Integrated Design Of Closed-Loop Self-Excitation Signal Generating Circuit For Micromechanical Resonator

As a new type of sensor,Micro-Electro-Mechanical System(MEMS)has many advantages,such as high integration,strong stability,high precision and strong compatibility.It has been widely used in the market.The output signal of MEMS is easily affected by noise,so the design of reasonable and effective signal excitation and detection circuit is one of the core issues to improve the measurement accuracy.Compared with the open-loop,the closed-loop detection circuit can dynamically track the change of output signal in real time,and it has higher measurement accuracy and sensitivity.In this paper,a fully integrated closed-loop self-excitation/detection scheme is proposed by analyzing the structure of MEMS excitation and detection circuit.The key unit circuits include LC Voltage-Controlled Oscillator based on Phase-Locked Loops,frequency divider,waveform converter and variable gain amplifier.LC VCO adopts differential coupling structure,which generates high frequency oscillation signal.It is divided frequency through frequency divider.The divided pulse wave is converted into sine wave by filter structure.And the output gain is controlled linearly by variable gain amplifier in a certain range of control voltage.The structure can not only realize the high-precision detection and high-efficiency real-time tracking function of MEMS dynamic signal,but also make the closed-loop self-excitation/detection structure more stable and perfect.Based on the CMOS technology of TSMC 0.18?m,this design uses ADS2015RF simulation software to simulate.The simulation results show that the frequency range of low power dissipation LC VCO is 1.26GHz to 1.33GHz when the control voltage is 0V to 1.8V,and the phase noise is-126.448d Bc/Hz@1MHz and the power consumption of 3.21m W.TSPC dynamic frequency divider can realize 2¹⁴frequency division.The pass band range of the waveform conversion circuit without phase difference designed by Chebyshev filter structure is 7.94k Hz to 10.15k Hz.VGA achieves a phase difference free output with a gain range of–10d B to 16d B within the control voltage range of 0.4V to 0.6V.The layouts of LC VCO,frequency divider and VGA integrated modules are drawn by Cadence software and verified by DRC and LVS.The layout areas of 659.83?m×446.71?m and 49.68?m×138.86?m are obtained respectively.The chip test results show that when the control voltage V_ctrl is 0.3V,the phase noise of LC VCO is-125.87d Bc/Hz@1MHz in low frequency and when V_ctrl is 1.6V,the phase noise of LC VCO is-123.3d Bc/Hz@1MHz in high frequency.The circuit can realize self-excitation and signal tracking detection.When it realizes effective integration and increases the stability and reliability of the system,the circuit greatly reduces the volume and power consumption of the circuit module.The mode of excitation and detection of MEMS sensors are improved,which is of great significance to the performance optimization of dynamic tracking with the MEMS resonators resonant frequency.