One of the dual-purpose external clock outputs becomes the fbin input pin in this mode. The external
feedback input pin, fbin is phase-aligned with the clock input pin. Aligning these clocks allows you to
remove clock delay and skew between devices.
When using EFB mode, you must use the same I/O standard on the input clock, feedback input, and clock
outputs.
This mode is supported only on the corner fractional PLLs. For Cyclone V E A2 and A4 devices, and
Cyclone V GX C3 device, EFB mode is supported only on the left corner fractional PLLs.
Figure 4-31: EFB Mode in Cyclone V Devices
inclk
C0
C1
C2
C3
C4
C5
C6
C7
C8
M
fbout
fbin
fbin[n]
fbout[n]
fbout[p]
fbin[p]
2
10
I/O / FPLL_<#>_CLKOUT0
/ FPLL_<#>_CLKOUTp /
FPLL_<#>_FB
I/O / FPLL_<#>_CLKOUT1 /
FPLL_<#>_ CLKOUTn
I/O /FPLL_<#>_FBp
I/O / FPLL_<#>_FBn
÷
N
PFD
VCO 0
CP/LF
Multiplexer
External board connection for one
single-ended clock output and one
single-ended feedback input for
single-ended EFB support.
For single-ended EFB mode,
FPLL_<#>_CLKOUT1 is the fbout
output pin; while the FPLL_<#>_FB is
the fbin input pin.
External board connection for one
differential clock output and one
differential feedback input for
differential EFB support.
For differential EFB mode,
FPLL_<#>_CLKOUT[p,n] are the
fbout[p,n] output pin; while
FPLL_<#>_FB[p,n] are the fbin[p,n]
input pins.
External
Board Trace
EXTCLKOUT[0]
EXTCLKOUT[1]
Figure 4-32: Example of Phase Relationship Between the PLL Clocks in EFB Mode
Dedicated PLL
Clock Outputs
PLL Clock at
the Register
Clock Port
fbin Clock Input Pin
Phase Aligned
PLL Reference
Clock at the
Input Pin
The PLL clock outputs
can lead or lag the fbin
clock input.
Clock Networks and PLLs in Cyclone V Devices
Altera Corporation
CV-52004
External Feedback Mode
4-30
2014.01.10