CDR

Models a clock data recovery circuit

Since R2019a

• 

Libraries:
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:

$$\text{Bandwidth}=\frac{1}{\text{Symbol time }·\text{ Early/late threshold count }·\text{ Step}}$$

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

IBIS-AMI parameters

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.

More About

Phase Detector Model

You can select which phase detector model the block uses in the clock recovery: bang-bang (Alexander) or baud-rate type-A (Mueller-Muller). To view the phase detector model used in Simulink^®, you need to look under the mask of the block and double click the CDR System object™ to open the block parameter dialog box.

If the SerDes Designer exports a CDR block to Simulink that uses bang-bang phase detector model, the app automatically defines the clock position. If you change the phase detector option to baud-rate type-A Simulink, you need to manually add the reserved parameter Rx_Decision_Time. To add the parameter, open the AMI-Rx tab of the SerDes IBIS-AMI Manager dialog box. Adding reserved parameter also requires refreshing the Init function. For more information, see Define Clock Position in Statistical Eye.

If the SerDes Designer exports a CDR block to Simulink that uses baud-rate type-A phase detector model, the app automatically uses the reserved AMI parameter Rx_Decision_Time in the AMI-Rx tab of the SerDes IBIS-AMI Manager dialog box to define the clock position.

Version History

Introduced in R2019a