A 1.5V multirate multibit sigma delta modulator for GSM/WCDMA in a 90nm digital CMOS process.

摘要

The development of low-voltage and low-power mixed signal CMOS integrated circuits has been one of the key objectives in the last decade. Thus, a significant amount of effort has been devoted for this purpose. There are two main reasons that fuel this need. First reason is the increasing demand for portable battery operated systems. The second one is the ongoing transistor scaling. Analog to digital converters based on Sigma Delta modulators are widely used in the analog front ends of various mixed signal integrated circuits. Hence they have to operate from low supply voltages as well as with minimum power dissipation.; This dissertation investigates the use of digital techniques to replace some of the functionalities that were traditionally performed by analog circuits. By doing so, the aim is to increase the share of digital blocks in the Sigma Delta system and decrease area and power consumption of the modulator. This dissertation also investigates the design techniques of low-voltage, power efficient analog building blocks that are used in the design of a Sigma Delta modulator for wireless applications (i.e., GSM and W CDMA).; In order to demonstrate the techniques presented here, a prototype Sigma Delta modulator is designed and fabricated in a 90nm five metal single poly n-well CMOS process. The modulator is realized with fully-differential stray insensitive switched capacitor integrators. Both integrator stages use a fully differential folded cascode operational transconductance amplifier with switched capacitor common mode feedback to set the common mode voltages of the output nodes. A careful capacitor scaling is performed in the second integrator stage in order to take advantage of the noise shaping that is due to the first integrator stage. The presented Sigma Delta modulator achieves 68.6/42.8dB peak Signal-to-Noise and Distortion ratio (SNDR) and dissipates 1.1/1.9mA of current in GSM (200 kHz) and WCDMA (1.94 MHz) modes, respectively.