Altera Stratix - Board Layout; Vcca & Gnda

1–50 Altera Corporation
Stratix Device Handbook, Volume 2 July 2005
Board Layout
Board Layout
The enhanced and fast PLL circuits in Stratix and Stratix GX devices
contain analog components embedded in a digital device. These analog
components have separate power and ground pins to minimize noise
generated by the digital components. Both Stratix and Stratix GX
enhanced and fast PLLs use separate VCC and ground pins to isolate
circuitry and improve noise resistance.
VCCA & GNDA
Each enhanced and fast PLL uses separate VCC and ground pin pairs for
their analog circuitry. The analog circuit power and ground pin for each
PLL is called PLL<PLL number>_VCCA and PLL<PLL number>_GNDA.
Connect the VCCA power pin to a 1.5-V power supply, even if you do not
use the PLL. Isolate the power connected to VCCA from the power to the
rest of the Stratix and Stratix GX device or any other digital device on the
board. You can use one of three different methods of isolating the VCCA
pin: separate V
CCA
power planes, a partitioned V
CCA
island within the
V
CCINT
plane, and thick V
CCA
traces.
Separate V
CCA
Power Plane
A mixed signal system is already partitioned into analog and digital
sections, each with its own power planes on the board. To isolate the
VCCA pin using a separate V
CCA
power plane, connect the VCCA pin to the
analog 1.5-V power plane.
Partitioned V
CCA
Island within V
CCINT
Plane
Fully digital systems do not have a separate analog power plane on the
board. Because it is expensive to add new planes to the board, you can
create islands for VCCA_PLL. Figure 1–23 shows an example board layout
with an analog power island. The dielectric boundary that creates the
island should be 25 mils thick. Figure 1–23 shows a partitioned plane
within V
CCINT
for V
CCA
.