Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – With specific source of supply or bias voltage
Reexamination Certificate
2000-12-08
2002-06-04
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
C327S537000
Reexamination Certificate
active
06400210
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a charge-pump circuit used for a power supply circuit, and relates in particular to a charge-pump circuit that can freely adjust a boosting voltage at a step whereat a voltage is smaller than a power voltage, and that can provide circuit efficiency that is greatly improved.
A charge-pump circuit developed by Digson is so designed that pumping packets are connected in series at multiple stages, and a voltage higher than the power source Vdd of an LSI chip is generated due to the fluctuation of the voltage in each pumping packet. This charge-pump circuit is used, for example, to generate a voltage for programming/erasing flash memories.
This example charge-pump circuit employs an output load current of several tens of &mgr;A. This low load current charge-pump circuit is effective because all the MOSFETs that serve as coupling capacitors or diodes can be incorporated in a single LSI. Recently, as the voltage used for flash memories has been lowered, a charge-pump circuit has been proposed that generates a high voltage and that provides improved boosting efficiency.
Aside from this, the portable devices, such as video cameras, digital cameras and portable telephones, that have recently become popular require high voltages and large currents (several mA) for liquid crystal displays, and for these devices, switching regulators are used as voltage generators.
In accordance with the principle on which a switching regulator is based, a large current flows to a coil while a counterelectromotive force raises the voltage precipitously. The switching regulator is characterized by its efficient production of a high voltage and a large current, and thus it is an appropriate means for providing the power efficiency (output power/input power) that is especially important for portable devices. However, when a large current flows across the coil, harmonic noise is generated, and shielding is required for the power supply circuit in order to prevent the harmonic noise from having an adverse affect. For a portable device, the generation of a high voltage with little attendant noise is desirable because of the reduced size of the unit and the increased sensitivity this entails.
When a voltage loss, such as the threshold value for a diode, is ignored, theoretically, at each stage the pumping packets of the charge-pump circuit receive a boost equivalent to the power voltage Vdd. So that when the input voltage Vin of the charge-pump circuit is defined as Vdd and the pumping packets that are arranged at n stages are connected in series to the power source circuit, the voltage can be boosted by (n+1)×(Vdd−Vt), wherein Vdd denotes the power voltage, and Vt denotes the threshold voltage of a diode in the forward direction. To simplify the following explanation, Vt=0V.
FIG. 8
is a schematic circuit diagram showing a conventional charge-pump circuit (n=4). In
FIG. 8
, diodes D1 to D5 are connected in series, and capacitors C1 to C4 are each connected at one end to a junction of two of the diodes D1 to D5 and at the other end to a clock driver
1
that supplies clocks &PHgr;1 and &PHgr;2, which have reverse phase clock pulses, to the capacitors C1 to C4. A current load
2
is driven by the boosting voltage VH and the output current I
out
that are output by the diode D5. And the charge-pump circuit has four pumping packets and corresponds to a charge-pump circuit having a four-stage arrangement.
The operation of this charge-pump circuit will now be described. When the clock &PHgr;1 at level L and the clock &PHgr;2 at level H are output by the clock driver
1
, the current 2×I
out
flows in the direction indicated by solid-line arrows and I
out
denotes the current output at the final stage by the diode D5.
Then, when the clock &PHgr;1=level H and the clock &PHgr;2=level the current 2×I
out
flows in the direction indicated by broken-line arrows. Since these are alternately flowing currents, voltage boosting is performed at the individual stages, until at the final stage, a boosted voltage VH of 5 Vdd is output by the diode D5.
Supposing that the current output from the diode D5 at the final stage is I
out
, on the average, the current input to the diode D1 at the first stage is equal to I
out
as are the currents flowing in the directions indicated by the solid-line arrows and the broken-line arrows. Therefore, when the efficiency &eegr; of the charge-pump circuit is defined as &eegr;=output power/input power (%), the efficiency &eegr; of the circuit is represented as follows.
&eegr;=5
Vdd×I
out
/Vdd×
5
I
out
=100%
That is, under the operating conditions described above, the efficiency &eegr; of the charge-pump circuit is 100%.
As is described above, the charge-pump circuit outputs the boosted voltage (n+1)×Vdd, wherein n denotes the number of pumping steps in the charge-pump circuit and Vdd denotes a power voltage. Therefore, when Vdd=5V, the theoretical value VHn of the output voltage of a charge pump circuit having n steps is the step voltage for the Vdd step, i.e., when n=1, VH
1
=2×Vdd=10V; when n=2, VH
2
=3×Vdd=15V; and when n=3, VH
3
=4×Vdd=20V.
When the charge-pump circuit is employed as a high voltage generator, a voltage may be adjusted by a regulator in order to set a desired high voltage.
FIG. 9
is a schematic circuit diagram showing an n-step charge-pump circuit that includes a regulator. The same reference numerals as are used in
FIG. 8
are used to denote corresponding or identical components in
FIG. 9
, and no further explanation for them will be given.
In
FIG. 9
, diodes D1 to Dn are connected in series. A boosted voltage VHn output at the final stage by the diode Dn is dropped by a regulator
3
, and the obtained voltage is supplied to a current load
2
. When the final output voltage obtained via the regulator
3
is defined as Vout and the output current is defined as lout, the efficiency &eegr; of the charge pump circuit is defined as
&eegr;=output power/input power=
Vout×Iout
/(
n+
1)×
Vdd×Iout=Vout
/(
n+
1)
Vdd.
When the number n of charge pump steps is large, i.e., the voltage boosting ratio=VHn/Vdd is large, the charge-pump circuit can attain a substantially high efficiency. But when the power voltage fluctuation range is wide and Vout/Vdd is small, efficiency is deteriorated. Assume, then, that the number n of charge pump steps is variable and that Vdd=4 to 5.5V and Vout=6.5V. For this assumption, the step number n=1 is optimal, and for the charge-pump circuit, the efficiency ratios &eegr; provided by Vdd=4V, 5V and 5.5V are as follows.
Vdd = 4 V
n = 1
VH = 8 V
&eegr; = 81%
Vdd = 5 V
n = 1
VH = 10 V
&eegr; = 65%
Vdd = 5.5 V
n = 1
VH = 11 V
&eegr; = 59%
As is apparent, an increase in the power voltage Vdd is accompanied by a deterioration in the efficiency ratio &eegr;. But when n=0.5, the following high efficiency ratios &eegr; can be provided.
Vdd = 4 V
n = 1
VH = 8 V
&eegr; = 81%
Vdd = 5 V
n = 0.5
VH = 7.5 V
&eegr; = 86%
Vdd = 5.5 V
n = 0.5
VH = 8.25 V
&eegr; = 79%
This means that a charge-pump circuit can use 0.5 Vdd steps to boost voltage. However, conventional charge-pump circuits use Vdd steps to boost voltage, and up to the present no charge-pump circuit has been proposed that can use steps smaller than Vdd to boost voltage.
SUMMARY OF THE INVENTION
It is, therefore, one object of the present invention to provide a charge-pump circuit that can use a voltage step smaller than Vdd to boost voltage, and that can attain an improved circuit efficiency ratio &eegr;. Specifically, since the charge-pump circuit proposed by this inventor can theoretically provide output volta
Cunningham Terry D.
Fish & Richardson P.C.
Sanyo Electric Co,. Ltd.
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