CN102624397A - High-linearity fully differential digital micro-accelerometer interface circuit system - Google Patents

Abstract

The invention belongs to the field of MEMS (Micro-Electro-Mechanical Systems) inertia devices, and particularly relates to a capacitance type micro-accelerometer digital output fully differential digital micro-accelerometer interface circuit system. The system comprises a drive signal generating part, a fully differential charge integrator, a fully differential post-amplifier, a fully differential pre-distorter, a relative dual-sampling and sampling retaining circuit, a fully electric integrator, a dynamic comparator, a D/A (Digital/Audio) converter and an electrostatic force feedback device. The system improves the linearity of an accelerometer system, effectively lowers the quantization noise of D/A conversion, restrains zero shift, reduces common mode interference generated by switching charge injection and a substrate noise, improves power supply rejection ration (PSRR), and reduces harmonic distortion.

Description

The digital micro-acceleration gauge interface circuit of a kind of high linearity fully differential system

Technical field

The invention belongs to MEMS inertia device field, be specifically related to the fully differential digital acceleration meter interface circuit system of a kind of capacitance microaccelerator numeral output.

Background technology

Micro-electromechanical system (MEMS) (Micro Electromechanical System) is on the basis of microelectric technique, to grow up, and the device that adopts the MEMS fabrication techniques is widely used in Aero-Space, automobile, biomedicine, environmental monitoring and all spectra that touches of people almost because of having advantages such as miniaturization, intellectuality, integrated, high reliability.Micro-mechanical accelerometer is one of most important MEMS device, and its market sales volume is only second to pressure sensor.Micro-acceleration gauge has that volume is little, low in energy consumption, good stability, reliability is high and be beneficial to advantage such as batch process, extensively applies to auto industry, aerospace field, and in the consumption electronic product.

The application of current a lot of inertial sensors will be used computer, microprocessor and other some digital devices; For can be in the field processing signals; Be necessary analog-to-digital conversion and sensor signal processing circuit are integrated on the same chip; Integrated digital sensor not only provides more function, and has reduced the cost of whole system.Sigma-Delta (∑ Δ) modulation technique is to realize analog-to-digital important way, and along with the development of MEMS technology, ∑ Δ modulation technique is introduced in the micro-mechanical accelerometer design.The sensitive structure of micro-acceleration gauge can be used as a second order es modulator and uses; Yet because the low-down DC current gain of sensitive structure part; Make second order structure be difficult to realize low quantizing noise, high stage structure is to reduce the valid approach of system quantifies noise.

In addition; Because sensitive structure is three terminal device, i.e. two fixed electrodes and as middle the movable electrode of output, so the current single-ended detection mode that generally adopts is handled this output signal; Its advantage be simple in structure, control clock few; Feedback is easy to realize that its shortcoming is that null offset is more serious that the drive signal noise is more serious to the output influence.In fact, also can adopt the fully differential testing circuit that signal is handled of the output of two fixed electrodes, can reduce the common mode disturbances that switch-charge is injected and substrate noise produces like this, improve PSRR, reduce harmonic distortion as sensitive structure.

Yet for fully differential ∑ Δ signal processing structure, a subject matter of existence is: in the differential configuration; Drive signal is applied to float electrode, therefore can only feedback voltage be carried in fixed electrode, during feedback; Float electrode ground connection, one of two fixed polar plate connect feedback voltage V _Fb, another also is connected on 0 current potential, forms the electrostatic force opposite with inertia force, and the suffered static of float electrode is made a concerted effort and feedback voltage is a quadratic relation, has reduced the system linear degree.

Summary of the invention

The object of the present invention is to provide the fully differential digital acceleration meter interface circuit system of a kind of high linearity, high accuracy number output.

The objective of the invention is to realize like this:

The present invention includes drive signal generation portion (101), fully differential charge integrator (102), fully differential post-amplifier (103), fully differential predistorter (104), correlated-double-sampling and sampling hold circuit (105), fully differential electricity integrator (106), 1 dynamic comparer (107), 1 figure place weighted-voltage D/A converter (108) and 1 electrostatic force feedback (109) is characterized in that:

Drive signal generation portion (101) produces two phase high-frequency drive square-wave signals, is carried in two fixed electrodes of sensitive structure respectively;

Fully differential charge integrator (102) changes the small capacitance of sensitive structure and converts differential voltage signal into and export to fully differential post-amplifier (103);

Difference post-amplifier (103) carries out the anti-phase amplification with signal and exports to fully differential predistorter (104);

Fully differential predistorter (104) is exported to correlated-double-sampling after the preposition phase place and is kept (105) with sampling for the HFS of signal provides;

Correlated-double-sampling and sampling hold circuit (105) erasure signal high frequency 1/f noise and amplifier imbalance, compensation amplifier finite bandwidth and finite gain influence send to fully differential electricity integrator (106) behind the demodulation high-frequency signal;

Fully differential electricity integrator (106) provides low-frequency gain to signal, sends to 1 dynamic comparer (107) behind the reduction signal quantization noise;

1 figure place weighted-voltage D/A converter (108) receives the output signal of 1 dynamic comparer (107), judges the feedback voltage of electricity integrator;

1 electrostatic force feedback (109) receives the output signal of 1 dynamic comparer (107), judges the feedback force direction that feeds back to sensitive structure.

Beneficial effect of the present invention is:

The present invention proposes a kind of bilateral electrostatic force feedback mode,, greatly improved the accelerometer system linearity than the current one-sided electrostatic force feedback that generally adopts; Utilize the second-order low-pass filter characteristic of micro mechanical structure self to combine the electricity integrator effectively to reduce analog-to-digital quantizing noise; The signal processing mode of fully differential structure has suppressed null offset, has reduced the common mode disturbances that switch-charge is injected and substrate noise produces, and has improved PSRR, has reduced harmonic distortion.

Description of drawings

Fig. 1 is a high linearity fully differential digital acceleration meter interface circuit system block diagram;

Fig. 2 is one-sided electrostatic force feedback schematic diagram;

Fig. 3 is a bilateral electrostatic force feedback schematic diagram.

Embodiment

Fig. 1 representes the high linearity fully differential digital acceleration meter interface circuit system block diagram of this execution mode.

As shown in Figure 1, this interface circuit system has: drive signal generation portion 101, fully differential charge integrator 102; Fully differential post-amplifier 103, fully differential predistorter 104, correlated-double-sampling and sampling hold circuit 105; 106,1 dynamic comparers of fully differential electricity integrator, 107,1 figure place mould (D/A) transducers 108; 1 electrostatic force feedback 109, clock signal generator 110.

Sensitive structure 100 by micro-acceleration gauge is formed the integrator in the ∑ Delta modulator jointly with fully differential electricity integrator 106; Under clock signal generator control; High low-frequency gain is provided; Obtain high-precision 1 bit digital output, and constitute the fully differential closed loop configuration by 1 figure place mould D/A converter 108 and 1 electrostatic force feedback 109.Fully differential predistorter 104 is considered with compromise between precision and stability by the degree of depth of the sum of series mechanical configuration parameter decision pre-compensating of fully differential charge integrator.1 figure place weighted-voltage D/A converter is positive and negative according to the feedback voltage of the output level of 1 dynamic comparer decision fully differential charge integrator 1.1 electrostatic force feedback is applied to the direction of the electrostatic force of responsive mass according to the output level decision of 1 dynamic comparer.Feedback adopts bilateral electrostatic force feedback mode, improves the system linear degree.

Acquisition in conjunction with Fig. 2 and Fig. 3 illustrative system high linearity.Fig. 2 is the one-sided electrostatic force feedback mode of generally using now that is applicable to fully differential ∑ Δ interface circuit, during feedback, and float electrode ground connection, one of two fixed polar plate connect feedback voltage V _Fb, another also is connected on 0 current potential, forms the electrostatic force F opposite with inertia force _Fb

$F_{\mathrm{fb}}=\frac{1}{2}\frac{C_{S0}}{d_0}{V}_{\mathrm{fb}}^2---\left(1\right)$

Can know that by following formula the suffered static of float electrode is made a concerted effort and feedback voltage is a quadratic relation, has reduced the system linear degree.

The bilateral electrostatic force feedback schematic diagram of Fig. 3 for proposing among the present invention.During feedback, float electrode meets negative supply voltage V _SS, on two-plate, apply feedback voltage V respectively _FbWith-V _Fb, therefore, the suffered static of mass makes a concerted effort to be:

$F_{\mathrm{fb}}=\frac{1}{2}\frac{C_{S0}}{d_0}{(V_{\mathrm{SS}}-V_{\mathrm{fb}})}^2-\frac{1}{2}\frac{C_{S0}}{d_0}{(V_{\mathrm{SS}}+V_{\mathrm{fb}})}^2=-\frac{{2C}_{S0}}{d_0}{V}_{\mathrm{SS}}{V}_{\mathrm{fb}}---\left(2\right)$

This shows that this mode has improved the system linear degree.During feedback, also can float electrode be connected positive voltage V _CCOn, at this moment, exchange as long as will feed back to the voltage of fixed electrode.

The present invention utilizes drive signal generation circuit to produce the two-phase square wave driving signal that do not overlap; This drive signal is applied to the fixed plate electrode up and down of sensitive structure respectively, and the sensitive structure capacitance variations that outer acceleration is caused in conjunction with charge integrator is converted into the output of fully differential voltage signal.Through post-amplifier faint signal is amplified, flow to late-class circuit and handle.Through predistorter system is carried out phase compensation, improve the stability of a system.Utilize correlated-double-sampling and sampling hold circuit to eliminate circuit high frequency 1/f noise and amplifier imbalance, realize simultaneously the high-frequency signal demodulation.Both as final 1 bit digital output, also as the control signal of electricity integrator feedback and 1 electrostatic force feedback, electrostatic force feedback partly taked the bilateral feedback system to improve the system linear degree greatly in the output of comparator.

Claims (1)

1. high linearity fully differential digital acceleration meter interface circuit system comprises that drive signal generation portion (101), fully differential charge integrator (102), fully differential post-amplifier (103), fully differential predistorter (104), correlated-double-sampling and sampling hold circuit (105), fully differential electricity integrator (106), 1 dynamic comparer (107), 1 figure place weighted-voltage D/A converter (108) and 1 electrostatic force feedback (109) is characterized in that:

Drive signal generation portion (101) produces two phase high-frequency drive square-wave signals, is carried in two fixed electrodes of sensitive structure respectively;

Fully differential charge integrator (102) changes the small capacitance of sensitive structure and converts differential voltage signal into and export to fully differential post-amplifier (103);

Difference post-amplifier (103) carries out the anti-phase amplification with signal and exports to fully differential predistorter (104);

Fully differential predistorter (104) is exported to correlated-double-sampling after the preposition phase place and is kept (105) with sampling for the HFS of signal provides;

Correlated-double-sampling and sampling hold circuit (105) erasure signal high frequency 1/f noise and amplifier imbalance, compensation amplifier finite bandwidth and finite gain influence send to fully differential electricity integrator (106) behind the demodulation high-frequency signal;

Fully differential electricity integrator (106) provides low-frequency gain to signal, sends to 1 dynamic comparer (107) behind the reduction signal quantization noise;

1 figure place weighted-voltage D/A converter (108) receives the output signal of 1 dynamic comparer (107), judges the feedback voltage of electricity integrator;

1 electrostatic force feedback (109) receives the output signal of 1 dynamic comparer (107), judges the feedback force direction that feeds back to sensitive structure.

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