Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – With specific source of supply or bias voltage
Reexamination Certificate
2001-10-10
2002-08-13
Callahan, Timothy P. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
With specific source of supply or bias voltage
C327S541000, C327S537000, C307S110000
Reexamination Certificate
active
06433619
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a pump circuit which, for example, is applied to a semiconductor integrated circuit, such as a dynamic RAM and a flash EEPROM, and generates a voltage higher than the supply voltage in the semiconductor integrated circuit.
Recently, low power consumption in semiconductor integrated circuits has been required, and according to this demand a supply voltage has been lowered. However, there are circuits that require a voltage higher than a supply voltage in a semiconductor integrated circuit. By this reason a so-called charge pump circuit is provided for boosting the supply voltage to a predetermined voltage in the semiconductor integrated circuit, and the voltage boosted by the pump circuit is supplied to the circuit requiring a high voltage.
FIG. 29
shows an example of a conventional charge pump circuit. This charge pump circuit constituted of an inverter circuit IV to which an input signal Sin is supplied, a capacitor C as a coupling capacitor whose one end is connected to an output terminal of the inverter circuit IV, and N-channel transistors TN
1
, TN
2
connected to the other end of the capacitor C. The inverter circuit IV is composed of a P-channel transistor TP
1
and an N-channel transistor TN
3
. In this circuit, the voltage of a node ND
1
is transmitted to a node ND
2
via the capacitor C so as to boost the voltage of the node ND
2
.
FIG. 30
is waveforms showing operations of FIG.
29
. The transistor TN
1
is activated at a time t
1
, and the node ND
2
is precharged to a supply voltage Vcc via the transistor TN
1
. After this, the input voltage Sin is made a low level at a time t
2
. Accompanied with this, the node ND
1
is made the supply voltage Vcc via the inverter circuit IV. Then, the electric potential of the node ND
2
is boosted to 2 Vcc via the capacitor C. Next, at a time t
3
, the transistor TN
2
is activated, and the electric potential of the node ND
2
is output as a boosted voltage Vpp via the transistor TN
2
. After this at a time t
4
the input voltage Sin is made a high level, and the inverter IV is inverted.
By the charge pump circuit shown in
FIG. 29
, a required boosted voltage Vpp can be generated. However, this circuit has a problem of a low current efficiency, that is, a high current consumption.
For example, as a method for improving the current efficiency of the charge pump circuit shown in
FIG. 29
, there is a pump circuit described in “An Efficient Charge Recycle and Transfer Pump Circuit for Low Operation Voltage DRAMs, Takeshi Hamamoto et al., 1996 Symposium on VSL
1
Circuit Digest of Technical Papers.” This circuit is constituted, for example, using a plurality of charge pump circuits as shown in
FIG. 29
, and the improvement of the current efficiency is attempted by recycling electric charge of the capacitors of the charge pump circuits.
FIG. 31
shows a conventional two-phase charge recycle pump circuit constituted using two pump circuits resembling the pump circuit described in the above mentioned literature. (In this two-phase charge recycle pump circuit, electric charge is transmitted through one path from a node with a high electric potential to a node with a low electric potential. Thus, this circuit is called two-phase serial charge recycle pump circuit.) Attaching numerals
1
,
2
are added to the same symbols of the same parts in
FIG. 31
as those in FIG.
29
. In this circuit, a transistor TN
4
is connected to charge coupling nodes ND
11
, NQ
12
of capacitors C
11
, C
12
each another. The electric charge of these nodes ND
11
, ND
12
is recycled via the transistor TN
4
.
FIG. 32
shows waveforms showing operations of the circuit shown in FIG.
31
. As shown in
FIG. 32
, in the circuit shown in
FIG. 31
, a P-channel transistor TP
1
is turned on according to a precharge signal PRE, and the node ND
11
is precharged to the supply voltage Vcc. An equalizing signal EQ is activated, and an N-channel transistor TN
4
is turned on, whereby the electric potentials of the node ND
11
and the node ND
12
are made equal. That is, a half of the electric charge of the node ND
11
is transferred to the node ND
12
.
With this, in the circuit shown in
FIG. 31
, since the electric charge of the nodes ND
11
, ND
12
is recycled by the N-channel transistor TN
4
operated according to the equalizing signal EQ, the current efficiency is improved. However, in the case of two-phase charge recycle pump circuit, the fluctuations of the voltages of the nodes ND
11
, ND
12
are decreased to 0.5 Vcc. Thus, the maximum voltage of the boosted voltage Vpp that can be output is reduced from 2 Vcc of the conventional to 1.5 Vcc.
FIG. 33
shows a conventional four-phase charge recycle pump circuit (four-phase serial charge recycle pump circuit) in which capacitors and transistors are further added to the circuit shown in
FIG. 31
, and
FIG. 34
shows waveforms illustrating operations of the circuit shown in FIG.
33
. In the case of four-phase charge recycle pump circuit, the electric charge of the node ND
11
is transferred to other nodes one after another according to the equalizing signal EQ and the precharge signal PRE. Accordingly, since the recycle frequency of the four-phase charge recycle pump circuit is higher compared with the two-phase charge recycle pump circuit, a utilization efficiency of current is improved so as to enable power-saving. However, in this pump circuit, the maximum voltage of the boosted voltage Vpp is reduced from 2 Vcc of the conventional to 1.25 Vcc.
In the case where the number of steps of a pump circuit is increased so as to obtain an n phase, when a maximum voltage Vpp is in vicinity of a supply voltage Vcc, a maximum current efficiency is increased to a level of 1/[1+(1
)]. However, a maximum boosted voltage is decreased to 1/[1+(1
)]Vcc. Accordingly, there is a problem that a high voltage cannot be output and efficiency is reduced in a high voltage area compared with a conventional pump circuit.
FIG. 35
shows an improved pump circuit of the circuit shown in FIG.
31
. This pump circuit is a conventional two-phase charge recycle pump circuit in which the electric charges charged in charge coupling nodes of two capacitors are mutually recycled. (In this two-phase charge recycle pump circuit, electric charge is transmitted bidirectionally from an arbitrary node with a high electric potential to a node with a low electric potential. Thus, this circuit is called two-phase parallel charge recycle pump circuit.)
FIG. 36
is waveforms showing operations of FIG.
35
.
In this pump circuit, the nodes NQ
12
, ND
11
are alternately precharged to a supply voltage Vcc according to precharge signals PRE
1
, PRE
2
. Then, the nodes ND
11
, ND
12
are equalized by an N-channel transistor TN
4
turned on according to the equalizing signal EQ. According to this equalizing operation the electric charges of the nodes ND
11
, NQ
12
are recycled. That is, electric charge is transferred from a node with a high electric potential to a node with a low electric potential by the operation that the nodes ND
11
, NQ
12
precharged to the supply voltage Vcc are equalized, whereby the electric charges remaining in each node ND
11
, ND
12
are recycled. Then, current is supplied from a power supply to the node where electric potential is boosted, and the node where electric potential is lowered is grounded. Operations like this are repeated so as to generate a high voltage.
However, in each conventional charge recycle pump circuit described above, electric charge is not fully recycled. For example, in the case of the circuit shown in
FIG. 35
, the electric charges of the nodes ND
11
, ND
12
are recycled only once. That is, the electric charge transferred in one recycle is the half of the electric charge remaining in each node, and the remaining ½ electric charge is not utilized. By this reason a large amount of current is required in order to obtain a high output voltage, thereby causing difficulty in obtaining a satisfactory current
Akita Hironobu
Banba Hironori
Tsuchida Kenji
Wada Masaharu
Callahan Timothy P.
Kabushiki Kaisha Toshiba
Nguyen Hai L.
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