The Design And Research Of MOSCAP-Based Ultra-low Power And Small-area Sigma-Delta Modulator

With the continuous development of modern integrated circuit (IC) technology, the implantable chips are widely applied to medical equipment. Featuring high resolution, low power and low cost, Sigma-Delta analog-to-digital converters (ADCs) become the preferred converters in implantable chips. This thesis focuses on the research and development of the analog part of Sigma-Delta ADC-Sigma-Delta modulator. The target is to develop a MOSCAP-based Sigma-Delta modulator with ultra-low power and small area.Based on the study of principles of MOSCAP structure, it was proposed that all the capacitors in Sigma-Delta modulator are replaced by PMOSFET MOSCAP with the higher capacitance density to reduce the occupied chip area. The system behavioral model of the Sigma-Delta modulator was built in MATLAB. Using the model, the system structure and parameters of the modulator were optimized and chosen. And a Sigma-Delta modulator, to which MOSCAP is applied, as well as its main blocks including switch Op-Amp and capacitor-string quantizer was successfully implemented. And the multi-bit quantified technology was implemented by the capacitor-sting multi-bit quantizer, which employs capacitor-string voltage dividers and dynamic comparators without pre-amplifier. Comparing with the traditional ones, it reduce most of static power consumption,All the circuit was simulated using Spectre in TSMC 0.35μm mixed signal CMOS process. The simulation results showed that the dynamic-range (DR) of the modulator is 103.5dB when the bandwidth of input signal is 8kHz and the sampling frequency is 512kHz. The modulator consumes totally 13.4μA under 1.5V supply voltage and its area is only 1.2mm* 1.2mm.. It is proved that the modulator features ultra-low power, high precision and high area-efficient.