Sigma-delta analog-to-digital converters are gaining in popularity in recent times because of their ability to trade-off resolutions in the time and voltage domains. In particular, continuous-time modulators are finding more acceptance at higher bandwidths due to the additional advantages they provide, such as better power efficiency and inherent anti-aliasing filtering, compared to their discrete-time counterparts. This thesis work presents the system level design of a continuous-time low-pass sigma-delta modulator targeting 11 bits of resolution over 100MHz signal bandwidth. The design considerations and tradeoffs involved at the system level are presented. The individual building blocks in the modulators are modeled with non-idealities and specifications for the various blocks are obtained in detail. Simulation results obtained from behavioral models of the system in MATLAB and Cadence environment show that a signal-to-noise-and-distortion-ratio (SNDR) of 69.6dB is achieved. A loop filter composed of passive LC sections is utilized in place of integrators or resonators used in traditional modulator implementations. Gain in the forward signal path is realized using active circuits based on simple transconductance stages. A novel method to compensate for excess delay in the loop without using an extra summing amplifier is proposed.

Sigma-delta analog-to-digital converters are gaining in popularity in recent times because of their ability to trade-off resolutions in the time and voltage domains. In particular, continuous-time modulators are finding more acceptance at higher bandwidths due to the additional advantages they provide, such as better power efficiency and inherent anti-aliasing filtering, compared to their discrete-time counterparts. This thesis work presents the system level design of a continuous-time low-pass sigma-delta modulator targeting 11 bits of resolution over 100MHz signal bandwidth. The design considerations and tradeoffs involved at the system level are presented. The individual building blocks in the modulators are modeled with non-idealities and specifications for the various blocks are obtained in detail. Simulation results obtained from behavioral models of the system in MATLAB and Cadence environment show that a signal-to-noise-and-distortion-ratio (SNDR) of 69.6dB is achieved. A loop filter composed of passive LC sections is utilized in place of integrators or resonators used in traditional modulator implementations. Gain in the forward signal path is realized using active circuits based on simple transconductance stages. A novel method to compensate for excess delay in the loop without using an extra summing amplifier is proposed.

An approach with ¡§consecutive orthogonal arrays (COA)¡¨ is proposed for solving the problems in designing power electronic circuits. This approach is conceptually based on the orthogonal array method, which has been successfully implemented in quality engineering. The circuit parameters to be determined are assigned as the controlled variables of the orthogonal arrays. Incorporating with the inferential rules, the average effects of each control variable levels are used as the indices to determine the control variable levels of the subsequent orthogonal array. By manipulating on COA, circuit parameters with the desired circuit performances can be found from an effectively reduced number of numerical calculations or experimental tests. In this dissertation, the method with COA is implemented on solving four problems often encountered in the design of power electronic circuits. The first problem one has to deal with is to find a combination with the best performance from a great number of analyzed results. The illustrative example is the design of LC passive filters. Using COA method, the desired component values of the filter can be effectively and efficiently found with far fewer calculations. The second design problem arises from the non-linearity of circuit. An experienced engineer may be able to figure out circuit parameters with satisfactory performance based on their pre-knowledge on the circuit. Nevertheless, they are always questioned whether a better choice can be made. The typical case is the self-excited resonant electronic ballast with the non-linear characteristics of the saturated transformer and the power transistor storage-time. In this case, the average effects of COA obtained from experimental tests are used as the observational indexes to search a combination of circuit parameters for the desired lamp power. The third problem is that circuit functions are mutually exclusive. The designers are greatly perplexed to decide the circuit parameters, with which all functions should be met at the same time. The method with COA is applied to design a filter circuit to achieve the goals of low EMI noise and high power factor simultaneously. Finally, one has to cope with the effects of the uncontrolled variables, such as: ambient temperature, divergence among different manufacturers, and used hours. By applying COA with inferential rules, electronic ballasts can be robustly designed to operate fluorescent lamps at satisfied performance under the influence of these uncontrolled variables.