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Study On The Closed Loop Self-excited Detection Circuit For Thermally Excited MEMS Resonator

Posted on:2012-09-01Degree:MasterType:Thesis
Country:ChinaCandidate:Z LiuFull Text:PDF
GTID:2178330335962795Subject:Microelectronics and Solid State Electronics
Abstract/Summary:PDF Full Text Request
Micro-mechanical resonant sensor is an important micro-sensor. In addition to the advantages of the ordinary silicon micro-machined sensors with small size, light weight, low cost, power consumption and easy integration, the micro-mechanical resonant sensor has high sensitivity, quasi-digital signal output and strong anti-interference ability. The closed-loop self-excitation and detection circuit is one of the most important technologies in developing the micro-resonant sensors, which can enhance the measurement accuracy and speed of the resonant frequency, expand the measurement range and improve the system dynamic characteristics.Based on the open-loop characteristics test and employing the precise frequency selecting and accurate frequency tracking performance of the PLL, a closed-loop self-excitation and detection circuit was developed in this paper, including low-noise differential amplifier, constant delay band-pass filter, phase shifter changing the phase from 0°to 180°, waveform converter transforming the sine to square, frequency divider, PLL with precise frequency selecting and accurate frequency tracking function and amplitude adjustment circuit. The detection system achieved closed-loop self-excited and high-precision measurement of the resonant frequency.The detection circuit's phase change caused by the frequency offset is a key factor influencing the stability and reliability of test results. In order to eliminate the phase change of the PLL caused by the frequency offset, the paper took advantage of relationship between the steady-state phase difference and the PLL loop filter transfer function and gave an optimization of the PLL circuit based on waveform generator MAX038 to realize frequency tracking function at the fixed phase difference. The PLL circuit, with simple structure and continent parameter selection, can achieve frequency and phase synchronization tracking of transmit signal.After analysis, simulation and debugging of each circuit unit, the design principles of each circuit unit were put forward, and the closed loop self-excited detection circuit for thermally excited MEMS resonator was developed. The closed-loop test result of thermally excited and piezoresistive detection double layers micro-cantilever resonator made of SiO2 and Si shows that the frequency stability of this system can achieve 0.1 Hz/h, so we can get the conclusion that the closed-loop self-excited system has high measurement precision and stability.
Keywords/Search Tags:Micromechanical Resonator, Closed Loop Self-excited System, Phase Lock Loop, Zero Phase Difference
PDF Full Text Request
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