External Memory Interfaces (EMIF) IP User Guide: Agilex™ 5 FPGAs and SoCs

ID 817467
Date 7/08/2024
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3.2.7. Agilex™ 5 EMIF Architecture: PLL Reference Clock Networks

Each HSIO sub-bank includes an I/O bank I/O PLL that can drive the PHY clock trees of that bank, through dedicated connections. In addition to supporting EMIF-specific functions, the I/O bank I/O PLLs can also serve as general-purpose PLLs for user logic.

The PLL reference clock must be constrained to the address and command sub-bank only.

Agilex™ 5 external memory interfaces that span multiple HSIO banks use the PLL in each bank. The Agilex™ 5 architecture allows for relatively short PHY clock networks, reducing jitter and duty-cycle distortion.

The following mechanisms ensure that the clock outputs of individual HSIO bank I/O PLLs in a multi-bank interface remain in phase:

  • A single PLL reference clock source feeds all HSIO bank I/O PLLs. The reference clock signal reaches the PLLs by a balanced PLL reference clock tree. The Quartus® Prime software automatically configures the PLL reference clock tree so that it spans the correct number of banks. This clock must be free-running and stable prior to FPGA configuration.
  • The EMIF IP sets the PLL configuration (counter settings, bandwidth settings, compensation and feedback mode setting) values appropriately to maintain synchronization among the clock dividers across the PLLs. This requirement restricts the legal PLL reference clock frequencies for a given memory interface frequency and clock rate. If you plan to use an on-board oscillator, you must ensure that its frequency matches the PLL reference clock frequency that you select from the displayed list.
Figure 8. PLL Balanced Reference Clock Tree

PLL Balanced Reference Clock Tree