Charge pump for low power consumption apparatus and associated methods

An apparatus includes a first set of circuits adapted to operate in a first mode of operation of the apparatus. The apparatus further includes a second set of circuits adapted to operate in a second mode of operation of the apparatus, where a power consumption of the apparatus is lower in the second mode of operation of the apparatus than in the first mode of operation of the apparatus. The apparatus also includes a charge pump adapted to convert a first supply voltage of the apparatus to a second supply voltage, and the second supply voltage powers the second set of circuits.

TECHNICAL FIELD

The disclosure relates generally to power converter apparatus and related methods. More particularly, the disclosure relates to charge pumps for providing supply voltages to low power apparatus, and associated methods.

BACKGROUND

Modern ICs have helped to integrate electronic circuitry to decrease size and cost. As a consequence, modern ICs can form complex circuitry and systems. For example, virtually all of the functionality of a system may be realized using one or a handful of ICs. Such circuitry and systems may receive and operate on both analog and digital signals, and may provide analog and digital signals.

The result has been a growing trend to produce circuitry and systems with increased numbers of transistors and similar devices. The growth in the number of devices usually leads to an increase in power consumption or power dissipation. Even for a device with a relatively modest number of devices, the power consumption may place a drain on the power source.

SUMMARY

An apparatus according to one exemplary embodiment includes a first set of circuits adapted to operate in a first mode of operation of the apparatus. The apparatus further includes a second set of circuits adapted to operate in a second mode of operation of the apparatus, where a power consumption of the apparatus is lower in the second mode of operation of the apparatus than in the first mode of operation of the apparatus. The apparatus also includes a charge pump adapted to convert a first supply voltage of the apparatus to a second supply voltage, and the second supply voltage powers the second set of circuits.

According to another exemplary embodiment, an apparatus includes a battery, and a microcontroller unit (MCU). The MCU includes a charge pump coupled to the battery. The charge pump is adapted to convert a voltage of the battery to a supply voltage. The supply voltage is lower than the battery voltage. The MCU also includes a first set of circuits adapted to be powered by the battery during a normal operating mode of the MCU. The MCU further includes a second set of circuits coupled to the charge pump. The second set of circuits is adapted to be powered by the supply voltage during a low-power operating mode of the MCU

According to yet another exemplary embodiment, a method of operating an apparatus includes converting, by using a charge pump, a first supply voltage of the apparatus to a second supply voltage. The method also includes operating a first set of circuits in a first mode of operation of the apparatus. The method further includes operating a second set of circuits in a second mode of operation of the apparatus, using the second supply voltage to power the second set of circuits, where the power consumption of the apparatus is lower in the second mode of operation of the apparatus than in the first mode of operation of the apparatus.

DETAILED DESCRIPTION

In various embodiments an apparatus may be provided to provide power to circuitry operating in a relatively low power mode, yet in an efficient manner. More specifically, the disclosure relates to apparatus and methods for using charge pumps to supply power to circuitry that is operational in a low power mode, such as a sleep mode, with relatively high efficiency.

FIG. 1shows an apparatus that includes a charge pump for supplying power to a set of circuits according to an exemplary embodiment. Broadly speaking, a set of circuits inFIG. 1, such as the set of circuits labeled as30, may correspond to an active or normal mode of operation of apparatus10, i.e., they are operational during the active or normal mode of operation. During the low power or sleep mode of operation, however, circuits30may be inactivated, put in a sleep mode, etc.

Without limitation, circuits30may include a variety of circuitry, such as controllers, memory, processor circuitry, clock generation and distribution circuits, power management circuitry, supervisory circuitry, input/output circuitry, and the like. Generally, circuits30may include any type or variety of circuit that is desired to be functioning during the active or normal mode of operation, but inactive during a low power or sleep mode of operation.

Apparatus10includes another set of circuits, such as the set of circuits labeled as25. Circuits25may correspond to a low power mode (compared to the normal or active mode) or sleep mode of operation of apparatus10. In other words, circuits25are operational during a low power or sleep mode of operation (as well as during the normal or active mode of operation). Without limitation, circuits25may include state-retained memory; universal asynchronous receiver transmitter (UART); registers; real time clock (RTC) circuitry; display circuitry, such as a liquid crystal display (LCD) controller; etc.

Note that, in some embodiments, part of a circuit may be desired to be available during the active mode of apparatus10, while another part of the circuit may be desired to function in a low power or sleep mode for at least some of the time. For example, RTC circuitry (not shown inFIG. 1) may include analog circuitry that is included in circuits25(to keep the clock running), and digital circuitry that may be included in circuits30. Other examples of such circuitry exist, as persons of ordinary skill in the art understand, depending on the specifications and desired performance or functionality of a given implementation.

In some embodiments, circuits30(e.g., controller45or other parts of circuits30) may communicate with circuits25. In the exemplary embodiment ofFIG. 1, such communication may take place via link30A. Using link30A, circuits25and30may communicate information, such as data, control signals, status signals, clock signals, and the like, as desired. As merely one example, circuits30may include a processor or controller that may use link30A to provide information to an LCD controller included as part of circuits25. As persons of ordinary skill in the art understand, depending on factors like the nature of the communication information and the specification of a particular implementation, link30A may include one or more wires, conductors, and the like.

Source15supplies power to various circuits in apparatus10. More specifically, source15provides supply voltage Vsto circuits30. Apparatus10includes charge pump20, which via supply line15A receives supply voltage Vsfrom source15. Charge pump20converts or scales supply voltage Vsto an output voltage Vcp, that is lower than supply voltage Vs. Thus, charge pump20has a voltage conversion factor, K, associated with it, such that K=Vcp/Vs. In some embodiments, K may have a value of approximately 0.5, i.e., the charge pump output voltage is given by Vcp≈0.5 Vs, with such a charge pump sometimes called a “half mode” charge pump.

In some embodiments, one or more circuits included in circuits30may control the operation of charge pump20. In the embodiment shown inFIG. 1, link33provides a mechanism for providing one or more control signals to charge pump20. If desired, link33may provide communication from the charge pump to circuits30, as persons of ordinary skill in the art understand.

According to one aspect of the disclosure, in some embodiments, circuits25and30and charge pump20may be integrated into a single integrated circuit (IC), labeled12inFIG. 1. Integrating one or more of the circuits described above can improve the overall performance in some applications, for example, flexibility, responsiveness, die area, cost, materials used, power consumption, reliability, robustness, and the like, as desired.

According to another aspect of the disclosure, in some embodiments, apparatus10may constitute a portable apparatus. In such situations, source15may constitute a battery. In other embodiments, even where apparatus10is semi-portable or non-portable, or where using other power sources might be inconvenient, source15may nevertheless be a battery. Use of the battery overcomes provision of power through other means, such as wires or cables coupled to other sources, such as the mains and associated power conversion circuitry. In some embodiments, whether portable or not, source15may constitute a renewable energy or power source, for example, a solar panel (and associated power processing circuitry, as desired).

FIGS. 2A-2Bshow more detailed block diagrams of apparatus10according to exemplary embodiments. Referring toFIG. 2A, apparatus10includes a multiplexer (MUX)40or, generally, a controlled switch (e.g., a single pole dual throw (SPDT) switch) to control provision of power to circuits25. More specifically, the inputs of MUX40receive Vsand Vcp, respectively. In response to control signal47, MUX40provides either Vsor Vcpto circuits25. In other words, one may selectively supply either Vsor Vcpto circuits25.

This capability allows more flexibility in providing a source of power to circuits25. Consider the situation where source15is a battery, or where the voltage and/or power provided by source15fluctuate over time or decrease over time. When source15provides a sufficiently high value of Vsthat the output voltage of charge pump20, Vcp, meets the specified supply voltage of circuits25, MUX40provides Vcpto circuits25. If the value of Vschanges such that Vcpis no longer suitable for powering circuits25(e.g., Vsfalls below a specific value), MUX40provides Vsto circuits25.

Monitor circuit35, included as part of circuits30, provides control signal47(the select signal for MUX40in the embodiment shown). Monitor circuit35receives as inputs the voltages Vsand Vcp. As described above, depending at least one of (or both) of the input voltages (Vsand Vcp), or depending on the relative values of the input voltages (or depending on another desired control scheme), monitor circuit35drives control signal47to appropriately provide power to circuits25. In other embodiments, monitor circuit35may receive the output voltage of MUX40, labeled VMinFIG. 2A, and use this voltage when determining the appropriate state of control signal47.

In some embodiments, circuits30include one or more of controller45. Referring toFIG. 2A, which shows one controller, controller45may provide desired information or data processing capabilities, including without limitation, numerical calculation capability. Controller45may perform any desired processing or calculation in IC12.

In some embodiments, rather than driving MUX40(or another switch or type of switch), monitor circuit35may interrupt or otherwise cause controller45to decide whether to supply Vsor Vcpto circuits25. In such embodiments, controller45may be programmed, for example, by using associated software or firmware, to control the supply of power to circuits25using a variety of criteria or considerations, for example, input from sensors, input from external sources, etc.

In addition to controller45, in some embodiments, IC12may include one or more of other circuitry, such as a power-on reset (POR) circuit, power management unit (PMU), host interface circuitry, brownout detector, watchdog timer, and the like. In some embodiments, one or more of the above circuits may be included in controller45, as desired, or may be included in circuits25.

According to one aspect of the disclosure, in some embodiments, part of a circuit or block may be included in circuits25, and another part of the circuit or block may be included in circuits30. For example, part of circuitry associated with displaying information on an LCD may be included in circuits25, so that the LCD can display information during all times or during desired times. Other LCD circuitry, on the other hand, may be included as part of circuits30. Thus, during the low power or sleep mode of operation of apparatus10, the LCD may display static information, whereas during the normal or active mode of operation, the other LCD circuitry is powered (as part of circuits30), and provides information to the LCD, for example, as requested by controller45.

According to another aspect of the disclosure, in some embodiments, part of a circuit or block may be included in circuits25A, integrated in IC12, and another part of the circuit or block may be included in circuits25B, external to IC12.FIG. 2Bshows such an arrangement according to an exemplary embodiment. As an example, and without limitation, in some embodiments, circuitry associated with an LCD may be included in circuits25A, whereas the LCD itself may be included in circuits25B (external to IC12). A variety of other arrangements may be used according to other embodiments, as persons of ordinary skill in the art understand.

Note that, rather than using one link30A, as shown in the example inFIG. 2B, separate links may be used between circuit30(controller45or other part of circuits30) and circuits25A and25B, respectively. Using such link(s) circuits25A and25B may communicate information, such as data, control signals, status signals, clock signals, and the like, as desired.

FIG. 3shows a circuit arrangement for a charge pump20for use in exemplary embodiments. Charge pump20includes four switches50,52,54, and56, labeled S1-S4, respectively. In addition, charge pump20includes capacitors58and60, labeled C1-C2, respectively. Switches50,52,54, and56constitute controlled or controllable switches. In other words, in response to control signals (not shown), switches50,52,54, and56may be opened or closed.

In exemplary embodiments, switches50,52,54, and56may be implemented as transistors, for example, metal oxide semiconductor (MOS) transistors. As persons of ordinary skill in the art understand, however, a variety of other devices may be used, depending on factors such as design and performance specifications, available fabrication technology, etc., for a given implementation.

A control signal, say, Φ1, controls switches50and56. A complementary control signal, say, Φ2, controls switches52and54.FIG. 4shows an exemplary set of switch control signals for charge pump20. Note that control signals Φ1and Φ2are not exactly complementary in order to avoid a crowbar current through charge pump20. More specifically, time periods (e.g., dead-time) labeled as t1and t2, added between the edges of control signals Φ1and Φ2, prevent switches50,52,54, and56from conducting at the same time. (Conduction by switches50,52,54, and56at the same time would effectively short Vsto ground.)

In exemplary embodiments, control signals Φ1and Φ2may have a desired frequency. In some embodiments, control signals Φ1and Φ2may have a frequency of 32.768 kHz, a frequency commonly used for RTCs. As persons of ordinary skill in the art understand, however, other frequencies may be used in other embodiments, depending on factors such as design and performance specifications, etc., for a given implementation.

Referring toFIGS. 3 and 4, when control signal Φ1is at a high level, switches50and56turn on, and couple capacitors58and60in series between Vsand ground. As a result, capacitors58and60charge. During this phase of operation, the node between capacitors58and60constitutes output20A of charge pump20. While control signal Φ1is at a high level, control signal Φ2is at a low level, which causes switches52and54to be off.FIG. 5shows the resulting circuit topology for this phase of operation of charge pump20.

Referring toFIGS. 3 and 4, when control signal Φ2is at a high level, switches52and54turn on, and couple capacitors58and60in parallel between output20A of charge pump20and ground. Thus, during this phase of operation, the coupled top terminals (the terminals not coupled to ground) of the capacitors constitute output20A of charge pump20. While control signal Φ2is at a high level, control signal Φ1is at a low level, which causes switches50and56to be off.FIG. 6shows the resulting circuit topology for this phase of operation of charge pump20.

Referring back toFIG. 3, during steady-state operation, a high level of control signal Φ2forces the same voltage (Bcp) across capacitors58and60. It may be shown that in steady state operation, the output voltage is approximately ½ the input voltage of charge pump20. In other words,

Vcp≈12⁢Vs.(Eq.⁢1)
Note that, as Equation 1 shows, the steady-state voltage conversion ratio of charge pump20, i.e., the ratio of Vcpto Vs, does not depend on the capacitances of capacitors58and60.

In exemplary embodiments, using a charge pump as shown inFIG. 3can achieve power conversion or transfer efficiencies of roughly 80%. As such, charge pump20exhibits a “transformer effect,” as its efficiency of 80% (0.8) is greater than the ratio of its output to input voltages, i.e., the ratio of the ratio of Vcpto Vs, which is about 0.5, as Equation 1 states. Thus, charge pump20provides better power efficiency than a conventional linear voltage regulator.

Furthermore, charge pump20reduces the current drawn from source15(seeFIG. 1). A Thévenin equivalent circuit of charge pump20, illustrated inFIG. 7, helps to illustrate this attribute. More specifically, the Thévenin equivalent circuit includes a voltage source65with a magnitude Voc(open-circuit output voltage), and a resistance68, with a resistance value RTH. Referring toFIG. 3, assuming that charge pump20includes a parasitic capacitor, Cp, between node62and ground, one may show that:

Voc=Vs·C2+Cp(2⁢⁢C2+Cp)≈Vs2,⁢and(Eq.⁢2)RTH=C2+Cp(2⁢⁢C2+Cp)·C1+C2+Cp2⁢f⁢⁢C1⁡(C1+C2)≈14⁢f⁢⁢C1,(Eq.⁢3)
where f represents the switching or clock frequency of charge pump20.

Using PLOSSto denote power loss in charge pump20, Equation 4 expresses the relationship between the input power (PIN) and output power (POUT) of charge pump20:
PIN=POUT+PLOSS.  (Eq. 4)
Given that:
PIN=Is·Vs,
POUT=IOUT·VCP,
and
PLOSS=IOUT2·RTH,
where ISand IOUTdenote, respectively the input and output currents of charge pump20, one may express Equation 4 as:
Is·Vs=IOUT·(VOC−IOUT·RTH)+IOUT2·RTH=IOUT·VOC,
and finally as:

As Equation 5 illustrates, the transformer effect of charge pump20reduces the current drawn from source15by a factor of about 2, i.e., the inverse of the voltage conversion ratio, which is roughly 0.5.

In addition to the transformer effect, charge pump20reduces the current drawn from source15during the low power or sleep mode of operation in another way. Specifically, supplying a reduced voltage (VCP) to circuits25(seeFIGS. 1-2) reduces the supply current that those circuits draw (compared to supplying those circuits with Vs). The reduced supply voltage also reduces the static leakage current of circuits25, thus additionally reducing the current draw from source15.

Referring toFIGS. 2A and 3, in some embodiments the function of MUX40can be performed by charge pump20. For example, the voltage Vscan be coupled to voltage VCPby closing switches50and52inFIG. 3. In this configuration, an advantage is provided by using capacitor60as decoupling for the voltage (VCP) at output20A of charge pump20. Furthermore, such an embodiment can provide an additional advantage by configuring switches54and56such that capacitor58is connected in parallel with capacitor60, thereby using both capacitors58and60as decoupling for the voltage (VCP) at output20A of charge pump20.

Referring to the figures, persons of ordinary skill in the art will note that the various blocks shown might depict mainly the conceptual functions and signal flow. The actual circuit implementation might or might not contain separately identifiable hardware for the various functional blocks and might or might not use the particular circuitry shown. For example, one may combine the functionality of various blocks into one circuit block, as desired. Furthermore, one may realize the functionality of a single block in several circuit blocks, as desired. The choice of circuit implementation depends on various factors, such as particular design and performance specifications for a given implementation. Other modifications and alternative embodiments in addition to those described here will be apparent to persons of ordinary skill in the art. Accordingly, this description teaches those skilled in the art the manner of carrying out the disclosed concepts, and is to be construed as illustrative only.

The forms and embodiments shown and described should be taken as illustrative embodiments. Persons skilled in the art may make various changes in the shape, size and arrangement of parts without departing from the scope of the disclosed concepts in this document. For example, persons skilled in the art may substitute equivalent elements for the elements illustrated and described here. Moreover, persons skilled in the art may use certain features of the disclosed concepts independently of the use of other features, without departing from the scope of the disclosed concepts.