@phdthesis{Apte2020, author = {Apte, Anisha}, title = {A new analytical design method of ultra-low-noise voltage controlled VHF crystal oscillators and it's validation}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-51386}, school = {BTU Cottbus - Senftenberg}, year = {2020}, abstract = {The design of high Q oscillators, using Crystals at lower frequencies, (and dielectric resonators at much higher frequencies), has long been considered a black art. This may be due to the fact that a systematic approach with optimized design guideline for crystal oscillators could not be found after extensive literature search. In this dissertation, after analyzing the first crystal oscillator by W.G. Cady (1921), other high performance crystal oscillators will be discussed, analyzed and calculated. A single transistor crystal oscillator design as used by HP (Hewlett Packard) in one of their designs, the HP10811A is considered in this thesis for mathematical analysis and CAD (Computer aided Design) simulation. This was also measured on state-of-the-art signal source analyzer. After validation, this design is scaled to 100MHz, the frequency of interest for this dissertation. Though most designers use a single transistor based oscillator circuit, it is not an optimized design because of limited control over key design parameters such as loop gain, dc current etc. This dissertation is an attempt to overcome the limitation due to the single transistor circuit and to give a step by step procedure, explaining the significance of a two transistor design with thorough analysis and design simulation results. This two stage transistor circuit is also not yet a best solution in terms of phase noise performance and output power, and some add-on circuitry will be needed for an optimized performance. An important contribution of this work is to show that since the voltage gain is the ratio of the collector resistor and the emitter resistor, the performance is practically independent of the VHF transistor and gives better control over various parameters of the oscillator, in order to optimize the design. A grounded-base amplifier is then introduced and added for improving the isolation and the output power. Unlike most oscillators, that take the output from the collector, a novel concept introduced by Rohde [14], is incorporated here, where the crystal is used as a filter that is then connected to the grounded base amplifier, a technique which many companies have been using. This dissertation will show that this technique increases the output power without significantly affecting the phase noise. Such a validation is needed for better understanding and as per my knowledge, has not been done so far. For the oscillator, the tuning diode sensitivity and flicker noise contribution are also taken into consideration, by calibrating the mathematics and its validation is shown. Crystal resonators of the type AT and stress-compensated (SC) cut devices will be considered as they give the best performance. The one port Colpitts type oscillator is considered first and the two port two transistor design later. Both will need a post amplifier/buffer stage. A complete step by step design procedure for an optimized 100MHz crystal oscillator is then presented. For completeness, CAD Simulation and Experimental results are provided for 10 MHz, 128 MHz and 155 MHz VCO circuits.}, subject = {Quartz crystal; Crystal oscillator; Phase noise; Reference source; Voltage controlled; Quarzkristall; Kristalloszillator; Phasenrauschen; Referenzquelle; Spannungsgesteuert; Quarzoszillator; UKW; CAD}, language = {en} } @phdthesis{Fleischmann2022, author = {Fleischmann, Manfred}, title = {A novel technique to improve the spurious-free dynamic range of digital spectrum monitoring receivers}, doi = {10.26127/BTUOpen-5898}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-58984}, school = {BTU Cottbus - Senftenberg}, year = {2022}, abstract = {This dissertation presents a novel technique for enhancing the spurious-free dynamic range of radio monitoring receivers with a bandwidth of several gigahertz. The improvement is based on suppressing the discrete spurious signals that occur at higher drive levels in the output spectrum of the required broadband analog-to-digital converter. The achievable improvement of the spurious-free dynamic range is typically more than 20 dB, allowing better, gap-free monitoring of wide frequency ranges. The attenuation of the spurious signals is achieved by a unique combination of two separate analog-to-digital converters working in parallel and subsequent digital signal processing. The developed solution is not limited to broadband radio monitoring receivers but can generally suppress certain types of spurious signals generated during analog-to-digital conversion.}, subject = {Broadband receiver; Spurious signals; Analog-to-digital converter; Spurious-free dynamic range; Digital signal processing; Breitbandempf{\"a}nger; St{\"o}rsignale; Analog-digital-Wandler; St{\"o}rungsfreier Dynamikbereich; Digitale Signalverarbeitung; Analog-Digital-Umsetzer; Breitbandempf{\"a}nger; Digitale Signalverarbeitung; St{\"o}rsignal}, language = {en} }