Frequency and intensity noise are characterized for Erbium-Doped Fiber and Brillouin random lasers based on Rayleigh distributed feedback mechanism. We propose a theoretical model for the frequency noise of an Er-doped fiber random lasers using the property of random phase modulations from multiple scattering points in ultra-long fibers. We find that the Rayleigh feedback suppresses the noise at higher frequencies by introducing a Lorentzian envelope over the thermal frequency noise of a long fiber cavity. The theoretical model and measured frequency noise agree quantitatively with two fitting parameters. A similar model, which also includes additional acoustic fluctuations and a distributed gain profile in the fiber, has been speculated for the Brillouin random laser. These random laser exhibits a frequency noise level of < 6 Hz^2/Hz at 2 kHz, which is lower than what is found in conventional narrow-linewidth EDF fiber lasers and Nonplanar Ring Laser oscillators (NPRO) by a factor of 166 and 2 respectively.

<p> This thesis focuses on the noise model verification at both device and circuit levels using circuit simulators. The techniques and procedures developed in this thesis are general and can be applied to any proposed RF noise model equations. To fulfil the two tasks, three main topics have been accomplished. First, a general noise source implementation method has been presented in detail in this thesis and is verified with measurements for both long and short-channel MOSFETs. This method provides a simple and effective way to implement the enhanced channel noise and induced gate noise of MOSFETs without increasing the simulation complexity for the simulators.</p> <p> Second, a systematic procedure to refine the model parameters used in noise calculation is presented. For a model to accurately predict the HF noise characteristics, the accuracy in the prediction of both DC and AC characteristics has to be ensured. The procedure proposed in this thesis provides both DC and AC model parameter verification and optimization for RF noise simulation purpose.</p> <p> Third, as for benchmark circuits to verify noise model at the circuit level, two LNA designs are proposed in the thesis. The first design gives the emphasis on the noise reduction technique and the LNA design procedure. The proposed noise reduction technique gives circuit designers more control on noise figure minimization through noise matching. The second design is used to experimentally verify the noise model at the circuit level.</p> / Thesis / Master of Applied Science (MASc)

Hydrogenated amorphous silicon thin-film transistors (a-Si:H TFTs) are used as charge switches in flat-panel X-ray detectors. The inherent noise in the TFTs contributes to the overall noise figure of the detectors and degrades the image quality. Measurements of the noise provide an important parameter for modeling the performance of the detectors and are a sensitive diagnostic tool for device quality. Furthermore, understanding the origins of the noise could lead to change a method of a-Si:H deposition resulting in a reduction of the noise level. This thesis contains measurements of the low-frequency noise in a-Si:H TFTs with an inverted staggered structure. The noise power density spectrum fits well to a power law with Ñ near one. The normalized noise power is inversely proportional to gate voltage and also inversely proportional to channel length in both the linear and saturation regions. The noise is nearly independent of the drain-source voltage and drain-source current. The noise is unaffected by degrading the amorphous silicon through gate-biasing stress. Hooge¡¦s parameter is in the range 1-2*E-3 or 2-4*E-4 depending on whether the parameter is calculated using the total number of charge carriers in the accumulation layer or just the number of free carriers. As an example, the signal to noise ratio is calculated for photodiode detector gated by a TFT using the results from the noise measurements.

Hydrogenated amorphous silicon thin-film transistors (a-Si:H TFTs) are used as charge switches in flat-panel X-ray detectors. The inherent noise in the TFTs contributes to the overall noise figure of the detectors and degrades the image quality. Measurements of the noise provide an important parameter for modeling the performance of the detectors and are a sensitive diagnostic tool for device quality. Furthermore, understanding the origins of the noise could lead to change a method of a-Si:H deposition resulting in a reduction of the noise level. This thesis contains measurements of the low-frequency noise in a-Si:H TFTs with an inverted staggered structure. The noise power density spectrum fits well to a power law with Ñ near one. The normalized noise power is inversely proportional to gate voltage and also inversely proportional to channel length in both the linear and saturation regions. The noise is nearly independent of the drain-source voltage and drain-source current. The noise is unaffected by degrading the amorphous silicon through gate-biasing stress. Hooge¡¦s parameter is in the range 1-2*E-3 or 2-4*E-4 depending on whether the parameter is calculated using the total number of charge carriers in the accumulation layer or just the number of free carriers. As an example, the signal to noise ratio is calculated for photodiode detector gated by a TFT using the results from the noise measurements.

No description available.

No description available.

O ruído de baixa frequência é um limitador de desempenho em circuitos analógicos, digitais e de radiofrequência, introduzindo ruído de fase em osciladores e reduzindo a estabilidade de células SRAM, por exemplo. Transistores de efeito de campo de metalóxido- semicondutor (MOSFETs) são conhecidos pelos elevados níveis de ruído 1= f e telegráfico, cuja potência pode ser ordens de magnitude maior do que a observada para ruído térmico para frequências de até dezenas de kHz. Além disso, com o avanço da tecnologia, a frequência de corner —isto é, a frequência na qual as contribuições dos ruídos térmico e shot superam a contribuição do ruído 1= f — aumenta, tornando os ruídos 1= f e telegráfico os mecanismos dominantes de ruído na tecnologia CMOS para frequências de até centenas de MHz. Mais ainda, o ruído de baixa frequência em transistores nanométricos pode variar significativamente de dispositivo para dispositivo, o que torna a variabilidade de ruído um aspecto importante para tecnologias MOS modernas. Para assegurar o projeto adequado de circuitos do ponto de vista de ruído, é necessário, portanto, identificar os mecanismos fundamentais responsáveis pelo ruído de baixa frequência em MOSFETs e desenvolver modelos capazes de considerar as dependências do ruído com geometria, polarização e temperatura. Neste trabalho é proposta uma técnica para análise de ruído de baixa frequência baseada na autocorrelação dos espectros de ruído em função de parâmetros como frequência, polarização e temperatura. A metodologia apresentada revela informações importantes sobre os mecanismos responsáveis pelo ruído 1= f que são difíceis de obter de outras formas. As análises de correlação realizadas em três tecnologias CMOS comerciais (140 nm, 65 nm e 45 nm) fornecem evidências contundentes de que o ruído de baixa frequência em transistores MOS tipo-n e tipo-p é composto por um somatório de sinais telegráficos termicamente ativados. / Low-frequency noise (LFN) is a performance limiter for analog, digital and RF circuits, introducing phase noise in oscillators and reducing the stability of SRAM cells, for example. Metal-oxide-semiconductor field-effect-transistors (MOSFETs) are known for their particularly high 1= f and random telegraph noise levels, whose power may be orders of magnitude larger than thermal noise for frequencies up to dozens of kHz. With the technology scaling, the corner frequency — i.e. the frequency at which the contributions of thermal and shot noises to noise power overshadow that of the 1= f noise — is increased, making 1= f and random telegraph signal (RTS) the dominant noise mechanism in CMOS technologies for frequencies up to several MHz. Additionally, the LFN levels from device-to-device can vary several orders of magnitude in deeply-scaled devices, making LFN variability a major concern in advanced MOS technologies. Therefore, to assure proper circuit design in this scenario, it is necessary to identify the fundamental mechanisms responsible for MOSFET LFN, in order to provide accurate LFN models that account not only for the average noise power, but also for its variability and dependences on geometry, bias and temperature. In this work, a new variability-based LFN analysis technique is introduced, employing the autocorrelation of multiple LFN spectra in terms of parameters such as frequency, bias and temperature. This technique reveals information about the mechanisms responsible for the 1= f noise that is difficult to obtain otherwise. The correlation analyses performed on three different commercial mixed-signal CMOS technologies (140-nm, 65-nm and 40-nm) provide strong evidence that the LFN of both n- and p-type MOS transistors is primarily composed of the superposition of thermally activated random telegraph signals (RTS).

This thesis investigates the direct measurement of the thermal noise spectral distribution. Long base line gravitational wave detectors, being commissioned around the world, are limited in sensitivity in the intermediate frequencies by the thermal noise. These detectors are utilising suspended test mirrors for the detection of gravitational waves by measuring their relative displacement. One of the fundamental noise sources in these detectors is the thermally induced displacement of the suspension onto and within the mirrors. This thermally induced motion of the test mirrors limits the displacement sensitivity of the gravitational wave detectors. Knowledge of the spectral behavior of thermal noise over a wide frequency range will improve predictions and understanding of the behavior of the suspension and test mirrors.¶ In this thesis the direct measurement of the thermal noise spectral distribution of a mechanical flexure resonator is described. The mechanical flexure resonator is an unidirectional ’wobbly table’ made from copper-beryllium, which hinges around four thin flexures 15 mm wide, 1 mm high and ~116 µm thick. The mechanical flexure resonator has a resonant frequency of 192 Hz, with a quality factor of ~3000.¶ The thermal noise induced displacement of the mechanical flexure resonator was measured using an optical cavity. The end mirror of a two mirror optical cavity was mounted on the mechanical flexure resonator. A laser was made resonant with the test cavity by use of a locking control system. Thermal noise induced displacement moved the test cavity away from resonance. By measuring the error-signal in the control system, the equivalent thermal noise displacement was obtained.¶ The thermal noise induced displacement of the mechanical flexure resonator was predicted to be in the order of 10^(−12) to 10^(−17) m/sqrtHz over a frequency range of 10 Hz to 10 kHz. All other external noise sources needed to be suppressed to below this level. A major noise source was the laser frequency fluctuations. When the test cavity was locked to the laser, the laser frequency fluctuations dominated the read out signal. To suppress the frequency fluctuations, the laser was locked to a rigid long optical reference cavity. This allowed the frequency fluctuations to be suppressed to below the equivalent thermal noise displacement of the test cavity over the frequency range of interest.¶ Acoustic noise was suppressed by placing the whole experiment inside a vacuum chamber, and evacuating the air inside the chamber down to a pressure level of 10^(−4) mbar. A seismic vibration isolation system was used to suppress the seismic noise in the laboratory to below 10^(−14) m/sqrtHz at frequencies above 4 Hz.¶ With the experimental set up, the thermal noise displacement of the mechanical flexure resonator has been measured. Due to the degradation of the isolator performance, measurement of the thermal noise behavior over a wide frequency range of the mechanical flexure resonator was unsuccessful. By using an analytical curve fitting routine around the fundamental and first order resonant modes of the resonator, a loss factor of (3.5 ± 1.5 − 3.7 ± 1.5) × 10^(−4) for the copper-beryllium mechanical flexure resonator was obtained and structural damping was inferred.

No description available.

The object of this thesis is to explore the low-frequency noise (LFN) in silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs) and lateral bipolar junction transistors (BJTs). The LFN of SiGe HBTs and lateral BJTs not only determines the lowest detectable signal limit but also induces phase noise in high-frequency applications. Characterizing the LFN behavior and understanding the physical noise mechanism, therefore, are very important to improve the device and circuit performance. The dissertation achieves the object by investigating the LFN of SiGe HBTs and lateral BJTs with different structures for performance optimization and radiation tolerance, as well as by building models that explain the physical mechanism of LFN in these advance bipolar technologies. The scope of this research is separated into two main parts: the LFN of SiGe HBTs; and the LFN of lateral BJTs. The research in the LFN of SiGe HBTs includes investigating the effects of interfacial oxide (IFO), temperature, geometrical dimensions, and proton radiation. It also includes utilizing physical models to probe noise mechanisms. The research in the LFN of lateral BJTs includes exploring the effects of doping and geometrical dimensions. The research work is envisioned to enhance the understanding of LFN in SiGe HBTs and lateral BJTs.