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An experimental investigation of very low frequency semiconductor noise

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NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. This thesis represents an attempt to more accurately characterize the statistics of the very low frequency noise of a particular semi conductor device (a grounded input bipolar integrated operational amplifier) than has previously been achieved. Power spectral density estimates are obtained for frequencies ranging from 250 Hz to [...] Hz. These estimates are based on data recorded over an uninterrupted period of approximately 1 year (355.9 days). Relatively high sample rates are maintained for each source, allowing a high degree of accuracy in these estimates without resorting to the questionable process of averaging the estimates for a number of noise sources [1]. The high sample rate also allows for a reduction in the errors due to aliasing by the use of digital filtering techniques. Spectral density estimates for six separate noise sources are presented. The preliminary objectives of the experiment were to search for a break in the [...] spectral density component of semiconductor noise and to attempt to establish the "true" value of [alpha] if a unique value exists. Very long time constant "popcorn" noise (ignored by one investigator because it is "as natural as flicker noise itself" [1, page 69]), proved to be an obstacle in measuring the "pure" l/f noise process and may not only be the reason for the wide range of values for a reported in the literature but, as suggested by some researchers [2], may be the cause of flicker noise. "Popcorn" noise was observed with apparent time constants greater than [...] seconds. The statistics of the observed "popcorn" noise were investigated and showed good agreement with the results of J. N. Puckett, Jr. [3] (who worked primarily with popcorn noise having time constants on the order of a few milliseconds) except for a few cases in which the waveform resembled that which might be expected if one popcorn component were to modulate another. The work of Puckett was also extended in that a test for burst waiting time dependency was performed. No evidence of dependency could be found. Popcorn noise components which were large enough to be clearly identified were removed in the time domain. This technique was found to be quite useful in improving the spectral estimates. As in previous experiments, power supply regulation and temperature control were found to be essential. In this experiment, however, the temperatures of the noise sources and the power supply fluctuations were measured concurrently with the noise data so that their contribution to the total observed noise could be more accurately ascertained. Neither a break frequency in the [...] trend nor a unique [alpha] were established, although the values of [alpha] obtained were all slightly larger than but closer to 1.0 than most reported values. A nearly periodic component (with a period of 1 year) was also observed in two of the noise sources which were contained in a plastic integrated circuit package. Since this component cannot be explained by temperature or power supply voltage it is conjectured that other external parameters such as humidity or barometric pressure (or even cosmic radiation) may account for some of the observed noise, although no such component could be observed in the other four noise sources (which were housed in metal packages).

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