Voltage Boosting Amplifier Techniques for Underwater Sensor Networks: Theory and Design

The innovations in wireless sensor networks has changed the way we communicate today. While radio based wireless communication has entered a mature phase of commercialization, underwater communication technology is still lagging behind. The most widely used type of communication for underwater is acoustic communication. This is due to the fact that acoustic communication allows long range underwater communication as compared to optical and radio based wireless communication. However issues with slow acoustic propagation, limited available bandwidth, variations in channel propagation and power efficiency makes the development of reliable and energy efficient Underwater Sensor Networks (USNs) a major challenge. However the development of reliable and low cost USNs has a great potential of revolutionizing many areas of underwater monitoring, sensing, navigation, detection and many more. The progress in USNs involves many key areas including signal processing, underwater channel modeling, transducer design, energy harvesting and efficient amplifier design, to name a few. In this thesis we focus on the techniques for an energy-efficient amplifier design, in particular the associated challenges in driving piezoelectric loads with limited supply voltages. Therefore to gain insight into the design aspects of the amplifier, different existing amplifier topologies suitable for driving piezoelectric transducers are reviewed with focus on wide bandwidth, low distortion and supply boosting. To improve power efficiency a voltage boosting amplifier that combines signal generation and supply boosting can be a good choice for driving piezoelectric transducers. Following the review of amplifier topologies, Peak Current Mode Control (PCMC) based feedback is chosen as a key candidate for voltage boosting amplifiers due to the advantage of achieving wideband along with ease of compensation. A modeling approach is presented that calculates an accurate open loop transfer characteristic for boost converters that employ PCMC. Many techniques exist for modeling a PCMC based boost converter, however all these techniques focus on purely resistive loads and are not always accurate for a purely capacitive load. In this thesis a new modeling technique is presented which is simple and gives accurate results for both capacitive and resistive loads. Furthermore, the useful expressions for DC gain and pole locations of a boost converter operating in Continuous-Conduction Mode (CCM) with PCMC are derived and compare well to simulations and measurements. Furthermore the presented modelling technique is extended by calculating the current-loop transfer characteristic of PCMC based converters running in CCM. The accuracy of the control-to-inductor current transfer is improved for capacitive loads, which is not correctly predicted by previous modeling methods. The resulting model for the control-to-output voltage transfer thus obtained is valid for the major basic converter topologies boost, buck and buck-boost. Finally the design of a high-voltage amplifier for a piezoelectric transducer is presented, which incorporates boosting and signal generation within a single boost converter stage improving the total efficiency of the system. The proposed architecture combines hysteretic ripple current-mode control with an adaptive soft switching technique to achieve improved power efficiency over the full output power range. This is achieved by dynamically controlling the inductor current ripple to keep the converter running in soft switching. The feedback control and the soft switching regulation are implemented in a 0.25µm 60V TSMC process with an external power stage. The system achieves a peak efficiency of 85% at 20W of output power up to 30 kHz signal frequency.