VITESSE
SEMICONDUCTOR CORPORATION
Target Specification
STS-12/STS-3 Multi Rate
Clock and Data Recovery Unit
VSC8115
Jitter Tolerance
Jitter Tolerance is the ability of the Clock and Data Recovery Unit to track timing variation in the received
data stream. The Bellcore and ITU specifications allow the received optical data to contain jitter. The amount
that must be tolerated is a function of the frequency of the jitter. At high frequencies the specifications do not
require the VSC8115 to tolerate large amounts, whereas at low frequencies many unit intervals (bit times) of jit-
ter have to be tolerated. Jitter tolerance is defined as the ratio of jitter on the output OC-N/STS-N signal to the
jitter applied on the input OC-N/STSN signal versus frequency. The VSC8115 is designed to tolerate this jitter
with margin over the specification limits, see Figure 2. The VSC8115 obtains and maintains lock based on the
data transition information. When there is no transition on the data stream, the recovered clock frequency will
be held to within +500ppm of the reference clock. The VSC8115 can maintain lock over 1000 bits of no switch-
ing on data stream.
Figure 2: Input Jitter Tolerance Specification
JITTER(UI P-P)
Bellcore Requirement
150
15
VSC8115 Typical
Jitter Tolerance
24
2.4
1.5
0.6
0.15
10
30
300
25K
250K 1M 2.5M
JITTER FREQ(HZ)
Jitter Generation
Jitter generation is defined as the jitter of the serial clock and serial data outputs while rms jitter is presented
to the serial data inputs. Maximum jitter generation is 0.01 U.I. when rms jitter of less than 14ps (OC-12) or
56ps (OC-3) is presented to the serial data inputs.
G52272-0, Rev. 1.1
9/29/00
Ó VITESSE SEMICONDUCTOR CORPORATION
741 Calle Plano, Camarillo, CA 93012 • 805/388-3700 • FAX: 805/987-5896
Page 5
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