EP2AGX95EF29C6N Datasheet, PDF (145/380 Pages) Altera Corporation – Device Interfaces and Integration

Chapter 5: Clock Networks and PLLs in Arria II Devices
PLLs in Arria II Devices
5–37
Equation 5–2 shows the coarse-resolution phase shifts are implemented by delaying
the start of the counters for a predetermined number of counter clocks.
Equation 5–2. Coarse-Resolution Phase Shifts for Arria II Devices
Φ_coarse =
C−1
f_Vco
(C − 1)N
=
Mf_REF
where C is the count value set for the counter delay time, (this is the initial setting in
the “PLL usage” section of the compilation report in the Quartus II software). If the
initial value is 1, C – 1 = 0° phase shift.
Figure 5–33 shows an example of a phase-shift insertion with the fine resolution with
the VCO phase taps method. The eight phases from the VCO are shown and labeled
for reference. For this example, CLK0 is based off the 0phase from the VCO and has the
C value for the counter set to one. The CLK1 signal is divided by four, two VCO clocks
for high time and two VCO clocks for low time. CLK1 is based off the 135x phase tap
from the VCO and also has the C value for the counter set to one. The CLK1 signal is
also divided by four. In this case, the two clocks are offset by 3 _fine. CLK2 is based off
the 0phase from the VCO but has the C value for the counter set to three. This
arrangement creates a delay of 2 _COARSE (two complete VCO periods).
Figure 5–33. Delay Insertion with VCO Phase Output and Counter Delay Time for Arria II Devices
1/8 t_VCO
t_VCO
0
45
90
135
180
225
270
315
CLK0
CLK1
CLK2
t_d0-1
t_d0-2
Use the coarse- and fine-phase shifts to implement clock delays in Arria II devices.
The ALTPLL megafunction allows you to enter the desired VCO phase taps and initial
counter value settings through the MegaWizard^™ Plug-In Manager in the Quartus II
software.
Arria II devices support dynamic phase-shifting of VCO phase taps only. The phase
shift is reconfigurable any number of times and each phase shift takes about one
SCANCLK cycle, allowing you to implement large phase shifts quickly.
July 2012 Altera Corporation
Arria II Device Handbook Volume 1: Device Interfaces and Integration