Miscellaneous active electrical nonlinear devices – circuits – and – Specific signal discriminating without subsequent control – By amplitude
Reexamination Certificate
2002-09-17
2004-01-06
Zweizig, Jeffrey (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific signal discriminating without subsequent control
By amplitude
Reexamination Certificate
active
06674311
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electronic device having a CMOS circuit, and more particularly to an electronic device having a CMOS circuit for which a low voltage operation is required.
2. Description of the Related Art
FIG. 4
is a schematic circuit diagram showing conventional voltage detecting circuit. As shown in
FIG. 4
, the conventional voltage detecting circuit is mainly made up of p-channel MOS transistors (hereinafter referred to as “PMOS”), n-channel MOS transistors (hereinafter referred to as “NMOS”), a depletion type n-channel MOS transistor (hereinafter referred to as “D-type NMOS”) which allows a drain current to flow even when a potential difference between the source and the gate is 0 V, and resistors. A first PMOS
304
has a source connected to a power supply terminal
101
and a drain connected to its gate, a drain of a D-type NMOS
305
and a gate of a second PMOS
306
, respectively, and the D-type NMOS
305
has a source connected to its gate and a GND terminal
102
. Also, the second PMOS
306
has a source connected to the power supply terminal
101
and a drain connected to a drain of a first NMOS
307
and a gate of a second NMOS
311
, and the first NMOS
307
has a source connected to the GND terminal
102
and a gate connected to a second electrode of a first resistor
109
and to a first electrode of a second resistor
108
, respectively. A first electrode of the first resistor
109
is connected to the power supply terminal
101
, and a second electrode of the second resistor
108
is connected to the GND terminal
102
. Also, an output resistor
110
has a first electrode connected to the power supply terminal
101
and a second electrode connected to an output terminal
103
and to a drain of the second NMOS
311
, and a source of the second NMOS
311
is connected to the GND terminal
102
.
Also, the power supply terminal
101
is connected to a plus side terminal of a power supply means such as a battery, and the GND terminal
102
is connected to a minus side terminal of the power supply means.
In the conventional voltage detecting circuit thus structured, a voltage detecting portion is made up of the first PMOS
304
, the second PMOS
306
, the D-type NMOS
305
and the first NMOS
307
, a bleeder resistor portion is made up of the first resistor
109
and the second resistor
108
, and an output portion is made up of the output resistor
110
, the output terminal
103
and the second NMOS
311
. Also the bleeder resister portion outputs a divided voltage generated by dividing the voltage of the power supply terminal
101
by the first resistor
109
and the second resistor
108
, and the voltage detecting portion detects the voltage of the divided voltage, to thereby indirectly detect the voltage of the power supply terminal
101
. The output portion reflects the detection result of the voltage detecting portion on the voltage of the output terminal
103
.
In addition,
FIG. 2
shows a graph of the voltage of the output terminal
103
(hereinafter referred to as “output voltage”) to the voltage of the power supply terminal
101
(hereinafter referred to as “power supply voltage”) of the voltage detecting circuit. A bold line and dotted line portion shown in
FIG. 2
is a graph of the above-mentioned conventional voltage detecting circuit. A bold line and thin line portion is a graph of a voltage detecting circuit according to the present invention which will be described later. As is apparent from
FIG. 2
, it is found that when the power supply voltage drops from a state where the output voltage is the power supply voltage, the output voltage becomes the voltage of the GND terminal (hereinafter referred to as “GND voltage”) with a boundary of a given power supply voltage. However, in the case where the output voltage originally drops down to the GND voltage, even if the power supply voltage further drops, the output voltage must naturally maintain the GND voltage. However, when the power supply voltage reaches a given voltage or lower, it is found that there occurs such as phenomenon that the output voltage becomes higher than the GND voltage. A region of the power supply voltage where such a phenomenon occurs is called “indefinite region”, which is caused by a fact that the conventional voltage detecting circuit structured as described above cannot operate due to a drop of the power supply voltage. Also, the above-mentioned conventional voltage detecting circuit enters the indefinite region from a high power supply voltage of about 0.6 V.
The above-mentioned conventional voltage detecting circuit suffers from a problem in that, in an electronic device having the above-mentioned conventional voltage detecting circuit and a load circuit which is driven by a power of the above-mentioned power supply means, the load circuit is reset by using the output voltage of the above-mentioned conventional voltage detecting circuit.
In this case, since the power supply voltage of the load circuit drops with a drop of the voltage of the power supply means such as the battery, when the power supply voltage of the load circuit becomes a given voltage or lower, the load circuit conducts unstable, resulting in a problem in that the electronic device is fatally damaged in a system or hardware fashion.
In order to prevent this problem, it is necessary that in the case where the power of the power supply means becomes a voltage or lower at which the load circuit conducts the unstable operation, the conventional voltage detecting circuit drops the output voltage to the GND voltage from the power supply voltage so as to reset the load circuit, and the conventional voltage detecting circuit maintains the output voltage to the GND voltage until the power of the power supply means becomes a voltage or lower at which the load circuit cannot operate at all, to thereby maintain the reset of the load circuit.
However, the conventional voltage detecting circuit is high in the power supply voltage that enters the indefinite region. Therefore, in the conventional voltage detecting circuit, the power of the power supply means is caused to enter the indefinite region at a voltage which is higher than the voltage at which the load circuit cannot operate at all. For that reson, since the reset of the load circuit is canceled by the power supply voltage at which the load circuit conducts the unstable operation, the problem in that the load circuit is fatally damaged in the systematic or hardware fashion cannot be prevented. Also, this problem becomes increasingly severe since the power supply voltage region where the load circuit unstably operates is also lowered in voltage with the lower voltage operation of the load circuit in recent years.
In order to prevent the above-mentioned problem, in the conventional voltage detecting circuit, there may be applied a method in which the threshold voltages of the respective PMOSs and the respective NMOSs shown in
FIG. 4
are lowered so as to drop the power supply voltage that enters the indefinite region. However, in this case, the leak currents of the respective PMOSs and the respective NMOSs increase with the result that there occurs a problem in that the current consumption of the conventional voltage detecting circuit applying the above method increases.
That is, summarizing the above contents, the conventional voltage detecting circuit has an object that the power supply voltage that enters the unstable region is dropped while preventing an increase in the current consumption in order to prevent the above-mentioned problems.
The above description is given of the problems on the voltage detecting circuit; however, it is needless to say that a CMOS circuit having other functions suffers from common problems in the case where the low voltage operation is required.
SUMMARY OF THE INVENTION
The present invention has been made under the above-mentioned circumstances, and therefore an object of the present invention is to provide a voltage detecting circuit which is capable o
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