ADN2817 Analog Devices, Inc., ADN2817 Datasheet - Page 18

• Manufacturer Part Number: ADN2817
• Description: Continuous Rate 10 Mbps To 2.7gb/s Clock And Data Recovery Ics
• Manufacturer: Analog Devices, Inc.

ADN2817/ADN2818
At medium jitter frequencies, the gain and tuning range of the
VCO are not large enough to track input jitter. In this case, the
VCO control voltage becomes large and saturates, and the VCO
frequency dwells at one extreme of its tuning range or the other.
The size of the VCO tuning range, therefore, has only a small
effect on the jitter accommodation. The delay-locked loop
control voltage is now larger, and so the phase shifter takes on
the burden of tracking the input jitter. The phase shifter range,
in UI, can be seen as a broad plateau on the jitter tolerance
curve. The phase shifter has a minimum range of 2 UI at all
data rates.
The gain of the loop integrator is small for high jitter
frequencies, so that larger phase differences are needed to make
the loop control voltage big enough to tune the range of the
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phase shifter. Large phase errors at high jitter frequencies
cannot be tolerated. In this region, the gain of the integrator
determines the jitter accommodation. Because the gain of the
loop integrator declines linearly with frequency, jitter accom-
modation is lower with higher jitter frequency. At the highest
frequencies, the loop gain is very small, and little tuning of the
phase shifter can be expected. In this case, jitter accommodation
is determined by the eye opening of the input data, the static
phase error, and the residual loop jitter generation. The jitter
accommodation is roughly 0.5 UI in this region. The corner
frequency between the declining slope and the flat region is
the closed-loop bandwidth of the delay-locked loop, which is
roughly 3 MHz at OC-48.