Silicon carbide (SiC) integrated circuits (ICs) can enable the emergence of robust and reliable systems, including data acquisition and on-site control for extreme environments with high temperature and high radiation such as deep earth drilling, space and aviation, electric and hybrid vehicles, and combustion engines. In particular, SiC ICs provide significant benefit by reducing power dissipation and leakage current at temperatures above 300 °C compared to the Si counterpart. In fact, Si-based ICs have a limited maximum operating temperature which is around 300 °C for silicon on insulator (SOI). Owing to its superior material properties such as wide bandgap, three times larger than Silicon, and low intrinsic carrier concentration, SiC is an excellent candidate for high-temperature applications. In this thesis, analog and mixed-signal circuits have been implemented using SiC bipolar technology, including bandgap references, amplifiers, a master-slave comparator, an 8-bit R-2R ladder-based digital-to-analog converter (DAC), a 4-bit flash analog-to-digital converter (ADC), and a 10-bit successive-approximation-register (SAR) ADC. Spice models were developed at binned temperature points from room temperature to 500 °C, to simulate and predict the circuits’ behavior with temperature variation. The high-temperature performance of the fabricated chips has been investigated and verified over a wide temperature range from 25 °C to 500 °C. A stable gain of 39 dB was measured in the temperature range from 25 °C up to 500 °C for the inverting operational amplifier with ideal closed-loop gain of 40 dB. Although the circuit design in an immature SiC bipolar technology is challenging due to the low current gain of the transistors and lack of complete AC models, various circuit techniques have been applied to mitigate these problems. This thesis details the challenges faced and methods employed for device modeling, integrated circuit design, layout implementation and finally performance verification using on-wafer characterization of the fabricated SiC ICs over a wide temperature range. / <p>QC 20170905</p>

This research looks into the design of an integrated in-phase/quadrature (I/Q) VCO operating at 5 GHz. The goal is to design a phase shifter that is implemented at the LO used for RF up conversion. The target application for the phase shifter is towards phased array antennas operating at 5 GHz. Instead of designing multiple VCOs that each deliver a variety of phases, two identical LC-VCOs are coupled together to oscillate at the same frequency and deliver four outputs that are 90 ° out of phase. By varying the amplitudes of the in-phase and quadrature signals independently using VGAs before adding them together, a resultant out-of-phase signal is obtained. A number of independently variable out-of-phase signals can be obtained from these 90 ° out-of-phase signals and this technique is better known as the vector sum method of phase shifting. Control signals to the inputs of the VGAs required to obtain 22.5 ° phase shifts were designed from simulations and are generated using 16-bit DACs. The design is implemented and manufactured using a 0.35 µm SiGe BiCMOS process and the complete prototype IC occupies an area of 2.65 × 2.65 mm2. The I/Q VCO with 360 ° variable phase outputs occupies 1.10 × 0.85 mm2 of chip area and the 16-bit DAC along with its decoding circuitry occupies 0.41 × 0.13 mm2 of chip area. The manufactured quadrature VCO was found to oscillate between 4.12 ~ 4.74 GHz and consumes 23.1 mW from a 3.3 V supply without its buffer circuitry. A maximum phase noise of -78.5 dBc / Hz at a 100 kHz offset and -108.17 dBc / Hz at a 1 MHz offset was measured and the minimum VCO figure of merit is 157.8 dBc / Hz. The output voltages of the 16 bit DAC are within 3.5 % of the design specifications. When the phase shifter is controlled by the 16 DAC signals, the maximum measured phase error of the phase shifter is lower than 10 %. / Dissertation (MEng)--University of Pretoria, 2009. / Electrical, Electronic and Computer Engineering / unrestricted