CHARGE PUMP VOLTAGE REGULATOR

Abstract

A regulator (104) for a charge pump (102) includes a clock amplitude modulator (150) that changes voltage of a clock signal used in operation of the charge pump in response to changes in magnitude of output voltage of the change pump. The clock amplitude modulator is powered by an output of an auxiliary circuit (120). The output of the auxiliary circuit is at a higher voltage than an input voltage of the charge pump. A maximum amplitude of the voltage of the clock signal is higher than the input voltage of the charge pump.

Description

BACKGROUND

1. Field

This invention relates generally to charge pump voltage regulators, and more specifically a charge pump voltage regulator for use under low input voltage conditions.

2. Related Art

Most charge pumps are implemented with high voltage transistors. In this context, high voltage transistors are transistors that can support a drain-to-source voltage and a gate voltage that are relatively higher than the drain-to-source and gate voltages that medium and low voltage transistors can support. The threshold voltage V_T of high voltage transistors is typically 700-800 mV and it could be sometimes higher. Many charge pumps do not work properly at low input voltage V_IN conditions (e.g., when V_IN is above the threshold voltage V_T of high voltage transistors by 150-200 mV or less) and at a proper clock frequency for the charge pump. Therefore, many charge pumps do not work properly when V_IN is less than about 1V.

A charge pump circuit comprises a charge pump and a regulator. Most charge pump circuits do not provide adequate line and load regulation when the input voltage goes below a nominal V_IN because known charge pumps have their line and load regulation limited by V_IN. Therefore, in low V_IN applications, such as when V_IN is provided by a low voltage battery, known regulators for charge pumps cannot always maintain a constant output voltage. For example, under certain low V_IN conditions, known charge pump circuits may have difficulty maintaining the output voltage at a target voltage when the battery becomes weak. When V_IN is about 1V or lower, and the target output voltage is higher than V_IN, known regulators may fail to maintain the target output voltage of known charge pumps.

Most charge pump circuits include a clock generator circuit for generating clock signals that are coupled to capacitors in the charge pump. The output voltage of most charge pumps is regulated by modulating the frequency of such clock signals.

In known regulators for known charge pumps, the clock generator circuit is powered by V_IN. Therefore, a maximum amplitude of clock signals that can be produced by the clock generator circuit of such known regulators is V_IN. Consequently, in battery-powered applications, the maximum amplitude of the clock signals that can be produced by the clock generator circuit is a voltage of a battery. A maximum output voltage of such known charge pumps is limited by the highest amplitude of the clock signals produced by the clock generator circuit. Therefore, in battery-powered applications, the maximum output voltage of such known charge pumps is dependent on, and limited by, the voltage of the battery. The output voltage V_OUT of a charge pump is also dependent, in part, on a number of stages in the charge pump, an amount of current drain on the charge pump, capacitance of an output capacitor, and a frequency of the clock signals coupled to the capacitors in the charge pump.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and is not limited by the accompanying figures, in which like references indicate similar elements. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale.

FIG. 1 is a simplified functional block diagram of one embodiment of a charge pump circuit including a charge pump and a charge pump voltage regulator in accordance with the invention.

FIG. 2 is a set of graphs illustrating simulated operation of the charge pump circuit of FIG. 1 under various input voltage conditions.

FIG. 3 is a set of graphs illustrating simulated operation of the charge pump circuit of FIG. 1 under various load current conditions.

DETAILED DESCRIPTION

FIG. 1 is a simplified functional block diagram of one embodiment of a charge pump circuit 100 in accordance with the invention including a charge pump 102 and a charge pump voltage regulator (hereinafter “regulator”) 104. The charge pump 102 has an input terminal 106 for receiving an input voltage V_IN and an output terminal 108 for outputting an output voltage V_OUT. For a battery-powered charge pump circuit 100, V_IN is the battery voltage. The charge pump circuit 100 includes an output capacitor 110 coupled between the output terminal 108 and a ground terminal. A load 112 may be coupled to the output terminal 108. A current I_LOAD flows from the output terminal 108 to a ground terminal though the load 112. The charge pump 102 has a clock input terminal 109 for receiving one or more clock signals.

The regulator 104 provides clock amplitude feedback for the charge pump 102. The regulator 104 controls a magnitude of the output voltage V_OUT of the charge pump 102 by modulating an amplitude of the one or more clock signals that are coupled to the charge pump. Advantageously, an absolute value of the maximum amplitude of the one or more clock signals is higher than an input voltage V_IN of the charge pump 102. The regulator 104 may also control the magnitude of the output voltage V_OUT of the charge pump 102 by modulating a frequency of the one or more clock signals. The regulator 104 may also control the magnitude of the output voltage V_OUT of the charge pump 102 by concurrently modulating the amplitude and the frequency of the one or more clock signals, wherein the maximum amplitude of the one or more clock signals is higher than the input voltage V_IN of the charge pump. The regulator 104 provides line and load regulation suitable in portable devices supplied by a low voltage battery. In one embodiment, a low voltage battery has a nominal voltage of 1.2V. The charge pump circuit 100 is suitable with a sub-1V input power supply voltage V_IN, and may advantageously continue to function properly after a low voltage battery (e.g., a battery having a nominal voltage of 1.2V) becomes weaker than its nominal voltage (e.g., the voltage falling to 0.9V).

The regulator 104 includes an auxiliary stage 120, a voltage divider 125, an amplifier 130, and a clock amplitude modulator 150.

The auxiliary stage 120 multiplies V_OUT and provides a supply voltage to the amplifier 130. The auxiliary stage 120 outputs an auxiliary voltage V_AUX. The regulator 104 is configured so that the value of V_AUX is at least greater than the value of V_IN. In one embodiment, the input voltage of the auxiliary stage 120 is the output voltage V_OUT of the charge pump 102. In such embodiment, V_AUX is not only greater than V_IN but also greater than V_OUT. The auxiliary stage 120 can be any circuit that generates a voltage greater than V_IN. In one embodiment, the auxiliary stage 120 is a charge pump, and the auxiliary stage 120 includes a circuit (not shown) for producing clock signals for use within the auxiliary stage, and an output capacitor 122. In one embodiment, the auxiliary stage 120 is a basic two-stage Dickson charge pump. In another embodiment, the auxiliary stage 120 is a voltage doubler with a bridge. In yet another embodiment, the auxiliary stage 120 is a voltage tripler with a bridge and a half. In still another embodiment, the auxiliary stage 120 is a boost switching power supply. In a further embodiment, the auxiliary stage 120 is any DC-to-DC converter. In yet a further embodiment, the auxiliary stage 120 is any voltage multiplier. Although in the embodiment illustrated in FIG. 1 the auxiliary stage 120 is powered by V_OUT, in still a further embodiment (not shown) the auxiliary stage is powered directly by V_IN.

The magnitude of the output voltage V_OUT of the charge pump 102 is affected by V_IN and I_LOAD. The output voltage V_OUT is fed into the voltage divider 125 that produces a voltage V_OUT* in response to V_OUT. In one embodiment, the voltage divider 125 is a resistive ladder comprising R₁ and R₂, which produces the voltage V_OUT* in response to V_OUT, as follows:

V_OUT*=V_OUTR₂/(R₁+R₂)

In one embodiment, R₁=4R₂.

The amplifier 130 compares V_OUT* to a reference V_REF and provides a proper V_X to regulate V_OUT. V_X is adjusted according to deviation in V_IN at the input terminal 106 of the charge pump 102 and/or deviation in load current drawn from the output terminal 108 of the charge pump. The amplifier 130 has an inverted input terminal 132 and a non-inverted input terminal 134. V_OUT* is fed into the inverted input terminal 132, and V_REF is fed into the non-inverted input terminal 134. In one embodiment, the value pre-selected for V_REF is related to V_IN. In one embodiment, V_REF is a fraction of V_IN. One example of V_REF is V_IN/2. Another example of V_REF is V_IN/3. In another embodiment, the value pre-selected for V_REF is related to a bandgap voltage. In one example, V_REF is the bandgap voltage. In another example, V_REF is a fraction of the bandgap voltage. Resistive values of R₁ and R₂ are pre-selected such that V_OUT* is equal to V_REF when V_OUT is at a target output voltage.

The amplifier 130 produces an amplified output signal V_X responsive to a difference between V_OUT* and V_REF. The value of V_X can vary. The value of V_X tracks the output voltage V_OUT of the charge pump 102. At any instant after completion of start-up, the value of V_X is representative of a present value of V_OUT. In one embodiment, the value of V_X is directly and linearly proportional to the value of V_OUT. In the event the magnitude of V_OUT begins dropping (because V_IN decreased and/or I_LOAD increased), the magnitude of V_OUT* also drops, and, as a result, the amplifier 130 outputs the signal V_X having a certain corresponding value to the clock amplitude modulator 150. In one embodiment, the amplifier 130 is powered by V_AUX from the auxiliary stage 120. In another embodiment, the amplifier 130 is powered by V_OUT directly from the charge pump 102. In yet another embodiment, the amplifier 130 is powered by V_IN directly from the battery. In a further embodiment, V_IN supplies the amplifier 130 with power during start-up only, and then the amplifier switches to V_AUX for its power supply.

The clock amplitude modulator 150 includes an input terminal 152 that receives the signal V_X from the amplifier 130. In one embodiment, the clock amplitude modulator 150 is powered by V_AUX. Advantageously, V_AUX is higher than V_OUT, and, therefore, also higher than V_IN. The clock amplitude modulator 150 includes a circuit (not shown) for producing a clock signal, such as an internal RC oscillator, a crystal oscillator, or another type of circuit that generates a periodic signal. The clock amplitude modulator 150 produces one or more clock signals that are non-overlapping with respect to each other. Each of the one or more clock signals has a different phase than the other clock signals. In one embodiment, the frequency of the one or more clock signals is approximately 1 MHz. The clock amplitude modulator 150 shifts up and down the amplitude of the one or more clock signals. The clock amplitude modulator 150 includes one or more output terminals 154 from which the one or more clock signals are outputted to the charge pump 102. The charge pump 102 includes a plurality of capacitors (not shown). Each of the one or more clock signals is coupled to a ground-side plate of one of the capacitors of the charge pump 102. The clock signals control operation of the charge pump 102. The amplitude or the amplitude and frequency of the clock signals affect the magnitude of V_OUT. The one or more clock signals have a voltage V_CLK whose amplitude depends on the value of the output V_X of the amplifier 130. In one embodiment, the voltage V_CLK may be equal to the value of V_X. The value of a maximum voltage of V_CLK is the value of V_AUX outputted by the auxiliary stage 120. The maximum voltage of V_CLK is V_AUX because the clock amplitude modulator 150 is powered by V_AUX. Advantageously, the value of maximum voltage of V_CLK is greater than the value of V_IN. In another embodiment, the clock amplitude modulator 150 is powered by the voltage V_OUT directly from the charge pump 102, and, although the voltage V_OUT is lower than V_AUX, the voltage V_OUT is, nevertheless, advantageously higher than the voltage V_IN.

The voltage divider 125, the amplifier 130 and the clock amplitude modulator 150 form part of a feedback loop from the output terminal 108 to the clock input terminal 109 of the charge pump 102. The feedback loop of the regulator 104 sets a new value for the amplitude of the at least one clock signal based on a present value of V_OUT. The feedback loop of the regulator 104 assures that the value of V_OUT* is always very close to the value of V_REF. The value of V_X varies to satisfy the equation V_OUT*=V_REF. The value of V_X increases or decreases according to variation of V_OUT, which, in turn, may be caused by variation of V_IN and/or I_LOAD.

The following is an example of operation of the regulator 104 when it is designed for maintaining V_OUT of the charge pump 102 at a desired 2.5V when V_IN of the charge pump is at a nominal 1.2V. If V_IN were to drop to 0.9V (such as due to a weak battery), a known regulator may fail to maintain V_OUT of the charge pump 102 at the desired 2.5V. Assuming that the known regulator is for a single-stage Dickson charge pump, a maximum V_CLK is disadvantageously V_IN. Such known regulator fails to achieve V_OUT at the desired 2.5V when V_IN drops to 0.9V because 1.8V=0.9V+0.9V (=V_IN+maximum V_CLK) is the maximum V_OUT that such known regulator can achieve. On the other hand, for the regulator 104 in accordance with the invention, if V_IN were to drop to 0.9V, V_OUT of the charge pump 102 would advantageously remain at 2.5V. For the regulator 104, when V_IN of the charge pump 102 is at the nominal 1.2V, V_OUT is 2.5V and V_AUX is 3.5V. For the regulator 104, when V_IN drops down to 0.9V, V_AUX goes down to about 2.8V (assuming the auxiliary stage 120 is a basic Dickson charge pump) because V_AUX depends, in part, on the voltage V_IN of the clock signal going into the auxiliary stage, which has gone down from 1.2V to 0.9V. For the regulator 104, when V_IN drops down to 0.9V, V_OUT would initially tend to drop. However, because V_AUX=2.8V is greater than the desired V_OUT=2.5V, the maximum voltage of the clock signal V_CLK for the charge pump 102 can be, and is, higher than the nominal V_IN=1.2V. Therefore, V_OUT advantageously does not drop below the desired V_OUT=2.5V. If V_IN=1.2V and a desired V_OUT is 2.5V, then, ideally, an amplitude of V_CLK of only 1.3V is needed; however, due to losses in the circuit, the regulator 104 is designed, in one embodiment, so that V_CLK=1.4 to 1.5V.

In one embodiment, when V_OUT decreases, the clock amplitude modulator 150 first increases the frequency of the clock signal until a maximum allowable frequency is reached, at which time, if the target V_OUT has not been attained, then the clock amplitude modulator increases the voltage of the clock signal V_CLK to values above V_IN. In another embodiment, when V_OUT decreases, the clock amplitude modulator 150 first increases the voltage of the clock signal V_CLK until it reaches V_AUX, at which time, if the target V_OUT has not been attained, then the clock amplitude modulator increases the frequency of the clock signal. In yet another embodiment, when V_OUT decreases, the clock amplitude modulator 150 concurrently increases the voltage and frequency of the clock signal. Of course, in each of these embodiments, when V_OUT increases, the clock amplitude modulator 150 decreases the voltage or the frequency, or both, of the clock signal.

FIGS. 2 and 3 illustrate examples of simulated operation of one embodiment of the regulator 104 designed for maintaining V_OUT of the charge pump 102 at a desired 3.0V when V_IN of the charge pump is at a nominal 1.5V. At V_IN values below about 900 mV, it becomes very difficult to bias the amplifier 130. As a result, the amplifier 130 would have low gain and the loop performance would be compromised. These simulations assume that the threshold voltage V_T of the devices of the regulator is 800 mV. These simulations assume that V_REF is related to a bandgap voltage of 600 mV. These simulations assume that the charge pump 102 is a single-stage Dickson charge pump that uses MOSFETs connected as diodes. The frequency of the clock signal in these simulations is fixed and set at 200 kHz.

Referring now to FIG. 2, which illustrates how the regulator 104 advantageously maintains the output voltage of the charge pump 102 at the target V_OUT value in spite of variation in I_LOAD. The four graphs demonstrate that the regulator 104 is able to maintain a constant output voltage V_OUT of the charge pump 102 when the load I_LOAD varies. The top graph shows that V_REF is fixed at 600 mV, and, at start-up of the charge pump circuit 100, that V_OUT* slowly increases and reaches V_REF about 4 ms after start-up. The bottom graph shows that from t=0 to about t=4 ms, the charge pump 102 is starting and that V_OUT reaches the target output voltage V_OUT=3V after about t=4 ms. The third graph shows that after the charge pump circuit 100 finishes starting, the output V_X of the amplifier 130 drops to about 2.5V, which is the value that maintains V_OUT at the target 3V. The third graph also shows that, when I_LOAD increases (see the second graph) to about 400 μA at about 7 ms, the value of V_X increases to about 4V to keep V_OUT at a constant value of 3V. The third graph also shows that, when I_LOAD decreases (see the second graph) to about 100 μA at about 9 ms, the value of V_X decreases to keep V_OUT at the constant value of 3V. The third graph shows that, when I_LOAD changes (see the second graph), there are advantageously no spikes or variations in the value of V_OUT. The value of V_X depends on V_IN and on the load current I_LOAD at the output of the charge pump 102. In the set of graphs illustrated in FIG. 2, the value of V_IN is not specified, but a constant value of V_IN, such as 1.5V, is being applied to the charge pump 102. The regulator 104 is configured so that the value of V_X keeps V_OUT constant.

Referring now to FIG. 3, which illustrates how the regulator 104 advantageously maintains the output voltage of the charge pump 102 at the target V_OUT value in spite of variation in V_IN. The top graph shows that V_X starts at about 1V and rises almost linearly to about 4V and then drops to 3V because V_X tracks V_OUT which starts at about 1V and rises to about 3V. The bottom graph shows that, at about 5 ms after the charge pump 102 starts, V_IN is changed from about 1.5V to about 1.8V. At about 8 ms after the charge pump 102 starts, V_IN is changed from about 1.8V to about 0.9V. The top graph shows than V_X changes in response to the aforesaid changes in V_IN. The middle graph shows that V_OUT reaches its target output voltage of 3V after about 4 ms. The middle graph also shows that when V_IN changes (see the bottom graph), there are advantageously no spikes or variations in the value of V_OUT. When V_IN becomes larger (going from about 1.5V to about 1.8V), a smaller V_X is needed. Therefore, in response to V_IN becoming larger, the amplifier 130 advantageously outputs a smaller V_X. When V_IN becomes smaller (going from about 1.8V to about 0.9V), a larger V_X is needed. Therefore, in response to V_IN becoming smaller, the amplifier 130 advantageously outputs a larger V_X. In the set of graphs illustrated in FIG. 3, the value of I_LOAD is not specified, but a constant load current, such as 200 μA, is being coupled to the output terminal 108 of the charge pump 102.

The charge pump circuit 100 has automatic gain control (AGC) implemented by clock amplitude feedback. The clock amplitude feedback is used to adjust the voltage gain of the charge pump circuit 100 according to its input voltage V_IN and current load I_LOAD, thereby keeping V_OUT constant.

A benefit of the regulator 104 is that it provides a wide range of the amplitude of the clock voltage that regulates V_OUT according to variations in values of I_LOAD and/or V_IN.

A benefit of the regulator 104 is that it provides good regulation of V_OUT with changes in I_LOAD when the V_IN is close to, or above, the threshold voltage V_T.

A benefit of the regulator 104 is that it provides good regulation of V_OUT with changes in V_IN when the V_IN is close to, or above, the threshold voltage V_T.

Although, in one embodiment, the regulator 104 is disposed on an integrated circuit fabricated using CMOS technology, the regulator 104 can also be disposed on an integrated circuit fabricated using other technologies. Although the invention has been described with respect to specific conductivity types or polarity of potentials, skilled artisans appreciated that conductivity types and polarities of potentials may be reversed.

The specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present invention. Any benefits, advantages or solutions to problems described herein with regard to specific embodiments are not intended to be construed as a critical, required or essential feature or element of any or all the claims. Unless stated otherwise, terms such as “first” and “second” are used to arbitrarily distinguish between the elements such terms describe.

Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements. Note that the term “couple” has been used to denote that one or more additional elements may be interposed between two elements that are coupled.

Although the invention is described herein with reference to specific embodiments, various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below.

Claims

1. A regulator for a charge pump, the charge pump having a clock input terminal, an input terminal for receiving an input voltage and an output terminal for outputting an output voltage higher than the input voltage, the regulator comprising:

an amplifier, coupled to the charge pump, for producing a VX signal responsive to the output voltage of the charge pump; and

a clock amplitude modulator coupled to the clock input terminal of the charge pump and to the amplifier, the clock amplitude modulator for producing at least one clock signal having an amplitude controlled by the VX signal, wherein a maximum amplitude of the at least one clock signal is a voltage higher than the input voltage of the charge pump,

wherein a magnitude of the output voltage of the charge pump is controlled, at least in part, by the amplitude of the at least one clock signal.

2. The regulator of claim 1, wherein the clock amplitude modulator is powered by a voltage higher than the input voltage of the charge pump.

3. The regulator of claim 2, wherein the clock amplitude modulator is powered by the output voltage of the charge pump, and wherein the maximum amplitude of the at least one clock signal is the output voltage of the charge pump.

4. The regulator of claim 1, including an auxiliary stage for producing an auxiliary voltage VAUX higher than the input voltage of the charge pump, wherein the clock amplitude modulator is powered by VAUX, and wherein the maximum amplitude of the at least one clock signal is VAUX.

5. The regulator of claim 4, wherein the auxiliary voltage VAUX is higher than the output voltage of the charge pump.

6. The regulator of claim 1, including a feedback loop from the output terminal of the charge pump to the clock input terminal of the charge pump, the feedback loop for setting a new value for the amplitude of the at least one clock signal based on a present value of the output voltage of the charge pump.

7. The regulator of claim 1, wherein the amplifier has an input terminal for receiving a reference voltage VREF and another input terminal for receiving VOUT*, and wherein a value of VX is produced as a result of comparing VREF and VOUT*.

8. The regulator of claim 7, wherein a value of reference voltage VREF is related to one of: a bandgap voltage and VIN.

9. A charge pump circuit, comprising:

a charge pump for producing an output voltage VOUT from an input voltage VIN, wherein VOUT is higher than VIN; and

a regulator, coupled to the charge pump, the regulator including: an amplifier, for producing a VX signal responsive to VOUT, and a clock amplitude modulator, coupled to the amplifier, for producing at least one clock signal having an amplitude controlled by the VX signal, wherein a maximum amplitude of the at least one clock signal is a voltage higher than VIN,

wherein a magnitude of VOUT is controlled, at least in part, by the amplitude of the at least one clock signal.

10. The charge pump circuit of claim 9, wherein the clock amplitude modulator is powered by a voltage higher than VIN.

11. The charge pump circuit of claim 10, wherein the clock amplitude modulator is powered by VOUT, and wherein the maximum amplitude of the at least one clock signal is VOUT.

12. The charge pump circuit of claim 9, including an auxiliary stage for producing an auxiliary voltage VAUX higher than VIN, wherein the clock amplitude modulator is powered by VAUX, and wherein the maximum amplitude of the at least one clock signal is VAUX.

13. The charge pump circuit of claim 9, wherein a magnitude of VOUT is controlled, at least in part, by the amplitude and frequency of the at least one clock signal.

14. The charge pump circuit of claim 9, in which the regulator includes a feedback loop from an output terminal of the charge pump to a clock input terminal of the charge pump, the feedback loop for setting a new value for the amplitude of the at least one clock signal based on a present value of VOUT.

15. The charge pump circuit of claim 14, wherein the amplifier and the clock amplitude modulator form at least part of the feedback loop.

16. The charge pump circuit of claim 15, wherein the feedback loop includes a voltage divider, coupled between the output terminal of the charge pump and the amplifier, that produces a voltage VOUT* from VOUT, wherein VOUT* is less than VOUT.

17. The charge pump circuit of claim 16, wherein the feedback loop of the regulator adjusts the amplitude of the at least one clock signal according to a present value of VIN and a present value of ILOAD of the charge pump to maintain a constant VOUT.

18. The charge pump circuit of claim 16, wherein the feedback loop of the regulator adjusts a voltage gain of the charge pump to maintain a constant VOUT under a varying VIN condition and/or a varying ILOAD condition.

19. A method for regulating an output voltage of a charge pump that has an input voltage and an output voltage higher than the input voltage, comprising:

producing, by a circuit other than the charge pump, an auxiliary voltage VAUX higher than the input voltage of the charge pump;

producing, by a second circuit, a VX signal responsive to the output voltage of the charge pump;

producing, by a third circuit powered by VAUX, at least one clock signal having a frequency and an amplitude, wherein the amplitude of the at least one clock signal is controlled by the VX signal, and wherein a maximum amplitude of the at least one clock signal is a voltage higher than the input voltage of the charge pump; and

controlling a magnitude of the output voltage of the charge pump, at least in part, by changing the amplitude of the at least one clock signal.

20. The method of claim 19, wherein the amplitude and the frequency of the at least one clock signal is controlled by the VX signal, and wherein the magnitude of the output voltage of the charge pump is controlled by changing the frequency of the clock signal concurrently with changing the amplitude of the at least one clock signal.