Cyclone V Device Handbook: Volume 2: Transceivers

ID 683586
Date 10/24/2018
Document Table of Contents

7.3. Transmitter Duty Cycle Distortion Calibration

The duty cycle calibration function tunes the transmitter to minimize duty cycle distortion.

The transmitter clocks generated by the CMU that travel across the clock network may introduce duty cycle distortions (DCD). Reduce DCD with the DCD calibration IP that is integrated in the transceiver reconfiguration controller.

Enabled the DCD calibration IP in Cyclone GT devices for better TX jitter performance, if either of the following conditions are met:

  • Data rate is ≥ 4915.2 Mbps
  • Clock network switching (TX PLL switching) and the data rate is ≥ 4915.2 Mbps

The following DCD calibration modes are supported:

  • DCD calibration at power-up mode
  • Manual DCD calibration during user mode

DCD calibration is performed automatically after device configuration and before entering user mode if the transceiver channels connected have the Calibrate duty cycle during power up option enabled. You can optionally trigger DCD calibration manually during user mode if:

  • You reconfigure the transceiver from lower data rates to higher data rates (≥ 4.9152 Gbps)
  • You perform clock network switching (TX PLL switching) and switch to data rates of ≥ 4915.2 Mbps

You do not have to enable DCD calibration if the transceivers are operating below 4.9152 Gbps.

When DCD calibration and offset cancellation are enabled, the reconfig_busy status signal from the reconfiguration controller is deasserted to indicate the completion of both processes. If DCD calibration is not enabled, the deassertion of reconfig_busy signal indicates the completion of the offset cancellation process.