CN102854399A - Detecting circuit of capacitance type MEMS (micro-electromechanical system) sensor - Google Patents

Abstract

The invention relates to a detecting circuit of a capacitance type MEMS (micro-electromechanical system) sensor. The detecting circuit comprises a resonance unit which is formed after a first capacitor to be detected is connected with a second capacitor to be detected; the resonance unit is connected with a differential frequency circuit through a frequency detecting unit; an output end of the frequency detecting unit is respectively connected with a first movable pole plate of the first capacitor to be detected and a second movable pole plate of the second capacitor to be detected; the first capacitor to be detected and the second capacitor to be detected are correspondingly connected with each other to form the resonance unit; resonance frequency can be generated in the resonance unit; the resonance unit can compensate energy damped due to resonance; and the frequency detecting unit drives the differential frequency circuit to output corresponding frequency signals according to the resonance frequency outputted by the resonance unit. An active circuit is used for compensating energy loss of an energy storage device, an electrostatic feedback mechanism is utilized to form a closed-loop system to stably output frequency, anti-interference ability is increased, and the detecting circuit is simple and compact in structure and high in measurement accuracy and anti-interference ability, facilitates monolithic integration, overcomes energy loss and is stable and reliable.

Description

A kind of testing circuit of capacitive MEMS sensor

Technical field

The present invention relates to a kind of testing circuit, especially a kind of testing circuit of capacitive MEMS sensor belongs to the technical field that the capacitive MEMS sensor detects.

Background technology

The capacitive MEMS sensor is widely used in the fields such as industry, civilian, Aero-Space, national defence.Because the cause of capacitive MEMS size sensor, the output signal of this class sensor is very faint, typical capacitive MEMS sensor output signal is the fF magnitude, the little importance that determines weak capacitive detection circuit to be measured like this, its performance has vital role for the MEMS system performance.

For improving MEMS sensor output linearity degree, suppressing common-mode noise, the sensitization capacitance in the capacitive MEMS sensor adopts the form of differential capacitance mostly.Existing tiny differential capacitance detection method mainly contains C-V conversion and direct current charges and discharge electrical method.Wherein, C-V transformation approach application of principle identical charges causes that at different sized capacitors two ends electric potential difference and capacitance size are inversely proportional to, by benchmark voltage and output voltage, calculate the testing capacitance size by the reference capacitance size, the shortcoming of the method is to be difficult to guarantee the transmission of electric charge equivalent, poor anti jamming capability in the charge transfer process.Direct current charges and discharge electrical method, namely simultaneously testing capacitance and reference capacitance discharged and recharged with constant current source, and when the electric capacity both end voltage reaches the Schmidt trigger turnover voltage, circuit upset, the circuit output two-way frequency signal relevant with capacitance size.Although output signal is anti-interference very strong frequency information, but the capacitor charge and discharge process directly related with frequency is very sensitive to voltage, and the transfer process that discharges and recharges is by transistor controls, and state switches moment and can have charge injection and electric charge feedthrough effect, has a strong impact on accuracy of detection.

In addition, the room builds up, " a kind of testing circuit of tiny differential capacitance " (patent No. is ZL200810112292.2) of the people such as Song Xing, Sheng Wei propose a kind of with testing capacitance and fixed inductance consist of frequency selection network and with the method for phaselocked loop tracking circuit composition resonant element Detection capacitance, the composition of its frequency selection network is too idealized, do not consider the characteristics that electronic component loss, energy constantly weaken in the actual conditions, restrict to a certain extent the precision of this method of testing; Adopt open cycle system, disturb to external world sensitivity, be unfavorable for stabilization signal output.

Said method all is not suitable for high precision MEMS capacitance detecting field, and the needs that detect for satisfying high precision need that a kind of measuring accuracy of design is high, antijamming capability strong, overcome energy loss, simple in structurely are beneficial to single chip integrated MEMS capacitance determining method.

Summary of the invention

The objective of the invention is to overcome the deficiencies in the prior art, a kind of testing circuit of capacitive MEMS sensor is provided, its compact conformation, measuring accuracy is high, and antijamming capability is strong, overcomes energy loss, is convenient to monolithic integrated, and is reliable and stable.

According to technical scheme provided by the invention, the testing circuit of described capacitive MEMS sensor, comprise the resonant element that forms for after linking to each other with the first testing capacitance, the second testing capacitance, described resonant element links to each other with differential frequency circuit by frequency detecting unit, but but the output terminal of frequency detecting unit link to each other with the first movable plate electrode of the first testing capacitance, the second movable plate electrode of the second testing capacitance respectively; The first testing capacitance, the second testing capacitance correspondence are connected to form and resonant element, can produce resonance frequency in the resonant element, and can be to the energy compensating of resonance oscillation attenuation; Frequency detecting unit drives frequency signal corresponding to differential frequency circuit output according to the resonance frequency of resonant element output.

Described resonant element comprises frequency selection network and active circuit; The two ends of described the first testing capacitance, the second testing capacitance all are parallel with the frequency-selecting inductance, to form frequency selection network; Described active circuit comprises PMOS pipe and the 2nd PMOS pipe, the drain electrode end of a described PMOS pipe links to each other with the gate terminal of the 2nd PMOS pipe and the first end of the first testing capacitance, the second end of the first testing capacitance links to each other with the drain electrode end of a NMOS pipe, and the gate terminal of a NMOS pipe links to each other with the drain electrode end of the 2nd NMOS pipe; The gate terminal of the 2nd NMOS pipe links to each other with the drain electrode end of a NMOS pipe, the drain electrode end of the 2nd NMOS pipe also links to each other with the second end of the second testing capacitance, the first end of the second testing capacitance links to each other with the drain electrode end of the 2nd PMOS pipe, the gate terminal of the 2nd PMOS pipe links to each other with the drain electrode end of a PMOS pipe, and the source terminal of PMOS pipe and the 2nd PMOS pipe all links to each other with power supply VCC; The source terminal of the source terminal of the one NMOS pipe and the 2nd NMOS pipe links to each other with current mirror; Form the first resonant element output terminal after the gate terminal of the drain electrode end of the one NMOS pipe and the 2nd NMOS pipe and the second end of the first electric capacity link to each other, form the second resonant element output terminal after the gate terminal of the drain electrode end of the 2nd NMOS pipe and a NMOS pipe and the second end of the second electric capacity link to each other.

Described current mirror comprises the 3rd NMOS pipe and the 4th NMOS pipe, the equal ground connection of source terminal of described the 3rd NMOS pipe and the 4th NMOS pipe; The gate terminal of the 4th NMOS pipe links to each other with the gate terminal of the 3rd NMOS pipe and the drain electrode end of the 3rd NMOS pipe; The drain electrode end of the 4th NMOS pipe links to each other with the source terminal of a NMOS pipe and the source terminal of the 2nd NMOS pipe by the arrowband inductance; Link to each other by source electric capacity between the drain electrode end of the source terminal of the 4th NMOS pipe and the 4th NMOS pipe; The drain electrode end of the 3rd NMOS pipe links to each other with bias current Ibias.

Described frequency detecting unit comprises the first Hi-pass filter, the second Hi-pass filter, the first Schmidt trigger and the second Schmidt trigger, the output terminal of resonant element links to each other with the first Hi-pass filter and the second Hi-pass filter respectively, the output terminal of the first Hi-pass filter links to each other with the input end of the first Schmidt trigger, but the output terminal of the first Schmidt trigger links to each other with the first movable plate electrode, and links to each other with differential frequency circuit; The output terminal of the second Hi-pass filter links to each other with the input end of the second Schmidt trigger, but the output terminal of the second Schmidt trigger link to each other with the second movable plate electrode, and link to each other with differential frequency circuit.

Described differential frequency circuit comprises d type flip flop.Described differential frequency circuit adopts d type flip flop, and the output terminal of the first Schmidt trigger links to each other with the D of d type flip flop end, and the output terminal of the second Schmidt trigger links to each other with the CP of d type flip flop end.

Described the first Hi-pass filter and the second Hi-pass filter include filter capacitor and filter resistance.

Advantage of the present invention: adopt active circuit compensation energy storage device energy loss, adopt the static feedback mechanism to consist of closed-loop system and stablize output frequency, antijamming capability strengthens, it is simple in structure that to be easy to monolithic integrated, compact conformation, and measuring accuracy is high, antijamming capability is strong, overcome energy loss, be convenient to monolithic integrated, reliable and stable.

Description of drawings

Fig. 1 is structured flowchart of the present invention.

Fig. 2 is the circuit theory diagrams of resonant element of the present invention.

Fig. 3 is the circuit theory diagrams of Hi-pass filter of the present invention.

Fig. 4 is the schematic diagram that Schmidt trigger sinusoidal signal of the present invention triggers.

Fig. 5 is that the present invention adopts d type flip flop to realize the schematic diagram of differential frequency circuit.

Description of reference numerals: 1-active circuit, 2-the first Hi-pass filter, 3-the first Schmidt trigger, 4-the second Hi-pass filter, 5-the second Schmidt trigger and 6-D trigger.

Embodiment

The invention will be further described below in conjunction with concrete drawings and Examples.

As shown in Figure 1: testing circuit of the present invention comprises the resonant element that forms for after linking to each other with the first testing capacitance C1, the second testing capacitance C2, described resonant element links to each other with differential frequency circuit by frequency detecting unit, but but the output terminal of frequency detecting unit link to each other with the first movable plate electrode M1 of the first testing capacitance C1, the second movable plate electrode M2 of the second testing capacitance C2 respectively; The first testing capacitance C1, the second testing capacitance C2 correspondence are connected to form and resonant element, can produce resonance frequency in the resonant element, and can be to the energy compensating of resonance oscillation attenuation; Frequency detecting unit drives frequency signal corresponding to differential frequency circuit output according to the resonance frequency of resonant element output, the frequency signal of described differential frequency circuit output is corresponding with the first testing capacitance C1 and the second testing capacitance C2, can access after calculating by the frequency signal to described output and the first testing capacitance C1, differential capacitance that the second testing capacitance C2 is corresponding.The embodiment of the invention is merely able to, and the first testing capacitance C1, the second testing capacitance C2 are the capacitive MEMS sensor, but the first testing capacitance C1 has the first movable plate electrode M1, but the second testing capacitance C2 has the second movable plate electrode M2.

As shown in Figure 2: described resonant element comprises frequency selection network and active circuit 1; The two ends of described the first testing capacitance C1, the second testing capacitance C2 all are parallel with frequency-selecting inductance L 0, to form frequency selection network; Described active circuit 1 comprises PMOS pipe PMOS1 and the 2nd PMOS pipe PMOS2, the drain electrode end of described PMOS pipe PMOS1 links to each other with the gate terminal of the 2nd PMOS pipe PMOS2 and the first end of the first testing capacitance C1, the second end of the first testing capacitance C1 links to each other with the drain electrode end of NMOS pipe NMOS1, and the gate terminal of NMOS pipe NMOS1 links to each other with the drain electrode end of the 2nd NMOS pipe NMOS2; The gate terminal of the 2nd NMOS pipe NMOS2 links to each other with the drain electrode end of NMOS pipe NMOS1, the drain electrode end of the 2nd NMOS pipe NMOS2 also links to each other with the second end of the second testing capacitance C2, the first end of the second testing capacitance C2 links to each other with the drain electrode end of the 2nd PMOS pipe PMOS2, the gate terminal of the 2nd PMOS pipe PMOS2 links to each other with the drain electrode end of PMOS pipe PMOS1, and the source terminal of PMOS pipe PMOS1 and the 2nd PMOS pipe PMOS2 all links to each other with power supply VCC; The source terminal of the source terminal of the one NMOS pipe NMOS1 and the 2nd NMOS pipe NMOS2 links to each other with current mirror; The drain electrode end that forms the first resonant element output terminals A 1, the two NMOS pipe NMOS2 after the gate terminal of the drain electrode end of the one NMOS pipe NMOS1 and the 2nd NMOS pipe NMOS2 and the second end of the first capacitor C 1 link to each other rear formation the second resonant element output terminals A 2 that links to each other with the second end of the gate terminal of NMOS pipe NMOS1 and the second capacitor C 2.

Described current mirror comprises the 3rd NMOS pipe NMOS3 and the 4th NMOS pipe NMOS4, the equal ground connection of source terminal of described the 3rd NMOS pipe NMOS3 and the 4th NMOS pipe NMOS4; The gate terminal of the 4th NMOS pipe NMOS4 links to each other with the gate terminal of the 3rd NMOS pipe NMOS3 and the drain electrode end of the 3rd NMOS pipe NMOS3; The drain electrode end of the 4th NMOS pipe (NMOS4) links to each other with the source terminal of NMOS pipe NMOS 1 and the source terminal of the 2nd NMOS pipe NMOS2 by arrowband inductance L tail; Link to each other by source capacitor C tail between the drain electrode end of the source terminal of the 4th NMOS pipe NMOS4 and the 4th NMOS pipe NMOS4; The drain electrode end of the 3rd NMOS pipe NMOS3 links to each other with bias current Ibias.

Described frequency detecting unit comprises the first Hi-pass filter 2, the second Hi-pass filter 4, the first Schmidt trigger 3 and the second Schmidt trigger 5, the output terminal of resonant element links to each other with the first Hi-pass filter 2 and the second Hi-pass filter 4 respectively, the output terminal of the first Hi-pass filter 2 links to each other with the input end of the first Schmidt trigger 3, but the output terminal of the first Schmidt trigger 3 links to each other with the first movable plate electrode M1, and links to each other with differential frequency circuit; The output terminal of the second Hi-pass filter 4 links to each other with the input end of the second Schmidt trigger 5, but the output terminal of the second Schmidt trigger 5 link to each other with the second movable plate electrode M2, and link to each other with differential frequency circuit.The first resonant element output terminals A 1 links to each other with the input end of the first Hi-pass filter 2 among the present invention, and the second resonant element output terminals A 2 links to each other with the input end of the second Hi-pass filter 4.

As shown in Figure 3: in the embodiment of the invention, described the first Hi-pass filter 2 and the second Hi-pass filter 4 include filter capacitor Ch and filter resistance Rh.The end of filter capacitor Ch links to each other with active circuit 1, and the other end is by filter resistance Rh ground connection.The end that filter capacitor Ch links to each other with filter resistance Rh links to each other with Schmidt trigger.

In the embodiment of the invention, differential frequency circuit adopts the output terminal of d type flip flop 6, the first Schmidt triggers 3 to link to each other with the D end of d type flip flop 6, and the output terminal of the second Schmidt trigger 5 links to each other with the CP end of d type flip flop 6.

Principle of work of the present invention is based on cross-couplings LC oscillatory circuit and obtains.The first testing capacitance C 1 and the second testing capacitance C2 are as differential capacitance to be measured, the first testing capacitance C1, the second testing capacitance C2 and frequency-selecting inductance L 0 formation frequency selection network in parallel, because the non-ideal factor of capacitor and inductor element exists in the frequency selection network in oscillatory process, concussion can decay, have access to source circuit 1 for making vibration continue to carry out this frequency selection network, 1 pair of damping capacity of this active circuit compensates, active circuit is selected the complementary CMOS structure, whole resonant element forms a complementary CMOS cross-couplings oscillator structure, as shown in Figure 2.

Known by resonance theory, resonance frequency is

According to resonance theory, the first resonant element output terminals A 1 output signal frequency is

The second resonant element output terminals A 2 output signal frequencies are

With the first resonant element output terminals A 1, the second resonant element output terminals A 2 respectively with the input end B1 of the first Hi-pass filter 2, the input end B2 of the second Hi-pass filter 4 connects, as shown in Figure 3, Hi-pass filter adopts the passive RC Hi-pass filter of simple single order, wave filter is used for high-frequency oscillation signal is carried out filtering filtering low-frequency noise, output terminal W1 from the first Hi-pass filter 2, the pure high-frequency signal of output terminal W2 output of the second Hi-pass filter 4, input end D1 with high-frequency signal and the first Schmidt trigger 3, the input end D2 of the second Schmidt trigger 5 is connected, as shown in Figure 4, when voltage is higher than Schmidt trigger high threshold level Vh, upset occurs and becomes low level Vlow in trigger, when voltage is lower than Schmidt trigger lower threshold level Vl, upset occurs and becomes high level Vhigh in trigger, the output terminal output pulse signal Vw1 suitable with frequency input signal f1 of the first Schmidt trigger 3, the output terminal output pulse signal Vw2 suitable with input signal f2 of the second Schmidt trigger 5.

Wherein resonant element is testing circuit most important components of the present invention, and its physical circuit implementation as shown in Figure 2.Frequency-selecting inductance L 0 and the first testing capacitance C1 that inductance value equates, the second testing capacitance C2 forms frequency selection network, access is by PMOS pipe PMOS1, the 2nd PMOS manages PMOS2, the one NMOS manages NMOS1, the active circuit 1 that the 2nd NMOS pipe NMOS2 forms, the energy of 1 pair of energy-storage travelling wave tube institute of this active circuit loss compensates, the biasing circuit of active circuit 1 is by the 3rd NMOS pipe NMOS3, the current mirror that the 4th NMOS pipe NMOS4 forms consists of, this structure is connected in series arrowband inductance L tail and source capacitor C tail in biasing circuit, arrowband inductance L tail and source capacitor C tail form a narrow band circuit, and make its resonance on the frequency of waveform two frequencys multiplication, be used for suppressing low-frequency noise and two times of audio-frequency noises of waveform that biasing circuit can produce, the topological structure of whole resonant element is a complementary type cross-couplings LC oscillatory circuit.

Draw two branch roads from the Schmidt trigger output terminal, one as the static feedback branch but pulse signal Vc1, Vc2 are fed back to differential capacitance the first movable plate electrode M1, but the second movable plate electrode M2, thus form a closed-loop system, further stablize output frequency, strengthen antijamming capability; Another branch road is connected with Enable Pin E2 with the input end E1 that rising edge enables d type flip flop 6, and namely the output terminal of the first Schmidt trigger 3 links to each other with the D end of d type flip flop 6, and the output terminal of the second Schmidt trigger 5 links to each other with the CP end of d type flip flop 6; D type flip flop 6 is realized the difference of the input pulse signal of frequency f 1, f2, the specific implementation process as shown in Figure 5, if be high level then output terminal Q output high level at rising edge trigger point input terminal voltage, be low level output end output low level such as input terminal voltage, the output end signal frequency is the poor of the new frequency of Enable Pin end and input end frequency.

Henry nH in the embodiment of the invention, electric capacity are the pF magnitude, and the high-frequency signal of output signal frequency MHz magnitude is very fast from the circuit stable output sinusoidal signal speed that powers on.The first testing capacitance C1, the second testing capacitance C2 are as the responsive source of signal variable capacitance, but its rate of change enters the speed of stable state much smaller than resonant element, the first testing capacitance C1, the second C2 to be measured can be considered as fixed capacity when therefore analyzing transient process.

The output signal of resonant element is introduced Hi-pass filter eliminate low-frequency noise, obtain the high-frequency signal that frequency is respectively f1, f2; Filtered signal is input to Schmidt trigger, as shown in Figure 3, when voltage is higher than Schmidt trigger high threshold level Vh, upset occurs and becomes low level Vlow in trigger, when voltage is lower than Schmidt trigger lower threshold level Vl, upset occurs and becomes high level Vhigh in trigger, the pulse signal that trigger output is suitable with frequency input signal.

The pulse signal that will be respectively from the frequency of the first Schmidt trigger 3,5 outputs of the second Schmidt trigger f1, f2 is divided into two-way, but but one tunnel the second movable plate electrode M2 that receives the first movable plate electrode M1, the second testing capacitance C2 of the first testing capacitance C1 forms the static feedback branch, namely form a closed-loop system, further stablize output frequency, strengthen antijamming capability, reach the purpose of stabilization signal frequency; Input end D and the Enable Pin CP of another road access d type flip flop 6, d type flip flop 6 is used for realizing the difference of f1, f2, its output frequency is

$f=f1-\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="HDA00002111232200011.png"\; state="\{\{state\}\}">f</figure-callout>}2=\frac{1}{2\mathrm{\&pi;}\sqrt{l_0{c}_1}}-\frac{1}{2\mathrm{\&pi;}\sqrt{l_0{c}_2}}---\left(1\right)$

In the formula, f1 is that the first testing capacitance C1 and frequency-selecting inductance L 0 form frequency selection network, and through active circuit 1 compensate and frequency detecting unit filtering detect after output signal frequency, f2 is that the second testing capacitance C2 forms frequency selection network with frequency-selecting inductance L 0, and after active circuit 1 compensation and frequency detecting unit filtering detection output signal frequency, L0 is the inductance of frequency selection circuit, usually, C1=C0+ Δ C is arranged, C2=C0-Δ C, C0 is balancing capacitance, and Δ C is differential capacitance to be measured.Abbreviation formula (1)

$f=\frac{1}{2\mathrm{\&pi;}\sqrt{L_0}}*\frac{\sqrt{C_0+\mathrm{\&Delta;C}}-\sqrt{C_0-\mathrm{\&Delta;C}}}{\sqrt{C_0^2-{\left(\mathrm{\&Delta;c}\right)}^2}}---\left(2\right)$

Because differential capacitance Δ C much smaller than C0, ignores the high-order event with formula (2) by Taylor expansion and gets

$f=\frac{\mathrm{\&Delta;<figure-callout\; id="2"\; label="C"\; filenames="HDA00002111232200011.png"\; state="\{\{state\}\}">C</figure-callout>}}{2\mathrm{\&pi;}\sqrt{L_0{C}_0^2}}---\left(3\right)$

Known by formula (3), the frequency of differential frequency circuit output signal is proportional to the size of differential capacitance to be measured, can calculate the differential capacitance size by the differential frequency circuit output frequency signal.

The content that is not described in detail among the present invention belongs to the prior art that input and MEMS field professional and technical personnel know altogether; No longer describe in detail herein.

The present invention adopts active circuit 1 compensation energy storage device energy loss, adopt the static feedback mechanism to consist of closed-loop system and stablize output frequency, antijamming capability strengthens, it is simple in structure that to be easy to monolithic integrated, compact conformation, and measuring accuracy is high, antijamming capability is strong, overcome energy loss, be convenient to monolithic integrated, reliable and stable.

Claims (7)

1. the testing circuit of a capacitive MEMS sensor, it is characterized in that: comprise the resonant element that forms for after linking to each other with the first testing capacitance (C1), the second testing capacitance (C2), described resonant element links to each other with differential frequency circuit by frequency detecting unit, the output terminal of frequency detecting unit respectively with the first testing capacitance (C1) but the first movable plate electrode (M1), the second testing capacitance (C2) but the second movable plate electrode (M2) link to each other; The first testing capacitance (C1), the second testing capacitance (C2) correspondence are connected to form and resonant element, can produce resonance frequency in the resonant element, and can be to the energy compensating of resonance oscillation attenuation; Frequency detecting unit drives frequency signal corresponding to differential frequency circuit output according to the resonance frequency of resonant element output.

2. the testing circuit of capacitive MEMS sensor according to claim 1, it is characterized in that: described resonant element comprises frequency selection network and active circuit (1); The two ends of described the first testing capacitance (C1), the second testing capacitance (C2) all are parallel with frequency-selecting inductance (L0), to form frequency selection network; Described active circuit (1) comprises PMOS pipe (PMOS1) and the 2nd PMOS pipe (PMOS2), the drain electrode end of described PMOS pipe (PMOS1) manages the gate terminal of (PMOS2) with the 2nd PMOS and the first end of the first testing capacitance (C1) links to each other, the second end of the first testing capacitance (C1) links to each other with the drain electrode end that a NMOS manages (NMOS1), and the gate terminal of NMOS pipe (NMOS1) links to each other with the drain electrode end that the 2nd NMOS manages (NMOS2); The gate terminal of the 2nd NMOS pipe (NMOS2) links to each other with the drain electrode end that a NMOS manages (NMOS1), the drain electrode end of the 2nd NMOS pipe (NMOS2) also links to each other with the second end of the second testing capacitance (C2), the first end of the second testing capacitance (C2) links to each other with the drain electrode end that the 2nd PMOS manages (PMOS2), the gate terminal of the 2nd PMOS pipe (PMOS2) links to each other with the drain electrode end that a PMOS manages (PMOS1), and the source terminal of PMOS pipe (PMOS1) and the 2nd PMOS pipe (PMOS2) all links to each other with power supply VCC; The source terminal of the source terminal of the one NMOS pipe (NMOS1) and the 2nd NMOS pipe (NMOS2) links to each other with current mirror; After linking to each other, the second end that the drain electrode end of the one NMOS pipe (NMOS1) and the 2nd NMOS manages the gate terminal of (NMOS2) and the first electric capacity (C1) forms the first resonant element output terminal (A1), the second end that the drain electrode end that the 2nd NMOS manages (NMOS2) and a NMOS manage the gate terminal of (NMOS1) and the second electric capacity (C2) rear formation the second resonant element output terminal (A2) that links to each other.

3. the testing circuit of capacitive MEMS sensor according to claim 2, it is characterized in that: described current mirror comprises the 3rd NMOS pipe (NMOS3) and the 4th NMOS pipe (NMOS4), the equal ground connection of source terminal of described the 3rd NMOS pipe (NMOS3) and the 4th NMOS pipe (NMOS4); The gate terminal of the 4th NMOS pipe (NMOS4) manages the gate terminal of (NMOS3) with the 3rd NMOS and the drain electrode end of the 3rd NMOS pipe (NMOS3) links to each other; The drain electrode end of the 4th NMOS pipe (NMOS4) links to each other with the source terminal of NMOS pipe (NMOS1) and the source terminal of the 2nd NMOS pipe (NMOS2) by arrowband inductance (Ltail); The source terminal of the 4th NMOS pipe (NMOS4) and the 4th NMOS manage between the drain electrode end of (NMOS4) and link to each other by source electric capacity (Ctail); The drain electrode end of the 3rd NMOS pipe (NMOS3) links to each other with bias current Ibias.

4. the testing circuit of capacitive MEMS sensor according to claim 1, it is characterized in that: described frequency detecting unit comprises the first Hi-pass filter (2), the second Hi-pass filter (4), the first Schmidt trigger (3) and the second Schmidt trigger (5), the output terminal of resonant element links to each other with the first Hi-pass filter (2) and the second Hi-pass filter (4) respectively, the output terminal of the first Hi-pass filter (2) links to each other with the input end of the first Schmidt trigger (3), the first Schmidt trigger (3) but output terminal link to each other with the first movable plate electrode (M1), and link to each other with differential frequency circuit; The output terminal of the second Hi-pass filter (4) links to each other with the input end of the second Schmidt trigger (5), the second Schmidt trigger (5) but output terminal link to each other with the second movable plate electrode (M2), and link to each other with differential frequency circuit.

5. the testing circuit of capacitive MEMS sensor according to claim 1, it is characterized in that: described differential frequency circuit comprises d type flip flop (6).

6. the testing circuit of capacitive MEMS sensor according to claim 4, it is characterized in that: described differential frequency circuit adopts d type flip flop (6), the output terminal of the first Schmidt trigger (3) links to each other with the D end of d type flip flop (6), and the output terminal of the second Schmidt trigger (5) links to each other with the CP end of d type flip flop (6).

7. the testing circuit of capacitive MEMS sensor according to claim 4, it is characterized in that: described the first Hi-pass filter (2) and the second Hi-pass filter (4) include filter capacitor (Ch) and filter resistance (Rh).

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