
2.0 Functional Description
CN8331/CN8332/CN8333
2.3 Receiver
Single/Dual/Triple E3/DS3/STS-1 Line Interface Unit
2-10
Conexant
100604B
2.3.4  The PLL Clock Recovery Circuit
The clock recovery circuit (RX PLL) extracts the embedded clock from the sliced 
data and provides this clock and the retimed data to the decoder (data mode). 
Upon startup (after the internal reset is deasserted), the RX PLL uses a reference 
clock (REFCLK, running at the symbol rate) and a phase-frequency detector to 
lock to the correct data rate (reference mode). During reference mode, the data 
outputs are squelched (set to 0). The RX PLL is kept in reference mode until a 
valid input is detected.
2.3.5  Loss Of Signal (LOS) Detector
The Receive Loss Of Signal (RLOS) is a digital function which monitors the 
retimed data from the clock recovery block. The AMI data is checked for a 
continuous run of zeroes. When a continuous run of 128 ± 1 consecutive zeroes 
occurs, the RLOS signal is asserted. After the RLOS signal is asserted, a 1s count 
is made on every block of 128 AMI symbols. The RLOS signal is deasserted 
when the 1s count within a block of 128 symbols is at least:
B3ZS: Minimum 1s density = 39 ± 1 count out of 128 (~30.5%)
HDB3: Minimum 1s density = 29 ± 1 count out of 128 (~22.7%)
The RLOS detector will always monitor the cable-side RX inputs. The 
detector is not affected by the state of remote or local looping.
2.3.6  Jitter Tolerance
The CN833x receiver is able to tolerate a specified amount of high-frequency 
jitter in the received signal while providing error-free operation (generally 
defined as a bit error rate of less than 10
-9
). The specifications (illustrated in 
Figure 2-7
) for jitter tolerance are discussed in the following documents:
E3 rate 
–
ITU-T G.823 and
ETSI TBR24
 contain frequency masks for input 
jitter tolerance.
NOTE:
 To meet jitter transfer requirements for loop-timed operation, an external 
jitter attenuator is required. The jitter attenuator lessens jitter from the 
receive clock.
DS3 rate
–
ITU-T G.823
 and 
Bellcore GR499
 specify jitter tolerance 
frequency masks for Category I and Category II interfaces.
STS-1 rate
–
Bellcore GR253
 specifies a jitter tolerance. It is noted that the 
STS-1 jitter tolerance differs from DS3 requirements only for Category II 
interfaces.
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