Voltage control circuit

Details Voltage control circuit Voltage control circuit

2000-11-28

2001-08-28

Berhane, Adolf Deneke (Department: 2838)

Electric power conversion systems

Current conversion

With voltage multiplication means

Reexamination Certificate

active

06282108

ABSTRACT:

FIELD OF THE INVENTION
The invention relates generally to a voltage control circuit, and more particularly to, a voltage control circuit by which the high voltage used in programming flash EEPROM is controlled, thus reducing the consumption power.
BACKGROUND OF THE INVENTION
Flash EEPROMs are programmed or erased by injecting electrons into the floating gate isolated between the control gate (or program gate) and the substrate or ejecting them therefrom.
Generally, in the NOR-type EEPROM cell, injecting electrons is called program, wherein channel hot electron method is usually used. That is, a voltage of about 9 volt is applied to the control gate, a voltage of about 5 volt is applied to the drain and the well and the source are grounded. In this condition, hot carriers are generated around the drain and electrons thereof are thus moved toward the gate by means of the electric field formed by the gate voltage. The program time at this time is about 5 &mgr;s~10 &mgr;s.
However, when a single outside power supply (Vcc is 5 volt, 3.3 volt, 2 volt, etc.) is used, in order to generate a high voltage necessary in programming, a charge pumping method is used. Then, after the voltage becomes higher, it is necessary to keep a constant voltage. The above-mentioned charge pumping method will be explained in detail.
The program voltage control circuit in the conventional flash EEPROM for realizing the charge pumping will be explained by reference to
FIGS. 1 and 2
.
As shown in
FIG. 1
, the conventional program voltage control circuit comprises a charge pump
20
for performing a pumping operation depending on a program signal PGM and an outside clock HVOSC that are inputted from the outside and an adjusting unit
30
for adjusting the output voltage from the charge pump
20
. Also, the adjusting unit
30
comprises a voltage divider
31
for dividing the voltage outputted from the charge pump
20
; a reference voltage generator
32
for generating a reference voltage; and a comparator
33
for comparing the dividing voltage REGLEVEL divided by the voltage divider with the reference voltage REGREF generated from the reference voltage generator
32
to control a leak path
34
depending on the output thereof, as shown in FIG.
2
.
The charge pump
20
and the adjusting unit
30
are enabled by the program signal PGM. The charge pump
20
starts the pumping operation according to the outside clock HVOSC to produce a pumping voltage VPPI.
The pumping voltage VPPI outputted from the charge pump
20
is inputted to the adjusting unit
30
. The pumping voltage VPPI is divided by the voltage divider
31
and is then inputted to the comparator
33
. At this time, the comparator
33
compares the divided voltage REGLEVEL divided by the voltage divider
31
with the reference voltage REGREF produced by the reference voltage generator
32
.
As a result of the comparison, when the divided voltage REGLEVEL becomes higher than the reference voltage REGREF, the comparator outputs a high signal. Due to this high signal, the transistor is turned on, so that remaining charges can be discharged via the leak path
34
.
FIGS. 3A and 3B
are the results of simulation showing variation of the voltage and the current, respectively. From the drawings, it could be seen that the current consumption by the output voltage of the charge pump
20
is similar around 9 volt.
In other words, as the charge pump is operated in a same cycle when the voltage is raised or kept constant, there is a problem that the consumption power is large because a constant amount of current is always consumed from the beginning the program to the end.
SUMMARY OF THE INVENTION
The present invention is contrived to solve the above-mentioned problem and has its object to provide a voltage control circuit in which a control signal is generated when a desired voltage is reached and the operating cycle is increased by the control signal, thus reducing the consumption of current.
In order to accomplish the above-mentioned object, the voltage control circuit according to the present invention is characterized in that it comprises a charge pump for generating a voltage depending on the clock signal inputted thereto; an oscillator for determining the cycle of the clock signal inputted to the charge pump; an adjusting unit for detecting the voltage generated from the charge pump to output an adjusting signal so that the oscillator can vary the cycle of the clock signal inputted to the charge pump.


REFERENCES:
patent: 4961007 (1990-10-01), Kumanoya et al.
patent: 5164889 (1992-11-01), Ruetz
patent: 5642072 (1997-06-01), Miyamoto et al.
patent: 5940283 (1999-08-01), Mihara et al.
patent: 6052022 (2000-04-01), Lee
patent: 6075403 (2000-06-01), Ishikawa et al.
patent: 6128242 (2000-10-01), Banba et al.
patent: 6236581 (2001-05-01), Foss et al.

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