EP2S90F1020C5 Datasheet, PDF (762/768 Pages) Altera Corporation – Stratix II Device Handbook, Volume 1

Simultaneous Switching Noise
■ Traces stretching from power pins to a power plane (or island, or a
decoupling capacitor) should be as wide and as short as possible.
This reduces series inductance, thereby reducing transient voltage
drops from the power plane to the power pin which, in turn,
decreases the possibility of ground bounce.
■ Use surface-mount low effective series resistance (ESR) capacitors to
minimize the lead inductance. The capacitors should have an ESR
value as small as possible.
■ Connect each ground pin or via to the ground plane individually. A
daisy chain connection to the ground pins shares the ground path,
which increases the return current loop and thus inductance.
Power Filtering & Distribution
You can reduce system noise by providing clean, evenly distributed
power to V_CC on all boards and devices. This section describes techniques
for distributing and filtering power.
Filtering Noise
To decrease the low-frequency (< 1 kHz) noise caused by the power
supply, filter the noise on power lines at the point where the power
connects to the PCB and to each device. Place a 100-F electrolytic
capacitor where the power supply lines enter the PCB. If you use a
voltage regulator, place the capacitor immediately after the pin that
provides the VCC signal to the device(s). Capacitors not only filter
low-frequency noise from the power supply, but also supply extra current
when many outputs switch simultaneously in a circuit.
To filter power supply noise, use a non-resonant, surface-mount ferrite
bead large enough to handle the current in series with the power supply.
Place a 10- to 100-F bypass capacitor next to the ferrite bead (see
Figure 11–34). (If proper termination, layout, and filtering eliminate
enough noise, you do not need to use a ferrite bead.) The ferrite bead acts
as a short for high-frequency noise coming from the V_CC source. Any
low-frequency noise is filtered by a large 10-F capacitor after the ferrite
bead.
11–26
Stratix II Device Handbook, Volume 2
Altera Corporation
May 2007