Integrated optical sigma-delta modulators
Ying, Stephen J.
Pace, Phillip E.
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Modern avionics equipment, such as super resolution direction-finding systems, now require resolutions on the order of 20 to 22 bits. Oversampled analog-to-digital converter architectures offer a means of exchanging resolution in time for that in amplitude and represent an attractive approach to implementing precision converters without the need for complex precision analog circuits. Using oversampling techniques based on sigma-delta modulation, a convenient tradeoff exists between sampling rate and resolution. One of the major advantages of integrated optics is the capability to efficiently couple wideband signals into the optical domain. Typically, sigma-delta processors require simple and relatively low-precision analog components and thus are well suited to integrated optical implementations. This thesis reviews the current sigma-delta methodology, the advantages of optical integrated circuits and presents the design of a second-order, integrated optical sigma-delta modulator. Simulation results for both a first and second order architecture are presented by evaluating the transfer characteristics numerically. Design parameters such as limit cycles are quantified and explained. Performance issues and future efforts are also considered.
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