2000-12-08

2002-05-07

Berhane, Adolf Deneke (Department: 2838)

Electricity: power supply or regulation systems

Self-regulating

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

C326S044000

Reexamination Certificate

active

06384586

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the design and fabrication of integrated circuit devices and, more particularly, to the design of a low-voltage reference generation circuit that provides low reference voltage with a controllable thermal coefficient.
2. Description of the Related Art
As is well known, bandgap voltage reference circuits are commonly deployed in the design of integrated circuit devices. The advantages associated with bandgap voltage reference circuits largely derive from the fact that such circuits are capable of providing a thermally stable voltage reference. In practice, the thermal coefficient of the voltage reference ideally approaches zero. An analysis of a number of embodiments of bandgap voltage reference circuits may be found in the textbook “Analog Integrated Circuit Design”, by David A. Jones and Ken Martin (John Wiley & Sons), pp. 353-364, which is hereby incorporated by reference.
FIG. 1
depicts a bandgap voltage reference circuit that is considered to be representative of the state of the prior art. As may be readily observed, the bandgap voltage reference circuit depicted in
FIG. 1
is realized through bipolar junction transistor technology, although other semiconductor device technologies, including MOS, may also be deployed. A realization of the invention based on MOS technology is described in detail in the Description below.
Referring now to
FIG. 1
, bipolar implementation of a bandgap voltage reference circuit is seen to include a current source I
o
that is coupled between a voltage source V
s
and the emitter of a pnp transistor Q
44
. Q
44
is coupled in a common-collector configuration between I
o
and GND. The voltage reference also includes npn transistors Q
41
, Q
42
and Q
43
, each of which has a collector coupled through a respective resistor, R
42
, R
43
or R
44
, to the emitter of Q
44
and to current source I
o
. The emitters of Q
41
and Q
43
are directly connected to GND, while Q
42
emitter is coupled to GND through resistor R
41
. The base electrodes of Q
41
and Q
42
are commonly connected Q
41
collector. Q
42
collector is in turn connected to Q
43
base, and Q
43
collector is connected to Q
44
base. The output voltage, V
out
, of the bandgap voltage reference circuit appears at the interconnection of I
o
and Q
44
emitter.
In order to apprehend the operation of the bandgap voltage reference circuit of
FIG. 1
, assume for pedagogical purposes that the emitter area of Q
42
is an order of magnitude (ten times) greater than the emitter area of Q
41
. Based on that assumption, an analysis of the operation of the bandgap reference circuit proceeds as follows. The base-to-emitter voltage of Q
41
, VBE(Q
41
), is identical to the voltage at Q
41
collector. At room temperature, approximately 300° K., this voltage is roughly 700 mV. In addition, as may be readily understood from
FIG. 1
, the voltage at Q
42
collector is equal to VBE(Q
43
). Consequently, the voltages across R
42
and R
43
are substantially equal. Therefore, if the resistance of R
42
is designed to be equal to the resistance of R
43
, then the currents respectively flowing through these resistors must likewise be equal. As a result, the currents respectively flowing across Q
41
and Q
42
must be very nearly identical. From the above, and recalling that the emitter area of Q
42
is an order of magnitude greater than the emitter area of Q
41
, it follows that:
I(Q
41
)=I
s
e
qVBE(Q41)
/
kT
=I(Q
42
)=10I
s
e
qVBE(Q42)
/
kT
,
where I(Q
41
) is the current in Q
41
, and I(Q
42
) is the current in Q
42
.
In the above equation, I
s
is understood to be reverse saturation current at a specified temperature. It is well known that the reverse saturation current of a bipolar transistor is proportional to its base-to-emitter junction area. Because Q
41
and Q
42
are fabricated on the same die, according to the same process, and the base-to-emitter junction area of Q
42
is ten times that of Q
41
, the reverse saturation current of Q
42
is ten times greater than the reverse saturation current of Q
41
. Also, in the above equation:
K is Boltgman's constant,
q is the charge of an electron, and
T is the absolute temperature.
Therefore, &Dgr;VBE=VBE(Q
41
)−VBE(Q
42
)=(kT/q)ln 10.
At room temperature, &Dgr;VBE is equal to 60 mV and has a positive temperature coefficient of 0.2 mV/°C. However, from inspection of
FIG. 1
, it is seen that &Dgr;VBE is precisely the voltage across R
41
. If R
43
=10R
41
, then the voltage across R
43
is 600 mV, with a temperature coefficient of 2 mV/°C. If VBE (Q
43
), the base-to-emitter voltage of Q
43
, has a magnitude of 700 mV, with a temperature coefficient of −2 mV/°C., then the reference voltage, V
out
, will have a magnitude of 1300 mV with a zero temperature coefficient.
Accordingly, the prior art provides a technique for synthesizing a temperature-independent voltage reference that, as might be expected, has widespread utility in integrated circuit design. Additionally, the voltage reference is largely insensitive to semiconductor processing variations. However, the bandgap voltage reference circuit that is described above imposes an inherent design constraint that has become increasingly less tolerable as system designs have evolved. That is, because present designs develop a voltage reference, V
out
, that is approximately 1300 mV, the voltage source, V
s
, must be comfortably greater than 1300 mV in order to drive current source I
o
. Although prior-art integrated circuit design and fabrication techniques have enabled operation from voltage sources as low as 1.5V, state-of-the-art designs are expected to be driven by power consumption and dissipation considerations to voltage sources as low as 1.2V, or even 1.0V. Clearly, what is required in order to operate from voltage sources as low as 1.2V, is a bandgap reference circuit design that generates a reference voltage much lower than the 1300 mV typically encountered.
SUMMARY OF THE INVENTION
The above and other objects, advantages and capabilities are achieved in one aspect of the invention by a circuit that generates a reference voltage having a magnitude less than the generally known silicon bandgap voltage. The circuit includes an amplifier having differential first and second inputs. Three current sources have control terminals coupled to the amplifier output and provide currents of equal magnitudes. The output of the first current source is connected to a first input of the amplifier, and is also coupled through a first junction device to GND. The output of the second current source is connected to a second input of the amplifier and is coupled through a second junction device and a resistance to GND. A third junction device is coupled between the output of a biasing device and GND. A voltage divider is coupled across the third junction device and has an output coupled to the output of the third current source.
Another aspect of the invention is manifest in a circuit for generating a voltage that is less than the semiconductor bandgap voltage. The circuit comprises voltage differential means, a feedback amplifier, first and second current sources, a voltage reference and a resistance element. The voltage differential means develops a voltage differential characterized by a temperature coefficient of a first polarity. A feedback amplifier has an input coupled to the voltage differential means. The first current source has a control terminal coupled to the output of the feedback amplifier and an output coupled to the voltage differential means. A voltage reference develops a voltage having a thermal coefficient of a second polarity, opposite to the first polarity. The second current source is also coupled at a control terminal to he output of the feedback amplifier, and has an output coupled to the voltage reference. The second current source provides a current in proportion to the voltage differential. The resistance element is coupled between the output of the se

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