Rohde & Schwarz RTP044 - Page 1058

Jitter analysis and clock data recovery
R&S
®
RTP
1058User Manual 1337.9952.02 ─ 12
"Constant
freq."
CDR uses the nominal bit rate to generate the clock signal. The
method assumes that the frequency of the signal is constant during
the complete acquisition.
"PLL"
PLL is the phase-locked loop control system. It can follow slow devia-
tions in the frequency of the data stream. Thus, it acts as highpass
filter regarding the jitter that remains on the signal.
"Feed For-
ward"
The feed forward algorithm is a mathematical optimization method
used for clock data recovery. Feed forward is available if standards
are of the listed serial used ("Custom"). It is faster than PLL, i.e., the
settling time is shorter. Feed forward is also more precise than PLL.
To set up the algorithm, set the bandwidth and the relative bandwidth.
Remote command:
CDR:SOFTware<m>:ALGorithm on page 2286
Sampling time
Sets a sampling time for the explicit clock signal, an offset for the clock edge in relation
to the bit start. The clock edge sets the beginning of the unit interval. The sampling
time is a number between 0 and 1. Value 0 sets the clock edge to the beginning of the
bit period; value 0.5 sets the clock edge to the middle of the bit period.
Remote command:
CDR:SOFTware<m>:SAMTime on page 2291
Bit rate estimation
Bit rate estimation analyzes the source signal based on the given "Nominal bit rate"
and corrects the value.
"Continuous"
Enables ongoing bit rate correction.
"Estimate"
Estimates the bit rate once, for the current acquisition.
Remote command:
CDR:SOFTware<m>:ESBRate:CONTinuous on page 2288
CDR:SOFTware<m>:ESBRate:BREStimate on page 2288
Nominal bit rate
Sets the quiescent frequency of the PLL. It corresponds to the data rate of the data
stream from which the clock is to be recovered.
Remote command:
CDR:SOFTware<m>:BITRate on page 2288
Algorithm settings
Phase-locked loop parameters are listed below.
Note: Nomial bit rate, bandwidth and relative bandwidth are interacting settings. Modi-
fying one parameter also changes one of the dependent parameters.
"Order"
Sets the order of the PLL: first or second order. PLL of higher order
can compensate for more complex jitter behavior.
"Damping"
Sets the damping factor, which is only relevant for second order PLL.
Clock data recovery