Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – With contact or lead
Reexamination Certificate
1999-06-11
2002-12-10
Potter, Roy (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
With contact or lead
C257S355000
Reexamination Certificate
active
06492721
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a high-voltage signal detecting circuit and, more particularly, to a high-voltage signal detecting circuit which is suitable for use in a semiconductor memory device for detecting a mode selection signal.
DESCRIPTION OF THE RELATED ART
In a semiconductor memory device having a plurality of operational modes such as a normal operational mode and a test mode, a high-voltage signal is generally used as a mode selection signal for specifying a mode other than the normal operational mode. The high-voltage signal has a potential higher than the power-source potential used for operating the semiconductor memory device. Thus, the semiconductor memory device has a high-voltage signal detecting circuit for detecting the high-voltage signal.
Referring to
FIG. 1
, a conventional high-voltage signal detecting circuit includes a signal transfer section including an nMOSFET
43
, a pMOSFET
44
and an nMOSFET
45
serially connected in this order from a first input terminal
42
for receiving a high-voltage signal to the ground (GND). The nMOSFET
43
is of a so-called non-doped transistor having a low threshold voltage, and has a gate and a drain connected together to the first input terminal
12
. The substrate of pMOSFET
44
is connected to the source thereof. The gates of pMOSFET
44
and nMOSFET
45
are connected to a second input terminal
41
for receiving a power-source potential. The node
49
connecting both the drains of pMOSFET
44
and nMOSFET
45
together is connected to an input of a potential detecting section including a pair of cascaded inverters
46
and
47
, the output of which constitutes an output terminal
50
.
In the conventional high voltage detecting circuit of
FIG. 1
, if a high-voltage signal having a higher potential than the power-source potential is supplied to the first input terminal
42
, with the second input terminal
41
maintained at the power-source potential, node
49
as well as node
48
connecting the sources of nMOSFET
43
and pMOSFET
44
together rises due to on-state of nMOSFET
44
and pMOSFET
45
in response to the high-voltage signal. Thus, the output of the high-voltage signal detecting circuit rises to a high level.
However, the conventional high-voltage signal detecting circuit has a disadvantage as detailed below.
FIG. 2
shows a specific timing chart of the conventional high-voltage signal detecting circuit of
FIG. 1
, wherein a significant potential which is higher than the ground potential and not higher than the power-source potential is applied to the first input terminal
42
at time instant t
1
before the power-source potential is applied to the second input terminal
41
at time instant t
2
. This may occur when the power switch is turned on to start operation of the semiconductor memory device. In this case, nMOSFET
43
substantially turns on at time instant t
1
due to a high level of the drain and gate potential compared to the source potential thereof. Similarly, pMOSFET substantially turns on at time instant t
1
due to a low level of the gate potential which is substantially at a ground potential at time instant t
1
although the gate potential is in fact at a floating state. Thus, the significant potential penetrates to nodes
48
and
49
, the potentials of which rise after time instant t
1
. The potential at nodes
48
and
49
fall after time instant t
2
due to a fixed power-source potential of the second input terminal
41
. The potential rise of node
49
is transmitted to the output terminal
50
of the high voltage detecting circuit as a high level.
In the fall of the potential at node
49
, nMOSFET
45
discharges electric charge from node
49
to the ground. In general, nMOSFET
45
is designed to have a lower current driveability in view of low penetrating current penetrating therethrough from the first input terminal
42
to the ground. Thus, the output of the high-voltage signal detecting circuit slowly falls down to a low level at time instant t
3
after a relatively long time period. This prevents a higher-speed start-up of the semiconductor memory device. It is generally desired that semiconductor devices including a semiconductor memory device have a short start-up time after switch-on of the semiconductor devices. This should be obtained without causing higher power dissipation due to large penetrating current of MOSFETs.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a high-voltage signal detecting circuit capable of reducing the time period for start-up of a semiconductor memory device without increasing the penetrating current during the normal operational stage of the high-voltage signal detecting circuit.
The present invention provides a high-voltage signal detecting circuit including: a signal transfer section having a first input terminal for receiving an input signal, a second input terminal connected to a first source line for receiving a power source potential, and a first node electrically coupled with the first input terminal and the second input terminal; a potential detecting section for detecting a potential of the first node to output an active signal when the input signal has a higher potential than the power source potential; and a discharge section for discharging electric charge from the first node before the second terminal receives the power source potential.
In accordance with the high-voltage signal detecting circuit of the present invention, the discharge section discharges electric charge from the first node before application of the source potential to the second input terminal. Thus, a quick start-up can be obtained in the semiconductor memory device having the high-voltage signal detecting circuit of the present invention.
REFERENCES:
patent: 61-140876 (1986-06-01), None
patent: 62-22079 (1987-01-01), None
patent: 62-121374 (1987-06-01), None
patent: 1-253670 (1989-10-01), None
patent: 7-12902 (1995-01-01), None
patent: 7229932 (1995-08-01), None
patent: 875801 (1996-03-01), None
patent: 10106299 (1998-04-01), None
NEC Corporation
Potter Roy
Young & Thompson
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