Transfer functions for four different kinds of phase and frequency detectors. (a) Ideal PFD with a dynamic range of and a saturation output of arbitrary units. (b) Same as (a) but with a dead zone of centered around 0 phase difference. (c) Ideal transfer function, assuming an APD/DFPD gain ratio of 5. (d) Approximation of (c) easily implemented with standard logic building blocks. Each step within the dynamic PFD range is wide.
Simplified block diagram of the DPFD. RF and LO have already been converted to digital signals. The optional cycle slip detection logic has been omitted.
Different possible APD–DPFD interfaces. (a) Both the rf and LO signals reaching the APD are analog. It requires two power splitters at 90° (power splitter (P.S.) 90°) and 0° (P.S. 0°) degrees and a digitally controlled rf switch. (b) The LO signal is digital while rf is still analog. The 90° power splitter is replaced by a digital 90° phase shifter while the APD output is gated by blocking the signal with an AND gate. (c) Same as (b) but rf is also a digital signal. No power splitters are required and the APD output is largely independent from rf amplitude. It can generate more phase noise than (a) and (b).
Closed loop beat note signal at 40 MHz. The servo bumps at 800 kHz and 3 MHz due to the slow and fast current loop are clearly visible. The resolution bandwidth is 10 kHz. The plot is the average of 100 scans.
Square modulus of the single-sided phase noise spectral density from 5 Hz to 10 MHz of the OPLL. The spectrum is divided in four different regions according to the power laws that they follow.
Contributions to the mean square phase noise angle of the OPLL and to the square of phase resolution of the interferometer [see Eq. (3)] from the four noise zones of .
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