The second CDR is designed for a tighter transfer bandwidth and a larger high frequency tolerance, and is slave to the clock of the first.
Its larger tolerance is obtained widening the range of the phase comparator:
CDR2 tolerance at low frequencies is inferior to the one of CDR1, but is in general more than adequate;
CDR2 tolerance at high frequencies is not affected by the lateral eye opening (LEO) tolerance of CDR1, because CDR2 samples pulses that have already been regenerated ;
the range of the phase comparator (or of the shift register, whichever is smaller) becomes the limit to high frequency jitter tolerance in CDR2;
the phase comparator of PLL2 may either:
use divided frequencies at its inputs to achieve a wider range, or
use a normal comparator (± 0.5 U.I.) with the added information of the pointer, in accordance to P + 1/2 C, where P is the pointer cell index (integer, negative for less than half register, 0 in the centre cell, etc.) and where C is the comparator output, ranging from -1 to +1.
The characteristic cut-off frequency of CDR2 is lower than CDR1, and sets the overall regenerator bandwidth.
to share – to copy, distribute and transmit the work
to remix – to adapt the work
Under the following conditions:
attribution – You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.
share alike – If you remix, transform, or build upon the material, you must distribute your contributions under the same or compatible license as the original.