DYNAMIC DAMPING IN OPTICAL RECEIVERS

Today's telecommunications involves ever-increasing amounts of optical communication. Besides being an important component of the long-haul network, optical communications are also being used in data centers, circuit boards, integrated circuits, and the next generation of mobile networks. This thesis proposes an optical receiver in which the damping factor of both the transimpedance and post amplifiers is modulated synchronously with incoming data. Modulation of the damping factor allows the fast response of the low-damping factor while mitigating the intersymbol interference (ISI) associated with underdamped systems. To investigate the modulated damping shunt-feedback transimpedance amplifier (SF-TIA), some methods, including switching the feedback resistor and modulating the damping factor by a sine wave, are used. Due to damping factor value limitation by changing the shunt-feedback and complexity of producing appropriate value of the sine wave with proper DC offset, amplitude and phase, damping factor modulation by a rail-to-rail square wave signal is presented where only phase adjustment is necessary and has better noise performance, Vertical Eye Opening (VEO) gain and gain to power ratio. The extension of dynamic damping to the post amplifier is investigated through simulation at 10 Gb/s. A shunt-feedback TIA with cross-coupled inverters at the output, optimized to reach minimum input-referred noise is used as a reference for creating SF-TIA and Cherry-Hooper post-amplifier (CH-PA) blocks. By modulating the damping factor in both blocks, the proposed system achieves more than three times the VEO and lower input-referred noise compared to the optimized reference. Alternatively, an equal-gain modulated system has 40 % lower power consumption compared to the reference design

Serial control of phonology in speech production

The aim of this thesis is to further our understanding of the processes which control the sequencing of phonemes as we speak: this is an example of what is commonly known as the serial order problem. Such a process is apparent in normal speech and also from the existence of a class of speech errors known as sound movement errors, where sounds are anticipated (spoken too soon), perseverated (repeated again later), or exchanged (the sounds are transposed). I argue that this process is temporally governed, that is, the serial ordering mechanism is restricted to processing sounds that are close together in time. This is in conflict with frame-based accounts (e.g. Dell, 1986; Lapointe & Dell, 1979), serial buffer accounts (Shattuck-Hufnagel, 1979) and associative chaining theories (Wickelgren, 1969). An analysis of sound movement errors from Harley and MacAndrew's (1995) corpus shows how temporal processing bears on the production of speech sounds by the temporal constraint observed in the pattern of errors, and I suggest an appropriate computational model of this process. Specifically, I show how parallel temporal processing in an oscillator-based model can account for the movement of sounds in speech. Similar predictions were made by the model to the pattern of movement errors actually observed in speech error corpora. This has been demonstrated without recourse to an assumption of frame and slot structures. The OSCillator-based Associative REcall (OSCAR) model, on the other hand, is able to account for these effects and other positional effects, providing support for a temporal based theory of serial control