Stability of the Master Oscillator for FLASH at DESY

4.3 1.3 GHz and 2.856 GHz phase locked loops 41
magnitude [a.u.]
1.4
1.2
1
0.8
0.6
0.4
0.2
0
−0.2
10 0
−0.4
10 1
lowpass filter for reference
highpass filter for SAW
10 2
10 3
10 4
offsetfrequency [Hz]
Figure 46: Transfer functions as ”seen” by the reference and the SAW
The filter shows a cut off at around 11 kHz what could be verified by measurements of the
closed loop phase noise what is sketched in figure 47. For the loop filter parameter estimation
the reference phase noise of the locked 81 MHz VCXO has been scaled by a factor of N = 16 29 ,
the phase noise of the freerunning SAW oscillator, the simulated locked loop phase noise and
the measured locked loop phase noise are sketched in figure 47.
phasenoise [dBc/Hz]
20
0
−20
−40
−60
−80
−100
−120
−140
10 0
−160
10 1
10 2
10 3
10 4
offsetfrequency [Hz]
10 5
10 5
10 6
SAW freerunning 1300 MHz
scaled Reference 81 MHz
simulation Sphi
measured locked PLL
Figure 47: Measured and simulated phase noise in locked SAW phase locked loop
The integrated timing jitter 30 is 70 fs.
29 roughly 24 dB
30 integration bandwidth from 10 Hz...1MHz
10 6
10 7
10 7