Current bandgap voltage reference circuits and related methods

Details Current bandgap voltage reference circuits and related methods Current bandgap voltage reference circuits and related methods

2001-08-24

2003-05-13

Wells, Kenneth B. (Department: 2816)

Miscellaneous active electrical nonlinear devices, circuits, and

Specific identifiable device, circuit, or system

With specific source of supply or bias voltage

C327S513000

Reexamination Certificate

active

06563371

ABSTRACT:

FIELD
This invention relates generally to bandgap voltage reference circuits, and in particular, to bandgap voltage reference circuits and related methods that add two currents having respectively opposite polarity temperature coefficients to generate a substantially temperature-invariant reference voltage.
GENERAL BACKGROUND
A bandgap voltage reference circuit is typically used to provide a voltage reference for other circuits to use in performing their intended operations. Generally, it is desired that the reference voltage generated by a bandgap circuit is substantially invariant. This is so even if there are substantial variations in the environment temperature. Thus, many, if not all, bandgap circuits incorporate temperature compensating circuitry in order to generate a substantially temperature-invariant reference voltage.
FIG. 1
illustrates a schematic diagram of a prior art bandgap voltage reference circuit
100
. The bandgap circuit
100
consists of PMOS transistors Q
11
, Q
12
, and Q
13
, and NMOS transistors Q
14
and Q
15
configured as current mirrors to generate substantially equal currents I
11
, I
12
, and I
13
. The bandgap circuit
100
further consists of resistor R
11
and diode D
11
coupled in series with PMOS transistor Q
11
and NMOS transistor Q
14
to receive current I
11
, a diode D
12
coupled in series with PMOS transistor Q
12
and NMOS transistor Q
15
to receive current I
12
, and resistor R
12
and diode D
13
coupled in series with PMOS transistor Q
13
to receive current I
13
. The diodes D
11
, D
12
, and D
13
are forward biased with their cathode coupled to ground terminal. The output reference voltage of the bandgap circuit
100
is generated at the node between the PMOS transistor Q
13
and resistor R
12
.
The temperature compensation of the output reference voltage of the bandgap circuit
100
operates as follows. The current I
12
generates a voltage V
13
across the diode D
12
. The voltage V
13
has a negative temperature coefficient −T&agr;V
13
. The current I
11
generates a voltage V
12
across the diode D
11
. The voltage V
12
also has a negative temperature coefficient −T&agr;V
12
that is more negative than the temperature coefficient −T&agr;
13
of voltage V
13
(i.e. −T&agr;V
12
<−T&agr;V
13
). The current mirror causes the voltage V
11
on the node between transistor Q
14
and resistor R
11
to be substantially equal to the voltage V
13
. Thus, the voltage VR
11
across the resistor R
11
(VR
11
=V
11
-V
12
) has a positive temperature coefficient +T&agr;R
11
due to −T&agr;V
12
being more negative than −T&agr;V
13
. Since the current I
11
through resistor R
11
is proportional to the voltage VR
11
across the resistor R
11
, the current I
11
likewise has a positive temperature coefficient +T&agr;I
11
.
The current mirror causes the current I
13
to be substantially equal to the current I
11
. Therefore, the current I
13
also has a positive temperature coefficient +T&agr;I
13
. It follows then that the voltage VR
12
across resistor R
12
has a positive temperature coefficient +T&agr;V
12
since VR
12
is proportional to the current I
13
. Additionally, the current I
13
generates a voltage V
14
across the diode D
13
that has a negative temperature coefficient −T&agr;V
14
. The reference voltage VREF is the sum of voltages VR
12
and V
14
, both of which have opposite polarity temperature coefficients. Thus, by proper design of the bandgap circuit
100
, the reference voltage VREF can be made substantially temperature invariant across a particular temperature range.
FIG. 2
illustrates a schematic diagram of another prior art bandgap circuit
200
. The bandgap circuit
200
operates similar to bandgap circuit
100
. Briefly, the voltage V
22
across the diode D
22
has a negative temperature coefficient −T&agr;V
22
and the voltage V
21
across the diode D
21
also has a negative temperature coefficient −T&agr;V
21
that is more negative than −T&agr;V
22
. The operational amplifier U
21
causes the voltage V
23
at the positive terminal of the operational amplifier U
21
to be substantially the same as voltage V
22
across diode D
22
, which also has a similar negative temperature coefficient −T&agr;V
23
. Since −T&agr;V
21
is more negative than −T&agr;V
23
, the voltage VR
21
across resistor R
21
has a positive temperature coefficient +T&agr;VR
21
, and accordingly the current I
21
through resistor R
21
also has a positive temperature coefficient +T&agr;I
21
. The current I
21
, as well as current I
22
through resistor R
22
, are derived from the current I
20
through PMOS transistor Q
21
. Thus, they all have a positive temperature coefficient. The reference voltage VREF is thus the addition of the voltage V
22
and the voltage drop across resistor R
22
, both of which have opposite polarity temperature coefficients which can be made to cancel out.
A drawback of the prior art bandgap circuits
100
and
200
stems from the reference voltage VREF being a combination of two voltage drops in series. In bandgap circuit
100
, the reference voltage VREF is a combination of V
14
across the diode D
13
and VR
14
across the resistor R
12
. In bandgap circuit
200
, the reference voltage VREF is a combination of V
22
across the diode D
22
and VR
22
across the resistor R
22
. Because of this, the power supply voltage VDD needs enough headroom to accommodate both voltages that form the reference voltage VREF in addition to the source-drain voltages of transistor Q
13
or Q
21
. The reference voltage VREF typically requires about 1.2V and the source-drain voltage of transistor Q
13
or Q
21
requires at least 0.2V. Thus, the minimum power supply voltage VDD required is about 1.4V, which makes the prior bandgap circuits
100
and
200
not compatible with emerging technologies that use VDD at significantly lower voltage than 1.4V, such as 1V.


REFERENCES:
patent: 5430395 (1995-07-01), Ichimaru
patent: 5796244 (1998-08-01), Chen et al.
patent: 6310510 (2001-10-01), Goldman et al.
Analysis and Design of Analog Integrated Circuits, Chapter 4, Transistor Current Sources and Active Loads, 1977.

Affiliated with

Also associated with

Rating

Current bandgap voltage reference circuits and related methods does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Current bandgap voltage reference circuits and related methods, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Current bandgap voltage reference circuits and related methods will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3075981