Tolerance and transfer curves of two CDRs with the same clock frequency, where the second (red) is locked to the first (blue). The characteristic frequencies (i.e. the transfer and tolerance low-pass corners) are different. The tolerances to high frequency jitter are also different. The first, wideband CDR has a lower tolerance, and vice-versa. The cascade tolerates the amount of sinusoidal jitter that is tolerated by both CDRs (the tolerance region is the AND of the two).