WO2014189245A1

WO2014189245A1 - Variable output voltage charge pump and mems microphone apparatus using same

Info

Publication number: WO2014189245A1
Application number: PCT/KR2014/004471
Authority: WO
Inventors: 소슬이; 이명진; 소명진
Original assignee: 주식회사 룩센테크놀러지; 주시회사 비에스이
Priority date: 2013-05-24
Filing date: 2014-05-19
Publication date: 2014-11-27
Also published as: KR20140138473A

Abstract

The MEMS microphone apparatus of the present invention comprises: a microphone chip in which are formed a MEMS diaphragm and a back plate; and a signal processing chip comprising a variable output voltage charge pump part outputting a variable output voltage for biasing between the MEMS diaphragm and the back plate, a detection part for outputting a detection signal upon detecting electrostatic capacitance variation between the MEMS diaphragm and the back plate according to external sound-wave vibration, and an amplification part for outputting a microphone output signal obtained by amplifying the detection signal. Here, the variable output voltage charge pump part can operate so as to output the variable output voltage by boosting a power supply voltage while being activated in accordance with a predetermined voltage selection signal and reference voltage that accord with the design characteristics of the MEMS diaphragm and the back plate.

Description

Variable output voltage charge pump and MEMS microphone device using same

The present invention relates to a charge pump, and more particularly, to a charge pump for a MEMS (Micro Electrical-Mechanical System) microphone.

Conventionally, the compact microphone has been mainly used an electret condenser microphone (ECM) type. The ECM type microphone measures the amount of change in capacitance when the gap between the polymer thin film (Electret, electret) having the residual permanent charge and the fixed back plate is changed by external sound waves, and outputs the voice signal as a voice signal.

Conventional miniature condenser microphones, including ECM microphones, can detect small and delicate sounds in a wide range of frequencies from high to low, but use polymer diaphragms with poor heat resistance. Technology) cannot be packaged with other semiconductor chips, and must be protected by a special spring-loaded housing because it is sensitive to moisture, shock, and vibration of PCB boards, and requires manual manual audio tuning for each product. It is relatively expensive and difficult to mass produce.

On the other hand, MEMS microphones using MEMS technology have a size that is about one tenth of the size of diaphragm, which is a key part of ECM microphones, which is very advantageous for miniaturization. It can withstand process temperatures (approximately 260 degrees Celsius), enabling packaging based on surface mount technology and mass production only in semiconductor processes with uniform quality and no manual work.

MEMS microphones generally include an active membrane that is moved by vibrations of sound entering from the outside, and a back plate formed therefrom with an air gap therebetween. When the change in pressure and space due to external sound between the two appear as a change in capacitance, the change in capacitance is detected, amplified and output as a voice signal.

Unlike ECM microphones, where semiconductor packaging is difficult, MEMS microphones can package semiconductor chips with diaphragms, thereby providing active biasing to the diaphragms. This results in very stable acoustics over the entire operating temperature range. A charge pump circuit is used to provide this active biasing.

Since conventional charge pumps for MEMS microphones are designed to generate active biasing voltages for specific specifications of MEMS diaphragms, charge pumps that fit different specifications must be individually designed to apply to various specifications of MEMS diaphragms. do.

However, redesigning the charge pump for each MEMS microphone specification can increase development and manufacturing costs and lead to inefficiencies, such as process changes and layout changes.

The problem to be solved by the present invention is to provide a variable output voltage charge pump and a MEMS microphone device using the same.

Variable output voltage charge pump circuit according to an aspect of the present invention,

Activate or deactivate according to the result of comparing the divided voltage obtained by multiplying the variable output voltage of the charge pump by the ratio n / N to the reference voltage according to the voltage selection signal specifying the division ratio n / N (a natural number of 1≤n≤N). A voltage level control unit for generating an oscillator control signal;

An oscillator for outputting a clock signal of a predetermined frequency when the oscillator control signal is activated; And

And a charge pump for boosting a power supply voltage while outputting the variable output voltage while the clock signal is applied from the oscillator.

According to one embodiment, the voltage level control unit

A voltage divider configured to receive the variable output voltage of the charge pump and generate N divided voltages divided at predetermined voltage intervals;

A voltage selector for selecting an nth division voltage corresponding to a division ratio n / N among the N division voltages by the voltage selection signal and outputting a selected nth division voltage; And

Comparing the nth division voltage and the reference voltage to generate the oscillator control signal to activate the operation of the oscillator if the nth division voltage is lower than the reference voltage, and otherwise to deactivate the oscillator. It may include a comparator.

According to one embodiment, the voltage divider is implemented with N series connected resistive elements or diodes,

The voltage selector selects, by the voltage select signal, an nth division voltage corresponding to a division ratio n / N of the voltage divider among the N division voltages respectively output from the nodes of the N series connected resistive elements or diodes. Select and output the selected nth divided voltage.

According to one embodiment, the variable output voltage charge pump circuit,

The apparatus may further include a low pass filter for removing a ripple component of the variable output voltage due to repetitive activation and deactivation of the charge pump.

MEMS microphone device according to another aspect of the present invention,

A MEMS microphone chip having a MEMS diaphragm and a back plate formed thereon; And

A variable output voltage charge pump unit for outputting a variable output voltage for biasing between the MEMS diaphragm and the back plate, and detecting and detecting a change in capacitance between the MEMS diaphragm and the back plate according to external sound wave vibration A MEMS microphone device comprising a signal processing chip including a detector for outputting a signal and an amplifier for outputting a microphone output signal amplified by the detection signal,

The variable output voltage charge pump unit

The variable output voltage may be output by boosting a power supply voltage while being activated according to a voltage selection signal and a reference voltage determined according to design characteristics of the MEMS diaphragm and the back plate.

According to one embodiment, the variable output voltage charge pump unit

According to one embodiment, the voltage level control unit

According to an embodiment, the apparatus may further include a low pass filter for removing a ripple component of the variable output voltage due to repetitive activation and deactivation of the charge pump.

According to still another aspect of the present invention, there is provided a method of driving a variable output voltage charge pump device including a voltage level controller, an oscillator, and a charge pump.

The voltage level control unit compares the divided voltage obtained by multiplying the variable output voltage of the charge pump by the division ratio n / N according to the voltage selection signal specifying the division ratio n / N (a natural number of 1 ≦ n ≦ N) with a reference voltage. Generating an oscillator control signal to be activated or deactivated according to;

Outputting, by the oscillator, a clock signal of a predetermined frequency when the oscillator control signal is activated; And

The charge pump may boost the power supply voltage while the clock signal is applied from the oscillator to output the variable output voltage.

According to one embodiment, the step of generating the oscillator control signal by the voltage level control unit,

The voltage level control unit,

Receiving N variable output voltages of the charge pump and generating N divided voltages at predetermined voltage intervals;

Selecting, by the voltage selection signal, an n-th division voltage corresponding to a division ratio n / N among the N division voltages, and outputting a selected n-th division voltage; And

Comparing the nth division voltage and the reference voltage to generate the oscillator control signal to activate the operation of the oscillator if the nth division voltage is lower than the reference voltage, and otherwise to deactivate the oscillator. It may include a step.

According to an embodiment, the N distribution voltages may be output at nodes of N series connected resistive elements or diodes, respectively.

According to one embodiment, the driving method of the variable output voltage charge pump device,

And low pass filtering the variable output voltage according to repetitive activation and deactivation of the charge pump.

According to the variable output voltage charge pump of the present invention and the MEMS microphone device using the same, even if the application is different, it can be applied to a new application by changing the output voltage setting without redesigning the charge pump, thereby providing versatility and expandability. can do.

1 is a block diagram illustrating a MEMS microphone device according to an embodiment of the present invention.

2 is a block diagram illustrating a variable output voltage charge pump according to an embodiment of the present invention.

3 is a circuit diagram illustrating a voltage divider of a variable output voltage charge pump according to an embodiment of the present invention.

4 is a circuit diagram illustrating a voltage selector of a variable output voltage charge pump according to an exemplary embodiment of the present invention.

5 is a graph illustrating output voltages of a variable output voltage charge pump according to an exemplary embodiment of the present invention.

6 is a flowchart illustrating a method of variably driving an output voltage of a charge pump according to an embodiment of the present invention.

7 is a flowchart specifically illustrating a procedure of generating an oscillator control signal for controlling the level of an output voltage of a charge pump according to an embodiment of the present invention.

With respect to the embodiments of the present invention disclosed in the text, specific structural to functional descriptions are merely illustrated for the purpose of describing embodiments of the present invention, embodiments of the present invention may be implemented in various forms and It should not be construed as limited to the embodiments described in.

Hereinafter, with reference to the accompanying drawings, it will be described in detail a preferred embodiment of the present invention. The same reference numerals are used for the same elements in the drawings, and duplicate descriptions of the same elements are omitted.

Referring to FIG. 1, the MEMS microphone device 1 includes a MEMS microphone chip 10 and a signal processing chip 20.

The MEMS microphone chip 10 and the signal processing chip 20 may each be formed on separate chips in separate processes and then packaged together, or may be formed during the same process on one wafer. For convenience of description, in FIG. 1, the two

chips

10 and 20 are separately formed and then packaged.

The MEMS diaphragm 11 and the backplate 12 are formed on the MEMS microphone chip 10.

The voltage between the diaphragm 11 and the backplate 12 is biased by the variable output voltage Vcpo applied through the bias terminal 13. When the diaphragm 11 vibrates due to external vibration, the capacitance between the diaphragm 11 and the back plate 12 changes, and the diaphragm 11 and the back plate 12 due to the change in the capacitance. The diaphragm voltage Vd between is output from the output terminal 14.

The signal processing chip 20 may largely include a variable output voltage charge pump unit 21, a detector 22, and an amplifier 23. The variable output voltage charge pump unit 21 boosts the power supply voltage Vcc according to the voltage selection signal Vsel and the reference voltage Vref according to the characteristics of the diaphragm 11 and the back plate 12 to change the variable output voltage. Output to (Vcpo)

The detector 22 detects a change in capacitance from the diaphragm voltage Vd and outputs a detection signal Vs. The amplifier 23 amplifies the detection signal Vs to the outside as a microphone output signal Vmic. Output

To describe in more detail the operation and configuration of the variable output voltage charge pump unit 21, FIG. 2 is a block diagram illustrating a variable output voltage charge pump for a MEMS microphone according to an embodiment of the present invention. to be.

Although referring to FIG. 1 together, the variable output voltage charge pump 21 of FIG. 2 may appear to be a circuit that can be used only in a MEMS microphone, but the variable output voltage charge pump of the present invention can be applied only to an application field of a MEMS microphone. The variable output of the present invention in any application, if it is not a limited circuit, and if it is desired to provide a different output DC voltage depending on the purpose or specification when designing a device that normally requires a charge pump. It should be understood that a voltage charge pump can be applied.

In FIG. 2, the variable output voltage charge pump unit 21 may include a voltage level controller 211, an oscillator 212, and a charge pump 213.

The voltage level control unit 211 is a voltage selection signal specifying a division ratio n / N (a natural number of 1≤n≤N) determined according to the specifications of the diaphragm 11 and the backplate 12 in the MEMS microphone chip 10 ( Vsel) controls the operation of the oscillator 212 according to the result of comparing the divided voltage V_n obtained by multiplying the variable output voltage Vcpo of the charge pump 213 by the division ratio n / N with the reference voltage Vref. Generate an oscillator control signal ENb that is activated or deactivated.

The bias voltage values corresponding to the specifications of the diaphragm 11 and the backplate 12 in the MEMS microphone chip 10 are, for example, within a range from the minimum output possible voltage of the charge pump 213 to the maximum output possible voltage. Can be selected.

In addition, in order for the variable output voltage Vcpo value to reach and maintain the desired bias voltage value, the division voltage V_n obtained by multiplying the variable output voltage Vcpo by the division ratio n / N must be equal to the reference voltage Vref. .

Accordingly, the division ratio n / N may be referred to as a ratio obtained by dividing the reference voltage Vref value by a desired bias voltage value, that is, a target variable output voltage Vcpo.

Therefore, the charge pump unit 21 of the present invention has a variable output voltage that is fixed at a high voltage level as the division ratio n / N is lowered within the range from the minimum output possible voltage to the maximum output possible voltage of the charge pump 213. (Vcpo) can be obtained and the variable output voltage (Vcpo) fixed at a low voltage level can be obtained by increasing the distribution ratio n / N.

Meanwhile, in FIG. 2, the oscillator control signal ENb is exemplified as a signal that is activated when the logic is low. However, the oscillator control signal ENb may be generated as a signal that is activated when the logic is high.

In detail, the voltage level controller 211 may include a voltage divider 2111, a voltage selector 2112, and a comparator 2113.

The voltage divider 2111 receives the variable output voltage Vcpo of the charge pump 213 and generates N divided voltages V_1... V_N that are divided at predetermined voltage intervals, preferably at equal voltage intervals.

For example, the voltage divider 2111 may be implemented with N series connected resistive elements or N series connected diodes D_1, D_2, D_3,..., D_n, ... D_N, as shown in FIG. 3. The divided voltages V_1, V_2, V_3,..., Vn,... V_N may be output at the contact node of the device or the two diodes, respectively.

The voltage selector 2112 is the n of the voltage divider 2111 corresponding to the division ratio n / N among the N division voltages V_1,..., V_N respectively output from respective nodes of the N series connected resistive elements or diodes. The second division voltage V_n is selected by the voltage selection signal Vsel, and the selected division voltage V_n is output.

Preferably, the voltage selector 2112 includes an nth node, i.e., an nth resistive element or diode below, corresponding to the division ratio n / N of the voltage divider 2111 among the N division voltages V_1,..., V_N. The nth division voltage V_n output from the node between the n + 1th resistive element or the diode is selected by the voltage selection signal Vsel, and the selected division voltage V_n is output.

At this time, the voltage selector 2112 selects the Nth division voltage V_N when the division ratio n / N is maximum (n = N), and the first division when the division ratio n / N is minimum (n = 1). Note that the voltage V_1 is selected.

For example, as shown in FIG. 4, the voltage selector 2112 has N switches SW_1 to SW_N connected in parallel to one side of the distribution voltage (one of V_1 to V_N) and the other to the comparator 2113, respectively. And the nth division voltage among the N division voltages V_1 to V_N provided from the voltage divider 2111 by selectively energizing only one of the switches SW_1 to SW_N by the voltage selection signal Vsel. (V_n) may be selectively output to the comparator 2113.

The comparator 2113 compares the nth division voltage V_n corresponding to the division ratio n / N and the reference voltage Vref so that the nth division voltage V_n corresponding to the division ratio n / N is greater than the reference voltage Vref. Low generates oscillator control signal ENb to activate the operation of oscillator 212 and otherwise disable the operation of oscillator 212.

Meanwhile, in FIG. 2, the comparator 2113 is illustrated as receiving an n-th division voltage V_n corresponding to the division ratio n / N at the (+) terminal and a reference voltage Vref at the (−) terminal. Oscillator 212 to increase the variable output voltage Vcpo while the nth division voltage V_n corresponding to the division ratio n / N is lower than the reference voltage Vref, that is, while the logic Low is output from the comparator 2113. Since the comparator 2113 exemplarily outputs an oscillator control signal ENb as the signal ENb that is activated when the logic is low.

According to an embodiment, the comparator 2113 may be implemented by receiving an n-th division voltage V_n corresponding to the division ratio n / N at the (-) terminal and a reference voltage Vref at the (+) terminal. . In this case, the variable output voltage Vcpo is increased while the nth division voltage V_n corresponding to the division ratio n / N is higher than the reference voltage Vref, that is, while the logic High is output from the comparator 2113. In order to operate the oscillator 212, the comparator 2113 may output an oscillator control signal as a signal that is activated when the logic is high.

Subsequently, the oscillator 212 may output clock signals CLK and CLKb of a predetermined frequency to the charge pump 213 according to whether the oscillator control signal ENb is activated. When the oscillator control signal ENb is deactivated (that is, when the divided voltage V_n of the division ratio n / N in the comparator 2113 in FIG. 2 becomes higher than the reference voltage Vref), the clock signal of the oscillator 212 ( The generation of CLK, CLKb) itself may be stopped.

The charge pump 213 boosts the power supply voltage Vcc while the clock signal CLK is applied from the oscillator 212 and outputs the variable output voltage Vcpo.

Until the variable output voltage Vcpo of the charge pump 213 reaches the desired voltage level, the output of the clock signal CLK is activated from the oscillator 212 by the oscillator control signal Enb of the voltage level controller 211. The variable output voltage Vcpo continues to rise.

When the variable output voltage Vcpo reaches a predetermined voltage level, the output of the clock signal CLK from the oscillator 212 is inactivated by the oscillator control signal Enb of the voltage level controller 211, so that The operation is also disabled. Accordingly, the variable output voltage Vcpo no longer rises and decreases according to the equivalent time constant inside the MEMS microphone chip 11, but the reduction width of the variable output voltage Vcpo is reduced in the comparator (V) in the voltage level controller 211. If it exceeds the level detected by 2113, the output of the clock signal CLK of the oscillator 212 is activated again, and the variable output voltage Vcpo is raised again. In this manner, the charge pump 213 keeps the size of the variable output voltage Vcpo constant while repeating activation / deactivation.

According to an embodiment, a low pass filter 214 including a capacitor at an output terminal of the charge pump 213 may remove a ripple component of the variable output voltage Vcpo according to activation / deactivation of the charge pump 213. It may be.

5 is a graph illustrating output voltages of a variable output voltage charge pump of a MEMS microphone device according to an embodiment of the present invention.

Referring to Fig. 5, the variable output voltage charge pump of the MEMS microphone device of the present invention is a bias voltage between the diaphragm 11 and the backplate 12, and according to the magnitude of the distribution ratio n / N, if the distribution ratio n / N is large ( As close to 1, one of the output voltages that vary close to the minimum level and close to the maximum level as the split ratio n / N decreases (close to 0) can be output as a bias voltage signal.

Referring to FIG. 6, the driving method of the variable output voltage charge pump device 21 including the voltage level controller 211, the oscillator 212, and the charge pump 213 may be described in step S61. 211 obtained by multiplying the distribution ratio n / N by the variable output voltage Vcpo of the charge pump 213 according to the voltage selection signal Vsel specifying the predetermined division ratio n / N (a natural number of 1 ≦ n ≦ N). Beginning with generating the oscillator control signal ENb which is activated or deactivated to control the operation of the oscillator 212 according to the result of comparing the divided voltage V_n with the reference voltage Vref.

Referring to FIG. 7 to describe step S61 in more detail, in step S611, the voltage level controller 211 receives a variable output voltage Vcpo of the charge pump 213 at a predetermined voltage interval. Preferably, N divided voltages V_1... V_N are divided at equal voltage intervals.

Subsequently, in step S612, the voltage level control unit 211 corresponds to the division ratio n / N among the N division voltages V_1... V_N respectively output from respective nodes of the N series connected resistive elements or diodes. The nth divided voltage V_n is selected by the voltage select signal Vsel, and the selected divided voltage V_n is output.

In step S613, the voltage level controller 211 compares the n-th division voltage V_n corresponding to the division ratio n / N and the reference voltage Vref, so that the n-th division voltage V_n corresponding to the division ratio n / N is obtained. Is lower than the reference voltage Vref to generate an oscillator control signal ENb to activate the operation of the oscillator 212, otherwise to deactivate the operation of the oscillator 212.

6, in step S62, the oscillator 212 outputs clock signals CLK and CLKb of a predetermined frequency to the charge pump 213 according to whether the oscillator control signal ENb is activated.

In step S63, the charge pump 213 boosts the power supply voltage Vcc while the clock signal CLK is applied from the oscillator 212 and outputs the variable output voltage Vcpo.

In this way, the variable output voltage charge pump device may output the variable output voltage Vcpo corresponding to the division ratio n / N by the voltage selection signal Vsel.

Optionally, in step S64, the variable output voltage Vcpo may be low pass filtered to remove the ripple component of the variable output voltage Vcpo according to the activation / deactivation of the charge pump 213.

As described above, although the present invention has been described by way of limited embodiments and drawings, the present invention is not limited to the above-described embodiments, which can be variously modified and modified by those skilled in the art to which the present invention pertains. Modifications are possible. Accordingly, the spirit of the invention should be understood only by the claims set forth below, and all equivalent or equivalent modifications will fall within the scope of the invention.

Claims

Activate or deactivate according to the result of comparing the divided voltage obtained by multiplying the variable output voltage of the charge pump by the ratio n / N to the reference voltage according to the voltage selection signal specifying the division ratio n / N (a natural number of 1≤n≤N). A voltage level control unit for generating an oscillator control signal;

An oscillator for outputting a clock signal of a predetermined frequency when the oscillator control signal is activated; And

And a charge pump that boosts a power supply voltage and outputs the variable output voltage while the clock signal is applied from the oscillator.
The method of claim 1, wherein the voltage level control unit

A voltage divider configured to receive the variable output voltage of the charge pump and generate N divided voltages divided at predetermined voltage intervals;

A voltage selector for selecting an nth division voltage corresponding to a division ratio n / N among the N division voltages by the voltage selection signal and outputting a selected nth division voltage; And

Comparing the nth division voltage and the reference voltage to generate the oscillator control signal to activate the operation of the oscillator if the nth division voltage is lower than the reference voltage, and otherwise to deactivate the oscillator. A variable output voltage charge pump circuit comprising a comparator.
The voltage divider of claim 2, wherein the voltage divider is implemented with N series connected resistive elements or diodes.

The voltage selector selects, by the voltage select signal, an nth division voltage corresponding to a division ratio n / N of the voltage divider among the N division voltages respectively output from the nodes of the N series connected resistive elements or diodes. And select, and output the selected nth divided voltage.
The variable output voltage charge pump circuit of claim 1, further comprising a low pass filter for removing the ripple component of the variable output voltage due to repeated activation and deactivation of the charge pump.
A MEMS microphone chip having a MEMS diaphragm and a back plate formed thereon; And

A variable output voltage charge pump unit for outputting a variable output voltage for biasing between the MEMS diaphragm and the back plate, and detecting and detecting a change in capacitance between the MEMS diaphragm and the back plate according to external sound wave vibration A MEMS microphone device comprising a signal processing chip including a detector for outputting a signal and an amplifier for outputting a microphone output signal amplified by the detection signal,

The variable output voltage charge pump unit

And boosting a power supply voltage to output the variable output voltage while being activated according to a voltage selection signal and a reference voltage determined according to design characteristics of the MEMS diaphragm and the back plate.
The method of claim 5, wherein the variable output voltage charge pump unit

Activate or deactivate according to the result of comparing the divided voltage obtained by multiplying the variable output voltage of the charge pump by the ratio n / N to the reference voltage according to the voltage selection signal specifying the division ratio n / N (a natural number of 1≤n≤N). A voltage level control unit for generating an oscillator control signal;

An oscillator for outputting a clock signal of a predetermined frequency when the oscillator control signal is activated; And

And a charge pump boosting a power supply voltage while the clock signal is applied from the oscillator to output the variable output voltage.
The method of claim 6, wherein the voltage level control unit

A voltage divider configured to receive the variable output voltage of the charge pump and generate N divided voltages divided at predetermined voltage intervals;

A voltage selector for selecting an nth division voltage corresponding to a division ratio n / N among the N division voltages by the voltage selection signal and outputting a selected nth division voltage; And

Comparing the nth division voltage and the reference voltage to generate the oscillator control signal to activate the operation of the oscillator if the nth division voltage is lower than the reference voltage, and otherwise to deactivate the oscillator. MEMS microphone device comprising a comparator.
The method of claim 7, wherein the voltage divider is implemented with N series connected resistive elements or diodes,

The voltage selector selects, by the voltage select signal, an nth division voltage corresponding to a division ratio n / N of the voltage divider among the N division voltages respectively output from the nodes of the N series connected resistive elements or diodes. Select and output the selected nth divided voltage.
7. The MEMS microphone device of claim 6, further comprising a low pass filter for removing ripple components of the variable output voltage due to repeated activation and deactivation of the charge pump.
A driving method of a variable output voltage charge pump device including a voltage level controller, an oscillator and a charge pump,

The voltage level control unit compares the divided voltage obtained by multiplying the variable output voltage of the charge pump by the division ratio n / N according to the voltage selection signal specifying the division ratio n / N (a natural number of 1 ≦ n ≦ N) with a reference voltage. Generating an oscillator control signal to be activated or deactivated according to;

Outputting, by the oscillator, a clock signal of a predetermined frequency when the oscillator control signal is activated; And

And charging the power supply voltage to output the variable output voltage while the charge pump applies the clock signal from the oscillator.
The method of claim 10, wherein the generating of the oscillator control signal by the voltage level controller comprises:

The voltage level control unit,

Receiving N variable output voltages of the charge pump and generating N divided voltages at predetermined voltage intervals;

Selecting, by the voltage selection signal, an n-th division voltage corresponding to a division ratio n / N among the N division voltages, and outputting a selected n-th division voltage; And

Comparing the nth division voltage and the reference voltage to generate the oscillator control signal to activate the operation of the oscillator if the nth division voltage is lower than the reference voltage, and to deactivate the operation of the oscillator otherwise. And a step of driving the variable output voltage charge pump device.
The method of claim 11, wherein the N divided voltages are output at nodes of N series connected resistive elements or diodes, respectively.
11. The method of claim 10, further comprising low pass filtering the variable output voltage according to repetitive activation and deactivation of the charge pump.