External Memory Interfaces Intel® Agilex™ FPGA IP User Guide

ID 683216
Date 1/31/2022

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3.1.7. Intel® Agilex™ EMIF Architecture: PLL Reference Clock Networks

Each 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.

  • A single-ended reference clock must be constrained to pin index 0 in lane 2. You cannot use pin index 1 in lane 2 as a general purpose I/O pin.
  • Differential reference clocks must be constrained to pin indices 0 and 1 in lane 2.

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

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

  • A single PLL reference clock source feeds all I/O bank I/O PLLs. The reference clock signal reaches the PLLs by a balanced PLL reference clock tree. The Intel® 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. The Intel® Agilex™ EMIF IP parameter editor automatically calculates and displays the set of legal PLL reference clock frequencies. 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 29. PLL Balanced Reference Clock Tree

Balanced Reference Clock Tree