Berlin, Techn. Univ., Diss., 2003. / Computerdatei im Fernzugriff.

Berlin, Techn. Univ., Diss., 2003. / Computerdatei im Fernzugriff.

Comprehensive two-dimensional gas chromatography (GC×GC) is among the most powerful methods used to separate complex samples. Two columns of different selectivities are coupled in series through a special interface (modulator). The main role of the modulator is to trap and/or sample the primary column effluent and inject it into the secondary column. This results in an enhanced sensitivity, increased peak capacity and structured chromatograms. Practically all thermal modulators in use today are equipped with two trapping stages to prevent problems related to analyte breakthrough, which makes their design more complicated. In this work, The sensitivity of GC×GC coupled to two different detectors, time-of-flight mass spectrometer (GC×GC-TOFMS) and flame ionization detector (GC×GC-FID) was compared to the sensitivity of conventional one-dimensional gas chromatography (GC-TOFMS and GC-FID) by determining the limits of detection (LOD) for a series of different compounds such as n-alkanes and alcohols using both approaches. Different modulation periods were used for GC×GC ranging from 2 to 8 seconds. In addition, different types of inlet ferrules were used to study their effect on both systems. In general, the LODs in GC×GC were lower by at least an order of magnitude. A new liquid nitrogen-based single-stage cryogenic modulator was developed and characterized. In addition, a new liquid nitrogen delivery system was developed. Band breakthrough was prevented using changes in the carrier gas viscosity with temperature to reduce the carrier gas flow during desorption. Injection band widths for n-alkanes of 30-40 ms at half height were obtained. Most importantly, even the solvent peak could be perfectly modulated, which is impossible with any commercially available thermal modulator. Moreover, the newly developed liquid nitrogen supply system reduced liquid nitrogen consumption to ~30 L per day versus 50-100 L per day for commercially available modulators. Evaluation of the newly developed system for the GC×GC separation of some real samples such as regular gasoline and diesel fuel showed that the analytical performance of this single-stage modulator rivals that of the more complicated dual-stage designs. The technique was tested in various applications. Headspace solid phase microextraction in combination with GC×GC coupled to time-of-flight mass spectrometry (HS-SPME-GC×GC-TOFMS) were used for the detailed investigation of the impact of malolactic fermentation (MLF) using three commercial Oenococcus oeni strains on the volatile composition of Pinotage wines. The technique was also applied for the characterization of Pinotage wine volatiles and blue honeysuckle berries volatiles.

Analog-to-digital (A/D) and digital-to-analog (D/A) converters are important blocks in signal processing system because they provide the link between the analog world and digital systems. Compared with Nyquist-rate data converters, oversampling data converters are more desirable for modern submicron technologies with low voltage supplies. Today, all existing oversampling modulators in popular use are derived from sigma-delta modulation. Stability is the most significant problem in the sigma-delta modulator, because the ultimate accuracy is limited by stability. As the aggressiveness of the design increases, the margin of stability diminishes rapidly. This thesis presents the design and experimental results of the first prototype circuit implementation of the novel oversampling modulation scheme proposed by Dr. Takis Zourntos. This new class of oversampling modulators are theoretically stable. With less stability limitation, the new class of modulators can potentially achieve higher signal-to-noise ratio (SNR) or less power by designing the modulator more aggressively. This thesis describes the methods and procedures of how the new oversampling modulation theory is implemented into a circuit. Some novel circuit architectures are proposed in this modulator, such as a filter which can provide status outputs for the controller and realize arbitrary zeros and poles, comparators with synchronization latches to eliminate the effect of metastability, and a digital-to-analog converter (DAC) with current calibration circuits for high linearity. A third-order continuous-time oversampling modulator employing 4-bit quantization is implemented in a 0.35-µm double-poly complementary metal oxide semiconductor (CMOS) technology, with a chip area of 2150 × 2150 µm2. Simulation results show it achieves 83.7-dB peak SQNR, 90-dB dynamic range over a 500kHz input signal bandwidth, and 60 mW power consumption.

Comprehensive two-dimensional gas chromatography (GC×GC) is among the most powerful methods used to separate complex samples. Two columns of different selectivities are coupled in series through a special interface (modulator). The main role of the modulator is to trap and/or sample the primary column effluent and inject it into the secondary column. This results in an enhanced sensitivity, increased peak capacity and structured chromatograms. Practically all thermal modulators in use today are equipped with two trapping stages to prevent problems related to analyte breakthrough, which makes their design more complicated. In this work, The sensitivity of GC×GC coupled to two different detectors, time-of-flight mass spectrometer (GC×GC-TOFMS) and flame ionization detector (GC×GC-FID) was compared to the sensitivity of conventional one-dimensional gas chromatography (GC-TOFMS and GC-FID) by determining the limits of detection (LOD) for a series of different compounds such as n-alkanes and alcohols using both approaches. Different modulation periods were used for GC×GC ranging from 2 to 8 seconds. In addition, different types of inlet ferrules were used to study their effect on both systems. In general, the LODs in GC×GC were lower by at least an order of magnitude. A new liquid nitrogen-based single-stage cryogenic modulator was developed and characterized. In addition, a new liquid nitrogen delivery system was developed. Band breakthrough was prevented using changes in the carrier gas viscosity with temperature to reduce the carrier gas flow during desorption. Injection band widths for n-alkanes of 30-40 ms at half height were obtained. Most importantly, even the solvent peak could be perfectly modulated, which is impossible with any commercially available thermal modulator. Moreover, the newly developed liquid nitrogen supply system reduced liquid nitrogen consumption to ~30 L per day versus 50-100 L per day for commercially available modulators. Evaluation of the newly developed system for the GC×GC separation of some real samples such as regular gasoline and diesel fuel showed that the analytical performance of this single-stage modulator rivals that of the more complicated dual-stage designs. The technique was tested in various applications. Headspace solid phase microextraction in combination with GC×GC coupled to time-of-flight mass spectrometry (HS-SPME-GC×GC-TOFMS) were used for the detailed investigation of the impact of malolactic fermentation (MLF) using three commercial Oenococcus oeni strains on the volatile composition of Pinotage wines. The technique was also applied for the characterization of Pinotage wine volatiles and blue honeysuckle berries volatiles.

No description available.

The recent and rapid growth of silicon photonics is driven by the ever-increasing demand for bandwidth inside and between data centres. Silicon photonics can offer an unparalleled performance in terms of scalability and power consumption with low-cost fabrication through the leveraging of CMOS fabrication techniques. This thesis describes research on the silicon micro-ring resonator modulator, a device which combines energy-efficiency with a compact footprint that is ideal for data centre applications. Both theoretical and experimental work is described in the context of improving the reachability, capacity and stability of the silicon micro-ring resonator modulator for inter/intra-data centre communication. Chapter 2 presents modeling work using MATLAB® that provides predictive results for both device-level and system-level performance. Chapter 3 studies the chirp characteristic of an over-coupled silicon micro-ring resonator modulator and its capability of generating a negative-chirp modulation. The resulting chirp-induced power penalty is measured to be as low as 2.5 dB after 100 km transmission. Chapter 4 focuses on the advanced modulation techniques that can be efficiently exploited for increasing the spectral efficiency in the typically band-limited system. A record single-polarization 104 Gb/s data rate per wavelength (direct-detect) was achieved by using digital signal processing to alleviate the modulation deficiencies that are specific to the silicon micro-ring resonator modulator. In Chapter 5, a generic resonance control method using intrinsic defect-mediated photocurrent is described and experimentally demonstrated to provide stability for the silicon micro-ring resonator modulator during high-speed operation. This control method can also lead to an “all-silicon” system without the need for power detection using germanium. / Thesis / Doctor of Philosophy (PhD)

This dissertation studies a unique delta sigma modulator (DSM), known as reversed hysteresis delta sigma modulator (R-HDSM). This modulator is appropriate for ultra-high speed analog-to-digital converters, which can be used for communications and signal processing systems and their applications. Furthermore, the procedure to design the binary delta sigma modulator (BDSM) with a delay is developed and then parameters deltaOFF and deltaON ; are calculated for the system. In addition, analysis of the BDSM with a delay is achieved and the theoretical and simulated values compared. The reversed hysteresis delta sigma modulators are also analyzed, and the theoretical and the simulated values compared. The dissertation evaluates the performance measure for the suggested systems with continuous DSM and BDSM in terms of the spurious free dynamic range (SFDR), the signal to noise ratio (SNR), and the root mean square error (RMS). It studies the second-order R-HDSM. Finally, it compares the first-order R- HDSM and the second-order R-HDSM in terms of the signal to noise ratio (SNR).

No description available.

The ever advance of CMOS digital circuit process leads tothe trend of digitizing an analog signal and performing digitalsignal processing as early as possible in a signal processingsystem, which in turn leads to an increasing requirement onanalog- to-digital converter (ADC). A wireless transceiver is asuch kind of signal processing system. Conventionaltransceivers manipulate (filter, amplify and mix) the signalmostly in analog domain. Since analog filters are difficult todesign onchip, the system integration level is low. Moderntransceivers shift many of these tasks to digital domain, wherethe filtering and channel selection can be realized moreaccurately and more compactly. However the price for the highintegration level is the critical requirement on the ADC,because the simplified analog part sends not only the weaksignal but also the unwanted strong neighboring channel to theADC. In order to digitize the needed signal in the presence ofstrong disturbances, a high dynamic-range and high-speed ADC isneeded. Sigma Delta ADCs are promising candidates for A/D conversionin modern wireless transceivers. They are naturally suitablefor high-resolution narrow-band A/D conversions. With thedevelopment of processing and design techniques, sigma deltaADCs are expanding their applications to moderate-band area,such as wireless communication baseband processing. Currentlymobile communication systems are migrating from 2G to 3G. In 2Gsystems the baseband width is in the order of hundred kHz,while in 3G systems the baseband width is in the order of MHz.To face the challenge of designing a high resolution sigmadelta ADC with large bandwidth, a multi-bit internal quantizeris often used. In this thesis special design considerations onmulti-bit sigma delta modulators are discussed. The biggestdrawback of multi-bit sigma delta modulators isthe need of anextra circuit to attenuate or compensate the internal multi-bitDAC non-linearity. This thesis provides a comprehensiveanalysis of the solution which combines a multi-bit quantizerwith a 1-bit DAC in a sigma delta modulator. The theoreticalanalysis result is verified by measurement results. Anothertopic addressed in the thesis is how to reduce the multi-bitquantizer complexity. It is shown that by using a semiuniformquantizer, the quantizer can reduce its complexity by one-bityet still maintain the same modulator dynamic range. Theperformance of the semi-uniform quantizer is also verified bymeasurement results.