UBC Theses and Dissertations
Integrated silicon bipolar wideband frequency modulation circuits for high-performance analog lightwave transmission Rosales, Roberto
This thesis describes the research done to achieve wideband frequency modulator and demodulator circuits for transmission of analog multi-channel cable television (CATV). These circuits were fabricated in an advanced silicon bipolar technology and resulted in the best-reported fully electronic implementation of a modulator for wideband frequency modulation (WFM) of CATV signals. Design of the modulator is achieved by using an emitter-coupled multivibrator (ECM) based oscillator. The viability of this approach is based on the ECM wideband tuning linearity at high-speed operation, particular noise requirements of CATV transmission, and a novel phase noise reduction technique. Results for an ECM-based current-controlled oscillator (ICO) show linear operation in the range of 1GHz to 2.5GHz. Results for a linearized ECM-based voltage-controlled oscillator (VCO) show linear operation in the range of 1.5GHz to 2GHz. Linearity, from static tuning measurements, show maximum deviations from an ideal linear fit of 15MHz, and 1.5MHz for the ICO and VCO respectively. Results for a wideband delay-line demodulator show linear operation in a range of 2.5GHz, with back-to-back modulator/demodulator modulation bandwidth of 1GHz. A state-of-the art phase noise measurement system, based on automatic data gathering with a spectrum analyzer followed by mathematical post-processing, is presented. This system measures the phase noise of a variable oscillator versus tuning input, at a fixed offset from the carrier, with better accuracy than the best dedicated commercial measurement instrument available at the time. The first study of phase noise in high-speed ECMs is presented from experimental measurements and circuit noise simulations. This study revealed new findings on the fundamental noise limits of ECMs. It was found that, at high frequencies, shot noise of the ECM core transistors dominates oscillator phase noise. Furthermore, phase noise was found to be directly proportional to the ECM tail current and inversely proportional to the square of ECM timing capacitor. This lead to a simple and novel optimization design approach to reduce phase noise by scaling up, by the same factor, the tail current and timing capacitor with minimal effects on tuning linearity. In addition, the modulator perspectives in a narrowcast WFM system are explored through system calculations.
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