NIST Technical Note 1337: Characterization of Clocks and Oscillators

Table 1. Guide to Selection of Measurement Methods. (continued)Measurement Time Time Frequen'1 Frequencg'Method Accuracy a Stability Accuracy Stability Advantages Disadvantages(1 day) 0'/7)m. Homodyne Methods Particularly useful for measurement Generally no used for measurementof phase noise.of time.1. Phase-Lock-Loop Methods Assure continuous quadrature of Care needed to assure that noise ofsignal and reference.interest is outside loop bandwidth.a. LODse-Phase-Lock LoopUseful for short-term time stabilityDepends on -10,7/(11 07) analysis as well as spectrum analysiscalibration which at 10 MHz and the detection of periodicity inof varicap is _10,14/ 7 noise as spectral lines; excellentsensitivity.Long-term phase measurements(beyond several seconds are notpractical.Measurement noise typically less Need voltage controlled referenceDepends on -10,7/(11 7) 0than oscillator instabilities for oscillator; frequency sensitivity isb. Tight-Phase-Lock Loop calibration which at 10 MHz 7 = 1 s and longer; good measure­ a function of varicap tuning curve,:t , of vancap · . 10. 14 IS - / 7 ment system bandwidth control; hence not conducive to measuring-...l dead time can be made small or absolute frequency differences.negligible.Requires no reference oscillator. Substantially less bandwidth than2. Discriminator Methods two-oscillator, homodyne methods;sensitivity low at low Fourier frequency.Depends on Depends on Requires no reference oscillator; Requires more difficult calibrationcharacteris­ characteris­ very easy to set up and high in to obtain any accuracy over evena. Cavity Discriminator tics of dis­ tics of dis­ sensitivity; practical at microwave modest range of Fourier frequencies;criminator criminator frequencies. accurate only for Fourier frequenciesless than 0.1 x bandwidth.Requires no reference oscillator;Depends on dynamic range set by propertiesb. Delay Line characteris­ of delay line; practical at microticsof delay wave frequencies.lineSubstantially less accurate than twooscillator,homodyne methods; cumbersomesets of delay lines neededto cover much dynamic range; considerabledelay needed for measurementsbelow 100 kHz from carrier.aAccuracy of the measurement cannot be better than the stability of the measurement. Accuracy is limited by the accuracy of the reference oscillator.t>rms is for a measurement bandwidth of 10 4 Hz; 11 0= frequency; 7 = measurement time.The dash (--) means that the method is not generally appropriate for this quantity.