SI5023 Datasheet, PDF (14/28 Pages) Silicon Laboratories – MULTI-RATE SONET/SDH CDR IC WITH LIMITING AMPLIFIER

Si5023
LOS signal hysteresis for the Si5023 CDR. The value of
R1 may be chosen to provide a range of hysteresis from
3 to 8 dB where a nominal value of 800 Ω adjusts the
hysteresis level to approximately 6 dB. Use a value of
500 Ω or 1000 Ω for R1 to provide 3 dB or 8 dB of
hysteresis, respectively.
Hysteresis is defined as the ratio of the LOS deassert
level (LOSD) and the LOS assert level (LOSA). The
hysteresis in decibels is calculated as 20log(LOSD/
LOSA).
40 mV
30 mV
4.9. Bit Error Rate (BER) Detection
The Si5023 uses a proprietary Silicon Laboratories
algorithm to generate a BER alarm on the BER_ALM
pin and a BER indicator on the BERMON pin.
The BERMON output is always enabled and functions
as a dynamic analog level that is proportional to the
detected bit error rate. This BERMON indicator can be
used to monitor the quality and error status on the
receive data input channel. The range of operation of
the BER processor is between 1E-09 to 1E-03 as
shown in Figures 8, 9, and 10. It is recommended that
the BERMON output be filtered with an active low-pass
filter configuration as shown in Figure 11. The external
LPF may be followed by a voltage comparator or
analog-to-digital converter where constant channel
monitoring is desired.
15 mV
40mV/V
10 mV
max
0 mV
0V
LOS Limited by Device Noise
1.00 V
1.50 V
LOS_LVL (V)
1.875 V
2.25 V 2.50 V
Figure 6. LOS_LVL Mapping (PRBS23 Data)
R1
Set LOS
Level
R2
3 _{LOS_LVL}
Si5023
10k
CDR
9
LOS
LOS Alarm
Figure 7. LOS Signal Hysteresis
4.10. Data Slicing Level
The Si5023 provides the ability to externally adjust the
slicing level for applications that require BER
optimization. Adjustments in slicing level of ±25 mV
(typical, relative to the internally-set input common
mode voltage) are supported. The slicing level is set by
applying a voltage between 0.75 V and 2.25 V to the
SLICE_LVL input. See Figures 12 and 13 for the
operation levels of the slice circuit.
When SLICE_LVL is driven below 500 mV, the slicing
level adjustment is disabled, and the slicing level is set
to the cross-point of the differential input signal.
Note: The slice circuit is designed to only work with pseudo-
random, dc-balanced data.
4.11. PLL Performance
The PLL implementation used in the Si5023 is fully-
compliant with the jitter specifications proposed for
SONET/SDH equipment by Bellcore GR-253-CORE,
Issue 3, September 2000 and ITU-T G.958.
4.11.1. Jitter Tolerance
The Si5023’s tolerance to input jitter exceeds that of the
Bellcore/ITU mask shown in Figure 14. This mask
defines the level of peak-to-peak sinusoidal jitter that
must be tolerated when applied to the differential data
input of the device.
Note: There are no entries in the mask table for the data rate
corresponding to OC-24 as that rate is not specified by
either GR-253 or G.958.
14
Rev. 1.25