Digital frequency generation in atomic frequency standards using digital phase shifting
First Claim
1. In a method of digitally generating a frequency-modulated physics package interrogation signal in an atomic frequency standard, the improvement comprisinggenerating a digital frequency component of the interrogation signal and a digital modulation frequency from a clock frequency, and varying the rate of phase change of the digital frequency component on alternate half-cycles of the digital modulation frequency.
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Abstract
In the generation of frequency-modulated interrogation frequencies for atomic frequency standards, the modulation characteristics can be tailored to the frequency discrimination characteristics of a physics package. The rate of phase change of a digital pulse train providing a frequency-modulated component of interrogation frequency for an atomic frequency standard can be varied, for example, by multiplexing a plurality of differently phased (delayed) pulse trains to vary the rate of phase change in a digital interrogation frequency component, or by effecting phase delays and phase advances through the addition and subtraction of pulses of a digital interrogation frequency component. In addition, fine frequency and/or modulation depth control, which can overcome physics package frequency offsets, can be effected through the addition and/or subtraction of increments of phase to and/or from a digital frequency component of the interrogation frequency at a variable phase change frequency (or drop rate count) to provide variable rates of phase change in alternate half-cycles of the modulation frequency in the synthesis of a frequency-modulated interrogation signal.
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Citations
40 Claims
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1. In a method of digitally generating a frequency-modulated physics package interrogation signal in an atomic frequency standard, the improvement comprising
generating a digital frequency component of the interrogation signal and a digital modulation frequency from a clock frequency, and varying the rate of phase change of the digital frequency component on alternate half-cycles of the digital modulation frequency.
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20. In digital means for generating a frequency-modulated physics package interrogation signal in an atomic frequency standard including means for generating a clock frequency, the improvement comprising means for generating a plurality of digital components of the interrogation signal from the clock frequency;
- means for varying the rate of phase change of one of the digital frequency components of the interrogation signal; and
means for combining the plurality of digital components of the interrogation signal and providing the frequency-modulated interrogation signal. - View Dependent Claims (21, 22, 23, 24)
- means for varying the rate of phase change of one of the digital frequency components of the interrogation signal; and
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25. In an atomic frequency standard including a controllable frequency source for generating a source output frequency, a physics package for generating an atomic transition frequency through the excitation of an atomic gas, means for generating, from the source output frequency, a modulated interrogation frequency, means for injecting and mixing said modulated interrogation frequency with said atomic transition frequency, means for generating a signal proportional to the difference between said atomic transition frequency and said modulated interrogation frequency and means for controlling said controllable frequency source from said signal and for locking said controllable frequency source to said atom transition frequency, the improvement wherein said means for generating, from the source output frequency, a modulated interrogation frequency comprises digital means for synchronously synthesizing a plurality of integrally-related submultiple frequencies of said source output frequency and an integrally-related modulation frequency, one of said integrally-related submultiple frequencies being frequency-modulated by the addition and subtraction of pulses at said integrally-related modulation frequency, and means for digitally mixing said plurality of integrally-related submultiple frequencies, including said frequency-modulated submultiple frequency, in synthesizing said modulated interrogation frequency.
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26. In a method of digitally synthesizing a frequency-modulated microwave signal for exciting a physics package of an atomic frequency package, the improvement comprising the steps of:
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generating from said clock frequency a submultiple frequency with a period T; generating from said submultiple frequency N variously delayed signals, each of said N signals comprising the submultiple frequency delayed by a time T/N from each of the other N signals; providing each of said N variously delayed signals to a multiplexer; generating a multiplexer operating signal by generating a phase change frequency (DRC) pulse train signal by dividing the clock signal by a substantial number, and generating a frequency modulation signal by dividing the phase change frequency (DRC) pulse train signal by a further substantial number, and combining the phase change frequency (DRC) pulse train signal and the frequency modulation signal for operation of said multiplexer to provide an output frequency with one or more periods of T between the transition edges of the phase change frequency (DRC) pulse train signal and with one period of (T+T/N) at each edge of each pulse of the phase change frequency (DRC) pulse train signal during one half-cycle of the frequency modulation signal, and for operation said multiplexer or provide an output frequency with one or more periods of T between the transition edges of the phase change frequency (DRC) pulse train signal and with one period of (T-T/N) at each edge of each pulse of the phase change frequency (DRC) pulse train signal during the other half-cycle of the frequency modulation signal.
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27. In a method of digitally synthesizing a frequency-modulated microwave signal from a clock frequency of an atomic frequency standard for use with a physics package in controlling the clock frequency, the improvement comprising:
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generating, by dividing said clock frequency, (a) a modulatable frequency, (b) a modulation frequency selected for effective interaction with the physics package, and (c) a phase change frequency (DRC) which is substantially smaller than the modulatable frequency and substantially larger than the modulation frequency, and modulating said modulatable frequency by adding phase shift to the modulatable frequency at the phase change frequency (DRC) during one half-cycle of the modulation frequency and by subtracting phase shift from the modulatable frequency at the phase change frequency (DRC) during the other half-cycle of the modulatable frequency, the phase shift of said modulatable frequency being zero over each cycle of the modulation frequency. - View Dependent Claims (28, 29, 30, 31)
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32. In an atomic frequency standard including means for generating from a clock frequency, a digital frequency-modulated microwave signal for application to a physics package the improvement comprising
means for generating, from said clock frequency, a microwave submultiple frequency with a period T and for generating from said microwave submultiple frequency a plurality of N pulse trains at said submultiple frequency, said pulse trains being delayed from each other by a period T/N; - and
means for generating, from said plurality of N delayed pulse trains, a frequency-modulated digital signal comprising means for combining said plurality of delayed pulse trains, said combining means being operated by a modulation frequency and a phase change frequency (DRC) pulse train, said phase change frequency (DRC) pulse train operating said combining means to switch its output among the plurality delayed pulse trains to provide a pulse train output with an instantaneous frequency of 1/T for one or more periods between the transition edges of the phase change frequency (DRC) pulse train and with an instantaneous frequency of 1/(T+T/N) for one period at each pulse edge of the phase change frequency (DRC) pulse train during one half-cycle of the modulation frequency signal, and for operation of said multiplexer to provide an output instantaneous frequency of 1/T for one or more periods between the transition edges of the phase change frequency (DRC) pulse train and with an instantaneous frequency of 1/(T-T/N) for one period at each pulse edge of the phase change frequency (DRC) pulse train during the other half-cycle of the modulation frequency.
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33. A method of controlling a frequency-modulated interrogation signal in an atomic frequency standard, comprising:
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generating, from a clock frequency of the atomic frequency standard, a frequency for modulation of the interrogation signal and a phase change frequency; using the phase change frequency to provide a different rate of phase change of the interrogation signal in alternate half-cycles of the modulation frequency; and controlling the rate of phase change in modulating the interrogation signal by varying the phase change frequency. - View Dependent Claims (34, 35)
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36. Means for generating a frequency-modulated component of an interrogation frequency from the clock frequency of an atomic frequency standard, comprising
means for generating a phase change frequency from said clock frequency; -
means for generating a modulation frequency from said clock frequency; means for generating, from said clock frequency, said phase change frequency and said modulation frequency, the frequency-modulated component of the interrogation frequency with different rates of phase change on alternate half-cycles of the modulation frequency. - View Dependent Claims (37, 38, 39, 40)
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Specification