MAX3676 Maxim, MAX3676 Datasheet - Page 13

• Manufacturer Part Number: MAX3676
• Description: 622Mbps / 3.3V Clock-Recovery and Data-Retiming IC with Limiting Amplifier
• Manufacturer: Maxim

allowable pattern-dependent jitter, peak-to-peak
(seconds); and BW = typical system bandwidth, nor-
mally 0.6 to 1.0 times the data rate (Hertz). If the PDJ is
still larger than desired, continue increasing the value of
C
MAX3676 analog inputs (ADI+, ADI-), it is important to
keep the low-frequency cutoff associated with C
below the corner frequency associated with C
(Table 1).
PDJ can also be present due to insufficient high-fre-
quency bandwidth (Figure 10). If the amplifiers are not
fast enough to allow for complete transitions during sin-
gle-bit patterns, or if the amplifier does not allow ade-
quate settling time, high-frequency PDJ can result.
Finally, PWD occurs when the midpoint crossing of a
0–1 transition and a 1–0 transition does not occur at the
Figure 10. Pattern-Dependent Jitter Due to High-Frequency
Rolloff
IN
. Note that to maintain stability when using the
LONG
CONSECUTIVE
BIT STREAM
0-1-0 BIT STREAM
Data-Retiming IC with Limiting Amplifier
______________________________________________________________________________________
HF PDJ
Pulse-Width Distortion
622Mbps, 3.3V Clock-Recovery and
TIME
MIDPOINT
IN
OLC
(f
C
)
same level (Figure 11). DC offsets and nonsymmetrical
rising and falling edge speeds both contribute to PWD.
For a 1–0 bit stream, calculate PWD as follows:
The internal clock and data alignment in the MAX3676
is well maintained close to the center of the data eye.
Although not required, this sampling point can be shift-
ed using the PHADJ inputs to optimize BER perfor-
mance. The PHADJ inputs operate with differential
input signals to approximately ±1V. A simple resistor
divider with a bypass capacitor is sufficient to set up
these levels. When the PHADJ inputs are not used, they
should be tied directly to V
Figure 11. Pulse-Width Distortion
PWD = [(width of wider pulse) -
(width of narrower pulse)] / 2
PWD RESULTS WHEN THE WIDTH
OF A ZERO DOES NOT EQUAL
THE WIDTH OF A ONE.
WIDTH OF A ZERO
WIDTH OF A ONE
CC
t
FALL
.
t
RISE
Phase Adjust
MIDPOINT
TIME
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