Patent Publication Number: US-11025162-B2

Title: Charge pump systems, devices, and methods

Description:
PRIORITY CLAIM 
     This application is a continuation patent application of and claims priority to U.S. patent application Ser. No. 15/940,458, filed Mar. 29, 2018 issued as U.S. Pat. No. 10,608,528, which is a continuation of and claims priority to PCT Application No. PCT/US2018/00069, filed Feb. 16, 2018, which claims priority to U.S. Provisional Patent Application Ser. No. 62/460,003, filed Feb. 16, 2017, the disclosures of which are incorporated herein by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     The subject matter disclosed herein relates generally to charge pumps. More particularly, the subject matter disclosed herein relates to configurations and operation of charge pumps used to charge a capacitor to a relatively higher potential than a voltage supply. 
     BACKGROUND 
     Charge pumps are used to generate a desired high voltage output in configurations where the supply voltage is comparatively low. Even where such a high-voltage output would be advantageous, however, various issues associated with charge pumps have prevented them from replacing other high voltage sources. For example, parasitics to ground, space required for charge pump elements (e.g., pump stages, control circuits, hold capacitor), and time to charge can all be seen as detrimental to certain circuits. For many of these reasons, the applicability of charge pumps has been limited despite the ability to generate a high voltage output from a comparatively low supply voltage. 
     SUMMARY 
     In accordance with this disclosure, charge pump devices, systems, and methods are provided. In one aspect, a charge pump is provided in which a plurality of series-connected charge-pump stages are connected between a supply voltage node and a primary circuit node, and a discharge circuit is connected to the plurality of charge-pump stages, wherein the discharge circuit is configured to selectively remove charge from the primary circuit node. 
     In another aspect, a method for regulating charge at a primary circuit node includes selectively driving charge between stages of a plurality of series-connected charge-pump stages connected between a supply voltage node and a primary circuit node, and selectively removing charge from the primary circuit node though a discharge circuit connected to the plurality of charge-pump stages. 
     In another aspect, a micro-electro-mechanical systems (MEMS) device according to the present subject matter includes at least one fixed electrode; a movable beam including at least one movable electrode that is spaced apart from the at least one fixed electrode and is movable with respect to the at least one fixed electrode; a plurality of series-connected charge-pump stages connected between a supply voltage node and a primary circuit node, wherein the primary circuit node is connected to one of the at least one movable electrode or the at least one fixed electrode; and a discharge circuit connected to the plurality of charge-pump stages, wherein the discharge circuit is configured to selectively remove charge from the primary circuit node. 
     Although some of the aspects of the subject matter disclosed herein have been stated hereinabove, and which are achieved in whole or in part by the presently disclosed subject matter, other aspects will become evident as the description proceeds when taken in connection with the accompanying drawings as best described hereinbelow. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features and advantages of the present subject matter will be more readily understood from the following detailed description which should be read in conjunction with the accompanying drawings that are given merely by way of explanatory and non-limiting example, and in which: 
         FIG. 1  is a schematic diagram of a charge pump according to an embodiment of the presently disclosed subject matter; 
         FIG. 2  is a schematic diagram of a charge pump according to an embodiment of the presently disclosed subject matter; 
         FIG. 3  is a schematic diagram of a charge pump according to an embodiment of the presently disclosed subject matter; 
         FIG. 4  is a graph illustrating voltage at a primary circuit node of a charge pump according to an embodiment of the presently disclosed subject matter; 
         FIG. 5  is a side view of a micro-electro-mechanical device that is driven by a charge pump according to an embodiment of the presently disclosed subject matter; 
         FIG. 6  is a schematic representation of a charge pump control system according to an embodiment of the presently disclosed subject matter; and 
         FIG. 7  is a schematic representation of a charge pump control system according to an embodiment of the presently disclosed subject matter. 
     
    
    
     DETAILED DESCRIPTION 
     The present subject matter provides charge pump devices, systems, and methods. In one aspect, the present subject matter provides a charge pump that both charges a capacitor or other element in communication with a primary circuit node to a relatively higher potential than a voltage supply and pumps down the high-voltage charge without any form of high-voltage switches. Referring to one example configuration illustrated in  FIG. 1 , a charge pump, generally designated  100 , can include a plurality of series-connected charge-pump stages  105 - 1  through  105 - n  connected between a supply voltage node  101  and a primary circuit node  102  (i.e., with the voltage output of one pump stage being the voltage input to the subsequent pump stage). 
     In some embodiments, for example, charge pump  100  can be a Dickson-type charge pump, where charge-pump stages  105 - 1  through  105 - n  include multiple stages of capacitors linked by a diode string. As used herein, the term ‘diode’ is not intended to be limited to semiconductor diodes but instead is used generally to refer to any two-terminal electronic component that conducts current primarily in one direction (i.e., bias-dependent), including MOSFET circuits that emulate a diode. In such an arrangement, charge is passed between the capacitors through the diode string by a two-phase clock (e.g., supplied by a clock driver circuit  106 ) such that it can only flow one way, and the charge builds up at the end of the string at primary circuit node  102 . The number of stages can be selected to generate the amount of voltage step-up desired from charge pump  100 . For instance, the number of stages can be selected based on the difference between the desired high voltage output at primary circuit node  102  and the charge pump&#39;s voltage supply at supply voltage node  101 . The number of stages is thereby generally fixed for any given application. 
     For example, one configuration for a charge pump design can include an even number of stages, half of which are clocked high on each rising clock edge and the other half are clocked high on the falling clock edge. In some embodiments, charge-pump stages  105 - 1  through  105 - n  include a plurality of diodes connected in a series arrangement between supply voltage node  101  and primary circuit node  102 . To drive charge across the diode chain, charge-pump stages  105 - 1  through  105 - n  further include a plurality of pump stage capacitors that are each connected to a cathode terminal of a corresponding one of the associated diodes to form each charge pump stage, and clock driver circuit  106  controls the charging of the pump stage capacitors. Although one example of a configuration of charge pump  100  is discussed here, those having ordinary skill in the art will recognize that charge pump  100  can be provided in any of a variety of other configurations in which charge is driven between stages of the plurality of charge-pump stages  105 - 1  through  105 - n.    
     In addition to this structure that is similar to conventional charge pump configurations, however, in some embodiments, charge pump  100  further includes a discharge circuit, generally designated  110 , that is connected to the plurality of charge-pump stages  105 - 1  through  105 - n , wherein discharge circuit  110  is configured to selectively remove charge from primary circuit node  102 . In some embodiments, discharge circuit  110  can include a plurality of discharge circuit elements  115 - 1  through  115 - n  that are each in communication with a respective one of charge-pump stages  105 - 1  through  105 - n . In some embodiments, for example, discharge circuit elements  115 - 1  through  115 - n  can be a plurality of transistors arranged in a cascaded array between primary circuit node  102  and a reference  103  (e.g., a ground), with each of the plurality of transistors being connected to one of the plurality of charge pump stages  105 - 1  through  105 - n . In some embodiments, discharge circuit elements  115 - 1  through  115 - n  can be provided as a field-effect transistor (FET) ‘follower’ that cascades the entire stack down to logic levels, with the gate of each FET being inserted between each of pump stages  105 - 1  through  105 - n.    
     Such a configuration can be integrated with the design of charge-pump stages  105 - 1  through  105 - n . For example, in some embodiments, the ‘diodes’ of charge-pump stages  105 - 1  through  105 - n  can be implemented using transistors, which can be operated in the typical way during charge pump ramp-up. When it is desired to draw down the charge at primary circuit node  102 , however, the transistors can be operated on a transient basis to short out and remove the high voltage. In some embodiments, the feed to the transistor driver at the high-voltage end of the string can be made into a cascade with a low voltage trigger. In some embodiments, this configuration for discharge circuit  110  can be controlled by gating the lower FET. 
     Referring to an example configuration illustrated in  FIG. 2 , charge pump  100  includes a stack of 16 charge-pump stages  105 - 1  through  105 - 16 . Discharge circuit elements  115 - 1  through  115 - 16  are connected to each of associated charge-pump stages  105 - 1  through  105 - 16  in the form of transistors  116 - 1  through  116 - 16  (e.g., NFET followers), which are cascaded with the subsequent and previous pump stages. This circuit creates over-voltage situations when discharging primary circuit node  102  to reference  103 . 
     To enable this discharge, a shorting switch  118  can be operated to trigger the removal of charge from primary circuit node  102 . In some embodiments, such as in  FIG. 2 , shorting switch  118  is an additional transistor connected between the plurality of discharge circuit elements  115 - 1  through  115 - 16  and reference  103 , although in other embodiments, the gate of transistor  116 - 1  (i.e., the one of the plurality of transistors  116 - 1  through  116 - 16  that is closest to reference  103 ) can be operable as shorting switch  118 . 
     In some embodiments, actuation of shorting switch  118  can be achieved by the selective activation of an input voltage source  119  in communication with shorting switch  118 . For example, where input voltage source  119  provides a potential of VIN=1, primary circuit node  102  is pumped to a high-voltage potential after several cycles of clock driver circuit  106 . In this way, the voltage output at each subsequent pump stage increases in stepped increments until a desired charge is achieved at primary circuit node  102 . Where input voltage source  119  is switched to provide a potential of VIN=0, discharge circuit  110  operates to cascade the high-voltage at primary circuit node  102  down to logic levels. In coordination with this pump down, clock driver circuit  106  can be gated off, and supply voltage node  101  can be floated or grounded. In this configuration, the gate of shorting switch  118  will remain charged when primary circuit node  102  is discharged. 
     In another example configuration shown in  FIG. 3 , discharge circuit elements  115 - 1  through  115 - n  can include a plurality of diodes  117 - 1  through  117 - n  connected from gate to drain at a respective one of the plurality of transistors  116 - 1  through  116 - 16  that are cascaded between primary circuit node  102  and reference  103 . In some embodiments, diodes  117 - 1  through  117 - n  facilitate the removal of charge from primary circuit node  102  by discharging the gates of transistors  116 - 1  through  116 - n  of discharge circuit elements  115 - 1  through  115 - n  and the associated one of charge-pump stages  105 - 1  through  105 - n  when primary circuit node  102  is connected to reference  103 . In this arrangement, diodes  117 - 1  through  117 - n  help the switches collapse safely (e.g., by preventing some of transistors  116 - 1  through  116 - n  from breaking down during the transient). Similar to the configuration discussed above with respect to  FIG. 2 , this circuit is designed to provide a logic translation to primary circuit node  102  when the potential at input voltage source  119  is ‘1’ and a logic low level when the potential at input voltage source  119  is ‘0’. Such a result is shown in  FIG. 4 , where the potential at primary circuit node  102  (upper waveform) corresponds to the state at input voltage source  119  (lower waveform). 
     In some embodiments, since the systems and methods discussed above provide high-voltage control without the need for high-voltage switches, charge pump  100  and/or discharge circuit  110  according to the present disclosure can be implemented using manufacturing methods that may only have low-voltage transistors. In some embodiments, for example, silicon-on-insulator (SOI) or other similar processes (e.g., SiGe) may be used. In particular with respect to a SOI implementation, the operation of charge pump  100  and/or discharge circuit  110  can be more efficient due to lower parasitics to ground compared to other technologies. In addition, low-voltage implementations can minimize the parasitic capacitances with minimum size transistors and not having the body tied to a substrate, resulting in charge pump  100  and/or discharge circuit  110  being comparatively efficient and small with small value coupling capacitors, and control that is more complex can be enabled compared to simple diode-connected FETs. In addition, a large depletion region would not be required for substrate isolation. 
     Regardless of the particular configuration of charge pump  100 , the present subject matter can provide advantages in a range of application. In some embodiments, for example, charge pump  100  as described herein can be used as a charge source for micro-electro-mechanical systems (MEMS) device. Referring to the arrangement illustrated in  FIG. 5 , a MEMS device, generally designated  120 , includes at least one fixed electrode  122  (e.g., provided on a substrate  121 ), and a movable beam  123  is suspended over fixed electrode  122 , movable beam  123  including at least one movable electrode  124  that is spaced apart from fixed electrode  122  and is movable with respect to fixed electrode  122 . Charge pump  100  is connected to this structure, with primary circuit node  102  being connected to one of fixed electrode  122  or movable electrode  124 , and the other of movable electrode  124  or fixed electrode  122  being connected to ground. In this configuration, the deflection of movable beam  123  can be driven directly by charge pump  100 . Thus, whereas conventional MEMS actuators generally require high voltage transistors to apply and remove the high-voltage from the MEMS, in some embodiments of MEMS device  120 , no high-voltage transistors are needed (e.g., for an SOI implementation). Furthermore, since charge pump  100  is charging the MEMS itself (i.e., rather than a separate hold capacitor), only a relatively low charge needs to be provided (e.g., only enough to achieve between about 50 fF and 1 pF of capacitance). As a result, charge pump  100  can be very small, which is further helpful to avoid large steps due to the small load. 
     Driving one or more such MEMS beams directly with charge pump  100  controls the deflection of movable beam  123  with charge rather than voltage. Thus, in contrast to conventional MEMS actuators, there will not be a pull-in but a progressive closure as charge is added and a progressive release as charge is removed. Although the time to charge may be greater in some embodiments as a result, such progressive closure can minimize ringing, which can result in a shorter total time to stable closure (e.g., compared to total time for snap-down plus time for ringing to subside). In addition, impact forces will be greatly reduced, avoiding fracturing and leading to far lower wear. 
     Furthermore, in another aspect of the present subject matter, an array including multiple such MEMS devices  120  can each be driven by a corresponding charge pump  100 . As illustrated in  FIG. 6 , for example, in some embodiments, an array, generally designated  200 , can include a plurality of charge pumps  100  that are each associated with an individual MEMS device  120 . A controller  210  or other input device in communication with each of charge pumps  100  provides an input digital control word that corresponds to the desired pattern of actuation of the MEMS devices  120  (e.g., corresponding to a desired total array behavior). In this arrangement, instead of having a single charge pump and an array of high-voltage level shifters driven by low-voltage digital words to control the array of devices, the bits from the low-voltage digital words can be used to actuate individual MEMS devices  120  by energizing selected respective individual charge pumps  100 . 
     In any configuration or application, the operation of charge pump  100  can include any of a variety of control and regulation systems. In some embodiments, a regulation system for charge pump  100  is provided in order to sense the available high voltage output at primary circuit node  102  to determine when charge pump  100  should be activated. The regulation system for the charge pump can be configured to determine the number of cycles that the charge pump is clocked as well as a voltage increment required at each stage of the charge pump. The number of cycles that the charge pump is clocked is determined by one or more of the design of the charge pump, load capacitance, or the voltage increment required at each stage of the charge pump to achieve the desired high voltage output. 
     In some embodiments, the threshold level for starting the clock and the number of clock cycles are set to enable stability in control of the charge pump. In that case, the regulation system can be combined with a fractional drive to throttle the charge pump as well as manage any voltage spikes. This would require more cycles for a given voltage rise, but give finer control of the charge pump stages. Additionally, it may take longer for the string to stabilize after the clock cycles stop and the initial states of the charge pump may be uneven along the string. 
     The voltage increment can be determined from a measurement comparison to a desired threshold voltage or reference voltage. Additionally, the number of cycles needed to achieve the desired high voltage output can be computed based on the difference between the measured and reference voltages. Alternatively, the measurement of a voltage at or below the threshold voltage can act as a trigger for a fixed number of operating cycles to be initiated. In some embodiments, the measurement taken to make the comparison can be taken on the charge pump diode string itself when the charge pump is not active. In this way, a separate voltage divider is not necessary, which can be advantageous since the use of a voltage divider would add a comparatively large amount of leakage to the charge pump, requiring the charge pump to be operated more often to maintain the desired high voltage output at the primary circuit node. 
     Referring to one configuration for a regulation system,  FIG. 6  illustrates a regulation system  150  that is configured to take a voltage measurement for charge pump  100 . In the illustrated configuration, this measurement can be taken near the bottom of the string of charge pump stages  105 - 1  through  105 - n , which provides regulation system  150  with a low voltage that is in direct proportion to the high voltage at the top of the string. Alternatively, regulation system  150  can be provided in communication with one of discharge circuit elements  115 - 1  through  115 - n  or with shorting switch  118 . 
     In any configuration, regulation system  150  can be configured to extrapolate the present voltage at primary circuit node  102  from the voltage measurement taken at the bottom of the string, such as is illustrated in  FIG. 7 . In particular, in embodiments in which charge pump  100  is implemented using SOI processes or other insulated substrate transistor technologies, the voltage division can be more uniform among charge pump stages  105 - 1  through  150 - n  than in other implementations (e.g., CMOS), and thus the measurement taken by regulation system  150  can be used to determine the voltage at primary circuit node  102 . The system extrapolates the present voltage by finding the difference between the reference voltage and the measured voltage corresponding to the desired high voltage output at primary circuit node  102 . Regulation system  150  then uses this information to calculate the number of clock cycles that charge pump  100  needs to be activated in order to achieve the desired voltage level at primary circuit node  102   
     In some embodiments, such a measurement on the diode string can be obtained by a high impedance input to avoid disturbing the voltage division. By avoiding the separate measurement divider, current consumption should be greatly reduced. Furthermore, a direct measurement on the charge pump will provide nearly instantaneous voltage measurement and therefore allow for tighter, more precise regulation of the charge pump, as well as a lower ripple during a static “on” state. By not requiring a separate divider string, it will greatly decrease the leakage from the primary circuit node, leading to lower DC current consumption and lower average noise. 
     The present subject matter can be embodied in other forms without departure from the spirit and essential characteristics thereof. The embodiments described therefore are to be considered in all respects as illustrative and not restrictive. Although the present subject matter has been described in terms of certain preferred embodiments, other embodiments that are apparent to those of ordinary skill in the art are also within the scope of the present subject matter.