Capacitance Detection Circuit Research Articles

A MEMS resonant vacuum gauge for high vacuum measurement

In this paper, a MEMS resonant vacuum gauge (MRVG) based on the squeezed film damping is proposed and its theoretical measurement model is established. The sensitive structure and electrodes of the MRVG were fabricated on SOI wafers and were wafer level packaged including intake hole. An resonance excitation and capacitive detection circuit consists of capacitive voltage converter (C/V) module, PLL and modulation and demodulation module was designed. Experimental tests were carried out in a standard vacuum calibration chamber, and the measurement results verified the theoretical model. The indication accuracy of the MRVG is less than ±20% in the vacuum range of 9×10−5 Pa ∼ 1 Pa. Moreover, the output voltage is still not saturated at the highest vacuum level (9×10−5 Pa), which lays the foundation for subsequent measurement of higher vacuum levels.

Research on high-resolution capacitance detection circuit based on T-type network

Abstract The capacitance detection circuit is a key component of the servo circuit of the quartz flexible accelerometer, which needs to ensure high-precision capacitance detection. The small capacitance change of the quartz flexible accelerometer pendulum will be affected by the noise of each device in the servo loop. To solve this problem, we design a single carrier modulation and demodulation capacitance detection circuit based on a T-type network from the capacitance detection model of a quartz flexible accelerometer. We established a circuit noise model, quantitatively analyzed the noise of the entire capacitance detection circuit from the theoretical level, and obtained the equivalent capacitance noise of the circuit. The rationality and effectiveness of the high-precision capacitance detection circuit are verified by theoretical calculation. We also verify the accuracy of the theoretical calculation through simulation and obtain the signal-to-noise ratio of the circuit. Finally, we prove that the scheme is a high-precision capacitance detection scheme.

Study on driving noise of quartz flexible accelerometer torquer

The distributed capacitance inside the quartz flexible accelerometer (QFA) coupled the high frequency voltage excitation signal in the differential capacitance detection circuit to the torquer coil, and superimposes the torquer driving current to form the driving noise. In this study, the values of the distributed capacitance inside the QFA were simulated. According to the formation mechanism of the QFA driving noise, the equivalent circuit model of the driving noise is established, and the driving noise characteristics of the detection circuit with single excitation and double excitation source are analyzed. The theoretical and experimental results show that the electric field coupled driving noise transmission system is a first-order system with high-pass characteristics. The driving noise of the single excitation detection circuit is larger than that of the dual excitation detection circuit (DEDC), and the DEDC can reduce the driving noise by 39.77% when the QFA shell is grounded. The equivalent acceleration of the electric field coupled driving noise is between tens of μg to hundreds of mg, which is one of the important noise sources that affect the measurement accuracy of the QFA. A measure was proposed to suppress the high-frequency driving noise by adding a low-pass filter after the sampling output of the driving current, which can reduce the driving noise to 1.85 μg and effectively reduce the influence of the driving noise on the measurement accuracy of the QFA.

Weak Capacitance Detection Circuit of Micro-Hemispherical Gyroscope Based on Common-Mode Feedback Fusion Modulation and Demodulation.

As an effective capacitance signal produced by a micro-hemisphere gyro is usually below the pF level, and the capacitance reading process is susceptible to parasitic capacitance and environmental noise, it is highly difficult to acquire an effective capacitance signal. Reducing and suppressing noise in the gyro capacitance detection circuit is a key means to improve the performance of detecting the weak capacitance generated by MEMS gyros. In this paper, we propose a novel capacitance detection circuit, where three different means are utilized to achieve noise reduction. Firstly, the input common-mode feedback is applied to the circuit to solve the input common-mode voltage drift caused by both parasitic capacitance and gain capacitance. Secondly, a low-noise, high-gain amplifier is used to reduce the equivalent input noise. Thirdly, the modulator-demodulator and filter are introduced to the proposed circuit to effectively mitigate the side effects of noise; thus, the accuracy of capacitance detection can be further improved. The experimental results show that with the input voltage of 6 V, the newly designed circuit produces an output dynamic range of 102 dB and the output voltage noise of 5.69 nV/√Hz, achieving a sensitivity of 12.53 V/pF.

Design of readout circuit for high sampling miniaturized MEMS wall shear force sensor

Wall shear stress is one of the important measurement parameters in wind tunnel experiments. In the shock wind tunnel, the duration of the flow field is very short, usually a few milliseconds. To ensure measurement accuracy, the sampling rate should not be less than 1kHz. Due to the limitation of model volume and experimental environment, it is necessary to design a miniaturized readout circuit with high precision and high sampling rate, which is highly integrated with the MEMS wall shear stress sensor. The circuit includes a micro capacitance detection module integrated with the sensor head and a host computer signal processing and display module. Aiming at the complex measurement environment of the shock tunnel, to ensure the measurement accuracy, stability, and anti-interference ability of the weak capacitance detection circuit, a miniaturized ceramic substrate circuit is fabricated by a microstrip circuit process. The test results show that the resolution of the micro capacitance of the circuit can reach 20fF at the detection frequency of 3kHz, which can meet the measurement requirements of Shock tunnel, and realize the real-time measurement and display of wall shear stress signal.

非接触施肥流量实时监测系统的设计与试验

Precision fertilization is one of the important links in the precision agricultural operation system. In recent years, the demand for precision fertilization in facility greenhouse has become more and more urgent. As such, this paper designs an accurate and practical fertilization on-line monitoring system. The system adopts capacitance conversion chip PCAP01 and SCM STM32F103C8T6 to build a capacitance detection circuit. The effective acquisition of differential capacitance sensor microcapacitor signal output under this system is realized. The response relationship between the mass flow and the sensor capacitance output was studied, and a linear fitting model of fertilization was established. According to the prediction, the model determination coefficient was 0.9997. The experiment shows that the system has good adaptability to ambient temperature. The average measurement error is 1.13%, which meets the technical requirements of flow measurement. The capacitive fertilization online measurement system provides an effective way for the on-line acquisition of fertilization flow. It is of great significance for the implementation of high-precision variable fertilization.

Low-cost capacitive sensor for detecting palm-wood moisture content in real-time

sIn this study, we analyze a non-invasive and low-cost wood moisture meter by means of a capacitive detection circuit. The process of the design and development of an oil-palm-wood moisture meter is described. As part of the study, two electrode structures, i.e., parallel-plate and coplanar electrodes, are tested. The capacitive detection circuit includes a square-wave-generator circuit, low-pass filter circuit, and signal-conditioning circuit. The frequencies of the square-wave excitation signal are in the range of 200 kHz and are analyzed via a microcontroller to interpret the percentage of oil-palm-wood moisture content. The applicability of the capacitive moisture measurement is investigated under various moisture conditions of the oil palm wood i.e., 5%–20%. The experimental results show that the measurement accuracy of the detection circuit is high, with an acceptable measurement error.

Design of a peanut moisture detector based on STM32and MATLAB

The measurement accuracy and repetition rate of the existing peanut moisture detector are poor. To solve this problem, this paper designs a capacitive peanut moisture detector based on the capacitance method. Firstly, the structure of coaxial cylindrical capacitive moisture sensor is optimized. STM32 chip microcomputer is used in the main control chip, and the change in capacitance is transformed to change in frequency by capacitance detection circuit. The temperature and quality of peanut kernel are measured by DS18B20 temperature sensor and weighing sensor respectively. The influence of particle size, moisture content, temperature and volume density on the output differential frequency of capacitance sensor are studied by using the differential frequency method. In the range of moisture content of 4.3%-19.1% and temperature of 10°C-40°C, a mathematical model for the relationship among moisture content, temperature, and differential frequency is established. The prediction test of peanut kernel’s moisture content shows that the measurement error of moisture content is within ±0.5%, indicating that the instrument has high measurement accuracy and repeatability when it is used to detect the moisture content of peanut kernels, and has a wide application prospect.

High-Sensitivity Encoder-Like Micro Area-Changed Capacitive Transducer for a Nano-g Micro Accelerometer.

Encoder-like micro area-changed capacitive transducers are advantageous in terms of their better linearity and larger dynamic range compared to gap-changed capacitive transducers. Such transducers have been widely applied in rectilinear and rotational position sensors, lab-on-a-chip applications and bio-sensors. However, a complete model accounting for both the parasitic capacitance and fringe effect in area-changed capacitive transducers has not yet been developed. This paper presents a complete model for this type of transducer applied to a high-resolution micro accelerometer that was verified by both simulations and experiments. A novel optimization method involving the insertion of photosensitive polyimide was used to reduce the parasitic capacitance, and the capacitor spacing was decreased to overcome the fringe effect. The sensitivity of the optimized transducer was approximately 46 pF/mm, which was nearly 40 times higher than that of our previous transducer. The displacement detection resolution was measured as 50 pm/√Hz at 0.1 Hz using a precise capacitance detection circuit. Then, the transducer was applied to a sandwich in-plane micro accelerometer, and the measured level of the accelerometer was approximately 30 ng/√Hz at 1Hz. The earthquake that occurred in Taiwan was also detected during a continuous gravity measurement.

Design and test of a capacitance detection circuit based on a transimpedance amplifier**Project supported by the National Natural Science Foundation of China (No. 61127008) and the Subsidized Program of the National High Technology Research and Development Program of China (No. 2011AA040404).

This paper presents a transimpedance amplifier (TIA) capacitance detection circuit aimed at detecting micro-capacitance, which is caused by ultrasonic stimulation applied to the capacitive micro-machined ultrasonic transducer (CMUT). In the capacitance interface, a TIA is adopted to amplify the received signal with a center frequency of 400 kHz, and finally detect ultrasound pressure. The circuit has a strong anti-stray property and this paper also studies the calculation of compensation capacity in detail. To ensure high resolution, noise analysis is conducted. After optimization, the detected minimum ultrasound pressure is 2.1 Pa, which is two orders of magnitude higher than the former. The test results showed that the circuit was sensitive to changes in ultrasound pressure and the distance between the CMUT and stumbling block, which also successfully demonstrates the functionality of the developed TIA of the analog-front-end receiver.

Portable surface stress biosensor test system based on ZigBee technology for health care

The paper presents a portable surface stress biosensor test system based on ZigBee technology for health care, which consists of a biosensor chip and an electronic test platform. The biosensor chip is a micro-scale and label-free polydimethylsiloxane micromembrane capacitive surface stress sensor. This chip consists of two micromembranes, in which one acts as the active unit and the other as reference. The signal difference of active and reference is acquired with the aid of capacitive detection circuit, which has high signal-to-noise ratio and speedy electrical readout. The electronic test platform is designed based on ZigBee technology to realize the accurate detection of small capacitance and the wireless signal transmission. The capacitive resolution of the system is 0.1 fF (femtofarad). The capacitance measured by the system is diminished and exaggerated with the increase and decrease of ethanol volume, which is corresponding to the capacitive formula. The haemoglobin test results from the system are consistent with the theoretical analysis and the test results from Agilent B1500A, which demonstrates that the system can be considered as a measurer of haemoglobin for clinical applications. The experiments also illustrate that the biosensor test system has good stability and multiplicity.

A high-order closed-loop ΣΔ interface for micro-machined accelerometer sensor

This paper presents a closed-loop interface for micro-machined accelerometer sensor based on a force-feedback sigma-delta loop. A high-order closed-loop accelerometer interface circuit is investigated, and a time-shared multiplexing electrostatic feedback technique is used to eliminate feedthrough between feedback signals and pick-up charge signals. A low noise capacitance detection circuit is proposed with correlated-double-sampling technique to eliminate the 1/f noise and offset of operational amplifier. The interface is fabricated in a standard 0.5 μm CMOS process and the active circuit area is about 13 mm2. The chip consumes 20 mW from a 5 V supply with a sampling clock of 250 kHz. The average noise floor of the digital accelerometer is about ?115 dBV/Hz1/2 over a 1.5 kHz bandwidth. Corresponding to a sensitivity of 302 mV/g, the measured resolution of the accelerometer system is about 6 μg/Hz1/2. The nonlinearity is 0.085 %. The figure of merit shows that the proposed sigma-delta interface achieves a good performance.

High resolution capacitance detection circuit for rotor micro-gyroscope

Conventional methods for rotor position detection of micro-gyroscopes include common exciting electrodes (single frequency) and common sensing electrodes (frequency multiplex), but they have encountered some problems. So we present a high resolution and low noise pick-off circuit for micro-gyroscopes which utilizes the time multiplex method. The detecting circuit adopts a continuous-time current sensing circuit for capacitance measurement, and its noise analysis of the charge amplifier is introduced. The equivalent output noise power spectral density of phase-sensitive demodulation is 120 nV/Hz1/2. Tests revealed that the whole circuitry has a relative capacitance resolution of 1 × 10−8.

Corn Moisture Measurement using a Capacitive Sensor

Corn moisture content is the main factor of effecting corn safe transportation and storage, and is also an indispensable measurement part when it it is used used to feed, food and industry. Due to to large particle size, corn will produce large large gap during measuring measuring moisture content. Because air air has has much influence influence on dielectric dielectric constant of the the device, moisture moisture content is not not precision. precision. In all kinds of corn moisture measurement measurement methods, capacitance method method becomes the the main method with simple structure, low cost cost and online measurement. This paper designs designs a sensor sensor for for measuring the corn moisture moisture that that uses a capacitance detection circuit circuit based based on the the relationship between the the capacitance and and the dielectric constant of the the corn. In addition, different different operating modes of the detection circuit circuit are analyzed. The relationship between the moisture moisture content of corn corn and the sensor capacitance is obtained through experiment and and a a binary binary cubic equation is obtained obtained by the least squares squares fitting method.

Design of a Capacitive Detection Circuit using MUX and DLC based on a νMOS

This paper describes novel scheme of a gray scale capacitive fingerprint image for high-accuracy capacitive sensor chip. The typical gray scale image scheme used a DAC of big size layout or charge-pump circuit of non-volatile memory with high power consumption and complexity by a global clock signal. A modified capacitive detection circuit of charge sharing scheme is proposed, which uses DLC(down literal circuit) based on a neuron MOS(vMOS) and analog simple multiplexor. The detection circuit is designed and simulated in 3.3V, standard CMOS process. Because the proposed circuit does not need a comparator and peripheral circuits, a pixel layout size can be reduced and the image resolution can be improved.

Design of a Capacitive Detection Circuit using MUX and DLC based on a νMOS

Design of a Capacitive Detection Circuit using MUX and DLC based on a νMOS

A Study of a High Performance Capacitive Sensing Scheme Using a Floating-Gate MOS Transistor

This paper proposes a novel scheme of a gray scale fingerprint image for a high-accuracy capacitive sensor chip. The conventional grayscale image scheme uses a digital-to-analog converter (DAC) of a large-scale layout or charge-pump circuit with high power consumption and complexity by a global clock signal. A modified capacitive detection circuit for the charge sharing scheme is proposed, which uses a down literal circuit (DLC) with a floating-gate metal-oxide semiconductor transistor (FGMOS) based on a neuron model. The detection circuit is designed and simulated in a 3.3 V, 0.35 μm standard CMOS process. Because the proposed circuit does not need a comparator and peripheral circuits, the pixel layout size can be reduced and the image resolution can be improved.

Design of Low Power Capacitive Sensing Circuit with a High Resolution in CMOS Technology

This paper describes the possibility of a lowpower, high-resolution fingerprint sensor chip. A modified capacitive detection circuit of charge sharing scheme is proposed, which reduces the static power dissipation and increases the voltage difference between a ridge and valley more than conventional circuit. The detection circuit is designed and simulated in 3.3V, 0.35μm standard CMOS process, 40MHz condition. The result shows about 27% power dissipation reduction and 90% improvement of difference between a ridge and valley sensing voltage. The proposed circuit is more stable and effective than a typical circuit.

용량성 지문센서를 위한 저전력 감지회로

A modified capacitive detection circuit of charge sharing scheme is proposed, which reduces the static power dissipation and increases the voltage difference between a ridge and valley more than a conventional circuit. The detection circuit is designed and simulated in 3.3V, 0.35µm standard CMOS process, 40MHz condition. The result shows about 47% power dissipation reduction and 90% improvement of difference between a ridge and valley sensing voltage. The proposed circuit is layout without area increasing of a one pixel.

Low voltage charge-balanced capacitance–voltage conversion circuit for one-side-electrode-type fluid-based inclination sensor

A low voltage detection circuit for a capacitance sensor is important for connection to a low voltage digital circuit interface. We studied two different charge-balanced capacitance–voltage ( C– V) conversion circuits configurations; the operational amplifier and the inverter amplifier. Both capacitance detection circuits were designed using 0.35 μm CMOS circuitry technology. Both amplifiers used in the detection circuits were not affected by offset voltage. The current consumption for capacitance detection circuit was reduced from 250 μA at V dd 3.3 V to 38 μA at V dd 1.3 V by switching from an operational amplifier to an inverter amplifier. These circuits were packaged with one-side-electrode-type fluid-based inclination sensors on ceramic substrates. The size of the sensor is ∅ 4.0 mm × 1.0 mm and pure propylene carbonate was used as electrolyte. Changes in temperature did not affect the output voltage of the sensor between −10 °C and 50 °C. This results show that the inverter amplifier used in the detection circuit was not affected by offset voltage and the output voltage V m is depends only on capacitor ratio. The capacitance detection circuit using the inverter amplifier shows a high-sensitivity of about 7 mV/deg over the operational amplifier at V dd 1.3 V. The response time, resolution and minimum moving angle of sensor were 0.7 s, 0.86° and 0.4°, respectively, at V dd 1.3 V for the inverter amplifier type of capacitance detection circuit.