CN102790524A - Charge pump device on basis of MEMS (Micro Electro Mechanical System) microphone bias circuit - Google Patents

Abstract

The invention discloses a charge pump device on the basis of a MEMS (Micro Electro Mechanical System) microphone bias circuit. The charge pump device comprises an oscillator, a reference voltage source, a clock amplitude doubling circuit, a Dickson charge pump, a low pass filter and the like. The oscillator is used for providing a two-phase non-overlapping clock with the duty cycle of 50 percent and regulating the amplitude of a two-phase non-overlapping clock signal into two times of the amplitude of a reference voltage. According to the invention, a reference voltage and clock amplitude defining circuit is added and can be used for implementing the stable high voltage output; and due to the adoption of a clock amplitude doubling technology, the number of stages of a diode-capacitance voltage unit is reduced by at least four stages, the area of a core circuit of the charge pump is at least shortened by 21 percent, the power consumption is at least reduced by 40 percent and the conversion efficiency is improved by nearly once.

Description

Charge pump apparatus based on MEMS microphone biasing circuit

Technical field

The present invention relates to the charge pump design of integrated circuit technique, more particularly to microphone bias circuit.

Background technology

Since proposing integrated charge pump circuit structure in the chips earliest from J.F.Dickson in 1976, Dickson charge pump is increasingly becoming DC-DC booster circuit the most commonly used in DRAM, EEPROM and flash memory.Due to the metal-oxide-semiconductor threshold voltage loss in charge pump, Dickson charge pump can not often reach preferable high output voltage at low supply voltages, and circuit overhead is very big, and conversion efficiency is low.For these problems, many solutions are proposed both at home and abroad, and such as static electric charge transfer switch technology, PMOS substitute nmos switch to compensate the technology of bulk effect.In the charge pump design that MEMS microphone provides biasing, it is related to some key factors：

(1) low-power consumption, MEMS microphone is applied in electronic equipment for consumption, the especially handheld devices such as MP3/MP4, PDA, phone, audiphone, and the requirement to power consumption is very high, and conversion efficiency should be improved as far as possible；

(2) voltage gain, handheld device is often powered using battery, therefore during normal use, supply voltage may as little as 1.3-1.5V, the regulated output voltage between 10-12V is obtained as the biasing of microphone, it is necessary to consider to use the problems such as stable reference voltage is as driving and voltage gain；

(3) area, the volume requirement of handheld device is typically relatively stricter, it is desirable to which charge pump chip occupying area is minimized；

(4) output voltage ripple, as the biasing of MEMS microphone, the influence of voice quality can be reduced by reducing charge pump output voltage ripple.

The content of the invention

The technical problems to be solved by the invention：

In order to weaken the influence of threshold voltage as far as possible, improve voltage gain, the present invention is on the basis of traditional Dickson charge pump structure, from the angle for improving charge pump clock signal amplitude, a kind of adaptation Low-voltage Low-power application needs, the improved charge pump configuration of high voltage gain are proposed.

The technical solution adopted in the present invention：

As shown in Figure 1.Compared with traditional Dickson charge pump structure, it adds clock amplitude double circuit, is made up of oscillator, reference voltage source, clock amplitude double circuit, Dickson charge pump and low pass filter etc..Wherein, oscillator provides the two-phase non-overlapp-ing clock that dutycycle is 50%；Clock amplitude double circuit is one of two cores of improved charge pump configuration, and it adjusts 2 times that two-phase non-overlapp-ing clock signal amplitude is reference voltage amplitude；Reference voltage source can provide stable reference voltage to clock amplitude double circuit and Dickson charge pump in the case of mains voltage variations and be used as driving；Dickson charge pump is another core；Low pass filter filter eliminates the high fdrequency component of output voltage.Physical circuit of the present invention, which is realized, to be included by PMOS M0, M1, M4, M5, M6, M8；NMOS tube M2, M3, M7, M9, and electric capacity C1 and C2 composition.The wherein described non-overlapped initial clock ck1 of two-phase with

It is the importation of clock amplitude double circuit, V_refIt is the reference voltage that reference voltage source is provided, the output of clock amplitude double circuit is that amplitude is 2V_refTwo-phase non-overlapp-ing clock ck with

.The concrete operating principle of the invention circuit is as follows：As ck1 ﹦ V_DDWhen, N-type metal-oxide-semiconductor M₂And M₃Turn on, now electric capacity C₁Lower step current potential is zero, and ck ﹦ 0, and then p-type metal-oxide-semiconductor M₀Conducting, reference voltage source passes through p-type metal-oxide-semiconductor M₀Give electric capacity C₁Top crown is charged to V_ref.As ck1 ﹦ 0, p-type metal-oxide-semiconductor M₁And M₄Conducting, electric capacity C₁The current potential of lower step is V_ref, because the voltage at electric capacity two ends will not be mutated, therefore electric capacity C₁Top crown current potential be 2V_ref.Analysis can be seen that more than：Ck1 and ck is anti-phase clock signal, and ck amplitude is 2V_ref.Similarly,WithIt is anti-phase clock signal, and amplitude is also 2V_ref。

Compared with prior art, its remarkable advantage is the present invention：In the case where output voltage meets MEMS microphone offset requirements, compared with traditional Dickson charge pump structure, improved charge pump configuration is based on the double trap CMOS technologies of SMIC 0.35um high pressures, using clock amplitude doubling techniques, the series of diode-capacitance boost unit reduces at least 4 grades, the area of charge pump core circuit at least reduces 21%, and power consumption at least reduces by 40%, and conversion efficiency is improved will by about one time.Under identical series, the output voltage of improved charge pump configuration is apparently higher than traditional Dickson charge pump structure, voltage gain is significantly improved, the need for fully meeting MEMS microphone biasing circuit and consumer electronics product low-power consumption, the application demand of small size.

Brief description of the drawings

Fig. 1 modified Dickson charge pump structures

Fig. 2 Dickson charge pump principles

Fig. 3 clock amplitude double circuits

Embodiment

Reference voltage source

In the application of MEMS microphone, it is allowed to supply voltage as little as 1.3V-1.5V.In the range of this voltage swing, using reference voltage source, the 1.1V reference voltage insensitive to supply voltage can be provided, to ensure that charge pump output voltage is stable, and the accuracy of charge pump output high-pressure is improved in the range of 10-12V.

Oscillator

In the application of MEMS microphone biasing circuit, based on reducing electromagnetic interference and improving the consideration of power-efficient, the clock signal that oscillator output frequencies are 250KHZ is selected.Ring oscillator in oscillator provides the square-wave signal that frequency is 500KHZ, master-slave RS trigger by this square-wave signal be converted into dutycycle be the non-overlapped initial clock signal ck1 of two-phase that 50%, frequency is 250KHZ with

.This will be converted into amplitude to initial clock signal for 2V by clock amplitude double circuit_refClock signal, to drive charge pump.

Dickson charge pump

Dickson charge pump principle is as shown in Fig. 2 it is one of two cores of whole improved charge pump configuration.The 1.1V reference voltage insensitive to supply voltage is provided as driving by reference voltage source, and it is that 250KHZ, amplitude are 2V to provide frequency by clock amplitude double circuit_ref, dutycycle be used as clock for the 50% non-overlapped signal of two-phase.

Clock amplitude double circuit and clock amplitude doubling techniques

Compared with traditional Dickson charge pump structure, most important improve of improved charge pump configuration is to apply clock amplitude doubling techniques, and the initial clock signal amplitude that oscillator is exported is adjusted to 2 times of reference voltage amplitude by clock amplitude double circuit as shown in Figure 3 by it.The non-overlapped initial clock ck1 of two-phase withIt is the importation of clock amplitude double circuit, V_refIt is the reference voltage that reference voltage source is provided, the output of clock amplitude double circuit is that amplitude is 2V_refTwo-phase non-overlapp-ing clock ck with

.The concrete operating principle of circuit is as follows：As ck1 ﹦ V_DDWhen, M₂And M₃Turn on, now C₁Lower step current potential is zero, and ck ﹦ 0, and then M₀Conducting, reference voltage source passes through M₀To C₁Top crown is charged to V_ref.As ck1 ﹦ 0, M₁And M₄Conducting, electric capacity C₁The current potential of lower step is V_ref, because the voltage at electric capacity two ends will not be mutated, therefore C₁Top crown current potential be 2V_ref.Analysis can be seen that more than：Ck1 and ck is anti-phase clock signal, and ck amplitude is 2V_ref.Similarly,

With

It is anti-phase clock signal, and amplitude is also 2V_ref。

The output voltage of the improved charge pump configuration of applied clock amplitude doubling techniques is：

（1）

After applied clock amplitude doubling techniques it can be seen from (1) formula, as long as

, the voltage gain of improved charge pump configuration is greater than traditional Dickson booster circuits.The approximate expression of improved charge pump configuration conversion efficiency is：

（2）

By the approximate expression of the conversion efficiency of traditional Dickson charge pump structure：

（3）

Compare (2) formula to can be found that with (3) formula, in the case of as remaining item, (2) formula Section 2 is more than (3) formula Section 2, therefore the conversion efficiency of improved charge pump configuration is higher than traditional Dickson charge pump structure.

Low pass filter

Low pass filter is used for filtering out the high fdrequency component of charge pump circuit output voltage, reduces output voltage ripple, by output voltage stabilization in the scope required by MEMS microphone normal work.

Claims (2)

1. a kind of charge pump apparatus based on MEMS microphone biasing circuit, it is characterised in that including following part：It is made up of oscillator, reference voltage source, clock amplitude double circuit, Dickson charge pump and low pass filter etc., oscillator provides the two-phase non-overlapp-ing clock that dutycycle is 50%.

2. the charge pump apparatus according to claim 1 based on MEMS microphone biasing circuit, is characterised by：Charge pump apparatus is main by PMOS M0, M1, M4, M5, M6, M8；NMOS tube M2, M3, M7, M9, and electric capacity C1 and C2 composition, the non-overlapped initial clock ck1 of two-phase with

It is the importation of clock amplitude double circuit, V_refIt is the reference voltage that reference voltage source is provided, the output of clock amplitude double circuit is that amplitude is 2V_refTwo-phase non-overlapp-ing clock ck with

。

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