Research And Design Of A Capacitive MEMS Accelerometer Interface Circuit Chip

Currently,micromachined capacitive accelerometer is one of the most widely used MEMS integrated sensors.It has very broad prospects of military and civil market.which has been widely used in the fields of Internet of things,motion monitoring,inertial navigation,consumer electronics,petroleum exploration,aerospace and so on.However,whether the technique research on micromachined accelerometer or the commercialization of the products is lagging behind the western countries.the related key technology and manufacturing technology still have a series of problems to be solved.Especially,with the development and application of the Internet of things,the design and implementation of lowvoltage and low-power MEMS micromachined accelerometer interface circuit chip with dynamically user selectable full scales not only has very important research significance,but also has extensive market application benefits.This paper is based on the purpose of the engineering application of micromachined accelerometers.Firstly,the relevant research background and application of MEMS acceleration sensor are introduced.Then the principles of three main circuit modules are explained,including mechanical sensor capacitor,charge voltage converter and Sigma Delta Modulator in the traditional MEMS capacitive accelerometer interface circuit.and some non-ideal factors such as noise and offset in the circuit are analyzed.Based on above introductions and analyses,according to the requirements of the design,the full differential switch capacitive open loop circuit architecture is used to design and realize the low-voltage and low-power accelerometer interface detection circuit chip.full differential switch capacitive circuit architecture can not only reduce the power consumption of the chip system but also helps to restrain even harmonic distortion,common mode interference and clock feed through effect.Verilog-A is used to conduct behavioral modeling and simulation of mechanical sensor capacitor in order to carry out joint simulation with the interface circuit.In terms of circuit performance,the design of low-voltage and low-power preamplifier,correlation double sampling technique(CDS)and bottom plate sampling technique decrease the influence of offset,1/f noise and parasitic capacitance.and the capacitance compensation array controlled by 3bits digital signal D0D1D2 is designed in the full differential variable gain charge voltage converter circuit,which can achieve dynamically user selectable full scales according to the different requirement of measurement range and resolution,besides,the capacitance compensation array controlled by 2bits digital signal S1S2 is deigned in common mode control circuit control,which can make up for the deviation of the mechanical sensor capacitance caused by the process error to a certain extent.finally,the digital output is realized by the Sigma Delta Modulators.The chip circuit has been implemented by the Dongbu Hi Tek 0.18 um 1.8V CMOS process in the Cadence and is simulated by Spectre emulator.The simulation results show that the overall power consumption of the accelerometer chip is 370 u A at the nominal supply voltage of 1.8V,dynamically user selectable full scales of ±20f F/±40f F/±240f F,the signal bandwidth is 2KHz,the sensor gain variation is less than 5%.