CDR
Models a clock data recovery circuit
- Library:
SerDes Toolbox / Datapath Blocks
Description
The CDR block provides clock sampling times and estimates data symbols at the receiver using a first order phase tracking CDR model. For more information, see Clock and Data Recovery in SerDes System..
Ports
Input
WaveIn — Input baseband signal
scalar
Input baseband signal. The input to the CDR must be applied as one sample at a time and not as a vector.
Data Types: double
Parameters
Phase offset (symbol time) — Clock phase offset
0 (default) | real scalar in the range [0, 0.5]
Clock phase offset, specified as a real scalar in the range [0, 0.5] in fraction of symbol time. Phase offset manually shifts clock probability distribution function (PDF) for better bit error rate (BER).
Programmatic Use
Use
get_param(gcb,'PhaseOffset')to view the current value of Phase offset (symbol time).Use
set_param(gcb,'PhaseOffset',value)to set CDR to a specific Phase offset (symbol time).
Data Types: double
Reference offset (ppm) — Reference clock offset impairment
0 (default) | real scalar in the range [0, 300]
Reference clock offset impairment, specified as a real scalar in the range [0, 300] in parts per million (ppm). Reference offset (ppm) is the deviation between transmitter oscillator frequency and receiver oscillator frequency.
Programmatic Use
Use
get_param(gcb,'ReferenceOffset')to view the current value of Reference offset (ppm).Use
set_param(gcb,'ReferenceOffset',value)to set CDR to a specific Reference offset (ppm).
Data Types: double
Early/late count threshold — Early or late CDR count threshold to trigger phase update
16 (default) | real positive integer ≥5
Early or late CDR count threshold to trigger a phase update, specified as a unitless real positive integer ≥5. Increasing the value of Early/late count threshold provides a more stable output clock phase at the expense of convergence speed. Because the bit decisions are made at the clock phase output, a more stable clock phase has a better bit error rate (BER).
Early/late count threshold also controls the bandwidth of the CDR which is approximately calculated by using the equation:
Programmatic Use
Use
get_param(gcb,'Count')to view the current value of Early/late count threshold.Use
set_param(gcb,'Count',value)to set CDR to a specific Early/late count threshold.
Data Types: double
Step (symbol time) — Clock phase resolution
0.0078 (default) | real scalar
Clock phase resolution, specified as a real scalar in fraction of symbol time. Step (symbol time) is the inverse of the number of phase adjustments in CDR.
Programmatic Use
Use
get_param(gcb,'Step')to view the current value of Sensitivity.Use
set_param(gcb,'Step',value)to set CDR to a specific Sensitivity.
Data Types: double
Sensitivity (V) — Sampling latch metastability voltage
0 (default) | real scalar
Sampling latch metastability voltage, specified as a real scalar in volts. If the data sample voltage lies within the region (±Sensitivity (V)), there is a 50% probability of bit error.
Programmatic Use
Use
get_param(gcb,'Sensitivity')to view the current value of Sensitivity (V).Use
set_param(gcb,'Sensitivity',value)to set CDR to a specific Sensitivity (V).
Data Types: double
Phase Offset — Include Phase Offset parameter in IBIS-AMI model
on (default) | off
Select to include Phase Offset as a parameter in the IBIS-AMI file. If you deselect Phase Offset, it is removed from the AMI files, effectively hard-coding Phase Offset to its current value.
Reference offset — Include Reference offset parameter in IBIS-AMI model
on (default) | off
Select to include Reference offset as a parameter in the IBIS-AMI file. If you deselect Reference offset, it is removed from the AMI files, effectively hard-coding Reference offset to its current value.