NIST Technical Note 1337: Characterization of Clocks and Oscillators

7. PHASE NOISE AND AM NOISE MEASUREMENTS 263-80-100;g -120CD ";" -140'-'-160_ PHASE-LOCKED _LOOP512-MHzOSCILLATOR-180'-----.....----'-----......----'------'10 103 10 4 105FOURIER FREQUENCY (Hz)FIG. II Phase-locked-loop characteristics of the H.P. 8640B signal generator. showingthe normalized phase-noise sideband power spectral density.4. Measurements, Calculations, and Data PlotsThe measurement sequence is automated except for the case where manualadjustments are required to maintain phase quadrature of the signals. Afterphase quadrature of the signals into the mixer is established, the {F attenuatoris returned to the zero-decibel reference setting. This attenuator isset to a high value [assumed to be 50 dB in Eq. (65)] to prevent saturationof the spectrum analyzer during the calibration process.The automated measurements are executed, and the direct measurementand data plot of fi'(f) is obtained in decibels (carrier) per hertz using theequationfi'(f) = - [carrier power level - (noise power level - 6 + 2.5- 10 log B-3)]. (69)The noise power (dBm) is measured relative to the carrier-power level(dBm), and the remaining terms of the equation represent corrections thatmust be applied because of the type of measurement and the characteristicsof the measurement equipment, as follows.(l) The measurement of noise sidebands with the signals in phasequadrature requires the -6-dB correction that is noted in Eq. (69).(2) The nonlinearity of the spectrum analyzer's logarithmic IF amplifierresults in compression of the noise peaks which, when average-detected,require the 2.5-dB correction.(3) The bandwidth correction is required because the spectrum analyzermeasurements of random or white noise are a function of the particularbandwidth used in the measurement.TN-214