Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – With specific source of supply or bias voltage
Reexamination Certificate
2003-01-13
2004-12-28
Tra, Quan (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
With specific source of supply or bias voltage
Reexamination Certificate
active
06836177
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to step-up circuits, and more particularly, step-up circuits that perform a charge pump operation.
To drive an LCD panel, for example, a voltage of 12-18V may be required when the duty is {fraction (1/100)}. However, since the power supply voltage of recent Integrated Circuits (“ICs”) is a DC voltage of 1.8-3.6V, the power supply voltage must be stepped up by a step-up circuit to drive a LCD panel with such voltages.
FIG.
9
(
a
) shows a state in which a step-up circuit is not operating. As indicated in FIG.
9
(
b
), when clock signals V
1
-V
4
are supplied to gates of transistors Q
1
-Q
4
, respectively, the step-up circuit starts its operation, and steps up a voltage between a first power supply potential V
DD
and a second power supply potential V
SS
to output an output potential V
OUT
.
In FIG.
9
(
b
), the transistors Q
2
and Q
4
are turned on, a current flows in a direction indicated by an arrow, and a charge is supplied to a flying capacitor C
1
. In this instance, the power supply potential V
DD
drops momentarily. If the same power supply potential V
DD
is also used in other circuits that are sensitive to changes in the power supply potential, these circuits may possibly malfunction. Furthermore, when a plurality of step-up circuits like the one indicated in FIGS.
9
(
a
) and
9
(
b
) are used, a change in the power supply potential V
DD
tends to become greater.
Accordingly, there is a need for step-up circuits that can reduce and/or possibly eliminate changes in the power supply potential upon starting a step-up circuit.
SUMMARY
A step-up circuit in accordance with a first aspect of the present invention is equipped with a step-up clock signal generation device that generates a clock signal to be used for voltage step-up, a plurality of step-up stages for successively stepping up a power supply voltage based on the clock signal, and a control device that controls, after starting an operation, the clock signal generated by the step-up clock signal generation device to be supplied to the plurality of step-up stages at different timings.
In some embodiments, the step-up clock signal generation device may generate a clock signal to be used for voltage step-up based on a clock signal applied, and the control device may include a counter that counts the clock signal applied to the step-up clock signal generation circuit, and a plurality of output control circuits that respectively supply, based on different output values of the counter, the clock signal generated by the step-up clock signal generation circuit to the plurality of step-up stages.
Alternatively, in other embodiments, the control device may include a counter that counts pulse signals applied, and a plurality of output control circuits that respectively supply, based on different output values of the counter, the clock signal generated by the step-up clock signal generation circuit to the plurality of step-up stages.
A step-up circuit in accordance with a second aspect of the present invention may be equipped with a step-up clock signal generation circuit that generates a clock signal to be used for voltage step-up, a plurality of step-up stages that successively step up a power supply voltage based on the clock signal, and a control device that, after a start of operation, activates the plurality of step-up stages at different timings.
In some embodiments, the step-up clock signal generation device may generate a clock signal to be used for voltage step-up based on a clock signal applied. The control device may include a counter that counts the clock signal applied to the step-up clock signal generation circuit. The plurality of output stages can be activated based on different output values of the counter.
Alternatively, the control device may include a counter that counts pulse signals applied. The plurality of step-up stages can be activated based on different output values of the counter.
A step-up circuit in accordance with a third aspect of the present invention is equipped with a step-up clock signal generation device that generates a clock signal to be used for voltage step-up, at least one step-up stage that steps up a power supply voltage based on the clock signal, and a control device that, after starting an operation, changes a frequency of the clock signal to be supplied to the step-up stage from a value lower than a normal value to the normal value.
In some embodiments, the control device may include a plurality of frequency-divider circuits that frequency-divide the clock signal generated by the step-up clock signal generation device, and respectively output a plurality of frequency-divided clock signals having different frequency division ratios, a selector circuit that selects, based on a control signal, one of the clock signal and the plurality of frequency-divided clock signals, and a counter that counts the clock signal selected by the selector circuit to thereby generate the control signal. The step-up stage may step up the power supply voltage based on the clock signal selected by the selector circuit.
Alternatively, the control device may include a plurality of frequency-divider circuits that frequency-divide a clock signal applied, and respectively output a plurality of frequency-divided clock signals having different frequency division ratios, a selector circuit that selects, based on a control signal, one of the clock signal and the plurality of frequency-divided clock signals, and a counter that counts the clock signal selected by the selector circuit to thereby generate the control signal. The step-up clock signal generation circuit may generate, based on the clock signal selected by the selector circuit, a clock signal to be used for voltage step-up.
In other embodiments, the control device may include a plurality of frequency-divider circuits that frequency-divide a clock signal applied, and respectively output a plurality of frequency-divided clock signals having different frequency division ratios, a counter that counts pulse signals applied, and a selector circuit that selects, based on an output value of the counter, one of the clock signal and the plurality of frequency-divided clock signals, and the step-up clock signal generation circuit may generate, based on the clock signal selected by the selector circuit, a clock signal to be used for voltage step-up.
In accordance with the first aspect of the present invention, after an operation is started, the clock signals generated by the step-up clock signal generation device are supplied to a plurality of step-up stages at different timings, such that changes in the power supply potential can be reduced at the time of starting an operation of the step-up circuit.
Also, in accordance with the second aspect of the present invention, after an operation is started, a plurality of step-up stages are activated at different timings, such that changes in the power supply potential can be reduced at the time of starting an operation of the step-up circuit.
Furthermore, in accordance with the third aspect of the present invention, after an operation is started, the frequency of a clock signal to be supplied to a plurality of step-up stages is changed from a value lower than a normal value to the normal value, such that changes in the power supply potential can be reduced at the time of starting an operation of the step-up circuit.
REFERENCES:
patent: 6100752 (2000-08-01), Lee et al.
patent: 6469569 (2002-10-01), Miyamitsu
patent: 6693483 (2004-02-01), Deml et al.
Hogan & Hartson LLP
Seiko Epson Corporation
Tra Quan
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