WO2007146002A2

WO2007146002A2 - Method and system for providing a charge pump for very low voltage applications

Info

Publication number: WO2007146002A2
Application number: PCT/US2007/013328
Authority: WO
Inventors: Emmanuel Racape
Original assignee: Atmel Corp
Current assignee: Atmel Corp
Priority date: 2006-06-07
Filing date: 2007-06-05
Publication date: 2007-12-21
Anticipated expiration: 2008-12-07
Also published as: TW200802398A; TWI355667B; DE112007001308T5; WO2007146002A3; CN101460903B; DE112007001308B4; CN101460903A; US7855591B2; US20070285150A1

Abstract

A method and system for providing an output voltage greater than a voltage provided by a voltage supply in a semiconductor device disclosed The method and system include providing a plurality of clock signals, providing a first stage and providing a second stage The first stage includes at least a first pumping node (144'), a pumping capacitor (142) and a device coupled with the pumping node (156'), and an auxiliary capacitor pan: (152/162) for providing an undershoot for the device for value(s) of the clock The auxiliary a pumping capacitors receive a first portion of the clock signals The second stage includes at least a second pumping node The first a second portions of the clock signals are provided to the first and second stages, respectively The first stage and the second stage are configured to alternately charge and fully discharge based on the clock signals

Description

METHOD AND SYSTEM FOR PROVIDING A CHARGE PUMP FOR VERY LOW

VOLTAGE APPLICATIONS

FIELD OF THE INVENTION

The present invention relates to semiconductor technology and more particularly to generation of higher voltage in low voltage devices.

BACKGROUND OF THE INVENTION

Semiconductor devices, such as EEPROMs or Flash devices, may be desired to he run using a voltage supply that provides a lower supply voltage. The lower supply voltage allows the device to consume less power and be shrunk to smaller geometries. For example, lower voltages are desired for applications such as EEPROMs used in smart cards. Although lower supply voltages are desired for the semiconductor devices, higher voltages may be desired for certain operations. For example, a voltage that is higher than the supply voltage may be required for operations such as programming memory cells, hi order to obtain the higher voltages, a conventional charge pump may be used.

FIG. 1 depicts a conventional charge pump 10, which can be used to increase voltages above the supply voltage or provide a reverse polarity voltage. The conventional charge pump 10 includes a conventional" capacitor-diode ladder 12 and a conventional oscillator 20 coupled with a voltage supply 22. The conventional capacitor-diode ladder 12 includes capacitor-diode pairs 13 (including capacitor 14 and diode 24), 15 (including capacitor 16 and diode 26), and 17 (that includes capacitor 18 and diode 28). The conventional oscillator 20 outputs clocks signals CLK and CLKB. The diodes 24, 26, and 28 are typically NMOS devices that function as diodes. The signal CLKB is the inverse of the signal CLK.

Based on the signals CLK and CLKB, the capacitor-diode pairs 13, 15, and 17 alternately charge to approximately the supply voltage and discharge. For example, the capacitor-diode pair 13 charges the capacitor 14, then discharges the capacitor 14 and transfers the energy to the next capacitor-diode pair 15. The charging and discharging of capacitors 14, 16, and 18 in the capacitor-diode ladder 12 allows for energy to be transferred between capacitor-diode pairs 13, 15, and 17, and output. This energy is also transferred at the output 30 of the conventional charge pump 10 by an output current provided at the output 30. The conventional charge pump 10, has a gain per capacitor- diode pair of V_dd - V_t, where V_dd is the supply voltage and Vt is the threshold voltage of the NMOS devices 24, 26, and 28. Thus, a voltage above that of the conventional voltage supply 22 can be provided.

Although the conventional charge pump 10 functions, one of ordinary skill in the art will readily recognize that the conventional charge pump 10 may have significant drawbacks, particularly for lower supply voltages. The number of capacitor-diode pairs, such as the capacitor-diode pairs 13, 15, and 17, that can be cascaded is limited by the amount of the voltage drop increase between the source and the bulk of an NMOS device in the capacitor-diode pairs 13, 15, and 17. This drop results in a dramatic increase in the threshold voltage in the final stages. Consequently, a limited number of capacitor- diode pairs and, therefore, a limited gain may be achieved. Another drawback is that thick oxide, high voltage dedicated transistors are necessary to reliably sustain a large voltage drop between gate and bulk. Thus, thin oxide, low voltage standard devices which can sustain a maximum drop of V_dd may not be used in the conventional charge pump 10. Moreover, when used in applications using a low supply voltage, the charge pump 10 provides a lower output current from the output 30 because charge is output at a lower rate from the capacitor-diode ladder 12. Furthermore, the high voltage from the conventional charge pump 10 may be on the order of the breakdown voltage of devices to which the voltage is applied, inducing breakdown leakage. As the output current of the conventional charge pump 10 decreases, the effect of the leakage becomes more marked. As a result, the ability of the conventional charge pump 10 to provide a sufficient output current in combination with a high voltage may be adversely affected.

Accordingly, what is needed is an improved method and system for providing a voltage higher than the supply voltage, particularly in lower supply voltage devices. The present invention addresses such a need.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a method and system for providing an output voltage greater than a voltage provided by a voltage supply in a semiconductor device. The method and system comprise providing a plurality of clock signals, providing a first stage and providing a second stage. The first stage includes at least a first pumping node, at least one pumping capacitor coupled with the at least first pumping node, at least one device coupled with the at least one pumping node, and at least a first and a second auxiliary capacitor for providing an undershoot for the at least one device for at least one value of the plurality of clock signals. The at least one auxiliary capacitor and the at least one pumping capacitor receive the first portion of the plurality of clock signals. The second stage includes at least a second pumping node. A first portion of the plurality of clock signals is provided to the first stage, while a second portion of the plurality of clock signals is provided to the second stage. The first stage and the second stage are configured to alternately charge and fully discharge based on the plurality of clock signals.

According to the method and system disclosed herein, the present invention provides a higher voltage in low voltage devices, such as lower voltage EEPROMS. In particular, the method and system may function for supply voltages approaching the threshold voltage of the at least one device.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is diagram depicting a conventional charge pump.

FIG. 2 is a diagram of a charge pump for use with lower supply voltages.

FIG. 3 is a diagram of clock signals for the charge pump fur use with lower supply voltages.

FIG. 4 is a diagram depicting one embodiment of a system in accordance with the present invention for providing a voltage higher than, a supply voltage.

FIG. 5 is a diagram depicting a preferred embodiment of a system in accordance with the present invention for providing a voltage higher than a supply voltage at very low supply voltages.

FIG. 6 is a diagram depicting clock signals for in one embodiment of a system in accordance with the present invention.

FIG. 7 is a diagram depicting one embodiment of a device using multiple systems in accordance with the present invention for providing a voltage higher than a supply voltage.

FIG. 8 is a flow chart depicting one embodiment of a method in accordance with the present invention for providing a system for providing a voltage higher than a supply voltage.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to semiconductor processing. The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the preferred embodiments and the generic principles and features described herein will be readily apparent to those skilled in the art. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features described herein.

The present invention provides a method and system for providing an output voltage greater than a voltage provided by a voltage supply in a semiconductor device. The method and system comprise providing a plurality of clock signals, providing a first stage and providing a second stage. The first stage includes at least a first pumping node, at least one pumping capacitor coupled with the at least first pumping node, at least one device coupled with the at least one pumping node, and at least one auxiliary capacitor for providing an undershoot for the at least one device for at least one value of the plurality of clock signals. The at least one auxiliary capacitor and the at least one pumping capacitor receive the first portion of the plurality of clock signals. The second stage includes at least a second pumping node. A first portion of the plurality of clock signals is provided to the first stage, while a second portion of the plurality of clock signals is provided to the second stage. The first stage and the second stage are configured to alternately charge and fully discharge based on the plurality of clock signals.

The present invention will be described in terms of a semiconductor device having particular components. However, one of ordinary skill in the art will readily recognize that the method and system in accordance with the present invention may utilize other components consistent with the present invention. The present invention is also described in the context of providing a voltage higher than the supply voltage. However, one of ordinary skill in the art will readily recognize that the method and system may be used to provide reverse polarity voltages.

FIG. 2 is a diagram of a charge pump 50 for use with lower supply voltages. The charge pump 50 is one scheme that has been proposed to address the inability of conventional charge pumps, such as the charge pump 10, to operate as desired at low supply voltages. The charge pump 50 includes pumping capacitors 60 and 74, auxiliary capacitors 68 and 72, PMOS devices 62, 64, 66, 70, 74, 76, input 84 and output 86. In addition, the charge pump 50 utilizes inputs 52, 54, 56, and 58 for the four-phase clock signal. FIG. 3 depicts the clock signals 90, 92, 94, and 96. The input 84 receives an input voltage, Vi_n, that is preferably the supply voltage, Vdd-

Using the four phase clock signals 90, 92, 94, and 96, the limitations on gain per stage due to the threshold voltage and body effect of the PMOS devices 62, 64, 66, 70, 74, and 76 can be substantially reduced or eliminated. In operation, a maximum voltage drop that is lower than the supply voltage V_dd is maintained on the PMOS devices 62, 64,

66, 70, 74, and 76. Thus, the charge pump 50 can produce a gain that is very close to Vdd- The gain per stage of the charge pump 50 is thus is limited only by parasitics. In addition, the PMOS devices 62, 64, 66, 70, 74, and 76 avoids limitations due to threshold voltage drop and body effect in NMOS devices because such limitations are not present with PMOS devices 62, 64, 66, 70, 74, and 76. Further, the voltage difference between all the nodes of the PMOS devices does not exceed V_dd on the charge pump 50. Consequently, thick gate oxides or triple wells are not needed for the charge pump 50.

Although the charge pump 50 functions, one of ordinary skill in the art will recognize that there is a lower limit to the supply voltages with which the charge pump 50 functions as desired. For the charge pump 50, the following conditions hold: V_gate- source device 62 > V_t, which means that V_node g4 — V_{node 67} > Vt, where Vt is the threshold voltage of a PMOS device 62, 64, 66, 70, 74, or 76. This conditions are analogous to Vgate-source device 74 > V_t and the V_node g4 - V_nod_e 7i > V_t. Thus, when clock signals 90 and 92 are low, the voltage at the node 82 is Vj_n and the voltage at node 67 is Vi_n + V_t — V_dd*C_r, where C_r is 1/(1 + C_para/C_Capacitor βs) and C_para is the total parasitic capacitance at the node

67. In order for the conditions above to be satisfied, V_dd ^> 2*V_t*(l + C_para/C_aux). If the parasitic capacitance is low, then the supply voltage with which the charge pump 50 can be used may be as low as approximately 2* V_t. Thus, the lower limit for the supply voltage Vdd for the charge pump 50 is approximately 2* Vt- This lower limit for the supply voltage at which the charge pump 50 functions may be higher than is desired for some applications. Moreover, when the signal 90 or 94 is low and the signal 92 or 96, respectively, is high, the discharge of the voltage at the node 67 or the node 71, respectively, may be incomplete. This is because the node 71 has a voltage of Vj_n + V_t. Because the discharge of the node 67 or 71 is incomplete, the ability of the charge pump 50 may be further compromised at low supply voltages.

In addition, one of ordinary skill in the art will recognize that the charge pump 50 is desired to be used in memories having cells that may be characterized by a relatively large leakage current. As a result, it is desirable to provide a larger output current via the output 86. In the case where V_dd ⁼ 1 volt and V_t is approximately 0.4 volt, the charge pump 50 may be at or near its operating limit. As a result, the charge pump 50 may be unable to provide the desired output current. Consequently, it is still desirable to provide a mechanism for providing a voltage that is higher than the supply voltage in devices having a very low supply voltage.

To more particularly describe the present invention, refer to FIG. 4, depicting one embodiment of a system 100 in accordance with the present invention for providing a voltage higher than a supply voltage. The system 100 is preferably a charge pump. The system 100 includes an input 102, an output 104, a first stage 110, and a second stage 140, which are driven by a clock 170. The clock provides a plurality of clock signals that are used to drive the first stage 110 and the second stage 140. In a preferred embodiment, six clock signals are used.

The first stage 110 includes at least one pumping node 114 that is preferably coupled with a pumping capacitor (not shown). Also in a preferred embodiment, the first stage includes auxiliary capacitor(s) 121 and a device 126 that is preferably a P-type device. The first stage is configured such that the pumping node 114 charges and fully discharges in response to a first portion of the plurality of clock signals provided by the clock 170. In a preferred embodiment, this is achieved using the auxiliary capacitor(s) 121 to undershoot the voltage on the gate of the device 126 during a portion of the period of the clock signals. Also in a preferred embodiment, the device 130 is a P-type device.

The second stage 140 is analogous to and coupled with the first stage 110. Consequently, the second stage 140 includes at least one pumping node 144 that is preferably coupled with a pumping capacitor (not shown). The second stage 140 also preferably includes auxiliary capacitor(s) 151 as well as a device 156 that is preferably a P-type device. The second stage is configured such that the pumping node 144 charges and fully discharges in response to a first portion of the plurality of clock signals provided by the clock 170. In a preferred embodiment, full discharge of the node(s) 158 is achieved using the auxiliary capacitor(s) 162 to undershoot the voltage on the gate of the device 156 during a portion of the period of the clock signals. In addition the first stage 110 and second stage 140 are configured to alternately charge and fully discharge the pumping nodes 114 and 144, respectively, in response to the clock signals from the clock 170.

Because of the configuration of the stages 110 and 140 as well as the clock signals from the clock 170, a high gain per stage may be achieved. This gain may be limited primarily by parasitic effects. In addition, degradation in the voltage provided due to the threshold voltage of the devices 126 and 156 may be avoided. Consequently, the system 100 may be used at very low supply voltages. In particular, the system 100 may function as desired for supply voltages that are greater than but approach the threshold voltage of the device 126 or 156. For example, for the charge pump 50, the supply voltage for desired operation is approximately 2V_t. In contrast, the system 100 may operate as desired for supply voltage of approximately V_t. In addition, the gain for the system 100 is optimized such that V_out = Vj_n 4- V_άd. Thus, even at very low voltages, the system 100 may provide the desired high voltage with sufficient output current.

FIG. 5 is a diagram depicting a preferred embodiment of a system 100' in accordance with the present invention for providing a voltage higher than a supply voltage. For clarity, the clock 170 is not explicitly shown. Only the signals provided are indicated. The system 100' includes inputs 102' that receives signal Vin, output 104' and stages 110' and 140'. The system 100' is a charge pump 100'. The stage 110' of the charge pump 100' includes pumping capacitor 112, auxiliary capacitors 122 and 132, PMOS devices 118, 120, 126', and 130, as well as inputs 116, 134, 136, and 124. In addition, the nodes 114' and 128 are also noted. The auxiliary capacitors 122 and 132 correspond to the auxiliary capacitor(s) 121 of FIG. 4. Referring back to FIG. 5, the stage 140' of the charge pump 100' includes pumping capacitor 142, auxiliary capacitors 152 and 162, PMOS devices 148, 150, 156', and 160, as well as inputs 146, 164, 166, and 154. The auxiliary capacitors 152 and 162 correspond to the auxiliary capacitor(s) 151 of FIG. 4. Referring back to FIG. 5, the nodes 144' and 158 are also noted. The inputs 136 and 166 receive an initialization signal for the node 144' and 114', respectively, of the previous stage 140' and 110% respectively. In addition, the components 112, 118, 120, 122, 126', 130, and 132 of the first phase 110' are preferably analogous to and have the size as their counterparts 142, 148, 150, 152, 156', 160, and 162, respectively, of the second phase 140'.

The pumping capacitors 112 and 142 axe coupling capacitors that preferably have a large capacitance and are used for the basic charge pumping operation. Thus, in one embodiment, the pumping capacitors 112 and 142 have a capacitance on the order of 4 pF. The P-type devices 120 and 150 are used to transfer charge from the nodes 114' and 144', respectively, to the output 104' and to prevent reversal current feedback from the output 104 to the nodes 114' and 144', respectively. The P-type devices 118 and 148 are used to connect the nodes 114' and 144% respectively, to the input 102 when the clock signals input to inputs 116 and 146, respectively, are low and thus the capacitors 112 and 142, respectively are not pumped. The P-type devices 126' and 156% are used to switch the gates of the P-type devices 118 and 148, respectively, in order to prevent reversal current feedback to the input 102 when the pumping capacitors 112 and 142, respectively, are boosted. Auxiliary capacitors 132 and 162 preferably have a small capacitance and are used to generate an under shoot for the gate of the P-type devices 126' and 156% respectively. For example, in one embodiment, each of the auxiliary capacitors 132 and 162 has a capacitance on the order of 7OfF when the capacitance of the pumping capacitors 112 and 142 is on the order of 4pF. Thus, the capacitances of the auxiliary capacitors 132 and 162 are significantly smaller than that of the pumping capacitors 112 and 142, respectively. Because of the undershoot for their gates, the potential at the gate of the P-type device 126' or 156' is lower than the voltage at the input 102'. Consequently, the node 128 or 158 is fully discharged to the node 114' or 144', respectively, when the clock provided to the inputs 124 or 152, respectively has a falling edge.

FIG. 6 is a diagram depicting clock signals 180, 181, 182, 183, 184, and 185 for in one embodiment of a system in accordance with the present invention. The clock signals 180, 181, 182, 183, 184, and 185 preferably vary between zero volts and the supply voltage, Vdd- Operation of the system 100' is described in the context of the clock signals 180, 181, 182, 183, 184, and 185. Referring to FIGS. 5 and 6, the capacitors 112 and 142 are preferably relatively large in size to transfer a greater amount of energy.

To further describe the operation of the charge pump 100% it can be assumed that initially, the clock signals 180 and 182 are low, while clock signals 181» 183, 184, and 185 are high. Thus, the nodes 144' and 158 are also initially at Vi_n + Vdd, where Vdd is the supply voltage. The nodes 161 and 131 are at Vj_n. The node 114' is at ^"VV The node 128 is at Viow, which is V_aux - C_rV_dd₅ where V_aUχ = Vin and C_r = 1/(1 + C_paraux/C_capi22), Cparaux is the total parasitic capacitance at node 128 from the devices 118 and 126'. In addition, the inputs 136 and 166 receive and initialization signal, hi embodiments in which multiple stages 110/110' and 140/140' are cascaded, as described below, the initialization signal may be from a previous stage 110/110' and 140/140'. In such a case, the initialization signal may be from the nodes corresponding to nodes 114' and 144% respectively, of a previous stage (not shown) or to the signals 183 and 180, respectively, only for the first stage. Consequently, the initial signal provided to node 136 is the voltage at node 144' - Vdd. Similarly, the initial signal provided to the node 166 is the voltage at the node 114' -V_dd-

The signal 182 switches high, to V_dd- Consequently, the node 128 rises to Vj_n due to the coupling capacitor 122. The clock signal 180 switches high, to V_dd- Thus, the voltage at node 114' rises to Vj_n + Vd_d. Similarly, the node 128 rises to V_jπ + V_dd, which is connected to the node 114' through the P-type device 126'. At substantially the same time, the P-type device 150 turns off and the node 161 keeps its initial value of Vj_n, but floats.

Next, the clock signal 183 goes low. As a result, the node 144' switches to Vin and the node 158 goes to Vauxi where V_HUXj — Vj_n ^■+- V_t through the P-type device ISβ^''. Because the node 144' is at Vj_n, the P-type device 120 turns on and charge transfer occurs from the node 114' to the output 104% Because the P-type devices 118 and 150 have their gates connected to Vj_n + V_dd, the P-type devices 118 and 150 are turned off and no reversal charge transfer occurs. The P-type device 130 is on and the voltage at node 131 is Vi_n. To reduce or eliminate the effects of a low V_dd, a dedicated phase is added to create a short pulse with the clock signal 184 on the coupling capacitor 162. This may allow all charge to be transferred from the node 158 to the node 144% Consequently, the voltage at the node 158 decreases to V_aux, where V_aux = Vj_n. As a result, the charge pump 100' can function at a very low supply voltage.

Next, the voltage at the node 161 varies from Vi_n to Vj_n - CsO/d_d) during the falling edge of the clock signal 184 and from Vi_n - C^(V _άd) to V;_n during the rising edge of the clock signal 184. The operator C3 is 1/(1 + C_parasitic/Ci62)_> where C_parasitic is the parasitic capacitance at the node 161 due to the P-type devices 160 and 156.

During the last phase, the clock signal 185 goes low. As a result, the node 158 switches to a low voltage and the P-type device 148 turns on. Consequently, charge is transferred from the input 102' to the node 144', which will be the next pumped node. Thus, the first half of the period of operation may be completed. During the first half of the period, charge is transferred from the node 114' to the output 104' and from the input 102' to the node 144'. When this charge transfer is completed, a second half of the period is commenced. The second half of the period is symmetric with respect to the first half of the period. The second half of the period commences when the clock signal 185 is switched high. Switching the clock signal 185 high raises the node 158 to Vj_n. Next, the clock signal 183 pulses high to boost the node 144' to V_1n + Vd_d as well as the node 158. Thereafter, the signal 180 pulses low, turning the P-type device 150 on and starting charge transfer from the node 144' to the output 104'. An undershoot for the voltage at the node 131 is generated by pulsing the clock signal 181 low to transfer the charge from the node 128 to the node 114'. The final portion of the period occurs when the clock signal 182 is switched low to turn the P-type device 1 18 on. Thus, during this second half of the period, charge from the input 102' to the node 114' and from the node 144' to the output 104'.

Thus, during the first half of the period for the clock signals depicted in FIG. 6, charge is transferred from the node 114' to the output 104'. At the same time, the node 144' receives charge from the input 102'. During the second half of the period, charge is transferred from the node 144' to the output 104'. At the same time, the node 114' receives charge from the input 102'. Thus, the stages 140' alternately charge and discharge. In addition, in order to ensure that the capacitors 112 and 142, and thus the nodes 128 and 158, are completely discharged, the auxiliary capacitors 132 and 162 are used. The auxiliary capacitors 132 and 162 generate an undershoot of the voltage on the gates of the P-type devices 126' and 156', respectively, during the falling edge of the clock signals 181 and 184, respectively. Thus, in the steady state operation of the charge pump 100', the pumping nodes 114' and 144' have a voltage that varies from Vj_n to Vj_n + Ci(V_dd), where Ci is 1/(1 + C_pai/Cm) and C_par is the parasitic capacitance at the node 114' due to the P-type devices 118, 120, 126', and 150. If it is assumed that the parasitic capacitance is small, then the variation in voltage at the pumping nodes 114' and 144' is approximately from Vi_n to V_dd- Thus, the variation in voltage for the pumping nodes 114' and 144' may be as large as possible, while it is ensured that charge is transferred alternately from the nodes 114' and 144'.

Furthermore, in a preferred embodiment, to achieve the desired functionality the gate-source voltages of the P-type devices 118 and 148 are higher than the threshold voltage, V_t, for a very low supply voltage. This condition is fulfilled using the P-type devices 130 and 160 as well as the small auxiliary capacitors 132 and 162. Between the falling edges of clock signals 180 and 182, a pulse is provided on the clock signal 181 to enable charge transfer from node 128 to node 114' or from node 158 to node 144', respectively. While the clock signal 180 is low and the clock signal 182 is high, the node 128 is at Vin + Vt. Before the falling edge of the clock signal 182, a pulse is generated on the clock signal 181 is generated to decrease the potential at the node 128 or 158. At such a time, the voltage at the node 128 or 158 is preferably V_in. After the clock signal 182 has changed state to zero, the potential at the node 128 is Vin - C_r(V_dd)₅ where C_r is 1/(1 + Cparai28/C_auχ)₅ C_par_ai2₈ is the parasitic capacitance at the node 128, respectively due to the devices 118 and 126'.

Thus, the condition for the desired functionality can be seen as: Vg₈ of P-type devices 118 and 148 is greater than V_t. In addition, the V_nOde 102 — V_nt>de 128 > V_t or V_node 102 — Vnode i58 > V_t. In the event that the clock signals 180 and 182 are low and that a pulse for the clock signal 181 is generated between the falling edges of the clock signals 180 and 182. This situation results in V node 12₈ ⁼ Vi_n - Vdd(C_r). Combining these conditions results in the minimum workable range of: Vdd > V_t(l + Cparam/Caux). For small parasitic capacitances, the lowest value of V_dd is very close to V₁.

Thus, the charge pump 100' may be operated at very low voltages while providing a higher than supply voltage. As described above, the charge pump 100' can operate at supply voltages approaching V_t, which is an improvement even over the charge pump 50. Thus, degradation due to threshold voltage may be reduced or eliminated. The gain for the charge pump 100' is preferably limited by parasitic capacitances only, and the optimal gain for the charge pump 100' may be provided. Thus, the gain for the charge pump 100' is V_<j_d (V_out ⁼ Vj_n + Vjd)- Consequently, the charge pump 100' is suitable for very low voltage applications.

FIG. 7 is a diagram depicting one embodiment of a device 200 using multiple systems in accordance with the present invention for providing a voltage higher than a supply voltage. Thus, the device 200 includes stages 201, 202, 203, through 204. Each of the stages 201, 202, 203, through 204 corresponds to the charge pump 100 or 100', respectively. Consequently, the output voltages from one stage 201, 202, or 203 can be fed into input of the next stage 202, 203, or another stage such as the stage 204, respectively. The stages 201, 202, 203, and 204 may be driven by clock(s) (not shown) such as the clock 170. Furthermore, each of the stages 201, 202, 203, and 204 provides a gain of approximately V_<j_d. In addition, the equation Vout = Vin + N*C_rVdd , where N is the number of stages, still holds, even for a weak supply voltage. The gain may thus be increased by cascading the stages 201, 202, 203, and 204. Consequently, the charge pump 100/100' may be scalable.

FIG. 8 is a flow chart depicting one embodiment of a method 300 in accordance with the present invention for providing a system for providing a voltage higher than a supply voltage. For clarity, the method 300 is described in the context of the system 100'. However, one of ordinary skill in the art that the method 300 may be used with other systems, including but not limited to the systems 100 and 200.

The clock 170 that drives the charge pump 100' is provided, via step 302. The clock provides a plurality of clock signals that are used to drive the first stage 110' and the second stage 140'. These multiple clock signals can otherwise be thought of as a clock signal having multiple, separate phases. In a preferred embodiment, a clock that provides six clock signals. Together, the clock signals provide a period of the system 100'. Further, each clock signal has transitions at different times from the remaining clock signals during the period. An example of one period of operation is shown in FIG. 6, described above.

The first stage 110' is provided, via step 304. Step 304 includes providing the pumping node(s) 114' that are preferably coupled with a pumping capacitor (not shown). Step 304 may also include providing auxiliary capacitor(s) 122 and a device 126' that is preferably a P-type device. The first stage is configured such that the pumping node 114' charges and fully discharges in response to a first portion of the plurality of clock signals provided by the clock 170. In a preferred embodiment, this is achieved using the auxiliary capacitor(s) 132 to undershoot the voltage on the gate of the device 126' during a portion of the period of the clock signals and a device 130 that is preferably a P-type device.

The second stage 140' is provided, via step 306. Step 306 is analogous to step 304 because the second stage is analogous to and coupled with the first stage 110'. Consequently, the second stage 140' includes at least one pumping node 144' that is preferably coupled with a pumping capacitor. Step 306 thus preferably includes providing auxiliary capacitor(s) 152 as well as a device 156' that is preferably a P-type device. The second stage is configured such that the pumping node 144' charges and fully discharges in response to a first portion of the plurality of clock signals provided by the clock 170. In a preferred embodiment, full discharge of the pumping node(s) 144' is achieved using the auxiliary capacitor(s) 162 to undershoot the voltage on the gate of the device 156' during a portion of the period of the clock signals and the device 160. In addition the first stage 110' and second stage 140' are configured to alternately charge and fully discharge the pumping nodes 114' and 144', respectively, in response to the clock signals from the clock 170. The steps 304-306 may then be optionally repeated to provide a semiconductor device, such as the device 200.

Thus, using the method 300, the system 100, 100' and/or 200 may be provided. As a result, the advantages of the systems 100, 100' and/or 200 may be achieved.

A method and system for providing an output voltage greater than a supply voltage provided by a voltage supply in semiconductor devices, such as EEPROMs. The present invention has been described in accordance with the embodiments shown, and one of ordinary skill in the art will readily recognize that there could be variations to the embodiments, and any variations would be within the spirit and scope of the present invention. Accordingly, many modifications may be made by one of ordinary skill in the art without departing from the spirit and scope of the appended claims.

Claims

CLAIMS We Claim:

1. A system for providing an output voltage greater than a voltage provided by a voltage supply in a semiconductor device, the system comprising: at least one clock providing a plurality of clock signals; a first stage including at least a first pumping node, at least one pumping capacitor coupled with the at least first pumping node, at least one device coupled with the at least one pumping node, and at least a first and a second auxiliary capacitor for providing an undershoot for the at least one device for at least one value of the plurality of clock signals, the at least one auxiliary capacitor and the at least one pumping capacitor receiving a first portion of the plurality of clock signals; and a second stage coupled with the first stage and including at least a second pumping node, the at least one clock providing the first portion of the plurality of clock signals to the first stage and a second portion of the plurality of clock signals to the second stage, the first stage and the second stage being configured to alternately charge and folly discharge based on the plurality of clock signals.

2. The system of claim 1 further comprising an output and wherein the first stage further includes a first stage initialization input, a first P-type device coupled the first auxiliary capacitor and the at least one pumping node, a second P-type device coupled between the at least one pumping node and the output, and a third P-type device coupled between the second auxiliary capacitor and the first stage initialization input.

3. The system of claim 2 wherein the at least one device includes at least one P-type device coupled between the first auxiliary capacitor and the second auxiliary capacitor and between each of the at least one auxiliary capacitor and the at least one pumping node.

4. The system of claim 1 wherein the device has a threshold voltage and wherein the voltage provided by the voltage supply is has a lower limit corresponding to the threshold voltage.

5. The system of claim 1 wherein the plurality of clock signals includes six clock signals.

6. The system of claim 1 further comprising: at least a third stage corresponding to the first stage, the third stage being coupled in series with the first stage; and at least a fourth stage corresponding to the second stage, the fourth stage being coupled in series with the second stage.

7. A system for providing an output voltage greater than a voltage provided by a voltage supply in a semiconductor device, the system comprising: a first stage including a first pumping node, a first pumping capacitor coupled with the first pumping node, a first device coupled with the first pumping node, and at least a first auxiliary capacitor and a second auxiliary capacitor for providing an undershoot for the first device for at least a first value of the plurality of clock signals; a second stage coupled with the first stage and including a second pumping node, a second pumping capacitor coupled with the second pumping node, a second device coupled with the second pumping node, and at least a third auxiliary capacitor for providing an undershoot for the second device for at least a second value of the plurality of clock signals; and at least one clock coupled with the first stage and the second stage, the at least one clock for providing a plurality of clock signals, a first portion of the plurality of clock signals being provided to the first stage and a second portion of the plurality of clock signals being provided to the second stage, the first stage and the second stage being configured to alternately charge and fully discharge the first pumping node and the second pumping node based on the plurality of clock signals.

8. The system of claim 7 wherein the least third auxiliary capacitor includes a third auxiliary capacitor and a fourth auxiliary capacitor.

9. The system of claim 8 further comprising an output; wherein the first stage further includes a first stage initialization input, a first P- type device coupled the first auxiliary capacitor and the first pumping node, a second P- type device coupled between the first pumping node and the output, and a third P-type device coupled between the second auxiliary capacitor and the first stage initialization input; and wherein the second stage further includes a second stage initialization input, a fourth P-type device coupled the third auxiliary capacitor and the second pumping node, a fifth P-type device coupled between the second pumping node and the output, and a sixth P-type device coupled between the second auxiliary capacitor and the first stage initialization input.

10. The system of claim 9 wherein the first device is a seventh P-type device coupled between the first auxiliary capacitor and the second auxiliary capacitor and between each of the first and second auxiliary capacitors and the pumping node, and wherein the second device is a eighth P-type device coupled between the third auxiliary capacitor and the fourth auxiliary capacitor and between each of the third and fourth auxiliary capacitors and the second pumping node.

11. A method for providing an output voltage greater than a voltage provided by a voltage supply in a semiconductor device, the system comprising: providing at least one clock providing a plurality of clock signals; providing a first stage including at least a first pumping node, at least one pumping capacitor coupled with the at least first pumping node, at least one device coupled with the at least one pumping node, and at least one a first and a second auxiliary capacitor for providing an undershoot for the at least one device for at least one value of the plurality of clock signals, the at least one auxiliary capacitor and the at least one pumping capacitor receiving a first portion of the plurality of clock signals; and providing a second stage coupled with the first stage and including at least a second pumping node, the at least one clock providing the first portion of the plurality of clock signals to the first stage and a second portion of the plurality of clock signals to the second stage, the first stage and the second stage being configured to alternately charge and fully discharge based on the plurality of clock signals.

12. The method of claim 11 further comprising: providing an output; and wherein the first stage further providing includes providing a first stage initialization input; providing a first P-type device coupled the first auxiliary capacitor and the at least one pumping node; providing a second P-type device coupled between the at least one pumping node and the output; and providing a third P-type device coupled between the second auxiliary capacitor and the first stage initialization input.

13. The method of claim 12 wherein the at least one device includes at least one P- type device coupled between the first auxiliary capacitor and the second auxiliary capacitor and between each of the at least one auxiliary capacitor and the at least one pumping node.

14. The method of claim 11 wherein the device has a threshold voltage and wherein the voltage provided by the voltage supply is has a lower limit corresponding to the threshold voltage.

15. The method of claim 11 wherein the plurality of clock signals includes six clock signals.

16. The method of claim 11 further comprising: providing at least a third stage corresponding to the first stage, the third stage being coupled in series with the first stage; and providing at least a fourth stage corresponding to the second stage, the fourth stage being coupled in series with the second stage.

17. A method for providing an output voltage greater than a voltage provided by a voltage supply in a semiconductor device, the method comprising: providing an output; providing a first stage including a first pumping node, a first pumping capacitor coupled with the first pumping node, a first P-type device coupled with the first pumping node, a first auxiliary capacitor for providing an undershoot for the first P-type device for at least a first value of the plurality of clock signals, a second auxiliary capacitor, a first stage initialization input, a second P-type device coupled the first auxiliary capacitor and the first pumping node, a third P-type device coupled between the first pumping node and the output, and a fourth P-type device coupled between the second auxiliary capacitor and the first stage initialization input, the first P-type device being coupled between the first auxiliary capacitor and the second auxiliary capacitor and between each of the first and second auxiliary capacitors and the pumping node; providing a second stage coupled with the first stage and including a second pumping node, a second pumping capacitor coupled with the second pumping node, a fifth P-type device coupled with the second pumping node, and a third auxiliary capacitor for providing an undershoot for the second device for at least a second value of the plurality of clock signals, and a fourth auxiliary capacitor, a second stage initialization input, a sixth P-type device coupled the third auxiliary capacitor and the second pumping node, a seventh P-type device coupled between the second pumping node and the output, and an eighth P-type device coupled between the second auxiliary capacitor and the first stage initialization input, the fifth P-type device being coupled between the third auxiliary capacitor and the fourth auxiliary capacitor and between each of the third and fourth auxiliary capacitors and the second, pumping node; and providing at least one clock coupled with the first stage and the second stage, the at least one clock for providing a plurality of clock signals, a first portion of the plurality of clock signals being provided to the first stage and a second portion of the plurality of clock signals being provided to the second stage, the first stage and the second stage being configured to alternately charge and fully discharge the first pumping node and the second pumping node based on the plurality of clock signals.

18. A method for providing an output voltage greater than a voltage provided by a voltage supply in a semiconductor device, the method comprising: generating a plurality of clock signals; and utilizing the plurality of clock signals to drive a first stage and a second stage, a first portion of the plurality of clock signals being provided to the first stage and a second portion of the plurality of clock signals being provided to the second stage, the first stage including a first pumping node, a first pumping capacitor coupled with the first pumping node, a first device coupled with the first pumping node, and at least a first auxiliary capacitor for providing an undershoot for the first device for at least a first value of the plurality of clock signals, the second stage coupled with the first stage and including a second pumping node, a second pumping capacitor coupled with the second pumping node, a second device coupled with the second pumping node, and at least a second auxiliary capacitor for providing an undershoot for the second device for at least a second value of the plurality of clock signals, the first stage and the second stage being configured to alternately charge and fully discharge the first pumping node and the second pumping node based on the plurality of clock signals.

19. The method of claim 18 wherein the at least the first auxiliary capacitor further includes a first auxiliary capacitor and a second auxiliary capacitor and the at least the second auxiliary capacitor includes a third auxiliary capacitor and a fourth auxiliary capacitor.

20. The method of claim 19 further comprising an output; wherein the first stage further includes a first stage initialization input, a first P- type device coupled the first auxiliary capacitor and the first pumping node, a second P- type device coupled between the first pumping node and the output, and a third P-type device coupled between the second auxiliary capacitor and the first stage initialization input; and wherein the second stage further includes a second stage initialization input, a fourth P-type device coupled the third auxiliary capacitor and the second pumping node, a fifth P-type device coupled between the second pumping node and the output, and a sixth P-type device coupled between the second auxiliary capacitor and the first stage initialization input.

21. The method of claim 20 wherein the first device is a seventh P-type device coupled between the first auxiliary capacitor and the second auxiliary capacitor and between each of the first and second auxiliary capacitors and the pumping node, and wherein the second device is a eighth P-type device coupled between the third auxiliary capacitor and the fourth auxiliary capacitor and between each of the third and fourth auxiliary capacitors and the second pumping node.