PhD ThesisData acquisition systems used in remote environmental monitoring equipment and biological
sensor nodes rely on limited energy supply soured from either energy harvesters or battery to
perform their functions. Among the building blocks of these systems are power hungry Analogue
to Digital Converters and Digital Signal Processors which acquire and process samples
at predetermined rates regardless of the monitored signal’s behavior. In this work we investigate
power efficient event driven data acquisition and processing techniques by implementing
an asynchronous ADC and an event driven power gated Finite Impulse Response (FIR) filter.
We present an event driven single slope ADC capable of generating asynchronous digital samples
based on the input signal’s rate of change. It utilizes a rate of change detection circuit
known as the slope detector to determine at what point the input signal is to be sampled. After
a sample has been obtained it’s absolute voltage value is time encoded and passed on to a Time
to Digital Converter (TDC) as part of a pulse stream. The resulting digital samples generated
by the TDC are produced at a rate that exhibits the same rate of change profile as that of the
input signal. The ADC is realized in 0.35mm CMOS process, covers a silicon area of 340mm
by 218mm and consumes power based on the input signal’s frequency.
The samples from the ADC are asynchronous in nature and exhibit random time periods between
adjacent samples. In order to process such asynchronous samples we present a FIR filter that is
able to successfully operate on the samples and produce the desired result. The filter also poses
the ability to turn itself off in-between samples that have longer sample periods in effect saving
power in the process