Charge pump having very low voltage ripple

Details Charge pump having very low voltage ripple Charge pump having very low voltage ripple

2002-03-18

2003-12-09

Berhane, Adolf D. (Department: 2838)

Electric power conversion systems

Current conversion

With voltage multiplication means

C327S536000

Reexamination Certificate

active

06661683

ABSTRACT:

FIELD OF INVENTION
The present invention relates to charge pump circuits. More particularly, the present invention relates to a charge pump circuit having very low output voltage ripple.
BACKGROUND OF THE INVENTION
The demand for less expensive, and yet more reliable integrated circuit components for use in communication, imaging and high-quality video applications continues to increase rapidly. As a result, integrated circuit manufacturers are requiring improved performance in the voltage supplies and references for such components and devices to meet the design requirements of such emerging applications.
One device utilized for providing a regulated voltage supply is a charge pump circuit. Charge pumps are DC/DC converters that utilize a capacitor instead of an inductor or transformer for energy storage, and are configured for generating positive or negative voltages from the input voltage. A common type of charge pump utilized in circuits comprises one configured for doubling the input voltage, i.e., a charge pump voltage doubler, while other frequently utilized charge pumps comprises tripler and inverter configurations. These charge pumps can operate to multiply the input voltage by some factor, such as by one-half, two, or three times or any other suitable non-integer or factor of the input voltage, to generate the desired output voltage.
Charge pumps typically utilize transistors and/or diodes as switching devices to provide current paths for charge transfer. For example, with reference to
FIG. 1
, a conventional positive charge pump
100
configured as a voltage doubler is illustrated. Charge pump doubler
100
comprises four switches M
1
, M
2
, M
3
and M
4
, a pump capacitor C
PUMP
, and an output or reservoir capacitor C
OUT
. The charging and discharging current of capacitor C
PUMP
is determined by the output load requirements, e.g., by the output load current I
LOAD
.
Charge pump doubler
100
is typically configured by a clock having a 50% duty cycle, i.e., a clock having a clock phase-A and phase-B. During clock phase-A, switches M
1
and M
2
are turned “on” to charge capacitor C
PUMP
to approximately the supply voltage V
IN
, while switches M
3
and M
4
remain in an “off” condition. During clock phase-B, switches M
3
and M
4
are turned “on”, while switches M
1
and M
2
are turned “off”, to charge output capacitor C
OUT
to a higher voltage potential.
If the output voltage V
OUT
is not otherwise regulated, output voltage V
OUT
will reach a value of approximately twice the supply voltage V
IN
if load current I
LOAD
is small. Further, the frequency of the refresh cycle, i.e., the frequency of the charging of output capacitor C
OUT
by charge capacitor C
PUMP
, can be suitably adjusted depending on the circuit load such that power efficiency can be maximized. However, this approach still produces a substantial amount of voltage ripple because output capacitor C
OUT
is only being refreshed 50% of the time, and thus the output load causes the output voltage V
OUT
to drop below its ideal unloaded voltage value. Further, this approach is highly susceptible to the ESR of output capacitor C
OUT
. In other words, the ESR of output capacitor C
OUT
causes additional output ripple as a result of the recharging current that occurs during the output refreshing periods.
Another approach to limit the level of voltage ripple to a tolerable level can include configuring the reservoir or output capacitor with a larger capacitance value. However, such an arrangement is not desirable in that such a larger value capacitor results in a larger total printed circuit board area and higher manufacturing costs.
Yet another approach to reducing the voltage ripple at the output of a charge pump includes the implementation of two charge pump capacitors that alternately refresh an output capacitor. For example, with reference to
FIG. 2
, a charge pump circuit
200
that comprises two flying charge pump capacitors, C
F1
and C
F2
, is illustrated. In this example, charge pump circuit
200
is configured with two control paths, with the charge pump output current split into two parts, I
CONT
and I
BASIC
, and with current I
CONT
and I
BASIC
being made proportional to I
LOAD
using a linear regulator
202
.
While this approach can improve the charge pump output ripple, charge pump circuit
200
still produces a significant amount of voltage ripple due to the existence of an amount of dead time when neither of charge pump capacitors C
F1
and C
F2
are refreshing output capacitor C
OUT
, i.e., the switching between charge pump capacitors C
F1
and C
F2
results in a period of time when no refreshing of output capacitor C
OUT
occurs. In addition, mismatch between output current parts, I
CONT1
and I
CONT2
, can cause additional error that results in additional output voltage ripple.
Yet another approach includes the implementation of a charge pump doubler, the output of which is followed by a low dropout regulator (LDO). For example, with reference to
FIG. 3
, a charge pump circuit
300
is configured to provide a boosted output provided by a charge pump doubler
302
, and then convert the boosted output with a low dropout regulator
304
to a low noise regulated output. However, to produce a low voltage output ripple at output terminal V
OUT
, low dropout regulator
304
has to reject the large ripple on the output of the charge pump doubler at large load currents, which is a difficult task. In addition, this approach is susceptible to any increases in output ripple because the input supply current to charge pump
300
can become quite noisy, and thus the high frequency line rejection characteristics of low dropout regulator
304
become of vital importance. As a result, to maintain low output ripple, the supply current that the low dropout regulator requires can increase as the load current increases so that the low dropout regulator can reject the larger voltage ripple from the charge pump doubler.
Furthermore, charge pump circuit
300
can produce voltages that are significantly higher than the maximum process voltage, i.e., charge pump circuit
300
can require a significantly higher voltage process since the input voltage V
IN
is doubled. For example, for a 4.4 volt input V
IN
, charge pump circuit
300
needs to support 8.8 volts at the output capacitor C
3
, which is significantly higher than the desired output voltage of 5.0 volts at the output V
OUT
. Thus, the voltage across some of the devices within the charge pumps may exceed the maximum allowable voltage for a given process. Accordingly, processes with higher breakdown voltages may be required for charge pump regulator
300
when implemented within integrated circuit applications, thus resulting in increased costs and circuit size compared to circuits implemented in low voltage processes.
Accordingly, a need exists for an improved charge pump circuit configured for providing a very low output ripple.
SUMMARY OF THE INVENTION
The method and circuit according to the present invention addresses many of the shortcomings of the prior art. In accordance with one aspect of the present invention, a charge pump circuit is configured to provide very low ripple as compared to that provided by the prior art charge pump circuits through continuous control of the output of the charge pump circuit. In accordance with an exemplary embodiment, a charge pump circuit is configured for continuous control of the output of the charge pump circuit through continuous use of at least one level-shifting device, such as a charge pump capacitor, coupled with a servo amplifier. During both phases of operation of the charge pump circuit, as well as during the switching phase, the output current from the servo amplifier can be set equal to the load current through a continuous feedback configuration. This servo amplifier configuration facilitates the continuous regulation of the load current, and as a result no load current is drawn from the output capacitor, thus requiring no recharge of the output capacitor.
In accordance with another aspec

Affiliated with

Also associated with

Rating

Charge pump having very low voltage ripple does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Charge pump having very low voltage ripple, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Charge pump having very low voltage ripple will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3151462