Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Amplitude control
Reexamination Certificate
2001-07-24
2003-05-20
Cunningham, Terry D. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Amplitude control
C327S538000
Reexamination Certificate
active
06566931
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor integrated circuit device incorporating a voltage detecting circuit; in particular it relates to a semiconductor integrated circuit device incorporating a voltage detecting circuit that can detect the drop in operating power supply voltage.
2. Description of the Prior Art
To prevent malfunction of a semiconductor integrated circuit device (hereafter, referred to as LSI) from occurring when voltage rises at the time of energization start-up, or when the power supply voltage drops during operation, a method that is well-known involves the monitoring of the power supply voltage by a power supply voltage detecting circuit provided and the transmission of a reset signal to halt the operation of the LSI when the power supply voltage becomes lower than that specified.
For example, in Japanese Patent Application Laid-Open No. Hei 2-228064 (hereafter, referred to as the well-known example), an example of a voltage detecting circuit that can detect a drop in operating power supply voltage is disclosed.
FIG. 1
is a block diagram showing the configuration of a detecting circuit that is disclosed in this well-known example.
Referring to
FIG. 1
, this conventional detecting circuit
550
, which comprises step-up circuit
513
, reference voltage generation circuit
515
, voltage dividing circuit
517
, comparator
519
, and interface circuit
521
, is mounted on a single semiconductor chip comprising both bipolar elements and CMOS elements.
Step-up circuit
513
with a configuration equivalent to that of a well-known DC—DC converter converts the power supply voltage Vcc, which is supplied to bipolar elements, (e.g., 1.5 V), which is supplied to terminal
511
to alternating voltage, steps it up, and then reconverts it to direct-current voltage V
DD
(e.g., 3.6 V) which can drive a CMOS circuit, and supplies voltage V
DD
to the CMOS logic circuit (not shown in the drawing) via terminal
514
.
Reference voltage generation means
155
consists of constant-current source Io, resistance R
11
, and PN junction diode Q
1
, generating reference first voltage V
N
at connection point P. V
N
can be set to a desired value by changing the resistance R
11
value. Diode Q
1
is connected between the base and the emitter of NPN transistor Q
2
, transistor Q
2
thus operates as a current source.
Voltage dividing means
517
, consisting of resistances R
12
and R
13
, provides second voltage V
d
at connection point S by dividing stepped-up voltage V
DD
. In other words, V
d
=V
DD
×(R
13
/(R
12
+R
13
)).
Comparator
519
is a differential amplifier that has PNP transistors Q
5
and Q
6
as load elements, NPN transistors Q
3
and Q
4
as driving elements, and NPN transistor Q
2
as a current source element. One input terminal IN
1
is connected to connection point S, whereas the other input terminal IN
2
is connected to connection point P. Output terminal OUT
1
is connected to interface circuit
521
via terminal
520
.
Interface circuit
521
consists of resistance R
14
and NPN transistor Q
7
. When voltage V
01
of comparator output terminal
520
is high level, voltage V
02
of detection signal transmission terminal
522
(connection point T) is equal to saturation voltage V
CE
(sat) between the collector and the emitter of transistor Q
7
; when voltage V
02
is low level, voltage V
02
is approximately equal to V
DD
.
FIG. 2
is a schematic for describing an overview of the operation of detecting circuit
550
, wherein the horizontal axis is time t, the vertical axis shows reference voltage (first voltage) V
N
, stepped-up voltage V
DD
, and second voltage (divided voltage) V
d
. When time t=0, standby mode is cancelled initiating the operation of step-up circuit
513
. Curves
541
,
542
, and
543
in
FIG. 2
indicate the relationships between each of V
N
, V
DD
, and V
D
and time t, respectively. V
DDX
is a preferred, to-be-detected stepped-up voltage that has been specified in advance. Circuit constants for reference voltage generation means
515
and voltage dividing means
517
are preset to values that satisfy the relationship of divided voltage V
dx
of stepped-up voltage V
DDX
being equal to reference voltage V
N
. Therefore, when V
DD
<V
DDX
, V
d
<V
N
and accordingly voltage information V
01
of output terminal
520
of the comparator is high level; whereas when V
DD
>V
DDX
, V
d
>V
N
, and consequently voltage information V
01
, is low level. Accordingly, the to-be-detected, stepped-up voltage V
DDX
can be detected.
In the conventional detecting circuit
550
described above, since reference voltage generation means
515
and comparator
519
, which are configured using bipolar elements that can be activated by a power supply that is externally supplied to bipolar elements of a low voltage to detect the stepped-up voltage, the detection of low voltage down to a certain point becomes sufficiently possible.
However, in the conventional detecting circuit
550
, both reference voltage generation means
515
and comparator
519
are driven by power supply voltage V
CC
, which is supplied for bipolar circuits. This configuration develops a problem where the stability of reference voltage V
N
that is generated by voltage generation means
515
against temperature change is degraded, particularly at the supplied voltage 1 V or lower; and accordingly, the fluctuation in the reference voltage becomes larger. This makes it difficult to generate, for example, a power-on/reset signal accurately in such a case of low voltage.
SUMMARY OF THE INVENTION
Accordingly, the objective of the present invention is to provide an LSI, which comprises a voltage detecting circuit that can detect the power supply voltage accurately and surely, even if the power supply voltage supplied externally falls to 1 V or less.
Therefore, an LSI, according to the present invention, which is driven by the first voltage as a power supply supplied to an external power supply terminal to drive internal circuits with desired functions, such as a CPU or peripheral circuits, comprises at least: a step-up circuit, which is driven by the first voltage supplied to an external power supply terminal as a power supply and which steps up the first voltage at a predetermined ratio into a second voltage and outputs it; a voltage detecting circuit, which is driven by the second voltage as a power supply and which compares a predetermined reference voltage to a divided voltage given by dividing the second voltage and outputs a first comparison result signal; and a level shift circuit, which is driven using the first voltage as a power supply and which changes the level of the first comparison result signal to outputs a second comparison result signal.
At this time, the voltage detecting circuit may comprise at least a reference voltage generating circuit, which generates a reference voltage; a dividing circuit which divides the second voltage into a divided voltage; and a comparison circuit which inputs the reference voltage and the divided voltage and outputs a first comparison result signal.
Furthermore, the level shift circuit may be configured so that the ratio of the second voltage to the first voltage is equal to that of the first comparison result signal level to the second comparison result signal level.
It is noted that the second comparison result signal may be used as a reset signal for resetting an internal circuit when the divided voltage is lower than the reference voltage.
Furthermore, it is preferable that the reference voltage generating circuit is structured with a bandgap circuit.
Features of the LSI according to the present invention are: including a voltage detecting circuit and other internal circuits; stepping up a detected voltage from the voltage detecting circuit onto an appropriate voltage by the step-up circuit; and driving the voltage detecting circuit by the stepped-up voltage, which is provided by the step-up circuit.
REFERENCES:
patent: 4996686 (1991-02-01), Imai
Cunningham Terry D.
Hayes & Soloway P.C.
NEC Electronics Corporation
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