초저전압 0.4-V 델타-시그마 모듈레이터 연구

Abstract

This dissertation presents delta-sigma modulators that operates at extremely low supply voltage of 0.4 V without using a clock boosting technique. A mixed differential difference amplifier (DDA) integrator and a hybrid switching integrator are proposed. To maintain the advantages of a discrete-time integrator in oversampled data converters, the mixed DDA integrator is developed that removes the input sampling switch in a switched-capacitor integrator. Conventionally, many low-voltage delta-sigma modulators have used high-voltage generating circuits to boost the clock voltage levels. The mixed DDA integrator with both a switched-resistor and a switched-capacitor technique is developed to implement a discrete-time integrator without clock boosted switches. The proposed mixed DDA integrator is demonstrated by a third-order delta-sigma modulator with a feedforward topology. The fabricated modulator shows a 68-dB signal-to-noise-plus-distortion ratio (SNDR) for 20-kHz signal bandwidth with an oversampling ratio of 80. The chip consumes 140 μWof power at a true 0.4-V power supply, which is the lowest voltage without a clock boosting technique among the state-of-the-art modulators in this signal band. The proposed hybrid switching integrator consists of both switched-resistor and switched-capacitor operations and significantly reduces distortion at a low supply voltage. Variation in the turn-on resistance, which is the main source of distortion, is avoided by placing the switches at the virtual ground node of the amplifier. The proposed low-voltage design scheme can replace commonly-used clock boosting techniques, which rely on internal high-voltage generation circuits. A fabricated modulator achieves a 76.1-dB SNDR and an 82-dB dynamic range (DR) at a 20-kHz bandwidth. The measured total power consumption is 63 μW from a 0.4-V supply voltage. The measured results show robust SNDR performance, even at ±10% supply voltage variations. The measured results also show stable performance over a wide temperature range.