Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – With specific source of supply or bias voltage
Reexamination Certificate
1998-12-10
2001-02-20
Tran, Toan (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
With specific source of supply or bias voltage
C327S142000
Reexamination Certificate
active
06191644
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
This invention is in the field of integrated circuits, and is more specifically directed to reference voltage circuits therein.
As is well known in the field, many modern integrated circuits incorporate voltage detection and comparison circuits for comparing the voltages applied to or generated within the circuits against a reference level. Many modem integrated circuits utilize on-chip voltage regulators to generate internal bias voltages that are stable over variations in temperature, power supply voltage, and processing parameters. Additionally, voltage detection and comparison circuits are sometimes used in determining the operating range within which an externally applied power supply voltage is biased in modern integrated circuits that can operate in either a low power supply voltage range (e.g., 3.3 volts±10%) or a higher power supply voltage range (e.g., 5 volts ±10%). Each of these types of circuit require a stable reference voltage to effect proper comparison and detection, as the comparisons carried out by these circuits are against absolute voltage levels (rather than as a differential comparison).
Bandgap reference circuits constitute one popular type of conventional reference voltage circuit. In general, bandgap reference circuits produce a reference voltage that depends upon two circuit elements with complementary temperature coefficients. Typically, the bandgap reference voltage depends upon the base-emitter voltage of a bipolar transistor (which may be a parasitic bipolar device in integrated circuits that are fabricated according to metal-oxide-semiconductor, or MOS, technologies) and also upon either the resistance value of a diffused resistor or upon a MOS transistor threshold voltage. Since the base-emitter voltage of a bipolar device has a temperature coefficient that is opposite from that of either of a differential base-emitter voltage of two bipolar transistors, a reference voltage that is generated from the combination of these characteristics can be quite stable over temperature. Accordingly, bandgap reference circuits are widely used in modem integrated circuits that require a stable reference voltage for internal voltage detection and comparisons.
Particularly in integrated circuits that detect the levels of the applied power supply voltage, it is important that the reference voltage circuits rapidly begin operation upon power-up of the integrated circuit. If a reference voltage circuit does not rapidly begin operation on power-up, it is possible for the integrated circuit to enter an unstable or indeterminate operating mode. For example, delayed power-up of the reference circuit may cause the incorrect detection of the power supply voltage operating range and, as a result, misconfiguration of internal circuits that are to be configured according to the power supply level. Other failures due to delayed generation of a reference voltage are well known in the art.
Accordingly, the use of power-up detection circuits to generate a signal upon power-up of the integrated circuit, and the application of these signals to initiate the operation of reference voltage circuits upon power-up, is known in the art. Referring now to
FIG. 1
, the construction and operation of an example of a conventiolal bandgap reference circuit in combination with a startup circuit for rapidly initiating operation of the bandgap reference circuit, according to the prior art, will now be described by way of background.
Bandgap reference circuit
10
in this conventional example is arranged as multiple current mirror legs, each including a bipolar transistor. The output leg of bandgap reference circuit
10
includes the series connection of the source/drain paths of p-channel transistors
12
p
and
14
p
; the source of transistor
12
p
is biased to power supply voltage V
dd
, and the drain of transistor
14
p
is connected to a resistor divider of resistors
16
,
18
. Resistors
16
,
18
(as well as the other resistors in bandgap reference circuit
10
), are preferably diffused resistors formed in p-type regions in the substrate of the integrated circuit within which bandgap reference circuit
10
is realized. P-n-p bipolar transistor
20
has its emitter connected to resistor
18
, at the opposing end of the resistor divider, and has its base and collector at ground. The output of bandgap reference circuit
10
on line VREF is taken from the node between resistors
16
,
18
in the resistor divider of this leg.
Two additional current mirror legs in bandgap reference circuit
10
are also provided. The middle leg includes the series source/drain connection of p-channel transistors
22
p
,
24
p
, with the source of transistor
22
p
at power supply voltage V
dd
and the drain of transistor
24
p
connected to one side of resistor
26
. In this middle leg, n-channel transistor
28
n
has its source/drain path connected between resistor
26
and resistor
29
. P-n-p bipolar transistor
30
has its emitter connected to resistor
29
, and its base and collector at ground. The first leg of bandgap reference circuit
10
also includes series source/drain connection of p-channel transistors
32
p
,
34
p
, with the source of transistor
22
p
at power supply voltage V
dd
. In this leg, the drain of transistor
34
p
is connected to the drain of n-channel transistor
38
n
at node NBIAS; the source of transistor
38
n
is connected to the emitter of p-n-p bipolar transistor
40
, which has its base and collector at ground.
The current mirroring in bandgap reference circuit
10
arises from the interconnection of the gates of transistors in the various legs. In this example, the gates of p-channel transistors
12
p
,
22
p
,
32
p
are connected in common at node PBIAS
1
, which is connected to the drain of transistors
24
p
. The gates of p-channel transistors
14
p
,
24
p
,
34
p
are connected in common at node PBIAS
2
, which is connected to the node between resistor
26
and the drain of transistor
28
n
. As illustrated in
FIG. 1
, the body nodes of transistors
14
p
,
24
p
,
34
p
are biased to their respective sources (rather than to V
dd
, as is the case for transistors
12
p
,
22
p
,
32
p
). The voltages established at nodes PBIAS
1
, PBIAS
2
may be forwarded to other circuits in the integrated circuit within which bandgap reference circuit is deployed, if desired, as illustrated in FIG.
1
. The gates of transistors
28
n
,
38
n
are connected in common at node NBIAS. Additionally, capacitor
39
is connected to node NBIAS, to provide common mode noise rejection relative to any noise that may appear at the bases of bipolar transistors
20
,
30
,
40
.
In normal operation, bandgap reference circuit
10
uses the mirrored currents to establish a stable voltage at node VREF. Current that is conducted through the first leg of transistors
32
p
,
34
p
,
38
n
,
40
is mirrored through the second leg of transistors
22
p
,
24
p
,
28
n
,
30
, and resistors
26
,
29
. The voltages that are established at nodes PBIAS
1
, PBIAS
2
by this current mirror operation similarly bias transistors
12
p
,
14
p
, establishing a current through the output leg of transistors
12
p
,
14
p
,
20
with resistors
16
,
18
. The voltage drop across resistor
18
and transistor
20
generated by this current sets the output reference voltage on line VREF. The voltage on line VREF thus depends upon the base-emitter voltage of transistors
20
,
30
,
40
, and upon the resistance of diffused resistors
18
and
29
. Because the temperature coefficient of the base-emitter voltage of the bipolar transistors varies in an opposite fashion from the resistance of diffused resistors
16
,
18
,
26
,
29
, the output reference voltage at line VREF will be relatively stable over temperature, as is known in the art.
The normal operation of bandgap reference circuit
10
described hereinabove commences upon the conducti
Smith Scott E.
Srinath Bangalore Kodandaram
Brady III Wade James
Nguyen Hiep
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
Tran Toan
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