Design Of A Fourth Order Bandpass Sigma-Delta Modulator Applied In Micro-gyroscope

Band-pass sigma-delta modulator is a core part of the digital interface circuit ofthe micro-mechanical gyroscopes. It and digital filter compose the sigma-delta ADC,which converts the analog output of micro-gyroscope detection circuit to digital. Aband-pass sigma-delta modulator applied in micro-gyroscope in the0.5μm CMOSprocess is proposed in this paper.Firstly, the principle of A/D converter and the effect of over-sample andnoise-shaping on raising SNR are deeply analyzed during the comparison ofsigma-delta and traditional nyquist A/D converters. After that, a modulator structurewith one bit single-loop in discrete time system is brought forward based on theanalysis of basic structures of band-pass sigma-delta modulators. Then, the idealsystem-level model design is operated in the environment of MATLAB/Simulink.Then, the nonideal factors that may exist in system-level and circuit-level areconsidered. Based on this, a system-level model that contains nonideal factors isdesigned and simulated in MATLAB/Simulink, which verifies the feasibility of thedesign scheme. What’s more, the performance indexes of the main circuit modules areconfirmed in this process.Finally, the transistor-level design and simulation of circuit modules such asoperational amplifier, switch, feedback logic and one-bit DAC circuit, quantizer, andclock generating circuit are carried out in0.5μmprocess according to the performancerequirements proposed in the behavior module. Based on this, the whole circuit iseventually joined and simulated. Then the output bit-stream of the whole circuit isimported to MATLAB for the FFT spectrum analysis which finally shows the SNR ofthe circuit-level modulator reaches78.5dB and that the effective number of bits(ENOB) reaches12. In conclusion, the design stated in this paper meets the expectedrequirements.