CDR

Models a clock data recovery circuit

• 

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 and optionally a second order frequency 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

CDR Mode — Determine CDR order

1st order (default) | 2nd order

Determine the CDR order to enable phase and frequency tracking.

• 1st order — Only tracks the phase.

• 2nd order — Tracks both the phase and frequency.

Programmatic Use

Block parameter: CDRMode

Type: character vector

Values: 1st order | 2nd order

Default: 1st order

Phase Detector — Clock phase detector option

BangBang (default) | BaudRateTypeA

Clock phase detector option used in the clock data recovery. You can choose between bang-bang (Alexander) or baud-rate type-A (Mueller-Muller).

Programmatic Use

Block parameter: PhaseDetector

Type: character vector

Values: BangBang | BaudRateTypeA

Default: BangBang

Phase Offset (symbol time) — Clock phase offset

0 (default) | real scalar in the range [-0.5,0.5]

Clock phase offset, specified as a real scalar in the range [-0.5,0.5] in fraction of symbol time. Phase Offset is used to manually shift clock probability distribution function (PDF) for better bit error rate (BER).

Programmatic Use

Block parameter: PhaseOffset

Type: character vector

Values: real scalar in the range [-0.5,0.5]

Default: 0

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

Block parameter: ReferenceOffset

Type: character vector

Values: real scalar in the range [0, 300]

Default: 0

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.

Programmatic Use

Block parameter: Count

Type: character vector

Values: real positive integer ≥5

Default: 16

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

Block parameter: Step

Type: character vector

Values: real scalar

Default: 0.0078

Data Types: double

Frequency tracking gain — Internal gain for frequency tracking

0.00048828125 (default) | nonnegative real scalar

Internal gain for the frequency tracking loop, specified as a nonnegative real scalar.

Dependencies

To enable this parameter, set the CDR Mode to 2nd order.

Programmatic Use

Block parameter: FrequencyStep

Type: character vector

Values: nonnegative real scalar

Default: 0.00048828125

Data Types: double

Frequency tracking update — Frequency tracking update

16 (default) | nonnegative integer scalar

Once every Frequency tracking update symbols, update the system phase rotator clock with the frequency estimate.

Dependencies

To enable this parameter, set the CDR Mode to 2nd order.

Programmatic Use

Block parameter: FrequencyCount

Type: character vector

Values: nonnegative real scalar

Default: 16

Data Types: double

Frequency step ramp — Number of symbol times required for initial internal frequency tracking gain to reach specified value

3000 (default) | nonnegative integer scalar

To help frequency tracking loop lock early in a simulation, the initial Frequency tracking gain starts at a high value of 1/(2*Frequency tracking update). Then the Frequency tracking gain gradually reduces to the specified value by roughly Frequency step ramp symbol times.

Dependencies

To enable this parameter, set the CDR Mode to 2nd order.

Programmatic Use

Block parameter: FrequencyStepRamp

Type: character vector

Values: nonnegative real scalar

Default: 3000

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

Block parameter: Sensitivity

Type: character vector

Values: real scalar

Default: 0

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