Huanming Wu

A TIA-based readout circuit with temperature compensation for MEMS capacitive gyroscope

This paper presents an integrated readout circuit based on trans-impedance amplifier (TIA) for MEMS capacitive gyroscope. The feedback resistors in TIA are realized in T-network pattern, which provides on-chip trans-impedance gains up to 22MΩ. A CMOS temperature-variable gain circuit is proposed to compensate the temperature induced sensitivity variance in MEMS and TIA. The demodulator, instrumental amplifier and low-pass filter for signal processing are also integrated on chip. In order to simulate the response of the circuit to the vibrating gyroscope, a gyroscope simulation model implemented in Verilog-A HDL is established, which can take the MEMS parameters influence into account. The circuits measure 0.8×1.7mm2 in a standard 0.35µm CMOS process. The simulation results show that the TIA achieves a capacitive resolution of 0.42aF/−Hz at 2.5kHz with 75ppm/°C temperature coefficient from a single 5V supply.

A TIA-based interface for MEMS capacitive gyroscope

This paper presents a CMOS readout and driving interface for micro-electro-mechanical systems (MEMS) capacitive gyroscope. A low-noise fully differential trans-impedance amplifier (TIA) scheme is used both in readout channel and driving loop for capacitive signal detection. A linear model of amplitude control loop and the design of an AGC-based analog drive loop for gyroscope are presented. The model allows the small signal analysis and behavior prediction of the driving loop. The interface circuits are designed and implemented in a 0.35µm 2P4M CMOS process. The simulation results show that the TIA readout circuit achieves a capacitive resolution of 0.73aF/√Hz and dynamic range of 93dB from a single 5V supply.

Integrated Gm-C based PI controller for MEMS gyroscope drive loop

PI controller is an important element in MEMS gyroscope drive loop design, which helps the loop to maintain stability and obtain an optimal transient response. This paper presents an integrated Gm-C based PI controller for MEMS gyroscope drive loop. An analysis of the drive loop with PI controller is first given. The analysis reveals that sufficient tunable properties and low integrator loss should be pursued for the PI controller design. Then in the controller implementation, only one OTA is used to realize the PI control and subtract function, which minimizes the power consumption and chip area. A passive RC network in the controller introduces only one extra pad, while still promises sufficient tunable properties and low integrator loss. The chip is fabricated in a 0.35µm CMOS technology with 5V supply voltage. The chip consumes less than 1mW and its area is only 0.18×0.08 mm2.

A Low-Cost Energy-Efficient Cableless Geophone Unit for Passive Surface Wave Surveys

The passive surface wave survey is a practical, non-invasive seismic exploration method that has increasingly been used in geotechnical engineering. However, in situ deployment of traditional wired geophones is labor intensive for a dense sensor array. Alternatively, stand-alone seismometers can be used, but they are bulky, heavy, and expensive because they are usually designed for long-term monitoring. To better facilitate field applications of the passive surface wave survey, a low-cost energy-efficient geophone system was developed in this study. The hardware design is presented in this paper. To validate the system’s functionality, both laboratory and field experiments were conducted. The unique feature of this newly-developed cableless geophone system allows for rapid field applications of the passive surface wave survey with dense array measurements.

Analysis and Design of a 3rd Order Velocity-Controlled Closed-Loop for MEMS Vibratory Gyroscopes

The time-average method currently available is limited to analyzing the specific performance of the automatic gain control-proportional and integral (AGC-PI) based velocity-controlled closed-loop in a micro-electro-mechanical systems (MEMS) vibratory gyroscope, since it is hard to solve nonlinear functions in the time domain when the control loop reaches to 3rd order. In this paper, we propose a linearization design approach to overcome this limitation by establishing a 3rd order linear model of the control loop and transferring the analysis to the frequency domain. Order reduction is applied on the built linear models transfer function by constructing a zero-pole doublet, and therefore mathematical expression of each control loops performance specification is obtained. Then an optimization methodology is summarized, which reveals that a robust, stable and swift control loop can be achieved by carefully selecting the system parameters following a priority order. Closed-loop drive circuits are designed and implemented using 0.35 μm complementary metal oxide semiconductor (CMOS) process, and experiments carried out on a gyroscope prototype verify the optimization methodology that an optimized stability of the control loop can be achieved by constructing the zero-pole doublet, and disturbance rejection capability (D.R.C) of the control loop can be improved by increasing the integral term.

Integrated readout and drive circuits for a microelectromechanical gyroscope

An ASIC is implemented for readout and drive of a bulk micromachined gyroscope utilizing electromagnetic actuation and sensing. A fully differential structure is used in the readout channel and drive loop to reduce the common-mode noise and interference. A low-noise front-end amplifier is designed to sense the rotation induced voltage signal. A switched-capacitor BPF with adjustable center frequency is proposed to track the resonance frequency and suppress the noise and harmonic components out of the signal bands. An AGC-based driving loop with PLL for demodulation clock generation is also designed and integrated on chip. The interface circuits are designed in a 0.35μm 2P4M CMOS process. The simulation results show that the readout circuit achieves an input referred noise voltage of 16.5nV/√Hz and dynamic range of 80dB over the 100Hz bandwidth from a single 5V supply.

A multi-mode interface for MEMS vibratory gyroscope with self-tuned filter

This paper presents a multi-mode ASIC interface with self-tuned filter to support a wide variety of MEMS gyroscope with various resonance frequencies and various output signal styles of sense/drive mode. A reconfigurable readout front-end circuit is used for signal readout in the sense channel and drive loop, which can sense the capacitive, voltage and current signal output. A gyroscope-resonance-based self-tuned band-pass filter (BPF) is proposed in sense channel, whose center frequency is self-tuned to the drive resonance frequency. The method helps the ASIC to interface with a wide-range of gyroscopes with different resonance frequency without changing the BPF design. The interface is implemented in 0.35μm CMOS process. The measurement with an electromagnetic gyroscope and an electrostatic gyroscope shows the validity of the method. The electromagnetic gyroscope achieves a sensitivity of 25.2mV/°/s with a noise floor 0.02°/s/vHz and ±50°/s full scale range with 50/00 nonlinearity.