Design Of High Order Mash Sigma-Delta Modulator Applied In Inertial Sensors

With the rapid development of technology, inertial sensors have attracted more and more attentions, high-performance inertial sensors are needed in many fields such as astronautics and medical, and converting the physics analog signal to digital signal is a key process to improve the sensor performance, traditional analog-digital converters have difficulty to meet the demand for high performance, yet Sigma-Delta ADCs have high performance, and the Sigma-Delta modulator is the most important module in a Sigma-Delta ADC. With over-sampling and noise-shaping technology, in-band noise is significant reduced in a Sigma-Delta modulator which can achieve a high SNR analog-digital converting, so far, Sigma-Delta modulators are applied in most low bandwidth inertial sensors.The theory of a Sigma-Delta modulator is introduced in this paper, based on this theory, a feedback2-1-1MASH Sigma-Delta modulator and a forward-feedback2-1-1MASH Sigma-Delta modulator are designed, and the coefficients in modulators are calculated. The system-level model of modulators are simulated in Simulink, the two structures of modulator are compared, and the feedback2-1-1MASH Sigma-Delta modulator is the final selection which has an ENOB of24bits when the Signal bandwidth is1kHz and the over-sampling rate is128. Then the circuits of modulator are designed, including integrator, comparator, multi-phase clock and the noise cancelling logic. The whole modulator is simulated in Candence, the SNR of modulator is125.4dB, and the ENOB is21.1bits that meets the technical requirements of the sensor.