Design Of A 16 Bits Digital-to-analog Converter For Micro-gyroscope

MEMS micro-machined gyroscope is a kind of sensor which can measure the angle velocity.Accuracy is the significant technique parameter.The micro-machined gyroscope consists of the sensitive elements and the interface circuits.The accuacy of the DAC influences the precision of output drive signal directly.For high-resolution digital to analog conversion,oversampling sigma-delta is the best design choice.In this context,this paper aimed at the research of gyroscope digital-to-analog interface circuit and designed a 16 bit sigma-delta DAC applying to micro-machined gyroscope interface circuit.Firstly,this paper analyzes the principle for the perspective of the dynamic theoretical of the micro-machined gyroscope.After that,this paper makes in-depth analysis on the whole sigma-delta DAC works and finishes the system-level and circuit-level design of each module.The sigma-delta DAC mainly includes interpolation filter,sigma-delta digital modulator and analog resconstruction.The interpolation filter has achieved 128 times interpolation function,using three-stage cascaded manner.The first stage is the half-band filter achieving 2 times interpolation.The second stage is the 1/4 band filter achieving 4 times interpolation.The last stage is the sampling hold circuit achieving 16 times interpoltion.Measured results show that the SNR is 102.3d B in the 10 k Hz bandwidth range.The digital modulator is implemented by 3 order 4 bit CIFB structure,coefficients are achieved by CSD code.The simulation results indecate that the SNR of the modulator is 109.3d B,effective digit is 17.86 bits.In order to reduce the impact of the nonlinear of the mismatch,the structure adopted DWA algorithms,which is to achieve the selection of rotsry for unit capacitence and eliminate reduce the mismatch errors of multi bit quantizing converter.The analog circuit is implemented by direct charge transfer DAC and 2order Chebyshev Sallen-Key RC filter.This paper uses the simulation software Matlab to simulate and model the system for better performance.This design is implemented in 0.18 ?m standard CMOS process.Finally,the whole sigma-delta DAC digital-analog hybrid simulation is completed.The simulation results meet design requirements with-98 d B system harmonic component,97.8d B signal-to-noise ratio,and 15.95 bits effective digit with 10 k Hz signal bandwith.The clock frequency is 3.2MHz.