Showing papers by "Fred L. Walls published in 1995"

Fundamental limits on the frequency stabilities of crystal oscillators

Abstract: The frequency instabilities of precision bulk acoustic wave (BAW) quartz crystal oscillators are reviewed. The fundamental limits on the achievable frequency stabilities, and the degree to which the fundamental limits have been approached to date are examined. Included are the instabilities as a function of time, temperature, acceleration, ionizing radiation, electromagnetic fields, humidity, atmospheric pressure, power supply, and load impedance. Most of the fundamental limits are zero or negligibly small, a few are finite. We speculate about the progress which may be achievable in the future with respect to approaching the fundamental limits. Suggestions are provided about the paths that may lead to significant stability improvements. >

The origin of 1/f PM and AM noise in bipolar junction transistor amplifiers

Abstract: In this paper we report the results of extensive research on phase modulation (PM) and amplitude modulation (AM) noise in linear bipolar junction transistor (BJT) amplifiers. BJT amplifiers exhibit 1/f PM and AM noise about a carrier signal that is much larger than the amplifier's thermal noise at those frequencies in the absence of the carrier signal. Our work shows that the 1/f PM noise of a BJT based amplifier is accompanied by 1/f AM noise which can be higher, lower, or nearly equal depending on the circuit implementation. The 1/f AM and PM noise in BJTs is primarily the result of 1/f fluctuations in transistor current, transistor capacitance, circuit supply voltages, circuit impedances, and circuit configuration. We discuss the theory and present experimental data in reference to common emitter amplifiers, but the analysis can be applied to other configurations as well. This study provides the functional dependence of 1/f AM and PM noise on transistor parameters, circuit parameters, and signal frequency, thereby laying the groundwork for a comprehensive theory of 1/f AM and PM noise in BJT amplifiers. We show that in many cases the 1/f PM and AM noise can be reduced below the thermal noise of the amplifier.

Design criteria for BJT amplifiers with low 1/f AM and PM noise

Abstract: In this paper we discuss guidelines for designing linear bipolar junction transistor (BJT) amplifiers with low 1/f amplitude modulation (AM) and phase modulation (PM) noise. These guidelines are derived from a new theory that relates AM and PM noise to transconductance fluctuations, junction capacitance fluctuations, and circuit architecture. We analyze the noise equations of each process for a common emitter (CE) amplifier and use the results to suggest amplifier designs that minimize the 1/f noise while providing other required attributes such as high gain. Although we use a CE amplifier as an example, the procedure applies to other configurations as well. Experimental noise results for several amplifier configurations are presented.

The Design of an Atomic Fountain Frequency Standard Prototype at NIST

Abstract: We are in the process of constructing and testing a prototype for possible future atomic fountain cesium frequency standards at NIST. The layout of the experiment is shown in Figure 1. The atoms are first accumulated in a magneto-opticai trap. The magnetic field is then switched off and the atoms are further cooled in optical molasses. The atoms are launched in a one dimensional vertical moving molasses with the atoms in the F=4 state. The moving molasses is created by detuning the upward beam to the red and the downward beam to the blue of the molasses frequency. The two beams have crossed linear polarizations (lin I lin configuration). Another cooling phase in the transverse directions may be added after the launch. The atoms first enter the lower "cleanup" microwave cavity. A one millisecond pulse of RF is applied to the atoms when they are in the center of the cleanup cavity. This n-pulse is tailored to drive only the I4,0> to I 3,0> transition. A laser beam is then directed downward onto the atomic sample. This laser beam is tuned to the F=4 to F'=5 optical transition, and removes the F=4 atoms from the sample with resonant light scattering forces, leaving a clean sample consisting only of I3,0> atoms. This will reduce both line pulling and collisional shifts.