General model for delayed feedback and its application to transimpedance amplifier's bandwidth optimization

Delays in real systems can be of two types: i) intrinsic delays - due to the physical principles of operation of each electronic device; ii) designed delays - due to extra circuits used to add the desired delay. Previous work established the possibility of achieving bandwidth improvements using small delays inside the feedback loop of feedback amplifiers. The modeling approach followed on these contributions used only one designed delay element. The bandwidth reduction effect due to intrinsic delays was not considered on these contributions. This paper extends the concept to the general case of feedback amplifiers that incorporates delays of both types. An experimental demonstration using a simple 0.35μm BiCMOS transimpedance amplifier further confirms the proposed model. © 2006 IEEE

A novel readout method for focal plane array imaging in the presence of large dark current

This research was an investigation of a novel readout method for focal plane array (FPA) optical imaging, especially for very sensitive detectors with large dark current. The readout method is based on periodically blocking the optical input enabling the removal of the dark current integration from the output. The research demonstrated that it is feasible to modulate the optical input with the designed readout circuit and thus achieve longer signal integration time to enhance the signal-to-noise ratio. Study of a proposed circuit model showed that in theory the correlated readout method could increase the output voltage swing and reduce the noise level by attenuating low frequency noise, thereby effectively improving the FPA dynamic range. Circuits based on standard CMOS circuitry were designed, simulated by PSpice, fabricated using Orbit 2µm n-well technology, and tested with a PI-4000 system. In the circuit evaluation, the output noise due to the clock switching phenomena, the gate signal feedthrough and the charge relaxation, was considered to be the critical problem. The most promising design for minimizing this problem had a CMOS current steering circuit at the input of a high CMRR operational amplifier. Simulation and test results showed that a modified capacitive transimpedance amplifier (CTIA) could subtract dark current output and reduce the output signal due to any difference between the frequencies of the optical input modulation signal and the switch modulation signal. In conclusion, the correlated readout circuit was shown to be a promising approach for advancing FPA technology

Delay-Line 3D Position Sensitive Radiation Detection

High-resistivity silicon(Si) in large volumes and with good charge carrier transport properties has been produced and achieved success as a radiation detector material over the past few years due to its relatively low cost as well as the availability of well-established processing technologies. One application of that technology is in the fabrication of various position-sensing topologies from which the incident radiation’s direction can be determined. We have succeeded in developing the modeling tools for investigating different position-sensing schemes and used those tools to examine both amplitude-based and time-based methods, an assessment that indicates that fine position-sensing can be achieved with simpler readout designs than are conventionally deployed. This realization can make ubiquitous and inexpensive deployment of special nuclear materials (SNM) detecting technology becomes more feasible because if one can deploy position-sensitive semiconductor detectors with only one or two contacts per side. For this purpose, we have described the delay-line radiation detector and its optimized fabrication. The semiconductor physics were simulated, the results from which guided the fabrication of the guard ring structure and the detector electrode, both of which included metal-field-plates. The measured improvement in the leakage current was confirmed with the fabricated devices, and the structures successfully suppressed soft-breakdown. We also demonstrated that fabricating an asymmetric strip-line structure successfully minimizing the pulse shaping and increases the distance through which one can propagate the information of the deposited charge distribution. With fabricated delay-line detectors we can acquire alpha spectra (Am-241) and gamma spectra (Ba-133, Co-57 and Cd-109). The delay-line detectors can therefore be used to extract the charge information from both ion and gamma-ray interactions. Furthermore, standard charge-sensitive circuits yield high SNR pulses. The detectors and existing electronics can therefore be used to yield imaging instruments for neutron and gamma-rays, in the case of silicon. For CZT, we would prefer to utilize current sensing to be able to clearly isolate the effects of the various charge-transport non-idealities, the full realization of which awaits the fabrication of the custom-designed TIA chip.Ph.D.Nuclear Engineering & Radiological SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/91556/1/mhjeong_1.pd

Development of an integrated microfluidic platform for oxygen sensing and delivery

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005.Includes bibliographical references (p. 115-120).Treatment for end stage lung disease has failed to benefit from advances in medical technology that have produced new treatments for cardiovascular disease, certain cancers, and other major illnesses in recent years. As a result, end stage lung disease remains a devastating condition with few therapeutic options. To address the need for improved methods of respiratory life support, a novel technology was developed capable of generating oxygen directly from water present in blood plasma. This technology is intended to provide a self-contained, mobile oxygen supply suitable for implantation or extracorporeal oxygenation in support of an acute or chronically disabled lung. The core technology couples an optoelectronic metal oxide film with a microfluidic capillary network to facilitate oxygen exchange with flowing blood and replicate pulmonary capillary respiration. This thesis focuses on the optimization of this microfluidic capillary network with respect to hemocompatibility, mass transfer, and dissolved oxygen detection. Microfluidic capillary devices were fabricated from silicone rubber using multilayer soft lithography to create dense 2D networks of bifurcating channels. To quantify the effectiveness of mass transfer in various channel geometries under differing experimental conditions, a mathematical model of oxygen convection and diffusion was generated. A novel integrated optical oxygen sensor based on an oxygen-quenched luminescent dye was developed to detect oxygen concentrations within the microfluidic device. Mass transfer within the microfluidic oxygenator was characterized experimentally, employing the integrated optical sensor, and analytically, using the convective model.(cont.) Excellent agreement was found between experimental and analytical results. We conclude that the microfluidic platform achieves rapid and efficient diffusion of oxygen into a liquid medium, effectively mimicking the function of the pulmonary system. The combination of precise oxygen delivery and detection, integrated into a miniature device, is widely applicable both to the photolytic artificial lung and to a broader class of applications related to detection of chemical species in biological microdevices.by Adam P. Vollmer.S.M

Ultra-Low Phase Noise Atomic Clock using Coherent Population Trapping (CPT) in Rubidium

This thesis describes the design and implementation of a complete atomic clock system from first principles. The system is based on Coherent Population Trapping (CPT) in 85Rb and incorporates an ultra-low phase noise multi-element local oscillator, consisting of a 10MHz crystal oscillator and 1.5GHz Dielectric Resonator Oscillator (DRO) in a phase locked configuration. It is shown that the crystal oscillator can achieve excellent close to carrier phase noise performance of -122dBc/Hz at 1Hz offset and -147.7dBc/Hz at 10Hz offset, as well as Allan deviation of 3×10^(-13) at 100ms averaging time. The DRO exhibits excellent medium offset and far from carrier performance with a noise floor of about -180dBc/Hz. When phase locked to the crystal oscillator, the phase noise at 1Hz is shown to approach that of the crystal oscillator (scaled up to 1.5GHz). A frequency synthesis chain, incorporating a Direct Digital Synthesizer (DDS), low noise digital divider, single sideband mixer and notch filter is used to upconvert the 1.5GHz local oscillator frequency to the ground state hyperfine splitting frequency of 85Rb (1.5178GHz). The DDS is controlled by a microcontroller and used to produce an offset frequency of 17.8MHz, which can be tuned, modulated or swept. The single sideband mixer is used to mix the 1.5GHz and 17.8MHz signals and suppress the lower sideband of the output. The notch filter is used to further suppress the LO feedthrough of the mixer by another >30dB. A Rb CPT physics package incorporates a vertical cavity surface-emitting laser, which is modulated by the output of the synthesizer and used to interrogate the atomic resonance in a 85Rb vapour cell. The package was built with custom made optical mounts, low noise laser driving electronics and temperature control loops. The parameters affecting the shape, amplitude and stability of the atomic resonance were experimentally investigated and the construction of the physics package was adjusted for the optimal conditions. A digital frequency locked loop is used to lock the local oscillator to the atomic resonance and the performance of the full system is tested

Performance Evaluation of Raman Amplifiers in Fibre Optic Communication Systems

This thesis presents an overview of Raman amplifiers in fibre optic transmission systems. Detailed analysis of the nonlinear accumulated noise and relative intensity noise (RIN) induced penalties are evaluated in discrete and distributed Raman amplifiers. In addition to these the thesis also includes different architectures of Raman amplifiers enabling multiband transmission. The parametric dependency of fibre chromatic dispersion (CD) on the accumulated nonlinear noise in discrete Raman amplifiers (DRAs) was studied both theoretically and experimentally. Analytical modelling was performed over different fibre types that are widely used as a gain medium in DRAs. It was found that systems using Raman gain fibres with a positive value of CD induce lower accumulated nonlinear noise in comparison to systems using Raman gain fibres with a negative value of CD. The results obtained from the analytical model were then validated experimentally over a long-haul transmission system with DRAs as an inline amplifier using a recirculation loop. RIN-induced penalties in distributed Raman amplifiers (DiRAs) were experimentally studied in two standard single-mode fibre (SSMF) G.654.E©TXF and G.652.D with different pumping schemes. Signal RIN for G.654.E© TXF was found to be lower in comparison to its counterpart G.652.D. The impact of RIN on the short-haul system was validated using both the test fibres pumped in a forward-pumped distributed Raman. Similarly, backward and bidirectional pumping was performed over a long-haul transmission system using a recirculation loop. It was experimentally observed that RIN-induced transmission penalties for G.654.E are lower in comparison to G.652.D making it a better choice of SSMF type for distributed amplification. Experiments on novel architectures such as cascaded dual-stage and dual-band designs were demonstrated over a coherent transmission system with S-, C- and L-band signals. It was observed that the dual-stage design requires a guard band of ~10 nm to prevent overlapping of the pumps and signal, reducing the overall transmission capacity. In contrast, for dual-band design, no such guard band was required, but this benefit comes at a cost of the additional pump requirement increasing the overall amplifier power consumption. The performances of novel multistage Raman amplifier structures were also evaluated over the E-, S-, C- and L-band. Experimental studies were performed independently using DRAs only, hybrid bismuth-DRA and hybrid distributed-DRA. The E- and S-band signals were seen to have higher performance penalties in comparison to C- and L-band signals in the case of DRAs only and hybrid bismuth-DRA. In contrast, for the hybrid distributed-discrete design, the E-band signals were seen to have a similar penalty as C- and L-band signals