Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE credits
Biosensor applications have made promising progress during the last decade, presenting potentials and challenges at the same time. Meanwhile, digital signal processing (DSP) has become even more powerful than before, due to Moore's Law. Bridging the biosensor applications and the digital circuits, analog-to-digital converters (ADCs) are a critical block that inuences the performance of the entire system, in terms of speed, accuracy and power. Particularly, incremental ΣΔ (IΣΔ) ADCs have recently received increasing research interest because of their high-resolution feature and the ability to time-multiplex different channels of input signals, making them especially suitable for neuro-science studies and brain-computer-interface (BCI). However, IΣΔ ADCs are less power-ecient than traditional ΣΔ ADCs.
To improve the power eciency and reduce the chip size, an inverter-based continuous-time (CT) Sigma-Delta (ΣΔ) modulator is proposed, to be integrated in a two-step I(ΣΔ) ADC previously designed. Inverter-based operational transconductance amplifers (OTA) have recently demonstrated their high power efficiency in multiple ΣΔ modulators, most of which are discrete-time (DT) implementation. CT implementation is investigated in this thesis for the possibility to further reduce power consumption, due to its more relaxed requirements on bandwidth and settling compared to the DT counterpart. In the circuit implementation of the modulator, fully-differential topology is used in inverter-based CT ΣΔ ADCs for the rst time. Compared to pseudo-differential topology, fully-differential topology has more precise control on the operating point and the quiescent power.
The post-layout simulation result shows that the modulator achieves a peak SNDR of 58.1 dB, and a dynamic range of 65.9 dB. The entire modulator consumes 1.28 μW from a 1.2 V supply voltage, on a chip area of only 0.07 mm2. This corresponds to a FoM of 243 fJ/(conv. step).
2014. , 67 p.