Browsing by Subject "1/f Noise"

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Open Access
1/f Noise characteristics of SEJ Y-Ba-Cu-O Rf-SQUIDs on LaAlO3 substrate and the step structure, film, and temperature dependence
(IEEE, 2001-03) Fardmanesh, M.; Schubert, J.; Akram, R.; Bick, M.; Zhang, Y.; Banzet, M.; Zander, W.; Krause, H. J.; Burkhart, H.; Schilling, M.
Step edge junction (SEJ) rf-SQUID magnetometers and gradiometers were fabricated using PLD Y-Ea-Cu-0 films on LaA10,(100) and SrTi0,(100) substrates. Effects of different step structure and the film properties on the yield, optimal operating temperature, and the l/f noise of the SQUIDs were investigated. The step structure was controlled using various IBE processes. The devices on LaAIO, showed higher sensitivity to the step structure compared to those on SrTiO,. This was due to re-deposition of substrate material at the steps prepared using the conventional IBE process resulting in a very low yield of unstable SQUIDs. High yield of low l/f noise stable SQUIDs was obtained on LaAIO, substrates with sharp steps prepared using an optimized IBE process. A typical l/f noise corner frequency of about lOHz at 77K with two major temperature dependencies was obtained. The temperature dependencies of the l/f noise could be correlated to the junction and the film of washer area of the SQUIDS. The white noise of our devices showed a dependency mainly on the amplitude of the flux to voltage transfer function signal. The operating temperature range of the SQUIDs could be controlled by the step structure and narrowed when the optimal operating temperature range was increased. All the measured junctions of our devices on the modified steps showed RSJ type behavior with a moderate decrease of the R, versus temperature.
Open Access
Low phase noise oscillator design and simulation using large signal analysis and low frequency feedback networks
(2013) Güngör, Çağatay Ertürk
Spectral purity of oscillators is of great importance in both commercial and military systems. Implementing communication, radar, and Electronic Warfare systems with increasingly higher frequencies, wider bandwidths, greater data rates, and more complex modulation schemes require low phase noise signal sources. There are still discrepancies in the literature about phase noise in signal sources. Although analytical models accomplish to describe the phase noise of known signal sources accurately, a unifying and reproducible model or method that provides a priori information for the design of a low phase noise oscillator is still not established. Due to this lack of methodical approach, mostly empirical design practices that are known to produce good results are widely adopted. Proposed design method is similar. Design and simulation of a low phase noise Dielectric Resonator Oscillator is studied. Noise sources in oscillators are briefly summarized. Phase noise models are compared. Dielectric resonators, which use small, disc-shaped ceramic materials that have high quality factors at microwave and millimeter-wave frequencies, are introduced with a concise theoretical coverage. Effect of circuit configuration on phase noise is studied on two different FET devices. Common-gate configuration gave best simulation results for both transistors. Parameters of coupling to the resonator are studied based on large signal analysis of the active device. The optimal parameters are described with supporting simulation results. Comparisons with suboptimal designs are provided, results indicate that optimization improves the phase noise on the order of tens of dBs. Low frequency feedback method is investigated. Simulation results showed significant improvement in close-in phase noise when such networks are used. A large data set is obtained with input parameters of frequency, device, bias point, and feedback configuration; and optimality of such schemes are discussed based on it. The methods for suppressing both close-in and away from the carrier phase noise are presented in the most generalized way, only to be reproduced for the intended device of operation.