Qisong Wu

A large dynamic range CMOS readout circuit for MEMS vibratory gyroscope

This paper presents a large dynamic range, low noise integrated circuit for readout of a bulk micro-machined vibratory gyroscope. With the proposed sinusoidal chopper technique and the differential-common Duo-Opamp structure, three main objectives are achieved: the low frequency noise cancellation; the biasing of the high impedance nodes in a traditional fully-differential circuit; and the high linearity capacitance-voltage conversion. These characteristics promise an enhanced dynamic range. Furthermore, the demodulation circuit is also a low noise and high linearity design, for the purpose of not deteriorating the overall readout performance. The chip measures 2 times 2.5 mm2 in a standard 0.35 mum CMOS process. The results show that the readout circuit can resolve input capacitance variations of 20aF in 100 Hz bandwidth with 106 dB dynamic range from a single 5 V supply.

A low-noise readout circuit for MEMS vibratory gyroscope

This paper presents a gain-programmable low-noise switched-capacitor circuit for readout of a bulk micromachined gyroscope with a resonance frequency of 3-4 kHz and signal bandwidth of 100 Hz. A charge transfer method is adopted which enables the common node of the sensing and driving structure in gyroscope to a stable biasing voltage, so that the driving force influence of the voltage fluctuation on the common node in the traditional readout method is eliminated. An offset cancellation scheme is used in the readout circuit to suppress the opamps offset and two programmable capacitor arrays are also implemented on-chip to compensate the initial capacitance offset from the MEMS gyroscope. In order to simulate the transient response of the circuit to the vibrating gyroscope, a simplified model is proposed which uses a time-varying voltage to generate a time-varying capacitor. The chip measures 2times2.5 mm2 in a standard 0.35 mum CMOS process. Simulation results show that the readout circuit can resolve input capacitance variations of 95 aF in 100 Hz bandwidth with 83.4 dB dynamic range from a single 5 V supply.

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.

A CMOS Field Programmable Analog Array for intelligent sensory application

A Field-Programmable Analog Array (FPAA) architecture designed for intelligent sensory application is presented, which consists of high performance and high flexible Configurable Analog Blocks (CABs). The CAB is developed to realize both continuous-time and discrete-time circuits for achieving optimal performance in different applications. In addition to employ coarse-grained reconfigurable CAB in FPAA, a fine-grained reconfigurable amplifier in the CAB is utilized to maximize programmability and flexibility. The precision of the analog processing is enhanced by employing fat-tree interconnection network topology to minimize the number of switches used in FPAA and using correlated double sampling (CDS) techniques to suppress the offset and noise. The FPAA is designed and implemented in SMIC 0.18μm CMOS process with a 3.3 V supply voltage. An instrumental amplifier and a capacitive sensor signal readout circuit are taken as application examples. The relative precision and dynamic range of the analog processing are 97.6% and 119dB respectively.

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 MEMS gyroscope readout circuit with temperature compensation

This paper presents a high precision integrated circuit for readout of a bulk micro-machined vibratory gyroscope. The fully differential circuit has adopted the chopper technique, combined with the differential-common duo-opamp structure, which has been proved excellent capability for low frequency noise cancellation. As the readout sensitivity is proportional with both the amplitude of the chopper modulation signal and the gain of the charge sensing amplifier, we have designed an on-chip modulation signal generator, of which the temperature coefficient is adjusted right opposite against the amplifier, so that temperature compensation is accomplished. The chip measures 2.1×2.1mm2 in a standard 0.35μm CMOS process. The simulation shows that with a single 5V supply, the readout circuit achieves 0.11aF/rtHz resolution, and 0.85mV/fF sensitivity with 30ppm/°C temperature drift.

A 1.3μW 0.7μV RMS chopper current-reuse instrumentation amplifier for EEG applications

This paper presents a low noise chopper-stabilized instrumentation amplifier (IA) for EEG recording. The current-reuse technology is adopted to reduce noise of the IA and the regulated cascode circuit is used to boost the open-loop gain of the amplifier. A ripple reduction loop (RRL) based on a novel output-resistance-tuning technology is proposed to reduce the intrinsic offset of the IA and reduce the output ripple of the chopper amplifier. Simulation results show the high-pass cutoff frequency of 0.15Hz, the input referred noise of 0.7μVRMS (BW=100Hz) and a NEF of 2.83. The attenuation to the chopping ripple is about 35dB with the novel output-resistance-tuning based RRL. The proposed IA achieves an average CMRR of 110dB, average PSRR of 105dB and average input-impedance of 1.5GΩ from Monte Carlo analysis. The overall IA consumes only 1.1μA current at a 1.2V supply.

A smart sensory platform based on field programmable analog array

This paper presents a smart sensory platform based on Field Programmable Analog Array (FPAA) to support a wide variety of MEMS sensors applications. A discrete-time (DT) and continuous-time (CT) dual-mode FPAA is proposed to improve the analog signal conditioning flexibility. A gain-programmable low-noise multi-mode sensor Readout Circuit (RoC) is designed for versatile sensor weak signal acquisition, which can sense capacitive, voltage or current signal. A microcontroller (MCU) and a 12-bit SAR ADC are used for digital signal processing and analog-digital conversion. The platform is implemented in 0.18μm CMOS process. The multi-mode sensor readout circuit achieves an input referred noise of 140nV/√Hz, 200pA/√Hz and 5aF/√Hz for voltage, current and capacitive signal readout mode, respectively. Analog signal processing functions, such as CT PGA, DT filter, CT adder and comparator, are realized through the configuration of the dual-mode FPAA. The SAR ADC shows 10.2bit effective number of bits with 450μA power consumption at 1Msps sampling rate.

A closed-loop switched-capacitor interface for high-quality microaccelerometer

This paper presents a closed-loop switched-capacitor interface for high-quality bulk micro-mechanical accelerometer. Analogue force feedback is realized to establish an electromechanical closed-loop so as to improve the dynamic range. The feedback accuracy is guaranteed by applying bottom-plate-sampling structure in the feedback controller. A proportional derivative controller is introduced to compensate the instability derived from the high-quality accelerometer, while offset cancellation structure is inserted to further improve the dynamic range. The chip measures 2.5×2.5mm2 in Chartered 0.18µm CMOS process. Simulation results show that the whole accelerometer system offers ±1.3g input range with 0.25% non-linearity from a single 6V supply, as well as a good degree of robustness.