CN103245840A - Port multiplexing interface circuit for capacitive sensor - Google Patents

Abstract

The invention discloses a port multiplexing interface circuit for a capacitive sensor. A Vds+ and a Vds- respectively correspond to fixed ports of the capacitive sensor and a Vma corresponds to a movable port of the capacitive sensor, i.e. the Vds+ and the Vds- are respectively connected with two input ends of a fully differential operational amplifier A1, the Vds+ and the Vds- are also respectively connected with two negative terminal inputs of a three-end input single-ended output operational amplifier A3, the Vds+ and the Vds- are respectively connected with a node Vs by other capacitors, and a positive terminal output of the A3 is connected with the node Vs by a switch; and the output end of the fully differential operational amplifier A1 is respectively connected with the input ends of a fully differential operational amplifier A2 by capacitors. According to the invention, at the same port, an electrostatic force can be applied and capacitance detection can be carried out; port multiplexing is implemented; due to adoption of a fully differential manner for implementation, the magnitude of the electrostatic force cannot be reduced; and power supply and common-mode noise can be effectively restrained.

Description

A kind of multiplexed port interface circuit for capacitance type sensor

Technical field

The present invention relates to a kind of multiplexed port circuit, particularly a kind of multiplexed port interface circuit for capacitance type sensor.Background technology

Tested mechanical quantity, the sensor that is converted to electric capacitance change as displacement, pressure etc. is called capacitance type sensor, since the end of the seventies, development along with integrated circuit technique, the capacitance type sensor that is packaged together with miniature measurement instrument has appearred, this novel sensor can make the influence of distributed capacitance greatly reduce, and its intrinsic shortcoming is overcome, and has therefore obtained using widely.

Capacitance type sensor has been compared the following advantage with sensors such as resistance-type, inductance types:

(1) high impedance, power are little, and electrostatic attraction is minimum between charged pole plate, so the required input energy is minimum, so suitable to especially solving the low measurement problem of input energy;

(2) temperature stability is good, and the capacitance of sensor is general irrelevant with electrode material, is conducive to the material of selecting temperature coefficient low, again because of own generate heat minimum, very little to stability influence;

(3) simple in structure, adaptability is strong, body to be measured be conductor or semiconductor equalizing can, can in rugged surroundings, work, capacitive sensor structure is simple, be easy to make, can do very small and exquisitely, with the measurement that realizes that some is special; And can be operated in the rugged environments such as high low temperature, intense radiation and high-intensity magnetic field, also can measure the workpiece that has magnetic.

Because these above-mentioned advantages, capacitance type sensor have been widely used in fields such as civilian industry control and military affairs.In the design of capacitance type sensor system, the capacitance type sensor interface circuit has determined the resolution of sensing system to detection limit to a certain extent, but the existing capacitance type sensor that is easy to integrated and extensive employing can only be used for the detection of electric capacity, purposes is single, use other functions then must carry out integrated with other circuit, complex structure uses inconvenient.

Summary of the invention

The objective of the invention is to overcome the deficiencies in the prior art, provide a kind of and can apply electrostatic force and a kind of multiplexed port interface circuit for capacitance type sensor that carries out capacitance detecting simultaneously at same port, this interface circuit can not reduce the size of electrostatic force when realizing capacitance detecting, employing fully differential mode realizes applying electrostatic force and carries out capacitance detecting, can effectively suppress power supply and common-mode noise.

The objective of the invention is to be achieved through the following technical solutions: a kind of multiplexed port interface circuit for capacitance type sensor, V _Ds+, V _Ds-The fixed port of the corresponding capacitance type sensor of difference, V _MaThe movable port of corresponding capacitance type sensor:

V _Ds+Pass through capacitor C _CdsAn input end V with fully differential operational amplifier A 1 _I1+Link to each other, by the another one capacitor C _FbAn output terminal V with fully differential operational amplifier A 1 _O1-Connect V _Ds+Also pass through capacitor C _CdssImport the negative terminal of single-ended output operational amplifier A3 with three ends and import V _Is2-Link to each other V _Ds+By the another one capacitor C _CmWith node V _sLink to each other;

V _Ds-Pass through capacitor C _CdsAnother input end V with fully differential operational amplifier A 1 _I1-Link to each other, by the another one capacitor C _FbAnother output terminal V with fully differential operational amplifier A 1 _O1+Connect V _Ds-Also pass through capacitor C _CdssImport another negative terminal of single-ended output operational amplifier A3 with three ends and import V _Is1-Link to each other V _Ds-By the another one capacitor C _CmWith node V _sLink to each other;

Three ends are imported the anode output of single-ended output operational amplifier A3 by a switch and node V _sLink to each other node V _sThen pass through two switches respectively at two DC voltage V _R+, V _R-Link to each other;

The output terminal V of fully differential operational amplifier A 1 _O1+, V _O1-Respectively by a capacitor C _S1Fully differential operational amplifier A 2 input end V with next stage _I2+, V _I2-Link to each other.

Three ends that described three ends are imported single-ended output operational amplifier A3 are input as two negative terminal inputs and an anode input, are output as an anode output.

The input end V of fully differential operational amplifier A 1 _I1+, V _I1-With output terminal V _O1-, V _O1+Respectively by switch and common mode voltage V _CmLink to each other;

Three ends are imported the direct and common mode voltage V of anode input of single-ended output operational amplifier A3 _CmLink to each other two negative terminal input V _Is1-And V _Is2-Respectively by switch and common mode voltage V _CmLink to each other, the anode output of A3 is also by switch and common mode voltage V _CmLink to each other, this anode output simultaneously also links to each other with ground behind the external electric capacity;

The input end V of fully differential operational amplifier A 2 _I2+, V _I2-With output terminal V _O-, V _O+Respectively by switch and common mode voltage V _CmLink to each other.

The input end V of fully differential operational amplifier A 2 _I2+Pass through capacitor C _F1Output terminal V with fully differential operational amplifier A 2 _O-Link to each other, simultaneously input end V _I2+Also pass through the output terminal V of a switch and fully differential operational amplifier A 2 _O-Link to each other; The input end V of fully differential operational amplifier A 2 _I2-Pass through capacitor C _F1Output terminal V with fully differential operational amplifier A 2 _O+Link to each other, simultaneously input end V _I2-Also pass through the output terminal V of a switch and fully differential operational amplifier A 2 _O+Link to each other.

The movable port V of described capacitance type sensor _MaAlso pass through two switches respectively at two DC voltage V _R+, V _R-Link to each other fixed port V _Ds+And V _Ds-Respectively by switch and the voltage V that produces electrostatic forcing _D+And V _D-Link to each other.

The output terminal V of described fully differential operational amplifier A 1 _O1-With input end V _I1+Polarity opposite, another output terminal V _O1+With input end V _I1-Polarity opposite.

The output terminal V of described fully differential operational amplifier A 2 _O-With input end V _I2+Polarity opposite, another output terminal V _O+With input end V _I2-Polarity opposite.

The anode output that three ends the are imported single-ended output operational amplifier A3 branch road that also links to each other with ground behind the external electric capacity can adopt behind the external capacitor replacement that links to each other with any one DC voltage.

The invention has the beneficial effects as follows: can apply electrostatic force simultaneously and carry out capacitance detecting at same port, realize the multiplexed port function, different with time-multiplexed implementation, circuit of the present invention can not reduce the size of electrostatic force when realizing capacitance detecting, a stable electrostatic force can be provided;

Employing fully differential mode realizes applying electrostatic force and carries out capacitance detecting, can effectively suppress power supply and common-mode noise, improves the accuracy rate of capacitance detecting and the stability of electrostatic force.

Description of drawings

Fig. 1 is circuit connection diagram of the present invention;

Fig. 2 is working timing figure of the present invention.

Embodiment

Further specify technical scheme of the present invention below in conjunction with accompanying drawing, but the content that the present invention protects is not limited to the following stated.

As shown in Figure 1, a kind of multiplexed port interface circuit for capacitance type sensor, V _Ds+, V _Ds-The fixed port of the corresponding capacitance type sensor of difference, V _MaThe movable port of corresponding capacitance type sensor:

V _Ds+Pass through capacitor C _CdsAn input end V with fully differential operational amplifier A 1 _I1+Link to each other, by the another one capacitor C _FbAn output terminal V with fully differential operational amplifier A 1 _O1-Connect V _Ds+Also pass through capacitor C _CdssImport the negative terminal of single-ended output operational amplifier A3 with three ends and import V _Is2-Link to each other V _Ds+By the another one capacitor C _CmWith node V _sLink to each other;

V _Ds-Pass through capacitor C _CdsAnother input end V with fully differential operational amplifier A 1 _I1-Link to each other, by the another one capacitor C _FbAnother output terminal V with fully differential operational amplifier A 1 _O1+Connect V _Ds-Also pass through capacitor C _CdssImport another negative terminal of single-ended output operational amplifier A3 with three ends and import V _Is1-Link to each other V _Ds-By the another one capacitor C _CmWith node V _sLink to each other;

Three ends are imported the anode output of single-ended output operational amplifier A3 by a switch and node V _sLink to each other node V _sThen pass through two switches respectively at two DC voltage V _R+, V _R-Link to each other;

The output terminal V of fully differential operational amplifier A 1 _O1+, V _O1-Respectively by a capacitor C _S1Fully differential operational amplifier A 2 input end V with next stage _I2+, V _I2-Link to each other.

Three ends that described three ends are imported single-ended output operational amplifier A3 are input as two negative terminal inputs and an anode input, are output as an anode output.

The input end V of described fully differential operational amplifier A 1 _I1+, V _I1-With output terminal V _O1-, V _O1+Respectively by switch and common mode voltage V _CmLink to each other;

Three ends are imported the direct and common mode voltage V of anode input of single-ended output operational amplifier A3 _CmLink to each other two negative terminal input V _Is1-And V _Is2-Respectively by switch and common mode voltage V _CmLink to each other, the anode output of A3 is also by switch and common mode voltage V _CmLink to each other, this anode output simultaneously also links to each other with ground behind the external electric capacity;

The input end V of fully differential operational amplifier A 2 _I2+, V _I2-With output terminal V _O-, _VO+Respectively by switch and common mode voltage V _CmLink to each other.

The input end V of fully differential operational amplifier A 2 _I2+Pass through capacitor C _F1Output terminal V with fully differential operational amplifier A 2 _O-Link to each other, simultaneously input end V _I2+Also pass through the output terminal V of a switch and fully differential operational amplifier A 2 _O-Link to each other; The input end V of fully differential operational amplifier A 2 _I2-Pass through capacitor C _F1Output terminal V with fully differential operational amplifier A 2 _O+Link to each other, simultaneously input end V _I2-Also pass through the output terminal V of a switch and fully differential operational amplifier A 2 _O+Link to each other.

The movable port V of described capacitance type sensor _MaAlso pass through two switches respectively at two DC voltage V _R+, V _R-Link to each other fixed port V _Ds+And V _Ds-Respectively by switch and the voltage V that produces electrostatic forcing _D+And V _D-Link to each other.

The output terminal V of described fully differential operational amplifier A 1 _O1-With input end V _I1+Polarity opposite, another output terminal V _O1+With input end V _I1-Polarity opposite.

The output terminal V of described fully differential operational amplifier A 2 _O-With input end V _I2+Polarity opposite, another output terminal V _O+With input end V _I2-Polarity opposite.

The anode output that described three ends the are imported single-ended output operational amplifier A3 branch road that also links to each other with ground behind the external electric capacity can adopt behind the external capacitor replacement that links to each other with any one DC voltage.

As shown in Figure 2, each end-point voltage of the present invention is respectively when each phase place:

1, T ₁Phase place: V _Ds+=V _D+, V _Ds-=V _D-, V _I1+=V _Cm, V _I1-=V _Cm, V _O1+=Vcm, V _O1-=V _Cm, V _I2+=V _Cm, V _I2-=V _Cm, V _Ma=V _R-, V _Is1-=V _Cm, V _Is2-=V _Cm, V _S=V _R+The voltage of bottom crown is V on this time sensor _D+And V _D-, the voltage of middle plate is V _R-, so just reaching the effect that applies electrostatic force, the input and output of all operational amplifiers simultaneously are set to fixed level.

2, T ₂Phase place: the capacitance change of inner sensor is very small during this period of time, like this and V _Ds+And V _Ds-The voltage of the voltage of these two nodes do not have electric current on all branch roads that two nodes link to each other, so can not change i.e.: V _Ds+=V _D+, V _Ds-=V _D-, V _I1+=V _Cm, V _I1-=V _Cm, V _O1+=V _Cm, V _O1-=V _Cm, V _I2+=V _Cm, V _I2-=V _Cm, V _Ma=V _R-, V _Is1-=V _Cm, V _Is2-=V _Cm, V _S=V _R+

3, T ₃Phase place: with T ₂Phase place is similar, according to principle of charge conservation, obtains: V _Ds+=V _D+, V _Ds-=V _D-, V _I1+=V _Cm, V _I1-=V _Cm, V _O1+=V _Cm, V _O1-=V _Cm, V _I2+=V _Cm, V _I2-=V _Cm, V _Ma=V _R-, V _Is1-=V _Cm, V _Is2-=V _Cm, V _S=V _R+

4, T ₄Phase place: the voltage V of sensor middle plate _MaBy V _R-→ V _R+, while V _Is2-, V _Is1-, V _I1+, V _I1-, V _I2+, V _I2-As the input end (for desirable operational amplifier, the input end current path of operational amplifier) of operational amplifier, the voltage of these points can not change, so V _I1+=V _Cm, V _I1-=V _Cm, V _I2+=V _Cm, V _I2-=V _Cm, V _Is1-=V _Cm, V _Is2-=V _Cm, according to top derivation, the input terminal voltage of operational amplifier does not change, so V _Ds+, V _Ds-Can not change, i.e. V yet _Ds+=V _D+, V _Ds-=V _D-These conclusions have been arranged, can calculate following result:

$V_S=\frac{C_S}{C_{\mathrm{cm}}}(V_{R-}-V_{R+})+V_{R+}$

$(V_{O1+}-V_{O1-})=\frac{2\mathrm{\ΔC}}{C_{\mathrm{fb}}}(V_{R+}-V_{R-})$

$(V_{O+}-V_{O-})=\frac{C_{S1}}{C_{F1}}\frac{2\mathrm{\ΔC}}{C_{\mathrm{fb}}}(V_{R+}-V_{R-})$

5, T ₅Phase place: V _Ds+=V _D+, V _Ds-=V _D-, V _I1+=V _Cm, V _I1-=V _Cm, V _O1+=V _Cm, V _O1-=V _Cm, V _I2+=V _Cm, V _I2-=V _Cm, V _Ma=V _R+, V _Is1-=V _Cm, V _Is2-=V _Cm, V _S=V _R-At this moment the voltage of bottom crown is V on the sensor _D+And V _D-, the voltage of middle plate is V _R-, so just reaching the effect that applies electrostatic force, the input and output of all operational amplifiers simultaneously are set to fixed level.

6, T ₆Phase place: the capacitance change of inner sensor is very small during this period of time, like this and V _Ds+And V _Ds-The voltage of the voltage of these two nodes do not have electric current on all branch roads that two nodes link to each other, so can not change i.e.: V _Ds+=V _D+, V _Ds-=V _D-, V _I1+=V _Cm, V _I1-=V _Cm, V _O1+=V _Cm, V _O1-=V _Cm, V _I2+=V _Cm, V _I2-=V _Cm, V _Ma=V _R+, V _Is1-=V _Cm, V _Is2-=V _Cm, V _S=V _R-

7, T ₇Phase place: with T ₆Phase place is similar, according to principle of charge conservation, obtains: V _Ds+=V _D+, V _Ds-=V _D-, V _I1+=V _Cm, V _I1-=V _Cm, V _O1+=V _Cm, V _O1-=V _Cm, V _I2+=V _Cm, V _I2-=V _Cm, V _Ma=V _R+, V _Is1-=V _Cm, V _Is2-=V _Cm, V _S=V _R-, the voltage of all nodes can not change in the moment that this phase place finishes.

8, T ₈Phase place: the voltage V of sensor middle plate _MaBy V _R+→ V _R-, while V _Is2-, V _Is1-, V _I1+, V _I1-, V _I2+, V _I2-As the input end (for desirable operational amplifier, the input end current path of operational amplifier) of operational amplifier, the voltage of these points can not change, so V _I1+=V _Cm, V _I1-=V _Cm, V _I2+=V _Cm, V _I2-=V _Cm, V _Is1-=V _Cm, V _Is2-=V _Cm, according to top derivation, the input terminal voltage of operational amplifier does not change, so V _Ds+, V _Ds-Can not change, i.e. V yet _Ds+=V _D+V _Ds-=V _D-These conclusions have been arranged, can calculate following result:

$V_S=\frac{C_S}{C_{\mathrm{cm}}}(V_{R+}-V_{R-})+V_{R-}$

$(V_{O1+}-V_{O1-})=\frac{2\mathrm{\ΔC}}{C_{\mathrm{fb}}}(V_{R-}-V_{R+})$

$(V_{O+}-V_{O-})=\frac{C_{S1}}{C_{F1}}\frac{2\mathrm{\ΔC}}{C_{\mathrm{fb}}}(V_{R+}-V_{R+})$

From phase place T ₁To T ₈Namely intactly finish the function that once applies electrostatic force and capacitance detecting, by repeating identical phase sequence, can realize applying the function of electrostatic force and capacitance detecting incessantly; According to top description, the voltage of bottom crown remains at V at a complete function in the cycle on the sensor as can be known _D+And V _D-About, so just guaranteed that the electrostatic force that applies can not diminish because of multiplexed port.

Claims (8)

1. a multiplexed port interface circuit that is used for capacitance type sensor is characterized in that: V _Ds+, V _Ds-The fixed port of the corresponding capacitance type sensor of difference, V _MaThe movable port of corresponding capacitance type sensor:

V _Ds+Pass through capacitor C _CdsAn input end V with fully differential operational amplifier A 1 _I1+Link to each other, by the another one capacitor C _FbAn output terminal V with fully differential operational amplifier A 1 _O1-Connect V _Ds+Also pass through capacitor C _CdssImport the negative terminal of single-ended output operational amplifier A3 with three ends and import V _Is2-Link to each other V _Ds+By the another one capacitor C _CmWith node V _sLink to each other;

V _Ds-Pass through capacitor C _CdsAnother input end V with fully differential operational amplifier A 1 _I1-Link to each other, by the another one capacitor C _FbAnother output terminal V with fully differential operational amplifier A 1 _O1+Connect V _Ds-Also pass through capacitor C _CdssImport another negative terminal of single-ended output operational amplifier A3 with three ends and import V _Is1-Link to each other V _Ds-By the another one capacitor C _CmWith node V _sLink to each other;

Three ends are imported the anode output of single-ended output operational amplifier A3 by a switch and node V _sLink to each other node V _sThen pass through two switches respectively at two DC voltage V _R+, V _R-Link to each other;

The output terminal V of fully differential operational amplifier A 1 _O1+, V _O1-Respectively by a capacitor C _S1Fully differential operational amplifier A 2 input end V with next stage _I2+, V _I2-Link to each other.

2. a kind of multiplexed port interface circuit for capacitance type sensor according to claim 1, it is characterized in that: three ends that described three ends are imported single-ended output operational amplifier A3 are input as two negative terminal inputs and an anode input, are output as an anode output.

3. a kind of multiplexed port interface circuit for capacitance type sensor according to claim 1 and 2 is characterized in that: the input end V of described fully differential operational amplifier A 1 _I1+, V _I1-With output terminal V _O1-, V _O1+Respectively by switch and common mode voltage V _CmLink to each other;

Three ends are imported the direct and common mode voltage V of anode input of single-ended output operational amplifier A3 _CmLink to each other two negative terminal input V _Is1-And V _Is2-Respectively by switch and common mode voltage V _CmLink to each other, the anode output of A3 is also by switch and common mode voltage V _CmLink to each other, this anode output simultaneously also links to each other with ground behind the external electric capacity;

The input end V of fully differential operational amplifier A 2 _I2+, V _I2-With output terminal V _O-, V _O+Respectively by switch and common mode voltage V _CmLink to each other.

4. a kind of multiplexed port interface circuit for capacitance type sensor according to claim 1 is characterized in that: the input end V of described fully differential operational amplifier A 2 _I2+Pass through capacitor C _F1Output terminal V with fully differential operational amplifier A 2 _O-Link to each other, simultaneously input end V _I2+Also pass through the output terminal V of a switch and fully differential operational amplifier A 2 _O-Link to each other; The input end V of fully differential operational amplifier A 2 _I2-Pass through capacitor C _F1Output terminal V with fully differential operational amplifier A 2 _O+Link to each other, simultaneously input end V _I2-Also pass through the output terminal V of a switch and fully differential operational amplifier A 2 _O+Link to each other.

5. a kind of multiplexed port interface circuit for capacitance type sensor according to claim 1 is characterized in that: the movable port V of described capacitance type sensor _MaAlso pass through two switches respectively at two DC voltage V _R+, V _R-Link to each other fixed port V _Ds+And V _Ds-Respectively by switch and the voltage V that produces electrostatic forcing _D+And V _D-Link to each other.

6. a kind of multiplexed port interface circuit for capacitance type sensor according to claim 1 is characterized in that: the output terminal V of described fully differential operational amplifier A 1 _O1-With input end V _I1+Polarity opposite, another output terminal V _O1+With input end V _I1-Polarity opposite.

7. a kind of multiplexed port interface circuit for capacitance type sensor according to claim 4 is characterized in that: the output terminal V of described fully differential operational amplifier A 2 _O-With input end V _I2+Polarity opposite, another output terminal V _O+With input end V _I2-Polarity opposite.

8. a kind of multiplexed port interface circuit for capacitance type sensor according to claim 3 is characterized in that: the anode output that described three ends the are imported single-ended output operational amplifier A3 branch road that also links to each other with ground behind the external electric capacity can adopt behind the external capacitor replacement that links to each other with any one DC voltage.

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