Design Of High Resolution Sigma-Delta Modulator

As an important member of the family of inertial sensor, silicon microgyroscopeapplied to everywhere in our daily life. We may find it no matter in industrialmanufacture or in military production. Because of its characteristics of high precisionand high degree of integration and low power dissipation, it has been focusresearched by the laboratories and research institutions. As the most importantcomponent of the silicon microgyroscope, Sigma-Delta modulator is different fromthe traditional modulator. It has higher SNR than the traditional modulator.Sigma-Delta modulator may be well developed in the adhibition of high resolutionmodulator.This paper designed a Fourth-Order Feed-Forward Sigma-Delta modulator. Itscharacteristics of high precision matching the requirements of siliconmicrogyroscope. The high SNR of Sigma-Delta modulator owes to over samplingtechnology and noise shaping technology. Over sampling technology could reducethe PSD by increasing the sampling rate. By the characteristic of low pass,Sigma-Delta modulator could raise the quantizing noise to the high frequency regionthen filtered by the filter. So the precision was improved. The main non-ideal factorsof switch are the effect of clock feed-through and the charge injection. Thecompensation structure of switch will inhibit the charge injection effectively. Theamplifier with fully differential structure could inhibit the even harmonic, the effectof clock feed-through, the noise and so on. The appropriate gain is needed to matchthe high precision Sigma-Delta modulator. In Fourth-Order Sigma-Delta modulator,the gain of40dB is always being needed.The system level of fourth-order feed-forward sigma-delta modulator wassimulated by Simulink. The signal bandwidth is20kHz, and sample frequency is10.24MHz. The PSD of ideal fourth-order feed-forward sigma-delta modulator showthat the SNR is145.5dB, and ENOB is23bit. By considering all of the non-idealfactors, the PSD of fourth-order feed-forward sigma-delta modulator shows that theENOB still is20bit. The noise floor of the modulator is lower than-140dB, and theharmonic wave is vanished in the noise floor of the modulator. It Proved that the system meet the design requirements. After designed the system circuit andsimulated by the Cadence, the PSD of fourth-order feed-forward sigma-deltamodulator shows that the ENOB is16bit, and the noise floor of the modulator islower than-120dB. We may naturally arrive at the conclusion that, the system meetsthe design requirements.