U.S. patent application number 14/138493 was filed with the patent office on 2015-06-25 for method and system for controlling a charge pump.
This patent application is currently assigned to NXP B.V.. The applicant listed for this patent is NXP B.V.. Invention is credited to Sergio Masferrer, Jukka Riihiaho, Maurits Mario Nicolaas Storms.
Application Number | 20150180458 14/138493 |
Document ID | / |
Family ID | 52023331 |
Filed Date | 2015-06-25 |
United States Patent
Application |
20150180458 |
Kind Code |
A1 |
Masferrer; Sergio ; et
al. |
June 25, 2015 |
METHOD AND SYSTEM FOR CONTROLLING A CHARGE PUMP
Abstract
Embodiments of a method for controlling a charge pump and a
control device for a charge pump are described. In one embodiment,
a method for controlling a charge pump involves monitoring a
power-on status of the charge pump, calculating a duty cycle of the
charge pump within a time period based on the power-on status of
the charge pump, and adjusting at least one of a clock frequency
setting and a capacitance setting of the charge pump in based on
the duty cycle of the charge pump. Other embodiments are also
described.
Inventors: |
Masferrer; Sergio;
(Eindhoven, NL) ; Storms; Maurits Mario Nicolaas;
(Best, NL) ; Riihiaho; Jukka; (Vantaa,
FI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NXP B.V. |
Eindhoven |
|
NL |
|
|
Assignee: |
NXP B.V.
Eindhoven
NL
|
Family ID: |
52023331 |
Appl. No.: |
14/138493 |
Filed: |
December 23, 2013 |
Current U.S.
Class: |
327/175 |
Current CPC
Class: |
H02M 3/07 20130101; H03K
5/1565 20130101 |
International
Class: |
H03K 5/156 20060101
H03K005/156 |
Claims
1. A method for controlling a charge pump, the method comprising:
monitoring a power-on status of the charge pump; calculating a duty
cycle of the charge pump within a time period based on the power-on
status of the charge pump; and adjusting at least one of a clock
frequency setting and a capacitance setting of the charge pump
based on the duty cycle of the charge pump.
2. The method of claim 1, wherein the time period is a multiple of
one clock time period of a clock signal.
3. The method of claim 1, wherein the time period is one clock time
period of a first clock signal with a frequency that is not
correlated with the frequency of a second clock signal.
4. The method of claim 1, wherein calculating the duty cycle of the
charge pump based on the power-on status comprises: determining an
amount of time that the charge pump is powered on during the time
period; and calculating the duty cycle as a ratio of the amount of
time that the charge pump is powered on to the time period.
5. The method of claim 1, wherein adjusting the at least one of the
clock frequency setting and the capacitance setting of the charge
pump comprises changing a frequency of a clock signal that is used
to drive the charge pump or a total pumping capacitance of the
charge pump if the duty cycle of the charge pump is larger than at
least one maximum threshold or smaller than at least one minimum
threshold within the time period.
6. The method of claim 5, wherein changing the frequency of the
clock signal that is used to drive the charge pump or the total
pumping capacitance of the charge pump comprises: increasing the
frequency of the clock signal that is used to drive the charge pump
or the total pumping capacitance of the charge pump if the duty
cycle of the charge pump is larger than the at least one maximum
threshold; and decreasing the frequency of the clock signal that is
used to drive the charge pump or the total pumping capacitance of
the charge pump if the duty cycle of the charge pump is smaller
than the at least one minimum threshold.
7. The method of claim 1, further comprising: defining or obtaining
a plurality of intensity levels of clock frequency settings and
capacitance settings of the charge pump, wherein each intensity
level comprises a unique combination of a frequency of a clock
signal that is used to drive the charge pump and a total pumping
capacitance of the charge pump.
8. The method of claim 7, wherein adjusting the at least one of the
clock frequency setting and the capacitance setting of the charge
pump comprises: changing an intensity level of the clock frequency
setting and the capacitance setting of the charge pump based on the
duty cycle of the charge pump within the time period.
9. The method of claim 8, wherein changing the intensity level of
the clock frequency setting and the capacitance setting of the
charge pump further comprises changing the intensity level of the
clock frequency setting and the capacitance setting of the charge
pump to a different intensity level in the intensity levels if the
duty cycle of the charge pump is larger than at least one maximum
threshold or smaller than at least one minimum threshold.
10. The method of claim 7, wherein adjusting the at least one of
the clock frequency setting and the capacitance setting of the
charge pump comprises: if the duty cycle of the charge pump is
larger than at least one maximum threshold, changing a current
intensity level of the clock frequency setting and the capacitance
setting of the charge pump to a different intensity level in the
intensity levels with a higher frequency of the clock signal that
is used to drive the charge pump or a larger total pumping
capacitance of the charge pump; and if the duty cycle of the charge
pump is smaller than at least one minimum threshold, changing the
current intensity level to a different intensity level in the
intensity levels with a lower frequency of the clock signal that is
used to drive the charge pump or a smaller total pumping
capacitance of the charge pump.
11. A control device for a charge pump, the control device
comprising: a monitor module configured to monitor a power-on
status of the charge pump; and a controller module configured to
calculate a duty cycle of the charge pump within a time period
based on the power-on status of the charge pump and to adjust at
least one of a clock frequency setting and a capacitance setting of
the charge pump based on the duty cycle of the charge pump.
12. The control device of claim 11, wherein the time period is a
multiple of one clock time period of a clock signal.
13. The control device of claim 11, wherein the time period is one
clock time period of a first clock signal with a frequency that is
not correlated with the frequency of a second clock signal.
14. The control device of claim 11, wherein the controller module
is further configured to change a frequency of a clock signal that
is used to drive the charge pump or a total pumping capacitance of
the charge pump if the duty cycle of the charge pump is larger than
at least one maximum threshold or smaller than at least one minimum
threshold within the time period.
15. The control device of claim 11, wherein the controller module
is further configured to: define or obtain a plurality of intensity
levels of clock frequency settings and capacitance settings of the
charge pump, wherein each intensity level comprises a unique
combination of a frequency of a clock signal that is used to drive
the charge pump and a total pumping capacitance of the charge
pump.
16. The control device of claim 15, wherein the controller module
is further configured to: change an intensity level of the clock
frequency setting and the capacitance setting of the charge pump
based on the duty cycle of the charge pump within the time
period.
17. The control device of claim 16, wherein the controller module
is further configured to change the intensity level of the clock
frequency setting and the capacitance setting of the charge pump to
a different intensity level in the intensity levels if the duty
cycle of the charge pump is larger than at least one maximum
threshold or smaller than at least one minimum threshold.
18. The control device of claim 15, wherein the controller module
is further configured to: if the duty cycle of the charge pump is
larger than at least one maximum threshold, change a current
intensity level of the clock frequency setting and the capacitance
setting of the charge pump to a different intensity level in the
intensity levels with a higher frequency of the clock signal that
is used to drive the charge pump or a larger total pumping
capacitance of the charge pump; and if the duty cycle of the charge
pump is smaller than at least one minimum threshold, change the
current intensity level to a different intensity level in the
intensity levels with a lower frequency of the clock signal that is
used to drive the charge pump or a smaller total pumping
capacitance of the charge pump.
19. An integrated circuit device comprising the control device and
the charge pump of claim 11.
20. A method for controlling a charge pump, the method comprising:
obtaining a plurality of intensity levels of clock frequency
settings and capacitance settings of the charge pump, wherein each
intensity level comprises a unique combination of a frequency of a
clock signal that is used to drive the charge pump and a total
pumping capacitance of the charge pump; calculating a duty cycle of
the charge pump within a time period based on a power-on status of
the charge pump; if the duty cycle of the charge pump is smaller
than at least one minimum threshold, changing an intensity level of
a clock frequency setting and a capacitance setting of the charge
pump to a different intensity level in the intensity levels with a
lower frequency of the clock signal that is used to drive the
charge pump or a smaller total pumping capacitance of the charge
pump; if the duty cycle of the charge pump is larger than at least
one maximum threshold, changing the intensity level of the clock
frequency setting and the capacitance setting of the charge pump to
a different intensity level in the intensity levels with a higher
frequency of the clock signal that is used to drive the charge pump
or a larger total pumping capacitance of the charge pump; and if
the duty cycle of the charge pump is smaller than the at least one
maximum threshold and larger than the at least one minimum
threshold, keeping the intensity level of the clock frequency
setting and the capacitance setting of the charge pump the same.
Description
[0001] Charge pumps are Direct Current (DC)-to-DC voltage converter
circuits that can increase or decrease a voltage level provided by
a voltage power source. Charge pumps are used in various
applications/devices, such as memory circuits, level shifters, and
battery devices. Conventional charge pumps are designed to meet
prescribed specifications under worst case process, voltage, and
temperature (PVT) conditions. However, under normal or best PVT
conditions, the performance of conventional charge pumps can
degrade. For example, the power consumption and the output current
of conventional charge pumps often rise to high levels under normal
or best case PVT conditions. Consequently, under normal or best
case PVT conditions, conventional charge pumps suffer from high
current peaks and high average currents. To deal with high current
peaks and high average currents, large low ohmic power switches and
large decoupling capacitors are included on substrates next to the
charge pumps to stabilize the voltage supply. In some cases,
additional Low-dropout regulators (LDOs) have to be used to
regulate supply voltages down to acceptable levels. In addition,
conventional charge pumps can suffer from high output ripples that
may damage their load circuits. Therefore, there is a need for a
charge pump that can perform well under various PVT conditions.
[0002] Embodiments of a method for controlling a charge pump and a
control device for a charge pump are described. In one embodiment,
a method for controlling a charge pump involves monitoring a
power-on status of the charge pump, calculating a duty cycle of the
charge pump within a time period based on the power-on status of
the charge pump, and adjusting at least one of a clock frequency
setting and a capacitance setting of the charge pump based on the
duty cycle of the charge pump. By monitoring the power-on status of
the charge pump, calculating the duty cycle of the charge pump, and
adjusting the setting of the charge pump based on the duty cycle of
the charge pump, the performance of the charge pump can be easily
managed to adapt to various PVT conditions. Other embodiments are
also described.
[0003] In one embodiment, a method for controlling a charge pump
involves monitoring a power-on status of the charge pump,
calculating a duty cycle of the charge pump within a time period
based on the power-on status of the charge pump, and adjusting at
least one of a clock frequency setting and a capacitance setting of
the charge pump based on the duty cycle of the charge pump.
[0004] In one embodiment, a control device for a charge pump
includes a monitor module configured to monitor a power-on status
of the charge pump and a controller module configured to calculate
a duty cycle of the charge pump within a time period based on the
power-on status of the charge pump and to adjust at least one of a
clock frequency setting and a capacitance setting of the charge
pump based on the duty cycle of the charge pump.
[0005] In one embodiment, a method for controlling a charge pump
involves obtaining intensity levels of clock frequency settings and
capacitance settings of the charge pump where each intensity level
includes a unique combination of a frequency of a clock signal that
is used to drive the charge pump and a total pumping capacitance of
the charge pump, calculating a duty cycle of the charge pump within
a time period based on a power-on status of the charge pump, if the
duty cycle of the charge pump is smaller than at least one minimum
threshold, changing an intensity level of a clock frequency setting
and a capacitance setting of the charge pump to a different
intensity level in the intensity levels with a lower frequency of
the clock signal that is used to drive the charge pump or a smaller
total pumping capacitance of the charge pump, if the duty cycle of
the charge pump is larger than at least one maximum threshold,
changing the intensity level of the clock frequency setting and the
capacitance setting of the charge pump to a different intensity
level in the intensity levels with a higher frequency of the clock
signal that is used to drive the charge pump or a larger total
pumping capacitance of the charge pump, and if the duty cycle of
the charge pump is smaller than the at least one maximum threshold
and larger than the at least one minimum threshold, keeping the
intensity level of the clock frequency setting and the capacitance
setting of the charge pump the same.
[0006] Other aspects and advantages of embodiments of the present
invention will become apparent from the following detailed
description, taken in conjunction with the accompanying drawings,
depicted by way of example of the principles of the invention.
[0007] FIG. 1 is a schematic block diagram of an IC device in
accordance with an embodiment of the invention.
[0008] FIG. 2 depicts an embodiment of the charge pump circuit
depicted in FIG. 1.
[0009] FIG. 3 depicts examples of waveforms of clock signals and a
power-on status signal of the charge pump circuit depicted in FIG.
2.
[0010] FIG. 4 is a flow chart that illustrates an operation of the
controller module depicted in FIG. 2.
[0011] FIG. 5 depicts some examples of operational parameters of
the charge pump depicted in FIG. 2.
[0012] FIG. 6 depicts an embodiment of the controller module
depicted in FIG. 2.
[0013] FIG. 7 is a process flow diagram that illustrates a method
for controlling a charge pump in accordance with an embodiment of
the invention.
[0014] Throughout the description, similar reference numbers may be
used to identify similar elements.
[0015] It will be readily understood that the components of the
embodiments as generally described herein and illustrated in the
appended figures could be arranged and designed in a wide variety
of different configurations. Thus, the following detailed
description of various embodiments, as represented in the figures,
is not intended to limit the scope of the present disclosure, but
is merely representative of various embodiments. While the various
aspects of the embodiments are presented in drawings, the drawings
are not necessarily drawn to scale unless specifically
indicated.
[0016] The described embodiments are to be considered in all
respects only as illustrative and not restrictive. The scope of the
invention is, therefore, indicated by the appended claims rather
than by this detailed description. All changes which come within
the meaning and range of equivalency of the claims are to be
embraced within their scope.
[0017] Reference throughout this specification to features,
advantages, or similar language does not imply that all of the
features and advantages that may be realized with the present
invention should be or are in any single embodiment. Rather,
language referring to the features and advantages is understood to
mean that a specific feature, advantage, or characteristic
described in connection with an embodiment is included in at least
one embodiment. Thus, discussions of the features and advantages,
and similar language, throughout this specification may, but do not
necessarily, refer to the same embodiment.
[0018] Furthermore, the described features, advantages, and
characteristics of the invention may be combined in any suitable
manner in one or more embodiments. One skilled in the relevant art
will recognize, in light of the description herein, that the
invention can be practiced without one or more of the specific
features or advantages of a particular embodiment. In other
instances, additional features and advantages may be recognized in
certain embodiments that may not be present in all embodiments of
the invention.
[0019] Reference throughout this specification to "one embodiment,"
"an embodiment," or similar language means that a particular
feature, structure, or characteristic described in connection with
the indicated embodiment is included in at least one embodiment.
Thus, the phrases "in one embodiment," "in an embodiment," and
similar language throughout this specification may, but do not
necessarily, all refer to the same embodiment.
[0020] FIG. 1 is a schematic block diagram of an IC device 100 in
accordance with an embodiment of the invention. In the embodiment
depicted in FIG. 1, the IC device includes a clock circuit 102, a
charge pump 104, and a charge pump controller 106. The charge pump
and the charge pump controller form a charge pump circuit 108. The
IC device can be used in various applications, such as automotive
applications, communications applications, industrial applications,
medical applications, computer applications, and/or consumer or
appliance applications. The IC device can be implemented in a
substrate, such as a semiconductor wafer or a printed circuit board
(PCB). In an embodiment, the IC device is packaged as a
semiconductor IC chip. The IC device may be included in a
microcontroller, which can be used for, for example, in device
control, identification, and/or wireless communications. In some
embodiments, the IC device is included in a memory device, such as
a flash memory module. Although the IC device 100 is shown in FIG.
1 as including certain components, in some embodiments, the IC
device includes less or more components to implement less or more
functionalities. For example, the IC device may include memory
cells or other circuit elements.
[0021] The clock circuit 102 is configured to generate a clock
signal, "CLK," for the IC device 100 with a frequency, "f.sub.CLK."
The clock circuit may include a crystal oscillator or other
suitable clock generator and the clock signal, "CLK," may be in the
form of a square wave or other suitable waveform. In an embodiment,
a clock signal, "CLK_GB," (with a frequency,
"f.sub.CLK.sub.--.sub.GB") of the charge pump controller 106 and a
clock signal, "CLK_PUMP," (with a frequency,
"f.sub.CLK.sub.--.sub.PUMP") that is used to drive the charge pump
104 are derived from the clock signal, "CLK." The clock signal,
"CLK," is typically an internal clock with a frequency,
"f.sub.CLK," that changes with process, voltage, and temperature
(PVT) conditions. Because the clock signal, "CLK_GB," is derived
from the clock signal, "CLK," the clock time period of the clock
signal, "CLK_GB," is adjusted to the changes of the clock signal,
"CLK" under various PVT conditions. The frequency,
"f.sub.CLK.sub.--.sub.GB," of the clock signal, "CLK_GB," that is
used to drive the charge pump controller is typically a fraction of
the frequency, "f.sub.CLK," of the clock signal, "CLK." The
frequency, "f.sub.CLK.sub.--.sub.PUMP," of the clock signal,
"CLK_PUMP," that is used to drive the charge pump may be the same
as, or a fraction of, the frequency, "f.sub.CLK," of the clock
signal, "CLK." However, in other embodiments, the clock signal,
"CLK_GB," that is used to drive the charge pump controller 106 is
not derived from the clock signal, "CLK," that is generated by the
clock circuit 102.
[0022] The charge pump 104 is a Direct Current (DC)-to-DC voltage
converter circuit that uses one or more energy storage elements 110
(e.g., capacitors) to increase or decrease a voltage level provided
by a voltage power source. The charge pump typically includes one
or more switching devices, such as n-channel MOSFET (NMOS)
transistors or p-channel MOSFET (PMOS) transistors. A charge pump
can control the charging and discharging of the energy storage
elements so as to increase or decrease an input voltage of the
charge pump to obtain a desired output voltage. The output voltage
of the charge pump 104 may be higher than, equal to, or lower than
the input voltage of the charge pump 104. The charge pump may be
used to generate the power supply for a memory circuit, such as a
non-volatile memory circuit, or any other suitable circuit. In an
embodiment, the charge pump up converts an input voltage into a
higher output voltage for a flash memory.
[0023] The charge pump controller 106 is configured to control the
charge pump 104. The charge pump controller, which can also be
referred to as a charge pump strength gear box, monitors the
activity of the charge pump continuously and adjusts/shifts a
setting of an operational parameter (e.g., at least one of a clock
frequency setting and a capacitance setting) of the charge pump.
For example, the charge pump controller can increase/divide the
clock frequency of the charge pump (e.g., the frequency,
"f.sub.CLK.sub.--.sub.PUMP," of the clock signal, "CLK_PUMP," that
that is used to drive the charge pump) and/or the total pumping
capacitance of the charge pump based on an operation status of the
charge pump. By continuously monitoring the activity of the charge
pump and adjusting/shifting the frequency of the charge pump clock
as well as the size of the charge pump capacitance, the charge pump
controller provides a continuous-time regulation loop that adapts
the power and output current of the charge pump through a range of
process, voltage, temperature (PVT), load capacitance and leakage
current variations. In addition, the charge pump controller is
self-adjustable or self-trimmed because the charge pump controller
provides a continuous-time regulation loop. Consequently, no
pre-calibration process is required for the charge pump controller
to control the charge pump.
[0024] The activity status of the charge pump 104 may include an
operation status of the charge pump, such as a power-on status of
the charge pump. In some embodiments, the charge pump controller
106 monitors the power-on status of the charge pump 104 and adjusts
at least one of a clock frequency setting and a capacitance setting
of the charge pump based on the power-on status. In an embodiment,
the power-on status of the charge pump specifies whether or not the
charge pump is powered on and how long the charge pump is powered
on. When the charge pump is powered on, the charge pump generates
an output voltage based on an input voltage. When the charge pump
is not powered on, the charge pump does not generate an output
voltage. Based on the power-on status of the charge pump, the
charge pump controller calculates a duty cycle of the charge pump
within a time period. In some embodiments, the time period is a
multiple of one clock time period of a clock signal (e.g., the
clock signal, "CLK,") or one clock time period of another clock
signal (e.g., the clock signal, "CLK_GB,") with a frequency that is
not correlated with (e.g., the same as) the frequency of the clock
signal. In an embodiment, the duty cycle of the charge pump is the
percentage of time that the charge pump is in an active state
(e.g., the powered-on state) as a fraction of the total time under
consideration. The charge pump controller may change the frequency,
"f.sub.CLK.sub.--.sub.PUMP," of the clock signal, "CLK_PUMP," that
is used to drive the charge pump or the total pumping capacitance
of the charge pump if the duty cycle of the charge pump is larger
than at least one maximum threshold or smaller than at least one
minimum threshold within the time period.
[0025] The charge pump controller 106 can determine an amount of
time that the charge pump 104 is powered on during a time period
and calculate the duty cycle of the charge pump as a ratio of the
amount of time that the charge pump is powered on to the time
period. In an embodiment, the charge pump controller calculates a
ratio of the time period to a unit clock period. The time period
may be one clock period of the clock signal, "CLK_GB," that is used
to drive the charge pump controller. The unit clock period may be
one clock period of the clock signal, "CLK," from the clock circuit
102. In this embodiment, for each unit clock period within the time
period, the charge pump controller determines whether the charge
pump is powered on and increases a counter value by one if the
charge pump is powered on. The charge pump controller calculates
the duty cycle as a ratio of the counter value to the clock
frequency ratio. However, in other embodiments, the duty cycle of
the charge pump is calculated or determined differently. The charge
pump controller can change a clock frequency of the charge pump or
a total pumping capacitance of the charge pump if the duty cycle of
the charge pump is larger than at least one maximum threshold (one
maximum threshold or a set of maximum thresholds) or smaller than
at least one minimum threshold (one minimum threshold or a set of
minimum thresholds) within the time period. For example, a duty
cycle above the at least one maximum threshold indicates that the
charge pump is too weak and a higher clock frequency or a larger
total pumping capacitance needs to be set while a duty cycle below
the at least one minimum threshold indicates that the charge pump
is too strong and a lower clock frequency or a smaller total
pumping capacitance needs to be set. The charge pump controller
increases the clock frequency of the charge pump or the total
pumping capacitance of the charge pump if the duty cycle of the
charge pump is larger than the at least one maximum threshold and
decreases the clock frequency of the charge pump or the total
pumping capacitance of the charge pump if the duty cycle of the
charge pump is smaller than the at least one minimum threshold.
[0026] In some embodiments, the charge pump controller 106
adjusts/shifts at least one of a frequency setting of the clock
signal, "CLK_PUMP," that is used to drive the charge pump (also
referred to as the clock frequency setting of the charge pump) and
a capacitance setting of the charge pump 104 in a stepwise manner
(i.e., step by step or setting by setting) based on an operation
status of the charge pump. For example, the charge pump controller
106 can adjust a setting of the charge pump 104 in steps of fixed
increments. The charge pump controller may define or obtain
multiple intensity levels of clock frequency settings and
capacitance settings of the charge pump. Each intensity level
includes a unique combination of a clock frequency and a total
pumping capacitance of the charge pump. In an embodiment, the
charge pump controller calculates a duty cycle of the charge pump
within a time period based on the power-on status of the charge
pump and changes an intensity level of the clock frequency setting
and the capacitance setting of the charge pump based on the duty
cycle of the charge pump within the time period. The time period
may be one clock period of the clock signal, "CLK_GB," that is used
to drive the charge pump controller. The charge pump controller may
change the intensity level of the clock frequency setting and the
capacitance setting of the charge pump to a different intensity
level in the intensity levels if the duty cycle of the charge pump
is larger than at least one maximum threshold or smaller than at
least one minimum threshold. For example, the charge pump
controller changes a current intensity level of the clock frequency
setting and the capacitance setting of the charge pump to a
different intensity level in the intensity levels with a higher
clock frequency of the charge pump or a larger total pumping
capacitance of the charge pump if the duty cycle of the charge pump
is larger than the at least one maximum threshold. The charge pump
controller can change the current intensity level to a different
intensity level in the intensity levels with a lower clock
frequency of the charge pump or a smaller total pumping capacitance
of the charge pump if the duty cycle of the charge pump is smaller
than the at least one minimum threshold.
[0027] FIG. 2 depicts an embodiment of the charge pump circuit 108
depicted in FIG. 1. In the embodiment depicted in FIG. 2, a charge
pump circuit 208 includes a charge pump 204 and a charge pump
controller 206. The charge pump circuit 208 depicted in FIG. 2 is
one possible embodiment of the charge pump circuit 108 depicted in
FIG. 1. However, the charge pump circuit 108 depicted in FIG. 1 is
not limited to the embodiment shown in FIG. 2.
[0028] The charge pump 204 is a DC-to-DC voltage converter circuit
that includes a switch module 222 and a capacitor module/bank 224
that includes multiple capacitors 228. The switch module includes
one or more switching devices, such as NMOS transistors or PMOS
transistors. The switch module 222 is configured to charge or
discharge the capacitors 228 in the capacitor module to generate a
desired output voltage from an input voltage. The output voltage of
the charge pump 204 may be higher than, equal to, or lower than the
input voltage to the charge pump 204. The capacitor module can
provide a variable capacitance for the charge pump 204. In the
embodiment depicted in FIG. 2, the capacitor module includes four
switches 226-1, 226-2, 226-3, 226-4 and four capacitors 228-1,
228-2, 228-3, 228-4 with identical capacitances. However, in other
embodiments, the capacitor module may include more than four
capacitors/switches or less than four capacitors/switches. In some
embodiments, the capacitor module may include capacitors with
different capacitances.
[0029] In the embodiment depicted in FIG. 2, the capacitors 228 of
the capacitor module 224 are connected in parallel with each other.
By turning on or turning off a switch 226 in the capacitor module,
a corresponding capacitor 228 is enabled or disabled. For example,
if only one of the switches in the capacitor module is turned on
and the other three switches in the capacitor module are turned
off, only one capacitor 228 in the capacitor module is enabled and
the other three capacitors in the capacitor module are disabled. In
this case, the capacitance of the capacitor module 224 is equal to
the capacitance, "C," of one capacitor 228-1, 228-2, 228-3 or
228-4. If all of the switches in the capacitor module are turned
on, all four capacitor 228 in the capacitor module are enabled. In
this case, the capacitance of the capacitor module 224 is equal to
"," four times of the capacitance, "C," of one capacitor 228-1,
228-2, 228-3 or 228-4.
[0030] The charge pump controller 206 monitors the activity of the
charge pump 204 and adjusts/shifts at least one setting of the
charge pump. In the embodiment depicted in FIG. 2, the charge pump
controller 206 includes a monitor module 232, a frequency divider
234, and a controller module 236. Although the charge pump
controller 206 is shown in FIG. 2 as including certain components,
in some embodiments, the charge pump controller 206 includes less
or more components to implement less or more functionalities. For
example, the charge pump controller 206 may include multiple
frequency dividers or a combination of a frequency divider and a
frequency multiplier.
[0031] The monitor module 232 monitors the power-on status of the
charge pump 204 and generates a power-on status signal for the
controller module 236. The monitor module may include a voltage
sensor or a current sensor. In the embodiment depicted in FIG. 2,
the monitor module includes a voltage sensor 238 configured to
monitor the output voltage of the charge pump 204 to determine
whether or not the charge pump 204 is powered on. For example, if
the output voltage is higher than a predefined voltage threshold
(e.g., zero) for a time period, the voltage sensor determines that
the charge pump 204 is powered on in that time period.
[0032] The frequency divider 234 generates a clock signal,
"CLK_GB," (with a frequency, "f.sub.CLK.sub.--.sub.GB") that is
used to drive the controller module 236 of the charge pump
controller 206 and a clock signal, "CLK_PUMP," (with a frequency,
"f.sub.CLK.sub.--.sub.PUMP") that is used to drive the charge pump
204 from the clock signal, (with a frequency, "f.sub.CLK,") from
the clock circuit 102 (depicted in FIG. 1). The frequency,
"f.sub.CLK.sub.--.sub.GB," of the clock signal, "CLK_GB," is
typically a fraction of the frequency, "f.sub.CLK," of the clock
signal, "CLK." The frequency, "f.sub.CLK.sub.--.sub.PUMP," of the
clock signal, "CLK_PUMP," may be the same as, or a fraction of, the
frequency, "f.sub.CLK," of the clock signal, "CLK." In some
embodiments, the charge pump controller 206 may include a first
frequency divider that generates the clock signal, "CLK_GB," for
the controller module 236 and a second frequency divider that
generates the clock signal, "CLK_PUMP," for the charge pump
204.
[0033] The controller module 236 is configured to adjust at least
one of a clock frequency setting and a capacitance setting of the
charge pump 204 based on the power-on status signal from the
monitor module 232 by controlling the frequency divider 234 and/or
the capacitor module 224 of the charge pump 204. In the embodiment
depicted in FIG. 2, the controller module generates a control
signal to control the frequency divider to change the frequency,
"f.sub.CLK.sub.--.sub.PUMP," of the clock signal, "CLK_PUMP," that
is used to drive the charge pump 204 or keep the frequency,
"f.sub.CLK.sub.--.sub.PUMP," the same (unchanged). In addition, the
controller module controls the capacitor module of the charge pump
204 by turning on or turning off the switches 226 to enable or
disable corresponding capacitors 228.
[0034] The controller module 236 calculates a duty cycle of the
charge pump 204 within a time period based on the power-on status
of the charge pump 204 within the time period. In some embodiments,
the controller module changes the frequency,
"f.sub.CLK.sub.--.sub.PUMP," of the clock signal, "CLK_PUMP," that
is used to drive the charge pump or the total pumping capacitance
of the charge pump if the calculated duty cycle of the charge pump
204 is larger than a maximum threshold or smaller than a minimum
threshold within one clock period of the clock signal, "CLK_GB," of
the controller module. The controller module increases the
frequency, "f.sub.CLK.sub.--.sub.PUMP," of the clock signal,
"CLK_PUMP," that is used to drive the charge pump or the total
pumping capacitance of the charge pump 204 if the calculated duty
cycle is larger than the maximum threshold. The controller module
decreases the frequency, "f.sub.CLK.sub.--.sub.PUMP," of the clock
signal, "CLK_PUMP," that is used to drive the charge pump or the
total pumping capacitance of the charge pump if the calculated duty
cycle is smaller than the minimum threshold. For example, if the
calculated duty cycle is larger than the maximum threshold, the
charge pump is determined as being too weak. In this case, the
controller module increases the frequency of the frequency of the
clock signal, "CLK_PUMP" that is used to drive the charge pump 204
by controlling the frequency divider 234 to reduce the frequency
division factor of the frequency divider or bypassing the frequency
divider 234 such that the clock signal, "CLK_PUMP," of the charge
pump 204 has the same frequency as the clock signal, "CLK," from
the clock circuit 102. The controller module increases the total
pumping capacitance of the charge pump 204 by turning on one or
more switches 226 that were previously turned off to enable one or
more corresponding capacitors 228. If the calculated duty cycle is
smaller than the minimum threshold, the charge pump is determined
as being too strong. In this case, the controller module decreases
the frequency of the clock signal, "CLK_PUMP" that is used to drive
the charge pump 204 by controlling the frequency divider 234 to
increase the frequency division factor of the frequency divider
(e.g., from 1 to 4 such that the frequency,
"f.sub.CLK.sub.--.sub.PUMP," of the clock signal, "CLK_PUMP,"
reduces by 75%) or to stop bypassing the frequency divider 234 such
that the clock signal, "CLK_PUMP," that is used to drive the charge
pump 204 has a lower frequency than the clock signal, "CLK," from
the clock circuit 102. The controller module decreases the total
pumping capacitance of the charge pump 204 by turning off one or
more switches 226 that were previously turned on to disable one or
more corresponding capacitors 228. If the calculated duty cycle is
between the minimum threshold and the maximum threshold, the
controller module may keep the frequency,
"f.sub.CLK.sub.--.sub.PUMP," of the signal, "CLK_PUMP," that is
used to drive the charge pump and the total pumping capacitance of
the charge pump the same (unchanged).
[0035] In some embodiments, the controller module 236 calculates a
duty cycle of the charge pump 204 within one clock period of the
clock signal, "CLK_GB," of the controller module. The controller
module calculates a clock frequency ratio of one clock period of
the clock signal, "CLK_GB," to a unit clock period, which is one
clock period of the clock signal, "CLK," from the clock circuit
102. For each unit clock period within the clock period of the
clock signal, "CLK_GB," the controller module can determine whether
the charge pump 204 is powered on and increase a counter value by
one if the charge pump 204 is powered on. The controller module
calculates the duty cycle as a ratio of the counter value to the
clock frequency ratio.
[0036] An example operation of calculating a duty cycle of the
charge pump 204 by the controller module 236 is described with
reference to FIG. 3. Specifically, FIG. 3 depicts examples of
waveforms of the input clock signal, "CLK," from the clock circuit
102, the clock signal, "CLK_GB," that is used to drive the
controller module 236, and a charge pump power-on status signal
from the monitor module 232. In the embodiment depicted in FIG. 3,
a high edge "1" of the power-on status signal indicates that the
charge pump 204 is powered-on and a low edge "0" of the power-on
status signal indicates that the charge pump 204 is powered-off. As
illustrated in FIG. 3, the charge pump 204 is powered on for 12
clock periods, "T.sub.U," of the clock signal, "CLK." The
controller module counts the number of clock periods, "T.sub.U," of
the clock signal, "CLK," that the charge pump 204 is powered on and
incrementally increases a power-on counter value to 12. As
illustrated in FIG. 3, the one clock period, "T.sub.GB," of the
clock signal, "CLK_GB," is equal to 16 times one clock period,
"T.sub.U," of the clock signal, "CLK." The controller module
calculates a clock frequency ratio as the ratio) of one clock
period, "T.sub.GB," of the clock signal, "CLK_GB," to one clock
period, "T.sub.U." The controller module calculates the duty cycle
of the charge pump 204 during the clock period, "T.sub.GB," of the
clock signal, "CLK_GB," as equal to the ratio of the number of
clock periods, "T.sub.U," of the clock signal, "CLK," that the
charge pump 204 is powered on to the clock frequency ratio between
the controller clock signal, "CLK_GB," and the input clock signal,
"CLK." In the embodiment depicted in FIG. 3, the duty cycle of the
charge pump 204 during the clock period, "T.sub.GB," of the clock
signal, "CLK_GB," is 12/16, which is equal to 75%.
[0037] Turning back to FIG. 2, the controller module 236
adjusts/shifts the frequency, "f.sub.CLK.sub.--.sub.PUMP," of the
clock signal, "CLK_PUMP," that is used to drive the charge pump 204
and/or the total capacitance of the capacitors 228 of the capacitor
module 224 the charge pump in a stepwise manner. The controller
module defines or obtains multiple intensity levels (also referred
to as gears) of the frequency, "f.sub.CLK.sub.--.sub.PUMP," and the
total capacitance of the capacitor module 224. Each intensity level
includes a unique combination of the frequency,
"f.sub.CLK.sub.--.sub.PUMP," of the clock signal, "CLK_PUMP," that
is used to drive the charge pump and the total capacitance of the
capacitor module. For example, the controller module defines or
obtains five intensity levels, including a first intensity level
(Gear 0) with the frequency, "f.sub.CLK.sub.--.sub.PUMP," of the
charge pump being equal to a quarter of the frequency, "f.sub.CLK,"
of the clock signal, "CLK," and the total capacitance of the
capacitor module being equal to the capacitance, "C," of one
capacitor 228, a second intensity level (Gear 1) with the
frequency, "f.sub.CLK.sub.--.sub.PUMP," being equal to half of the
frequency, "f.sub.CLK," and the total capacitance of the capacitor
module being equal to the capacitance, "C," of one capacitor 228, a
third intensity level (Gear 2) with the frequency,
"f.sub.CLK.sub.--.sub.PUMP," being equal to the frequency,
"f.sub.CLK," and the total capacitance of the capacitor module
being equal to the capacitance, "C," of one capacitor 228, a fourth
intensity level (Gear 3) with the frequency,
"f.sub.CLK.sub.--.sub.PUMP," being equal to the frequency,
"f.sub.CLK," and the total capacitance of the capacitor module
being equal to two times of the capacitance, "C," of one capacitor
228, and a fifth intensity level (Gear 4) with the frequency,
"f.sub.CLK.sub.--.sub.PUMP," being equal to the frequency,
"f.sub.CLK," and the total capacitance of the capacitor module
being equal to four times of the capacitance, "C," of one capacitor
228.
[0038] Based on the duty cycle of the charge pump 204 within one
clock period of the clock signal, "CLK_GB," of the controller
module 236, the controller module changes the current intensity
level of the charge pump 204 or keeps the current intensity level
of the charge pump the same (unchanged). The controller module
changes the intensity level of the charge pump to a different
intensity level (which can be an immediately next intensity level
or other suitable intensity level) if the duty cycle of the charge
pump is larger than a maximum threshold or a set of maximum
thresholds or smaller than a minimum threshold or a set of minimum
thresholds. If the duty cycle of the charge pump is larger than the
maximum threshold(s), the charge pump is determined as being too
weak. In this case, the controller module changes a current
intensity level of the charge pump 204 to a different intensity
level (which can be an immediately next intensity level or other
suitable intensity level) with a higher frequency,
"f.sub.CLK.sub.--.sub.PUMP," or a larger total capacitance of the
charge pump. For example, if the duty cycle of the charge pump is
larger than the maximum threshold(s), the controller module changes
the intensity level of the charge pump from Gear 1 to Gear 2 or
Gear 3. If the duty cycle of the charge pump is smaller than the
minimum threshold(s), the charge pump is determined as being too
strong. In this case, the controller module changes the current
intensity level to a different intensity level (which can be an
immediately next intensity level or other suitable intensity level)
with a lower frequency, "f.sub.CLK.sub.--.sub.PUMP," or a smaller
total capacitance of the charge pump. For example, if the duty
cycle of the charge pump is smaller than the minimum threshold(s),
the controller module changes the intensity level of the charge
pump from Gear 4 to Gear 3 or Gear 2.
[0039] One possible embodiment of a charge pump control algorithm
used by the controller module 236 is described with reference to
the following pseudo code. However, the charge pump control
algorithm used by the controller module may be implemented with
different code. The charge pump control algorithm samples the
activity of the charge pump 204 during each clock period of the
clock signal, "CLK_GB," of the controller module 236. The
frequency, "f.sub.CLK.sub.--.sub.GB," of the clock signal,
"CLK_GB," that is used to drive the controller module is generally
a fraction of the frequency, "f.sub.CLK.sub.--.sub.PUMP," of the
clock signal, "CLK_PUMP," that is used to drive the charge pump. In
the pseudo code, the frequency, "f.sub.CLK.sub.--.sub.PUMP," of the
clock signal, "CLK_PUMP," that is used to drive the charge pump 204
is defined as: [0040] , (1) where f.sub.CLK represents the
frequency of the clock signal, "CLK," and, "K.sub.CLK," represents
the frequency ratio of the frequency of the clock signal,
"CLK_PUMP," to the frequency of the clock signal, "CLK." In
addition, in the pseudo code, the capacitance coefficient,
"K.sub.CAP," of the charge pump capacitance is equal to the ratio
of the current charge pump capacitance to the maximum capacitance
of the capacitors 228 of the capacitor module 224. As an example,
the capacitance coefficient, "K.sub.CAP," of 0.25 means that the
total charge pump capacitance is one fourth (1/4) of the maximum
capacitance of the capacitor module (e.g., only one of the four
capacitors 228 is enabled in the capacitor module).
TABLE-US-00001 [0040] Charge Pump Strength Gear Box 1
K.sub.CLK=0.25; //f.sub.CLK.sub.--.sub.PUMP is initially set to the
minimum frequency 2 K.sub.CAP=0.25; //charge pump capacitor is
initially set to the 3 //smallest size 4 gear=0; //the gear is set
to the weakest as a starting point 5 Non=0; //Non counts how many
CLK cycles the pump is 6 //active during one clock period of CLK_GB
7 N.sub.GB=f.sub.CLK/f.sub.CLK.sub.--.sub.GB; //N.sub.GB is the
clock frequency ratio of CLK to 8 //CLK_GB 9 DClow_th=0.32; //this
duty cycle threshold defines when the 10 //pump is considered to be
too strong 11 DChigh_th=0.87; //this duty cycle threshold defines
when the 12 //pump is considered to be too weak 13
@always(T.sub.U.sub.--CLK) 14 if(pump_on=1) Non++; //if charge pump
is on, increase Non by 1 15 @always(T.sub.GB.sub.--CLK_GB begin 16
DC=Non/N.sub.GB; // every CLK_GB period the duty cycle of 17 //the
charge pump is calculated as the ratio between Non and N.sub.GB 18
if(DC<DClow_th &&gear>0); //the pump is too strong 19
gear--; //shift gear down by 1 20 else if(DC>DChigh_th
&&gear<4); //the pump is too weak 21 gear++; //shift
gear up by 1 22 Non=0; //reset Non at the end of a CLK_GB period 23
case (gear) begin 24 4: K.sub.CLK=1.00; K.sub.CAP=1.00; //strongest
gear 25 3: K.sub.CLK=1.00; K.sub.CAP=0.50; 26 2: K.sub.CLK=1.00;
K.sub.CAP=0.25; 27 1: K.sub.CLK=0.5; K.sub.CAP=0.25; 28 0:
K.sub.CLK=0.25; K.sub.CAP=0.25; //weakest gear 29 end
[0041] In the above-provided pseudo code, the frequency ratio,
"K.sub.CLK" and the capacitance coefficient, "K.sub.CAP," are
initially set to minimum values, the gear/intensity level, "gear,"
of the charge pump 204 and a power-on counter value, "Non," are
initially set to 0, and maximum and minimum thresholds,
"DChigh_th," "DClow_th," of the duty cycle of the charge pump are
set. The frequency ratio, "N.sub.GB," between the input clock
signal, "CLK," and the controller clock signal, "CLK_GB," is
calculated. Five gears/intensity levels (0, 1, 2, 3, 4) of the
charge pump with different combinations of the frequency ratio,
"K.sub.CLK" and the capacitance coefficient, "K.sub.CAP," are
defined. Gear/intensity level 4 is considered the strongest gear in
the five gears with a frequency ratio, "K.sub.CLK" of 1 and a
capacitance coefficient, "K.sub.CAP," of 1. Gear/intensity level 0
is considered the weakest gear in the five gears with a frequency
ratio, "K.sub.CLK" of 0.25 and a capacitance coefficient,
"K.sub.CAP," of 0.25. Although the pseudo code includes 5
gears/intensity levels of the charge pump, in other embodiments,
the number of required gears/intensity levels of the charge pump
may be large than or smaller than 5.
[0042] Within each clock period of the clock signal, "CLK," the
power-on counter value, "Non," is increased by one if the charge
pump is powered on (i.e., pump_on value being 1). At the end or the
beginning of each clock period of the controller clock signal,
"CLK_GB," the duty cycle, "DC," of the charge pump is calculated
and the gear/intensity level of the charge pump is kept the same or
shifted up/down depending on the duty cycle. Within one clock
period of the controller clock signal, "CLK_GB," the duty cycle,
"DC," of the charge pump is calculated as the ratio of the power-on
counter value, "Non," to the frequency ratio, "N.sub.GB." If the
duty cycle, "DC," of the charge pump is smaller than the minimum
threshold, "DClow_th" and the gear/intensity level, "gear," of the
charge pump is higher than 0, the current gear/intensity level,
"gear," of the charge pump is decreased/down shifted by 1. If the
duty cycle, "DC," of the charge pump is larger than the maximum
threshold, "DChigh_th" and the gear/intensity level, "gear," of the
charge pump is lower than 4, the current gear/intensity level,
"gear," of the charge pump is increased/up shifted by 1. As the
gear/intensity level is shifted/held, the frequency of the clock
signal that is used to drive the charge pump and the charge pump
capacitance are adapted through the frequency ratio, "K.sub.CLK,"
and the capacitance coefficient, "K.sub.CAP." The power-on counter
value, "Non," is reset to 0 at the end of a clock period of the
controller clock signal, "CLK_GB."
[0043] FIG. 4 is a flow chart that illustrates an operation of a
charge pump control algorithm used by the controller module 236
depicted in FIG. 2. The controller module begins operation, at step
400. At step 402, the controller module performs initial setup. The
controller module checks whether the charge pump 204 is powered on
within each clock period of the input clock signal, "CLK," from the
clock circuit 102 of one clock period of the controller clock
signal, "CLK_GB," at step 404. If the charge pump 204 is powered
on, the controller module increases a power-on counter value by 1,
at step 406. If the charge pump 204 is powered off or after the
power-on counter value is increased, the controller module checks
whether the current clock period of the input clock signal, "CLK,"
from the clock circuit 102 is the last one in the clock period of
the controller clock signal, "CLK_GB," at step 408. If the current
clock period of the input clock signal, "CLK," from the clock
circuit 102 is the last clock period within the clock period of the
controller clock signal, "CLK_GB," the controller module calculates
the duty cycle of the charge pump in the clock period of the
controller clock signal, "CLK_GB," at step 410. The controller
module checks whether the duty cycle is lower than a minimum
threshold and the current gear/intensity level of the charge pump
is higher than a minimum gear/intensity level, at step 412. If the
duty cycle is lower than the minimum threshold and the current
gear/intensity level of the charge pump is higher than the minimum
gear/intensity level, the controller module decreases/shifts down
the current gear/intensity level of the charge pump by 1, at step
414. Otherwise, the controller module checks whether the duty cycle
is higher than a maximum threshold and the current gear/intensity
level of the charge pump is lower than a maximum gear/intensity
level, at step 416. If the duty cycle is higher than the maximum
threshold and the current gear/intensity level of the charge pump
is lower than the maximum gear/intensity level, the controller
module increases/shifts up the current gear/intensity level of the
charge pump by 1, at step 418. Subsequently, the controller module
resets power-on counter value to zero, at step 420 and goes back to
step 404 to repeat the process of adjusting the setting of the
charge pump. The controller module ceases operation, at step
422.
[0044] FIG. 5 depicts some examples of operational parameters at
different gears/intensity levels of the charge pump 204 depicted in
FIG. 2. In the embodiment depicted in FIG. 5, five gears/intensity
levels (0, 1, 2, 3, 4) of the charge pump with different
combinations of the frequency ratio, "K.sub.CLK" and a normalized
capacitance coefficient, "K.sub.UCAP," are defined. Gear/intensity
level 4 is considered the strongest gear in the five gears with a
frequency ratio, "K.sub.CLK" of 1 and a uniform capacitance
coefficient, "K.sub.UCAP," of 4. Under gear/intensity level 4,
normalized output voltage ripple, "KVout_ripple," average input
current, "KIin_avg," input current peak, "KIin_peak," of the charge
pump are equal to 1. Gear/intensity level 0 is considered the
weakest gear in the five gears with a frequency ratio, "K.sub.CLK"
of 0.25 and a normalized capacitance coefficient, "K.sub.UCAP," of
1. Under gear/intensity level 0, normalized output voltage ripple,
"KVout_ripple," average input current, "KIin_avg," input current
peak, "KIin_peak," are equal to 1/4, 1/16, 1/4, respectively.
Consequently, the output voltage ripple, "KVout_ripple," average
input current, "KIin_avg," input current peak, "KIin_peak," of the
charge pump can be attenuated by the charge pump controller 206.
The charge pump controller adapts the strength of the charge pump
for PVT conditions, load capacitance and leakage currents and
reduces output voltage ripples as well as current peaks. Using the
charge pump controller, the average input current consumption of
the charge pump can be as low as 4 milli-ampere (mA). Consequently,
compared to a conventional charge pump that requires a power switch
and a decoupling capacitor of large dimensions, the charge pump 204
only needs a small decoupling capacitor and a small power switch.
In addition, the charge pump 204 does not need an additional
Low-dropout regulator (LDO) to regulate voltage supply to
acceptable levels.
[0045] FIG. 6 depicts an embodiment of the controller module 236
depicted in FIG. 2. In the embodiment depicted in FIG. 6, a
controller module 636 includes a processor 642 and a storage medium
644 that store instructions (e.g., programming codes) to be
executed by the processor. The processor may be a multifunction
processor and/or an application-specific processor. The processor
can be a microprocessor such as a central processing unit (CPU)
that provides microinstruction and data processing capability for
the charge pump controller 206. The storage medium can be an
electronic, magnetic, optical, electromagnetic, infrared, or
semiconductor system (or apparatus or device), or a propagation
medium. Examples of the storage medium include a semiconductor or
solid state memory, magnetic tape, a random access memory (RAM), a
read-only memory (ROM), and flash memory. The controller module 636
depicted in FIG. 6 is one possible embodiment of the controller
module 236 depicted in FIG. 2. However, the controller module 236
depicted in FIG. 2 is not limited to the embodiment shown in FIG.
6.
[0046] FIG. 7 is a process flow diagram that illustrates a method
for controlling a charge pump in accordance with an embodiment of
the invention. The charge pump may be the same as or similar to the
charge pump 104 depicted in FIG. 1 and/or the charge pump 204
depicted in FIG. 2. At block 702, a power-on status of the charge
pump is monitored. At block 704, a duty cycle of the charge pump
within a time period is calculated based on the power-on status of
the charge pump. At block 706, at least one of a clock frequency
setting and a capacitance setting of the charge pump is adjusted
based on the duty cycle of the charge pump.
[0047] Although the operations of the method herein are shown and
described in a particular order, the order of the operations of the
method may be altered so that certain operations may be performed
in an inverse order or so that certain operations may be performed,
at least in part, concurrently with other operations. In another
embodiment, instructions or sub-operations of distinct operations
may be implemented in an intermittent and/or alternating
manner.
[0048] In addition, although specific embodiments of the invention
that have been described or depicted include several components
described or depicted herein, other embodiments of the invention
may include fewer or more components to implement less or more
features.
[0049] Furthermore, although specific embodiments of the invention
have been described and depicted, the invention is not to be
limited to the specific forms or arrangements of parts so described
and depicted. The scope of the invention is to be defined by the
claims appended hereto and their equivalents.
* * * * *