VITESSE
SEMICONDUCTOR CORPORATION
Data Sheet
VSC8122
Multi-Rate SONET/SDH
Clock and Data Recovery IC
Outputs can also be AC terminated as shown in Figure 3. The output differential voltage and common-mode
voltage range are specified in Table 4, High-Speed Inputs and Outputs.
Figure 3: High-Speed Clock and Data Output AC Termination
VSC8122
V
CC
V
TERM
100Ω
CO+ / DO+
0.1µF
Z
o
= 50Ω
50Ω
CO- / DO-
100Ω
0.1µF
Z
o
= 50Ω
50Ω
V
CC
V
TERM
Clock Recovery
The VSC8122 has a selectable input data rate. Two pins (FSEL0 and FSEL1) select the data rate to be pro-
vided to the VSC8122.
Table 1: Input Data Rate Select
Input Data Rate
2.48832Gb/s or 2.5Gb/s
1.24416Gb/s or 1.25Gb/s
622.08Mb/s or 625Mb/s
155.52Mb/s or 156.25Mb/s
FSEL0
0
1
0
1
FSEL1
0
0
1
1
The incoming data is presented both to the clock recovery circuit and the data retiming circuit. When there
is a phase error between the incoming data and the on-chip Voltage-Controlled Oscillator (VCO), the loop filter
raises or lowers the control voltage of the VCO to null the phase difference.
The lock detector monitors the frequency difference between the REFCK (optionally divided by a pres-
caler) and the recovered clock divided by 128. In the event of the loss of an input signal, or if the input is switch-
ing randomly, the VCO will move in one direction. At the time the VCO differs by more than 1MHz from the
REFCK based 2.48832GHz rate, the lock detector will assert the LOL output. LOL is designed to be asserted
from between 2.3µs and 100µs after the interruption of data. The VCO will continue to be frequency-locked at
approximately 1MHz off of the REFCK based 2.48832GHz rate.
When NRZ data is again presented at the data input, the phase detector will permit the VCO to lock to the
incoming data. Hysteresis is provided which delays the deassertion of LOL until approximately 160µs following
the restoration of valid data.
The NOREF output will go high to indicate that there is no signal on the REFCK input, or that the REFCK
is more than approximately 25% above or below the expected value.
G52228-0, Rev 4.1
01/05/01
©
VITESSE
SEMICONDUCTOR CORPORATION
• 741 Calle Plano • Camarillo, CA 93012
Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: prodinfo@vitesse.com
Internet: www.vitesse.com
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