CN106154053A - A kind of detection chip of the weak capacitive realized based on carrier modulation and phase demodulation - Google Patents

Abstract

The invention discloses the detection chip of a kind of weak capacitive realized based on carrier modulation and phase demodulation, cordic algorithm is utilized to produce the binary numeral that sinusoidal carrier is corresponding, and control to be added on the electrode of differential capacitor C1 and C2 after D/A converter is converted into analog voltage signal, C/V conversion and signal conditioning circuit is utilized to carry out carrier modulation, and after being converted to digital signal by A/D converter, carrying out digital demodulation, demodulation result carries out data output by RS232 serial communication interface.The present invention is based on digital demodulation type high accuracy weak capacitance detection technology, there is not the Charge injection effect of mos pipe switch, it has the advantages that carrier wave degree of stability height, strong interference immunity and precision are high, system utilizes cordic algorithm to realize the generation of carrier signal, the error of digital demodulation is little, has higher stability and precision than traditional simulation detection system.

Description

A kind of detection chip of the weak capacitive realized based on carrier modulation and phase demodulation

Technical field

The present invention relates to a kind of chip, the inspection of a kind of weak capacitive realized based on carrier modulation and phase demodulation Survey chip.

Background technology

For sensor production manufacturing process and cost consideration, be applied to strain sensing the least (the about 1-of capacitance 10pf), and due to adaptability to changes the capacitance variations more small (about 0.01-2pf) produced, it is therefore desirable to extreme accurate detection skill Art ensures accuracy and the sensitivity of data.The main thought of high-accuracy capacitor detection is capacitance variations to be converted into be easy to survey The voltage of amount or current signal, then the change by the signal amplification circuit detection signal of voltage or electric current.Main method has Following 6 kinds: switching capacity method, alternating current bridge method, exchange phase locking technique, lax concussion method, electric charge amplifying method, constant current chaos method.Examine Consider to the complexity of circuit, integration, cost, speed, etc. factors.General employing in sensor chip switchs Electric capacity, lax concussion, that electric charge amplifies these three method is in the majority.

The integrated level of measuring method is low, precision is low for currently used major part.As bridge method utilizes bridge balance former Reason measures electric capacity, and measurement result is affected bigger by brachium pontis capacitive property；Succusion circuit result is simple, exists testing capacitance During below 100pF, in plate, electric capacity often can affect measurement result, and interference resistance is poor.And in the measurement to small capacitance Cheng Zhong, it is easier to by effect of noise, measuring accuracy there is also bigger challenge.Electric charge amplifying method and switching capacity method, Can suppress stray capacitance influences, improve precision, but both of which faces two big technical problems: one, both technology Theoretical foundation be all to be completed once to capacitor charge and discharge process by on-off circuit, thus calculate charge capacity.Due to mos The electric charge of pipe injects (charge-injection) effect, and measurement can be made to produce 10^-2The error of pF rank.The two, both skills Art is all to be converted into capacitance after DC voltage amplifies to measure, and creates the null offset that Amplifier Temperature is sensitive therewith Problem.Often it is used for additionally, due to strain transducer detecting flashy change, frequency response is required higher, to capacitance detecting The real-time of technology is it is also proposed that very high request.

Summary of the invention

It is an object of the invention to provide the detection core of a kind of weak capacitive realized based on carrier modulation and phase demodulation Sheet, with the problem solving to propose in above-mentioned background technology.

For achieving the above object, the present invention provides following technical scheme:

The detection chip of a kind of weak capacitive realized based on carrier modulation and phase demodulation, utilizes cordic algorithm to produce The binary numeral that sinusoidal carrier is corresponding, and control to be added to differential capacitor after D/A converter is converted into analog voltage signal On the electrode of C1 and C2, utilize C/V conversion and signal conditioning circuit to carry out carrier modulation, and be converted to number by A/D converter After word signal, carrying out digital demodulation, demodulation result carries out data output by RS232 serial communication interface.

As the present invention further scheme: use dual carrier modulation type capacitive detection circuit to complete C/V conversion, C/V The change of differential capacitance is converted to the change of carrier (boc) modulated signals amplitude by conversion and signal conditioning circuit, the carrier wave that two-way is anti-phase Signal loading is to the two ends of differential capacitance, and operational amplifier extracts signal from the common port of differential capacitance, and carrier signal is expressed as VcsinW_zT, the expression formula obtaining exporting Uo according to circuit theory is:

$Uo=\frac{C1-C2}{C3}{\mathrm{VcsinW}}_{z}t=2\frac{\mathrm{\Δ}C}{C3}{\mathrm{VcsinW}}_{z}t;$

Carrier (boc) modulated signals is converted into differential signal after processing and amplifying, enters chip number through A/D change-over circuit Word demodulates.

Compared with prior art, the invention has the beneficial effects as follows: the present invention is based on the digital demodulation type faint electricity of high accuracy Holding detection technique, there is not the Charge injection effect of mos pipe switch, it has carrier wave degree of stability height, strong interference immunity and precision High feature, system utilizes cordic algorithm to realize the generation of carrier signal, and the error of digital demodulation is little, than traditional simulation inspection Examining system has higher stability and precision, and uses Digital Logic in a large number so that the method is to manufacturing process and biography Sensor processing technique requires the lowest, is a technology being especially suitable for industrialization.

Accompanying drawing explanation

Fig. 1 is based on carrier modulation and the structural principle block diagram of the detection chip of the weak capacitive of phase demodulation realization；

Fig. 2 is the former of carrier modulation circuit in detection chip based on carrier modulation and the weak capacitive of phase demodulation realization Reason figure；

Fig. 3 is the former of signal conditioning circuit in detection chip based on carrier modulation and the weak capacitive of phase demodulation realization Reason figure.

Detailed description of the invention

Below in conjunction with the accompanying drawing in the embodiment of the present invention, the technical scheme in the embodiment of the present invention is carried out clear, complete Describe, it is clear that described embodiment is only a part of embodiment of the present invention rather than whole embodiments wholely.Based on Embodiment in the present invention, it is every other that those of ordinary skill in the art are obtained under not making creative work premise Embodiment, broadly falls into the scope of protection of the invention.

Refer to Fig. 1～3, in the embodiment of the present invention, a kind of weak capacitive realized based on carrier modulation and phase demodulation Detection chip, utilize cordic algorithm to produce binary numeral corresponding to sinusoidal carrier, and control D/A converter and be converted For being added to after analog voltage signal on the electrode of differential capacitor C1 and C2, C/V conversion and signal conditioning circuit is utilized to carry out carrier wave Modulation, and after being converted to digital signal by A/D converter, carry out digital demodulation, demodulation result is connect by RS232 serial communication Mouth carries out data output；Dual carrier modulation type capacitive detection circuit is used to complete C/V conversion, C/V conversion and signal conditioning circuit The change of differential capacitance is converted to the change of carrier (boc) modulated signals amplitude, and the anti-phase carrier signal of two-way is loaded into differential capacitance Two ends, operational amplifier extracts signal from the common port of differential capacitance, and carrier signal is expressed as VcsinW_zT, former according to circuit Reason obtains exporting the expression formula of UoCarrier (boc) modulated signals is through amplifying It is converted into differential signal after process, enters chip through A/D change-over circuit and carry out digital demodulation.

The operation principle of the present invention is: refer to Fig. 1, and the present invention includes that carrier signal produces, C/V changes and signal condition With the part such as phase demodulation, utilize cordic algorithm to produce the binary numeral that sinusoidal carrier is corresponding, and control D/A converter will It is added to after being converted to analog voltage signal on the electrode of differential capacitor C1 and C2, utilizes C/V conversion and signal conditioning circuit to enter Row carrier modulation, and after being converted to digital signal by A/D converter, carry out digital demodulation, demodulation result passes through RS232 serial Communication interface carries out data output.The change of differential capacitance is converted to the change of carrier (boc) modulated signals amplitude by carrier modulation circuit Change, reduce noise jamming.Carrier modulation circuit is made up of C/V change-over circuit and signal conditioning circuit two parts.Use double load Ripple modulation type capacitive detection circuit completes C/V conversion, and its circuit is as shown in Figure 2.

The anti-phase carrier signal of two-way is loaded into the two ends of differential capacitance, public from differential capacitance of operational amplifier End extracts signal, and carrier signal is expressed as VcsinW_zT, the expression formula obtaining exporting Uo according to circuit theory isFrom above formula, the amplitude of output voltage is proportional to Differential Detection electricity The variable quantity held.For ensureing certainty of measurement, carrier (boc) modulated signals is converted into differential signal after processing and amplifying, changes through A/D Circuit enters chip and carries out digital demodulation.

Signal conditioning circuit is as it is shown on figure 3, U1B and U1C is inverting amplifier, and U1B exports inversion signal, and U1C exports In-phase signal, collectively forms differential signal, by adjusting the amplification of the resistance adjustable amplifier of R11 and R4 so that poor Divided voltage signal matches with the input range of A/D converter.

System uses phase demodulation algorithm to demodulate the amplitude of carrier modulation circuit output signal, thus obtains capacitance variations Amount.Assuming that measured signal is v1=A1cos (ω t+ θ), reference signal is v2=A2cos ω t, then measured signal and reference signal Output signal after being multiplied is: Vo=0.5A1A2cos θ+0.5A1A2cos (2 ω t+ θ).Output signal passes through low pass filter DC component obtained by after filtering off 2 harmonics represents the amplitude of measured signal.System utilizes digital multiplier and numeral Wave filter completes phase demodulation in chip.

It is obvious to a person skilled in the art that the invention is not restricted to the details of above-mentioned one exemplary embodiment, Er Qie In the case of the spirit or essential attributes of the present invention, it is possible to realize the present invention in other specific forms.Therefore, no matter From the point of view of which point, all should regard embodiment as exemplary, and be nonrestrictive, the scope of the present invention is by appended power Profit requires rather than described above limits, it is intended that all by fall in the implication of equivalency and scope of claim Change is included in the present invention.Should not be considered as limiting involved claim by any reference in claim.

Although moreover, it will be appreciated that this specification is been described by according to embodiment, but the most each embodiment only wraps Containing an independent technical scheme, this narrating mode of description is only that for clarity sake those skilled in the art should Description can also be formed those skilled in the art through appropriately combined as an entirety, the technical scheme in each embodiment May be appreciated other embodiments.

Claims (2)

1. the detection chip of the weak capacitive realized based on carrier modulation and phase demodulation, it is characterised in that utilize Cordic algorithm produces binary numeral corresponding to sinusoidal carrier, and controls D/A converter and be converted into analog voltage signal After be added on the electrode of differential capacitor C1 and C2, utilize C/V conversion and signal conditioning circuit to carry out carrier modulation, and pass through A/D After transducer is converted to digital signal, carrying out digital demodulation, it is defeated that demodulation result carries out data by RS232 serial communication interface Go out.

The detection chip of the weak capacitive realized based on carrier modulation and phase demodulation the most according to claim 1, it is special Levying and be, use dual carrier modulation type capacitive detection circuit to complete C/V conversion, C/V conversion and signal conditioning circuit are by differential electrical The change held is converted to the change of carrier (boc) modulated signals amplitude, and the anti-phase carrier signal of two-way is loaded into the two ends of differential capacitance, Operational amplifier extracts signal from the common port of differential capacitance, and carrier signal is expressed as VcsinW_zT, obtains according to circuit theory The expression formula of output Uo is:

$Uo=\frac{C1-C2}{C3}{\mathrm{VcsinW}}_{z}t=2\frac{\mathrm{\Δ}C}{C3}{\mathrm{VcsinW}}_{z}t;$

Carrier (boc) modulated signals is converted into differential signal after processing and amplifying, enters chip through A/D change-over circuit and carries out digital solution Adjust.