Embodiment
Fig. 1 is the structural representation of the example part of MEMS sensor circuit 105 and sensor circuit 110, and wherein, sensor circuit 110 is electrically connected on MEMS sensor circuit 105 with the variation of monitoring MEMS transducer output.MEMS sensor circuit 105 can be capacitive accelerometer, makes monitoring in response to the capacitance variations of the transducer that acts on the acceleration on the transducer in 110 pairs of described capacitive accelerometer of sensor circuit.
Typical MEMS capacitive accelerometer comprises the removable detection mass (proof mass) with capacitive element, and described capacitive element is connected in the reference configuration by mechanical Suspension.As shown in Figure 1, two capacitive elements of MEMS transducer are circuit capacitor, are labeled as C1mem and C2mem.Actual capacitive element can be made of a plurality of pole plates that are electrically connected (such as parallel connection), to produce capacitor C1mem and the represented total capacitance of C2mem among the figure.Described capacitor forms two outputs from MEMS sensor circuit 105 to the bridge the omnibus circuit node 145, and described omnibus circuit node 145 can represent that the circuit of described removable detection mass connects.Pole plate or the pole plate group of each capacitor can be connected in removable detection mass, simultaneously another one pole plate or pole plate group transfixion.
The detection of the charge unbalance by differential capacitance bridge both sides that capacitor C1mem, C1ofs, C2mem and C2ofs are formed comes the induction acceleration signal.Capacitor C1mem and C1ofs form a brachium pontis of differential capacitance bridge, and capacitor C2mem and C2ofs form the second brachium pontis of differential capacitance bridge.Two inputs of described difference bridge are: 1) circuit node 145, and it is to detect mass by the MEMS that drive circuit 140 drives to connect; And 2) with the mode driven circuit node 150 anti-phase with node 145.The output of described difference bridge is circuit node 155 and 160.Like this, node 155 and 160 forms the transducer input of sensor circuit 110.Any difference of capacitor is unbalance in the described capacitance bridge circuit will display at node 155 and 160 places with the form of differential charge, and sensor circuit 110 will be measured this differential charge.
Acceleration on the MEMS accelerometer causes the movement of described detection mass.The displacement of described detection mass changes the spacing between the capacitor plate.Described displacement approximately with two capacitive elements between the difference of the capacitance that causes be directly proportional.With described detection mass and mechanical Suspension as flexible member, this so that acceleration can be determined by displacement according to Hooke's law (Hooke ' s Law).
In general, the right capacitance variations of capacitor is relevant with the linear acceleration of a direction.Perpendicular to right another capacitor of described the first capacitor to the acceleration on the second direction is determined.This can provide the diaxon accelerometer.Three capacitors are to realizing three axles or three-dimensional (3D) accelerometer.
Sensor circuit 110 is responded to the capacitance variations of MEMS transducers, and the capacitive character variation is converted to voltage.Therefore, sensor circuit 110 plays the effect of capacitance-voltage change-over circuit or capacitance-voltage (C2V) transducer.Described capacitance-voltage change-over circuit receives the MEMS sensor output signal from MEMS sensor circuit 105.Described capacitance-voltage change-over circuit comprises difference sigma-delta analog to digital converter (ADC) circuit, described difference sigma-delta analog to digital converter (ADC) circuit is sampled to difference MEMS sensor output signal, and the digital signal of capacitance variations in the expression MEMS sensor circuit 105 is provided.As seen from the figure, the capacitor in the MEMS sensor circuit 105 and biased electrical container C1ofs and C2ofs together use as the sense capacitor of sigma-delta ADC; Effectively the capacitance-voltage induction is merged with the sigma-deltaADC circuit.
In example shown in Figure 1, the sigma-delta adc circuit comprises integrating circuit and comparator circuit 120.Described integrating circuit in the example is the First-order Integral circuit, and comprises operational amplifier (opamp) circuit 125.In some instances, described integrating circuit comprises the more integrating circuit of high-order (such as second order).Described comparator circuit provides digital output signal, and is provided with thereafter low pass filter in order to reduce to the MEMS transducer output generation switching noise of sampling.
Described capacitance-voltage change-over circuit also comprises difference chopper circuit path, and described difference chopper circuit path receives difference MEMS sensor output signal and the polarity of difference chopper circuit path is reversed.The additive method of induction MEMS transducer output comprises described MEMS sensor output signal is carried out correlated-double-sampling.In MEMS accelerometer AFE (analog front end) sensor circuit, chopping method has improved the noise reduction of 1/f noise.Chopping method also adopts than correlated-double-sampling method capacitor still less.The minimizing of capacitors count has reduced thermal noise (KT/C) and has reduced the usable floor area of the upper electric capacity-voltage conversion circuit of integrated circuit (such as application-specific integrated circuit (ASIC) or ASIC).The minimizing of capacitors count can also reduce the stabilization time (settling time) of amplifier (opamp that for example, uses in the integrating circuit).The minimizing of stabilization time can reduce power consumption.Based on noise-reduction method described here, single order sigma-delta adc circuit can provide the dynamic range greater than 100 decibels.
Difference chopper circuit path is realized by chopping switch matrix circuit (115A, 115B, 115C).Fig. 2 shows an example of chopping switch matrix circuit 215.Circuit comes work according to copped wave clock signal C K_A and the CK_B that copped wave clock circuit 230 provides.When described chopping switch matrix circuit provides clock by copped wave clock phase CK_A, then the differential signal of circuit input end is passed.When described chopping switch matrix circuit provides clock by copped wave clock phase CK_B, the then differential signal of circuit input end counter-rotating.When CK_A was effective or " connection ", CK_B was for turn-offing, and vice versa.
In the example of Fig. 1, difference chopper circuit path be included in opamp circuit 125 input counter-rotating difference chopper circuit path polarity the first chopping switch matrix circuit 115A and at the second chopping switch matrix circuit 115B of the output counter-rotating difference chopper circuit path polarity of opamp circuit 125.In some instances, difference chopper circuit path comprises the 3rd chopping switch matrix circuit 115C, the polarity of differential feedback circuit pathways in described the 3rd chopping switch matrix circuit 115C conversion difference sigma-delta adc circuit.Shown in example in, the differential feedback circuit pathways extends to the input of the 3rd chopping switch matrix circuit 115C from the output of the second chopping switch matrix circuit 115B.
Fig. 3 shows another example of the capacitance-voltage change-over circuit with difference chopper circuit path.This example only comprises two chopping switch matrix circuit 315A and 315B in difference chopper circuit path.Difference chopper circuit path also comprises the differential feedback circuit pathways that extends to the input of the first chopping switch matrix circuit 315A from the output of the second chopping switch matrix circuit 315B.
Return Fig. 1, drive circuit 140 can be electrically connected to MEMS sensor circuit 105, the square wave excitation signal is added to the driving input of MEMS transducer.Described driving input can be electrically connected to the circuit node 145 that detects mass in the expression MEMS sensor circuit 105.Sensor circuit 110 can comprise the phase clock circuit (not shown) that produces the first computing clock phase (Ph1) and the second computing clock phase (Ph2).Computing clock phase Ph1 and Ph2 are non-overlapping and have opposite polarity.During Ph1, the first chopping switch matrix circuit 115A is with MEMS sensor circuit 105 and the isolation of difference sigma-delta adc circuit electricity.The second chopping switch matrix circuit 115B and the 3rd chopping switch matrix circuit 115C keep the original value of described sensor output signal.
During Ph2, first, second, and third chopping switch matrix circuit 115A, 115B and 115C reverse the polarity of difference chopper circuit path.The capacitance of MEMS sensor circuit 105 can be sampled about pumping signal.The first computing clock phase and the second computing clock phase Ph1, Ph2 can have frequency and the duty ratio identical with described square wave excitation signal.The second chopping switch matrix circuit and the 3rd chopping switch matrix circuit 115B, 115C can switch together by the copped wave clock.The first chopping switch matrix circuit 115A can switch by the signal that described copped wave clock and Ph2 clock is carried out logical AND (AND).
The sigma-delta adc circuit is subject to the impact of dead band (dead-bands) or dead band (dead-zones).When signal is sampled, described output comprises 1 and 0 repeat pattern, sometimes is called as idle tone (idle tone).For the input signal of little amplitude, the sigma-delta circuit can the repeat pattern continuous wave output.The input signal of described little amplitude can be not sigma-delta ADC by the dead band scope that causes input signal encode.Yet, preferably the signal of little amplitude is encoded, to utilize the whole dynamic range of the difference sigma-delta adc circuit shown in Fig. 1 and Fig. 3.
The capacitance-voltage change-over circuit can comprise to difference chopper circuit path to be provided periodically or the copped wave clock circuit of regular copped wave clock signal.In order to prevent or minimize the dead band in the difference sigma-delta adc circuit, the capacitance-voltage change-over circuit can comprise the copped wave clock circuit that the pseudorandom clock signal is provided to difference chopper circuit path.Described pseudorandom clock signal comprises random transition from high to low, meanwhile guarantees only to have when CK_B turn-offs CK_A to connect, and vice versa.Described pseudorandom clock has reduced to cause the limit cycle (limit cycle) of the integrating circuit of dead band.
Prevent or minimize that the another kind of method of dead band is to add jittering noise in comparator circuit 120 in the difference sigma-delta adc circuit.The capacitance-voltage change-over circuit can comprise pseudo noise circuit for generating 135, and described pseudo noise circuit for generating 135 is electrically connected to described comparator circuit jittering noise is added to the input of comparator circuit.If the output of comparator is carried out evaluation at the end of the second computing clock phase Ph2, then pseudorandom jittering noise signal just can add to during Ph2 in the comparator to remove the dead band idle tone.Jittering noise forces the output of described sigma-delta adc circuit to leave described dead band.
Release as mentioned, the MEMS sensor circuit can be the diaxon accelerometer.In this case, the MEMS sensor circuit can change the first capacitance in response to the linear acceleration on the first direction, and can be in response to the linear acceleration on the second direction direction of described first direction quadrature (for example with) and change the second capacitance.Described sensor circuit can comprise the first capacitance-voltage change-over circuit and the second capacitance-voltage change-over circuit, wherein, described the first capacitance-voltage change-over circuit produces the first digital signal of the variation of described the first electric capacity of expression, and described the second capacitance-voltage change-over circuit produces the second digital signal of the variation of described the second electric capacity of expression.The output of triaxial accelerometer can be responded to by the 3rd capacitance-voltage change-over circuit.
Fig. 4 is the flow chart that falls low noise method 400 in the MEMS accelerometer sensor circuit.At square frame 405, the output of MEMS transducer is sensed, to produce the differential sensor output signal.At square frame 410, the output of MEMS transducer is added to difference chopper circuit path, to reduce the noise in the circuit.In order to realize copped wave, the polarity of described difference chopper circuit path is reversed according to the time interval.In some instances, according to certain time interval the polarity of described circuit pathways is reversed, and in some instances, described polarity is reversed or copped wave according to the pseudorandom time interval.At square frame 415, sample by the MEMS sensor output signal of difference sigma-delta adc circuit after to copped wave, to produce the digital signal of capacitance variations in the described MEMS transducer of expression.
Copped wave is carried out in the output that obtains from the MEMS sensor sample, reduced 1/f noise and thermal noise, so that single order sigma-delta adc circuit has the dynamic range greater than 100dB.In order to utilize described dynamic range fully, can carry out signal copped wave with the appearance of dead band in the output that minimizes the sigma-delta adc circuit according to the pseudorandom time interval, and can apply jittering noise to remove idle tone to difference sigma-delta adc circuit.
Complementary annotations and example
Example 1 can comprise or use the theme that comprises the capacitance-voltage change-over circuit (such as device), and described capacitance-voltage change-over circuit is configured to be electrically connected to the MEMS sensor circuit.Described capacitance-voltage change-over circuit can comprise difference chopper circuit path and difference sigma-delta analog to digital converter (ADC) circuit, wherein, described difference chopper circuit path is configured to receive difference MEMS sensor output signal and the polarity of described difference chopper circuit path is reversed; Described difference sigma-delta analog to digital converter (ADC) circuit is configured to described difference MEMS sensor output signal is sampled and the digital signal of capacitance variations in the described MEMS transducer of expression is provided.
In example 2, the described theme of example 1 comprises alternatively: difference sigma-delta adc circuit and pseudo noise circuit for generating, wherein, difference sigma-delta adc circuit comprises comparator circuit, and the pseudo noise circuit for generating is electrically connected to described comparator circuit and is configured to jittering noise is added to the input of described comparator circuit.
In example 3, the described theme of an example or any example combination comprises the copped wave clock circuit alternatively in the example 1 and 2, and described copped wave clock circuit is configured to provide the pseudorandom clock signal to difference chopper circuit path.
In example 4, the described theme of an example or any example combination comprises alternatively in the example 1 to 3: difference sigma-delta adc circuit, the first chopping switch matrix circuit and the second chopping switch matrix circuit, wherein, described difference sigma-delta adc circuit comprises the opamp circuit, described the first chopping switch matrix circuit is configured at the input of opamp circuit the polarity of described difference chopper circuit path be reversed, and described the second chopping switch matrix circuit is configured at the output of opamp circuit the polarity of described difference chopper circuit path be reversed.
In example 5, the described theme of example 4 comprises the 3rd chopping switch matrix circuit alternatively, and described the 3rd chopping switch matrix circuit is configured to change the polarity of differential feedback circuit pathways in the described difference sigma-delta adc circuit.Described differential feedback circuit pathways extends to the input of described the 3rd chopping switch matrix circuit alternatively from the output of described the second chopping switch matrix circuit.
In example 6, the described theme of example 4 comprises the differential feedback circuit pathways alternatively, and described differential feedback circuit pathways extends to the input of described the first chopping switch matrix circuit from the output of described the second chopping switch matrix circuit.
In example 7, the described theme of an example or any example combination comprises the phase clock circuit alternatively in the example 1 to 6, and described phase clock circuit is configured to produce the first computing clock phase and the second computing clock phase.During described the first computing clock phase, described the first chopping switch matrix circuit is configured to alternatively with described MEMS sensor circuit and the isolation of difference sigma-delta adc circuit electricity; During described the second computing clock phase, described the first chopping switch matrix circuit and the second chopping switch matrix circuit are configured to the polarity of described difference chopper circuit path is reversed alternatively.
In example 8, the described theme of an example or any example combination comprises the drive circuit that is electrically connected on described MEMS transducer alternatively in the example 1 to 7.Described drive circuit is configured to the square wave excitation signal is added to the driving input of described MEMS transducer alternatively, and described the first computing clock phase has frequency and the duty ratio identical with described square wave excitation signal with the second computing clock phase.
In example 9, the described theme of an example or any example combination comprises the MEMS sensor circuit alternatively in the example 1 to 8.Described MEMS sensor circuit is configured to change electric capacity in response to the linear acceleration on the first direction alternatively.
Example 10 can comprise following theme (as device) or alternatively with example 1 to 9 in example or arbitrarily the example combination as described in theme combine to comprise following theme: comprising: the capacitance-voltage change-over circuit that is configured to be electrically connected to the MEMS sensor circuit.Described capacitance-voltage change-over circuit can comprise difference channel path and difference sigma-delta adc circuit, wherein, described difference channel path is configured to receive difference MEMS sensor output signal, and described difference sigma-delta adc circuit is configured to described difference MEMS sensor output signal is sampled and the digital signal of capacitance variations in the described MEMS transducer of expression is provided.Described difference sigma-delta adc circuit can comprise comparator circuit, described capacitance-voltage change-over circuit can comprise the pseudo noise circuit for generating, wherein, described pseudo noise circuit for generating is electrically connected to described comparator circuit and is configured to jittering noise is added to the input of described comparator circuit.
In example 11, the described theme of example 10 comprises the MEMS sensor circuit alternatively.Described MEMS sensor circuit is configured to change electric capacity in response to the linear acceleration on the first direction alternatively.
In example 12, the described theme of example 11 comprises alternatively: switching circuit, drive circuit and phase clock circuit, wherein, described switching circuit is electrically connected to described MEMS transducer, described drive circuit is electrically connected to described MEMS transducer and is configured to the square wave excitation signal is added to the driving input of described MEMS transducer, and described phase clock circuit is electrically connected to described switching circuit and is configured to produce the first computing clock phase and the second computing clock phase.Described the first computing clock phase has frequency and the duty ratio identical with described square wave excitation signal alternatively with the second computing clock phase.During described the first computing clock phase, described switching circuit is configured to alternatively with described MEMS sensor circuit and the isolation of described difference sigma-delta adc circuit electricity, and described MEMS sensor circuit is configured to linear acceleration is sampled.
In example 13, the described theme of an example or any example combination comprises alternatively in the example 11 and 12: MEMS sensor circuit, the first capacitance-voltage change-over circuit and the second capacitance-voltage change-over circuit, wherein, described MEMS sensor circuit is configured to change the first electric capacity in response to the linear acceleration on the first direction, and changes the second electric capacity in response to the linear acceleration on the second direction; , described the first capacitance-voltage change-over circuit produces the first digital signal of the variation of described the first electric capacity of expression; Described the second capacitance-voltage change-over circuit produces the second digital signal of the variation of described the second electric capacity of expression.
Example 14 can comprise that following theme is (such as the machine readable media of method, means or the include instruction of execution action, when described instruction is carried out by machine, can make described machine execution action) or alternatively with example 1 to 13 in the described theme of example or arbitrarily example combination combine to comprise following theme: comprising: the output of MEMS transducer is responded to produce the differential sensor output signal; The output of described MEMS transducer is added to difference chopper circuit path, wherein, the polarity of described difference chopper circuit path is reversed according to the time interval; And the digital signal of the MEMS sensor output signal after the copped wave being sampled to produce capacitance variations in the described MEMS transducer of expression.These themes can comprise the method for the output of MEMS transducer being responded to produce the differential sensor output signal, and the illustrative example of the method can comprise electric charge-voltage conversion circuit.These themes can comprise the method that the output of described MEMS transducer is added to difference chopper circuit path, and the illustrative example of the method can comprise electric charge-voltage conversion circuit.These themes can comprise the method for the MEMS sensor output signal after the copped wave being sampled to produce the digital signal of capacitance variations in the described MEMS transducer of expression, and the illustrative example of the method can comprise difference adc circuit and sigma-delta adc circuit.
In example 15, the described theme of example 14 comprises alternatively: the MEMS sensor output signal after using difference sigma-delta adc circuit to copped wave is sampled, and jittering noise is added to described difference sigma-delta adc circuit.
In example 16, the described theme of an example or any example combination comprises alternatively in the example 14 and 15: provide the random clock signal to difference chopper circuit path.
In example 17, the described theme of an example or any example combination comprises alternatively in the example 14 to 16: the MEMS sensor output signal after using difference sigma-delta adc circuit to copped wave is sampled, input at the opamp of described difference sigma-delta adc circuit circuit reverses to the polarity of described difference chopper circuit path, and at the output of described opamp circuit the polarity of described difference chopper circuit path is reversed.
In example 18, the described theme of example or arbitrarily example combination comprises alternatively in the example 14 to 17: the difference output of described opamp circuit is fed back to the difference input of described opamp circuit, and the polarity of described differential feedback circuit pathways is reversed according to the time interval.
In example 19, the described theme of an example or any example combination comprises alternatively in the example 14 to 18: during the first computing clock phase, with described MEMS sensor circuit and the isolation of described difference sigma-delta adc circuit electricity; And during the second computing clock phase, the polarity of described difference chopper circuit path is reversed.
In example 20, the described theme of an example or any example combination comprises alternatively in the example 14 to 18: the driving input that the square wave excitation signal is added to described MEMS transducer, like this, described the first computing clock phase has frequency and the duty ratio identical with described square wave excitation signal with the second computing clock phase; And during described the first computing clock phase, use described MEMS transducer that described linear acceleration is sampled.
In example 21, the described theme of example or arbitrarily example combination comprises alternatively the capacitance variations in response to the described MEMS transducer of the linear acceleration on the first direction is responded in the example 14 to 20.
In example 22, the described theme of example or arbitrarily example combination comprises alternatively in the example 14 to 21: respond to the first output of described MEMS transducer, so that the capacitance variations in response to the MEMS transducer of the linear acceleration on the first direction is responded to; And the second output of responding to described MEMS transducer, so that the capacitance variations in response to the MEMS transducer of the linear acceleration on the second direction is responded to.
Example 23 can comprise following theme or can combine to comprise following theme with any one or the arbitrary portion of Multi-instance in the example 1 to 22 or the combination of arbitrary portion according to circumstances: can comprise the means of carrying out in the example 1 to 22 any one or a plurality of functions, or the machine readable media of include instruction, when described instruction was carried out by machine, described instruction can make described machine carry out in the example 1 to 22 any one or a plurality of function.
Each nonrestrictive example can independently exist, perhaps can with one or more other examples with the appearance that combines of various arrangement or combining form.
Above-mentioned embodiment comprises the reference to accompanying drawing, and accompanying drawing forms the part of embodiment.Accompanying drawing shows the present invention in illustrational mode can be in order to the specific embodiment of practice.In this, these embodiment are also referred to as " example ".Involved all publications, patent and the patent document of the application be all as reference content of the present invention, although they are respectively in addition references.Use difference if exist between the application and the reference paper, then the use of reference paper should be considered as used in this application replenishing; If there is implacable difference between the two, then the use with the application is as the criterion.
In this application, normally used the same with patent document, term " " or " a certain " expression comprise one or more, are different from other example or the usage of " at least one " or " one or more ".In this application, except as otherwise noted, otherwise use the term "or" refer to without exclusiveness or, " A or B " comprising: " A but be not B ", " B but be not A " and " A and B ".In the appended claims, term " comprises " and " therein " is equal to that each term " comprises " and the popular English of " wherein " and using.And, in following claim, term " comprises " and " comprising " is open, namely, comprise system, device, article or the step of the key element those listed after the term such in claim key elements, still be considered as dropping within the scope of this claim.And in following claim, term " first ", " second " and " the 3rd " etc. are not that its object is had quantitative requirement only with making a check mark.
Above execution mode is intended to explain and is unrestricted.In other embodiments, the example of above execution mode (or one is individual or many aspects) can mutually combine use.For example, those of ordinary skills can use other embodiment by looking back above execution mode.Summary is provided to meet 37C.F.R. § 1.72 (b), thereby so that the reader can determine the type of technological invention fast.Should be understood that, this summary will be not used in scope or the meaning of explaining or limiting claim.And in above embodiment, various features can be combined in together to simplify the present invention.This open feature that should not be construed as failed call is absolutely necessary concerning any claim.On the contrary, creationary theme can with than all features of specific disclosed embodiment still less feature and exist.Thereby following claim is incorporated in the embodiment as the mode of independent embodiment with each claim.Scope of the present invention should be determined with reference to appended claim and with the affiliated suitable gamut of these claims.