NIST Technical Note 1337: Characterization of Clocks and Oscillators

268A. L. LANCE, W. D. SEAL, AND F. LABAARTUNERVARIABLESHORTCIRCUITDELAY LINE(.1 (01OSCILLATORUNDER TEST---+'\.-J-------{DI RECTIONALCOUPLERDELAY LINEMIXERLOW-NOISEAMPLIFIERDIGITALSIGNALANALYZERIFFTI(c)FIG. 15 Single-oscillator phase-noise measurement techniques: (a) cavity discriminator;(b) reflective-type delay-line disenmmator; (e) one-way delay line.Ashley et al. (1968). Ashley et al. (1968) proposed the reflective-type delaylinediscriminator shown in Fig. ISb. The cavity can also be used to replacedelay line. The one-way delay line shown in Fig. 15c is implemented in theTRW measurement systems. The theory and applications set forth in thissection are based on a system of this particular type.A. THE DELAY LINE AS AN FM DISCRIMINATORI. The Single-Oscillator Measurement SystemThe single-oscillator signal is split into two channels in the system shownin Fig. 15. One channel is called the nondelay or reference channel. It is alsoreferred to as the local-oscillator (LO) channel because the signal in thischannel drives the mixer at the prescribed impedance level (the usual LOdrive). The signal in the second channel arrives at the mixer through a delayline. The two signals are adjusted for phase quadrature with the phaseshifter, and the output of the mixer is a fluctuating voltage, analogous to thefrequency fluctuations of the source, centered on approximately zero dcvolts.The delay line yields a phase shift by the time the signal arrives at thebalanced mixer. The phase shIft depends on the instantaneous frequency ofTN-219