Recently, smart dust or wireless sensor networks are gaining more attention.These autonomous, ultra-low power sensor-based electronic devices sense and process burst-type environmental variations and pass the data from one node (mote) to another in an ad-hoc network. Subsystems for smart dust are typically the analog interface (AI), analog-to-digital converter (ADC), digital signal processor (DSP), digital-to-analog converter (DAC), power management, and transceiver for communication.

This thesis project describes an event-driven (ED) digital signal processing system (ADC, DSP and DAC) operating in continuous-time (CT) with smart dust as the target application. The benefits of the CT system compared to its conventional counterpart are lower in-band quantization noise and no requirement of a clock generator and anti-aliasing filter, which makes it suitable for processing burst-type data signals.

A clockless EDADC system based on a CT delta modulation (DM) technique is presented. The ADC output is digital data, continuous in time, known as “data token”. The ADC employs an unbuffered, area efficient, segmented resistor-string (R-string) feedback DAC. A study of different segmented R-string DAC architectures is presented. A comparison in component reduction with prior art shows nearly 87.5% reduction of resistors and switches in the DAC and the D flip-flops in the bidirectional shift registers for an 8-bit ADC, utilizing the proposed segmented DAC architecture. The obtained SNDR for the 3-bit, 4-bit and 8-bit ADC system is 22.696 dB, 30.435 dB and 55.73 dB, respectively, with the band of interest as 220.5 kHz.

The CTDSP operates asynchronously and process the data token obtained from the EDADC. A clockless transversal direct-form finite impulse response (FIR) low-pass filter (LPF) is designed.

Systematic top-down test-driven methodology is employed through out the project. Initially, MATLAB models are used to compare the CT systems with the sampled systems. The complete CTDSP system is implemented in Cadence design environment.

The thesis has resulted in two conference contributions. One for the 20th European Conference on Circuit Theory and Design, ECCTD’11 and the other for the 19th IFIP/IEEE International Conference on Very Large Scale Integration, VLSI-SoC’11. We obtained the second-best student paper award at the ECCTD.