GTS Transceiver PHY User Guide: Agilex™ 3 FPGAs and SoCs

ID 848344
Date 8/04/2025
Public
Document Table of Contents

2.6.1. Reference Clock Network

There are two types of clock lines in the reference clock network; local and regional reference clock lines. In a GTS transceiver bank, there are two independent differential reference clock input pins. The following figure shows the reference clock network and reference clock input pins for GTS the transceiver bank.
Figure 16. Reference Clock Network for Agilex™ 3 C-Series Devices

In Agilex™ 3, both the local and regional input reference clock pins reach all four channels in the GTS transceiver bank. They also connect to the system PLL. There is also a CDR clock out pin, which can be configured to output the recovered clock from the CDR in any of the four channels. Only one channel can send a CDR recovered clock at a time.

Additionally, the system PLL can also receive its input reference clock from outside the GTS transceiver bank. Adjacent to the GTS transceiver bank, there is a high voltage IO (HVIO) bank. There are 4 single-ended input reference clock pins in the HVIO bank that can be used by the system PLL as a secondary option for the reference clock input source.
Table 10.  Reference Clock Source Comparison
Description Local Reference Clock Regional Reference Clock HVIO Reference Clock CDR Clock Out Pin
Used by PMA and system PLL PMA and system PLL System PLL CDR
Reach All PMA channels and system PLL within a GTS transceiver bank All PMA channels and system PLL within a GTS transceiver bank System PLL in the GTS transceiver bank Any one of the four CDRs within the GTS transceiver bank
Recovered clock output Not Available Not available Not available Yes
Input/Output Input only Input only Input only Output only
Pin location GTS Transceiver bank GTS Transceiver bank HVIO5B bank GTS Transceiver bank
Signal type Differential Differential Single ended Differential
Reference clock to FPGA core9 Yes Yes Yes No
The PMA (TX PLL and CDR) reference clock sources are:
  • Local reference clock input
  • Regional reference clock input

You can also route both the local and regional reference clocks in the GTS transceiver banks to the FPGA core.

System PLL reference clock sources are:
  • Local reference clock input
  • Regional reference clock input
  • Dual purpose single ended pins (up to two) from the HVIO5B bank.

The CDR in any one of the four PMA channels within the GTS transceiver bank can send the recovered clock externally, for example to feed an external jitter cleaner. The output recovered clock is fed to the CDR clock out pin.

9 Refer to the device datasheet for the supported frequencies of the different reference clock pins.