CN104406612A - Capacitive sensor interface circuit - Google Patents
Capacitive sensor interface circuit Download PDFInfo
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- CN104406612A CN104406612A CN201410624541.1A CN201410624541A CN104406612A CN 104406612 A CN104406612 A CN 104406612A CN 201410624541 A CN201410624541 A CN 201410624541A CN 104406612 A CN104406612 A CN 104406612A
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Abstract
The invention discloses a capacitive sensor interface circuit, which comprises an MEMS capacitor driving circuit, a DC stabilizing circuit, a first-level buffer amplifier, a differential difference amplifier and a demodulation circuit. Circuit noises are reduced under the same power consumption conditions through a continuous detection circuit by using the capacitive sensor interface circuit provided by the invention.
Description
Technical field
The invention belongs to technical field of electronic devices, relate to a kind of sensor interface circuitry, be specially capacitor type MEMS sensor interface circuit.
Background technology
In more than ten years in the past, the capacitor type micro mechanical sensor of monolithic is employed more and more extensive, such as capacitor type accelerometer and capacitor type gyroscope.The advantage of capacitor type MEMS (micro electro mechanical system) (MEMS) sensor is that sensor itself has lower temperature coefficient, the CMOS manufacturing technology of easy compatibility standard.
Overall output noise weighs an important indicator of sensor, complete capacitance type transducers comprises MEMS part and interface circuitry portions, MEMS and interface circuit all have contribution to output noise, wherein the noise of MEMS causes primarily of the Brownian movement of air molecule, and the noise of circuit comprises the thermonoise of device, flicker noise etc.Reducing overall output noise is the direction that all types of sensor will be studied and strive for, and along with the continuous reduction of the noise of MEMS own, at present, the noise of circuit itself all creates the impact of can not ignore in commercial product and Research Literature.
Switched-capacitor circuit uses maximum circuit structures in capacitance type transducers interface circuit, this kind of circuit structure has good robustness, but the aliasing of noise, all result in this kind of circuit higher than the circuit noise of continuous detecting circuit in higher KT/C circuit thermonoise and on-off circuit.
Summary of the invention
Goal of the invention: for problems of the prior art, the present invention proposes a kind of capacitance type transducers interface circuit, by continuous type testing circuit, at identical consumption conditions decline low circuit noise.
Technical scheme: a kind of capacitance type transducers interface circuit, comprising:
MEMS capacitor drive circuit, described MEMS capacitor drive circuit is connected with MEMS electric capacity, for modulating the ac-excited signal be added on MEMS electric capacity, is convenient to the change of normal Detection capacitance;
DC stabilization circuit, described DC stabilization circuit is connected with MEMS electric capacity and first order buffer amplifier connects, and for the stable DC voltage with interface circuit contact, avoids, because MEMS electric capacity does not have DC channel, causing circuit to enter abnormal duty;
First order buffer amplifier, for optimizing the noise of input stage and providing certain gain;
Differential difference amplifier, described differential difference amplifier is connected with first order buffer amplifier, for dynamically eliminating direct current and exchanging imbalance;
Demodulator circuit, described demodulator circuit is connected with differential difference amplifier, for the high-frequency signal solution of modulation is transferred to low frequency.
Described MEMS capacitor drive circuit is square wave driving circuit; Described square wave driving circuit is made up of switch S 1, S2, S3 and S4, and the chopping frequency of this circuit is tens to hundreds of KHZ.
Described DC stabilization circuit is made up of direct current biasing switch S 5 and S6, and every 16 clock period conductings once, the noise aliasing caused by switch is reduced to 1/16 of switched-capacitor circuit to described direct current biasing switch.
Described first order buffer amplifier provides the enlargement factor being less than 10 times to signal.
Described differential difference amplifier also comprises dc and calibrates path and ac calibration path, and wherein dc calibrates path for eliminating the DC maladjustment of circuit itself, has low-pass characteristic, would not calibrate path like this have an impact to signal and ac; Ac calibrates the imbalance that path brings for calibrating MEMS sensor itself.
Beneficial effect: compared with prior art, tool of the present invention has the following advantages: by continuous type testing circuit, under identical consumption conditions, reduce circuit noise.
Accompanying drawing explanation
Fig. 1 is the structural representation of capacitance type transducers interface circuit of the present invention;
Fig. 2 is the integrated circuit schematic diagram of capacitance type transducers interface circuit of the present invention;
Fig. 3 is the two-stage calculation amplifier structural representation of capacitance type transducers interface circuit of the present invention;
Fig. 4 is the signal sequence schematic diagram of capacitance type transducers interface circuit of the present invention.
Embodiment
Below in conjunction with the drawings and specific embodiments, illustrate the present invention further, these embodiments should be understood only be not used in for illustration of the present invention and limit the scope of the invention, after having read the present invention, those skilled in the art have all fallen within the application's claims limited range to various equivalents of the present invention.
Capacitance type transducers interface circuit as shown in Figure 1, comprise: MEMS capacitor drive circuit, because MEMS electric capacity is not by direct current signal, in order to normally detect the change of electric capacity, often need to add ac-excited signal on MEMS electric capacity, square-wave signal is normally most suitable; DC stabilization circuit, because MEMS electric capacity does not have DC channel, needs special DC bias circuit to come stable DC working point with the DC voltage of interface circuit contact, in order to avoid make circuit enter abnormal duty; First order buffer amplifier, for optimizing the noise of input stage and providing certain gain; Differential difference amplifier, for dynamically eliminating direct current and exchanging imbalance; Demodulator circuit, for being transferred to low frequency by the high-frequency signal solution by square-wave frequency modulation.
Fig. 2 is the integrated circuit schematic diagram of capacitance type transducers interface circuit of the present invention, in figure, Cs1-Cs4 is MEMS electric capacity, switch S 1-S4 constitutes square wave driving circuit, when S1, S3 conducting time, S2, S4 disconnect, time S1, S3 disconnect, and S2, S4 conducting, the square-wave signal that such amplitude is identical, phase place is contrary has just been applied to MEMS two ends, i.e. chopping modulation.Cutting wave frequency is generally selected on the Frequency point of tens to hundreds of KHz, on this frequency band, and the leading impact that Blang's noise plays.
Because MEMS electric capacity can not transmit direct current signal, so the DC voltage of input point needs other biasing circuit to realize, breaker in middle S5, S6 are direct current biasing switch on way, biased witch every 16 clock period conductings once, input point is biased on DC voltage Vb, when biased witch conducting time, modulated square wave temporarily stops.Every 16 clock period conductings benefit is once that the noise aliasing caused by switch is reduced to 1/16 of switched-capacitor circuit.Signal sequence as shown in Figure 4.
Signal amplifies path and adopts two-layer configuration, fundamental purpose is to optimize the parameters such as input capacitance size, noise and bandwidth, first order amplifier has less input capacitance, and second level amplifier can carry out independent optimization according to noise and bandwidth to input stage.First order amplifier provides less gain, signal is provided to the enlargement factor being less than 10 times.The agent structure of second level amplifier is a differential difference amplifier, and amplifier has three cover inputs: signal input, dc calibration input and ac calibration input, and wherein signal input connects the signal output of first order amplifier; Dc calibrates the DC maladjustment that path is used for eliminating circuit itself, and dc feedback network has low-pass characteristic, would not calibrate path like this have an impact to signal and ac; Ac path is used for calibrating the imbalance that brings of MEMS sensor itself.Two-stage calculation amplifier as shown in Figure 3, the input Vin of signal can be expressed as Vsig+Vdc+Vac, and after two-stage amplifier, output signal can be expressed as:
Vout=AinAmianVsig+ AinAmainVdc/(1+Adc)+AinAmainVac-AcalVcal (1)
From formula 1, the enlargement factor of signal is AinAmain, if Adc is enough large, dc offset voltage can be decayed significantly, and Vcal signal is used for eliminating the imbalance that ac signal brings.
Demodulator circuit is made up of switch S 7-S10, and chopping modulation is above demodulated to low frequency to the signal of high frequency by demodulator circuit.Like this, residual dc noise is modulated onto high frequency, finally at output terminal by low-pass filtering by filtering.
Claims (6)
1. a capacitance type transducers interface circuit, is characterized in that, comprising:
MEMS capacitor drive circuit, described MEMS capacitor drive circuit is connected with MEMS electric capacity, for modulating the ac-excited signal be added on MEMS electric capacity;
DC stabilization circuit, described DC stabilization circuit is connected with MEMS electric capacity and first order buffer amplifier connects, for the stable DC voltage with interface circuit contact;
First order buffer amplifier, for optimizing the noise of input stage and providing certain gain;
Differential difference amplifier, described differential difference amplifier is connected with first order buffer amplifier, for dynamically eliminating direct current and exchanging imbalance;
Demodulator circuit, described demodulator circuit is connected with differential difference amplifier, for the high-frequency signal solution of modulation is transferred to low frequency.
2. capacitance type transducers interface circuit as claimed in claim 1, is characterized in that: described MEMS capacitor drive circuit is square wave driving circuit.
3. capacitance type transducers interface circuit as claimed in claim 2, is characterized in that: described square wave driving circuit is made up of S1, S2, S3 and S4, and the chopping frequency of this circuit is tens to hundreds of KHZ.
4. capacitance type transducers interface circuit as claimed in claim 1, it is characterized in that: described DC stabilization circuit is made up of direct current biasing switch S 5 and S6, described direct current biasing switch every 16 clock period conductings once.
5. capacitance type transducers interface circuit as claimed in claim 1, is characterized in that: described first order buffer amplifier provides the enlargement factor being less than 10 times to signal.
6. capacitance type transducers interface circuit as claimed in claim 1, is characterized in that: described differential difference amplifier also comprises dc and calibrates path and ac calibration path, and wherein dc calibrates path for eliminating the DC maladjustment of circuit itself, has low-pass characteristic; Ac calibrates the imbalance that path brings for calibrating MEMS sensor itself.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201410624541.1A CN104406612A (en) | 2014-11-07 | 2014-11-07 | Capacitive sensor interface circuit |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201410624541.1A CN104406612A (en) | 2014-11-07 | 2014-11-07 | Capacitive sensor interface circuit |
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| CN104406612A true CN104406612A (en) | 2015-03-11 |
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| CN201410624541.1A Pending CN104406612A (en) | 2014-11-07 | 2014-11-07 | Capacitive sensor interface circuit |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108768317A (en) * | 2018-08-30 | 2018-11-06 | 孙茂友 | Mems microphone preamplifier |
| CN112526169A (en) * | 2019-09-18 | 2021-03-19 | 中国科学院微电子研究所 | MEMS capacitive accelerometer signal readout circuit |
-
2014
- 2014-11-07 CN CN201410624541.1A patent/CN104406612A/en active Pending
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108768317A (en) * | 2018-08-30 | 2018-11-06 | 孙茂友 | Mems microphone preamplifier |
| CN108768317B (en) * | 2018-08-30 | 2024-02-27 | 孙茂友 | MEMS microphone preamplifier |
| CN112526169A (en) * | 2019-09-18 | 2021-03-19 | 中国科学院微电子研究所 | MEMS capacitive accelerometer signal readout circuit |
| CN112526169B (en) * | 2019-09-18 | 2022-10-28 | 中国科学院微电子研究所 | MEMS capacitive accelerometer signal readout circuit |
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Application publication date: 20150311 |