Miscellaneous active electrical nonlinear devices – circuits – and – Specific signal discriminating without subsequent control – By amplitude
Reexamination Certificate
1998-11-18
2001-08-28
Tran, Toan (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific signal discriminating without subsequent control
By amplitude
C327S081000, C327S143000
Reexamination Certificate
active
06281716
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to potential detect circuits, and more particularly, to a potential detect circuit for detecting whether the potential at the output node of a potential generation circuit has arrived at a predetermined target potential level or not.
2. Description of the Background Art
In a flash memory, data “0” or “1” is stored in a memory cell by drawing out or injecting charge from/to a floating gate of the memory cell (refer to FIG.
3
). High voltage is required in drawing out or injecting the charge. The level of the high voltage must be set accurately in order to exactly control the amount of charge drawn out or injected with respect to the floating gate of the memory cell.
This high voltage is generated by a high voltage generation circuit (for example, a charge pump circuit) in the device. However, the voltage generated by the high voltage generation circuit is altered in accordance with the operating condition of the circuit (for example, the power supply voltage level and temperature). The operation of the high voltage generation circuit had to be controlled using a circuit that detects the high voltage.
FIG. 23
is a circuit diagram showing a structure of a conventional high voltage detect circuit. Referring to
FIG. 23
, this high voltage detect circuit includes two resistance elements
101
and
102
connected in series between an output terminal
100
of the high voltage generation circuit and the line of ground potential GND, a comparator
103
formed of P channel MOS transistors
104
and
105
and N channel MOS transistors
106
and
107
, and an inverter
108
. Resistance elements
101
and
102
form a voltage divider circuit. When the potential of output terminal
100
of the high voltage generation circuit is VP and the resistance values of resistance elements
101
and
102
are R
5
and R
6
, respectively, the potential VO of a node N
101
between resistance elements
101
and
102
is VO=VP·R
6
/(R
5
+R
6
).
MOS transistors
104
and
106
and MOS transistors
105
and
107
are connected in series between respective lines of power supply potential VCC and ground potential GND. P channel MOS transistors
104
and
105
have their gates both connected to the drain of P channel MOS transistor
104
. P channel MOS transistors
104
and
105
form a current mirror circuit. N channel MOS transistors
106
and
107
receive potential VO and reference potential Vr
5
at their gates, respectively. The drain of P channel MOS transistor
105
is the output node
103
a
of comparator
103
. The output signal of comparator
103
is inverted by inverter
108
to become a high voltage detect signal /DE.
When potential VP is lower than the target potential and VO is lower than Vr
5
, the resistance value of N channel MOS transistor
106
becomes greater than the resistance value of N channel MOS transistor
107
, whereby node
103
a
is pulled down to an L level to drive signal /DE to an H level. When potential VP exceeds the target potential and VO becomes higher than Vr
5
, the resistance value of N channel MOS transistor
106
becomes smaller than the resistance value of N channel MOS transistor
107
, whereby node
103
a
is pulled up to an H level to drive signal /DE to an L level. The high voltage generation circuit is rendered active and inactive in response to signal /DE of an H level and an L level, respectively. Accordingly, the potential of output terminal
100
is maintained at the target potential.
FIG. 24
is a circuit block diagram showing a structure of another conventional high voltage detect circuit. The high voltage detect circuit of
FIG. 24
differs from the high voltage detect circuit of
FIG. 23
in that resistance element
101
is substituted with a variable resistance circuit
110
.
Referring to
FIG. 24
, variable resistance circuit
110
includes a plurality (three in the drawing) of resistance elements
101
a
-
10
c
connected in series between output terminal
100
and node N
101
, and P channel MOS transistors
111
a
-
111
c
connected in parallel to resistance elements
101
a
-
101
c
, respectively. P channel MOS transistors
111
a
-
111
c
have their gates connected to a control circuit
112
.
The conductive resistances of P channel MOS transistors
111
a
-
111
c
are smaller than resistance values R
5
a
-R
5
c
of resistance elements
101
a
-
101
c
. By rendering conductive a desired one of P channel MOS transistors
111
a
-
111
c
by control circuit
112
, resistance value R
5
of variable resistance circuit
110
can be modified. Since VO/VP becomes smaller as resistance value R
5
becomes greater, VP can be increased by matching VO with Vr
5
. In contrast, VO/VP becomes greater as resistance value R
5
is reduced, so that VP can be set smaller by matching VO with Vr
5
. Therefore, by using this high voltage detect circuit and one charge pump, the level of the high voltage can be switched in response to change in resistance value R
5
of variable resistance circuit
110
.
In the above-described conventional high voltage detect circuit, the voltage conversion factor &Dgr;VO/&Dgr;VP becomes &Dgr;VO/&Dgr;VP=R
6
/(R
5
+R
6
). Since R
6
/(R
5
+R
6
)<1, the voltage conversion factor becomes lower. A lower voltage conversion factor degrades the detection accuracy of the high voltage detect circuit, which in turn reduces the setting accuracy of the level of the high voltage.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of the present invention is to provide a potential detect circuit of high potential detect accuracy.
According to an aspect of the present invention, a voltage detect circuit includes a first resistance element and a constant current circuit connected in series between the output node of a voltage generation circuit and the line of a first reference potential. A second reference potential which is the target potential shifted to the first reference potential side by the voltage generated across the electrodes of the first resistance element is compared with the potential at the node between the first resistance element and the constant current circuit. Therefore, the potential conversion factor becomes 1 to improve the detection accuracy.
Preferably, the current of the constant current circuit is variable. In this case, the target potential can be modified by maintaining the second reference potential constant.
Also preferably, the constant current circuit includes a first transistor and a second resistance element connected in series between the lines of first and second power supply potentials, a control circuit controlling the input voltage of the first transistor so that the potential across the first transistor and the second resistance element matches a third reference potential, and a second transistor connected in series with the first resistance element to conduct a current according to the first transistor. Accordingly, a constant current circuit can be easily implemented.
Also preferably, the resistance value of the second resistance element is variable. In this case, the current of the constant current circuit can be modified by changing the resistance value of the second resistance element.
Also preferably, the current ratio of the first transistor to the second transistor is variable. In this case, the current of the constant current circuit can be modified by changing the current ratio of the first and second transistors.
Also preferably, the resistance value of the first resistance element is variable. In this case, the target potential can be modified by maintaining the first reference potential constant.
Also preferably, the first resistance element is divided into a plurality of third resistance elements connected in series. The second transistor is provided corresponding to each third resistance element, and has a first electrode electrically coupled to the potential of the constant current circuit side of the third resistance element. The potential detect circuit further includes a select
McDermott & Will & Emery
Mitsubishi Denki & Kabushiki Kaisha
Tran Toan
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