Charge pump circuit having variable oscillation period

Details Charge pump circuit having variable oscillation period Charge pump circuit having variable oscillation period

1999-12-27

2001-09-25

Cunningham, Terry D. (Department: 2816)

Miscellaneous active electrical nonlinear devices, circuits, and

Specific identifiable device, circuit, or system

With specific source of supply or bias voltage

C327S102000

Reexamination Certificate

active

06294950

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a boosting circuit for a semiconductor memory device, and in particular to a charge pump circuit which can vary an oscillation period in proportion to charge consumption of a charge pump.
2. Description of the Background Art
FIG. 1
illustrates a conventional charge pump circuit having a single oscillation period. As shown therein, the conventional charge pump circuit having the single oscillation period includes: a voltage divider
100
dividing a boosting voltage Vboot to a predetermined level; a comparator
102
comparing a divided voltage Vdiv outputted from the voltage divider
100
with a reference voltage Vref, and outputting a control voltage Vcon; a ring oscillator
104
outputting a pulse signal OSC having a fixed oscillation period in accordance with the control voltage Vcon outputted from the comparator
102
; and a charge pump
106
performing a pumping operation in accordance with the pulse signal OSC outputted from the oscillator
104
, and outputting a boosting voltage Vboot.
The ring oscillator
104
includes a plurality of inverters composing a ring. An RC integral circuit is inserted between the inverters, respectively. In addition, a last inverter of the plurality of inverters is a clocked inverter controlled by the control voltage Vcon of the comparator
102
.
The charge pump
106
includes a first pumping capacitor Cp
1
connected between an input node (a) and a first node (b); an output transistor
11
connected between the first node (b) and an output node (e), and transmitting a voltage of the first pumping capacitor Cp
1
to the output node (e); an inverter IN
1
and a second pumping capacitor Cp
2
which are sequentially connected between the input node (a) and a second node (c); a diode type n-channel MOSFET
12
connected between a power supply voltage Vdd and the first node (b), and precharging the first pumping capacitor Cp
1
; a third pumping capacitor Cp
3
connected between the input node (a) and a third node (d); and a diode type n-channel MOSFET
14
connected between a common node of the third node (d) and the output transistor
11
and the power supply voltage. Here, the first pumping capacitor Cp
1
has a considerably large size, as compared with the second and third pumping capacitors Cp
2
, Cp
3
which have an identical size.
The operation of the thusly-constituted charge pump circuit having the single oscillation period will now be described with reference to the accompanying drawings.
When the power supply voltage Vdd is applied, and the reference voltage Vref is inputted, a high-level control signal Vcon is outputted from the comparator
102
, thereby enabling the ring oscillator
104
. The enabled ring oscillator
104
outputs the pulse signal OSC having a fixed oscillation frequency.
FIG. 4A
illustrates an example of the pulse signal OSC outputted in a standby mode and an active mode in the conventional charge pump circuit having the single oscillation period. Accordingly, the charge pump
106
performs the pumping operation pursuant to the level of the pulse signal OSC outputted from the ring oscillator
104
, thereby outputting the boosting voltage Vboot having a predetermined level.
The pumping operation of the charge pump will now be explained in more detail.
In case the pulse signal PSC is at a high level, the second pumping capacitor Cp
2
is charged up with a voltage Vdd-Vth
2
dropped by a threshold voltage Vth
2
of the diode type n-channel MOSFET
12
. When the pulse signal PSC is at a low level, the third pumping capacitor Cp
3
is charged up with a voltage Vdd-Vth
3
dropped by a threshold voltage Vth
3
of the diode type n-channel MOSFET
14
. Here, the voltage of the second and third nodes (c), (d) is Vdd-Vth
2
and Vdd-Vth
3
, respectively.
Therefore, when it is presumed that the pulse signal OSC outputted from the ring oscillator
104
is at a low level, the second pumping capacitor Cp
2
charged up at the Vdd-Vth
2
level in a previous cycle carries out the pumping operation in accordance with the pulse signal OSC inverted in the inverter IN
1
, and thus the voltage of the Vdd-Vth
1
level dropped by a threshold voltage Vth
1
of the n-channel MOSFET
13
is precharged in the first node (b).
Thereafter, when the pulse signal OSC is transited from low to high, the first and third pumping capacitors Cp
1
, Cp
3
perform the charge pumping operation, and the second pumping capacitor Cp
2
is re-charged up at the Vdd-Vth
2
level by the diode type n-channel MOSFET
12
. As a result, the output transistor
11
is turned on by the voltage of the third node (d), and thus the voltage of the first node (b) boosted in the first pumping capacitor Cp
1
is outputted into the output node (e) via the output transistor
11
.
Accordingly, the voltage divider
100
divides the boosting voltage Vboot outputted from the charge pump
106
, and the comparator
102
compares the divided voltage Vdiv outputted from the voltage divider
100
with the reference voltage Vref, and judges whether to keep performing the pumping operation of the charge pump
106
. That is, when the divided voltage Vdiv is smaller than the reference voltage Vref, the ring oscillator
104
is enabled, thereby keep performing the pumping operation of the charge pump
106
. In case the divided voltage Vdiv is greater than the reference voltage Vref, the ring oscillator
104
is disabled, thereby stopping the pumping operation of the charge pump
106
.
However, in the conventional charge pump circuit having the single oscillation period, referring to
FIG. 5
, an oscillation frequency of the ring oscillator
104
is fixed to have a value f
1
in order to maximally maintain the pumping efficiency Emax of the charge pump
106
both in the active mode and the standby mode. Accordingly, the conventional charge pump circuit having the single oscillation period has a disadvantage in that power consumption is increased in the standby mode.
In addition, in the conventional charge pump circuit having the single oscillation period, the first pumping capacitance Cp
1
of the charge pump
106
must be maintained to be considerably large in order to satisfy a maximal charge consumption demand (maximal pumping efficiency). Consequently, the conventional charge pump circuit having the single oscillation period has another disadvantage in that a size of the charge pump
106
is increased by the first pumping capacitor Cp
1
.
FIG. 2
illustrates a conventional charge pump circuit having a dual oscillation period. As shown therein, the charge pump circuit having the dual oscillation period further includes an oscillator delay unit
108
, as compared with the conventional charge pump circuit having the single oscillation period. The oscillator delay unit
108
is constituted identically to the ring oscillator
104
, and connected to or disconnected from the ring oscillator
104
by first and second switches SW
1
, SW
2
.
Accordingly, the first and second switches SW
1
, SW
2
are operated pursuant to a mode discriminating signal MDS, and connect the oscillator delay unit
108
to the ring oscillator
104
in the active mode, and disconnect the oscillator delay unit
108
therefrom in the standby mode. As a result, the oscillation frequency of the pulse signal OSC outputted from the ring oscillator
104
is fixed to have a different value in the active mode and the standby mode. That is to say, the oscillation frequency of the ring oscillator
104
is fixed to be a value f
1
(high frequency) for satisfying the maximal charge consumption demand in the active mode, and to be a value (low frequency) for satisfying low charge consumption in the standby mode.
FIG. 4B
illustrates an example of the pulse signal OSC outputted in the standby mode and the active mode in the conventional charge pump circuit having the dual oscillation period.
However, in the conventional charge pump circuit having the dual oscillation period, the capacitance of the first pumping capacitor Cp
1
must satisfy the maximal ch

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