High Performance Ultra-low Voltage Continuous-Time Delta-Sigma Modulators

The scaling of the feature sizes of CMOS technologies results in a continuous reduction of supply voltage (VDD) to maintain reliability and to reduce the power dissipation per unit area for increasingly denser digital integrated circuits. The VDD for low-power digital circuits is predicted to drop to O.5V in about ten years. Ultra-low voltage (ULV) operation will also be required for the analog-to-digital converter, a universal functional block in mixed-signal integrated circuits, in situations where the benefits of using a single VDD out-weigh the overhead associated with multi-V DD solutions.;Continuous-time (CT) Delta-Sigma Modulators (DSMs) have re-gained popularity recently for oversampling analog-to-digital conversion, because they are more suitable for low supply voltage implementation than their discrete-time (DT) counterparts, among other reasons. To the state of art at the low voltage front, a CT O.5-V audio-band DSM with a return-to-open feedback digital-to-analog converter has been reported. However, the O.5-V CT DSM has a limited performance of 74-dB SNDR due to clock jitters and other factors caused by the ultralow supply.;In this thesis, three novel ULV audio-band CT DSMs with high signal-to-noise-plus-distortion ratio (SNDR) are reported for a nominal supply of O.5V. The first one firstly realizes a switched-capacitor-resistor (SCR) feedback at O.5V, enabled by a fast amplifier at O.5V, for reduced clock jitter-sensitivity. Fabricated in a O.13mum CMOS process using only standard VT devices, the 3rd order modulator with distributed feedback occupies an active area of O.8mm2. It achieves a measured SNDR of 81.2dB over a 25-kHz signal bandwidth while consuming 625muW at O.5-V. The measured modulator performance is consistent across a supply voltage range from O.5V to O.8V and a temperature range from -20°C to 90°C. Measurement results and thermal-noise calculation show that the peak SNDR is limited by thermal noise.;The second ULV CT DSM employs a feed-forward loop topology with SCR feedback. Designed in O.13mum CMOS process, the modulator achieves a post-layout simulation (thermal noise included) result of 89dB SNDR over a 25-kHz signal bandwidth. The 0.13mum CMOS chip consumes an active area of O.85mm2 and 682.5muW at O.5-V supply. It achieves an excellent measured performance of 87.8dB SNDR over a 25-kHz signal bandwidth and al02dB spurious-free dynamic range. To the best of our knowledge, this performance is the highest for DSMs in this supply voltage range. Thanks to the proposed adaptive biasing technique, the measured modulator performance is consistent across a supply voltage range from O.4V to O.75V and a temperature range from -20°C to 90°C.;Finally, a O.5-V 2-1 cascaded CT DSM with SCR feedback is proposed. A new synthesis method is presented. Transistor-level simulations show that a 98dB SNDR is achieved over a 25-kHz signal bandwidth with a 6.4MHz sampling frequency and 350muW power consumption under a 0.5-V supply.