Photonic front-end and comparator processor for a sigma-delta modulator

Abstract

This thesis examines the role of photonics and integrated optics (IO) for use in analog-to-digital conversion in electronic warfare (EW) intercept receivers. The IO approach uses a continuous wave (CW) distributed feedback (DFB) laser diode at a peak wavelength of 1550 nm to oversample two Mach-Zehnder interferometers (MZIs). The MZIs are part of sigma-delta modulator-based analog-to-digital converter (ADC) oversampling architecture. A ring resonator accumulator is embedded within a feedback loop in the modulator to spectrally shape the quantization noise of the system. The experimental and simulation results are evaluated as a narrow-band proof of concept for the use of photonics technology in the sampling of wide-band radio frequency (RF) signals. Taking the characteristics of the real components and the experimental results, a pulse to pulse computer simulation of an oversampled first-order single-bit sigma-delta modulator was accomplished using RSoft OptSim. The performance characteristics of this subsystem were compared with the narrow-band results produced in the laboratory. In addition, a comparator processor circuit for the signal oversampling subsystem was designed and simulated in SIMUCAD SmartSpice. The analysis of the comparator processor circuit was evaluated. The lack of high-speed components limited the experimental and simulation results. With the system integrated with high-speed components, a wide-band direct digital antenna architecture can be demonstrated.