Xilinx Virtex-5 RocketIO GTP User Manual

Virtex-5 RocketIO GTP Transceiver User Guide www.xilinx.com 213
UG196 (v1.3) May 25, 2007
Providing Power
R
Description
Linear Regulator Selection Criteria
The selection criteria for the linear regulator are:
• Meet or exceed the characteristics specified in the Virtex-5 Data Sheet.
• The PSRR of the linear regulator must provide attenuation in a frequency range where
the sourcing power supply or regulator emits noise. Use an adjustable regulator so
that the voltage can be changed, if necessary.
The PSRR over frequency of a linear regulator (see Figure 10-10) is temperature and load-
current dependent. Because the PSRR of the regulator in this example has a local minimum
of rejection around 300 kHz, extra care must be taken if the sourcing power supply has
spurs or high-amplitude noise in this frequency range.
If the sourcing power supply cannot be changed or a different power supply cannot be
selected, an additional filter network between the output of the sourcing power supply
and the input of the linear regulator is required to prevent substantial noise from passing
through the linear regulator at the minimum of attenuation. Because the capacitor on the
output of the regulator is part of the regulator control loop, this capacitor not only impacts
the regulator stability but the PSSR as well.
Figure 10-10: PSRR over the Frequency of a Linear Regulator
Frequency (Hz)
UG196_c10_10_100506
Ripple Rejection (dB)

Xilinx Virtex-5 RocketIO GTP Specifications

General

Brand	Xilinx
Model	Virtex-5 RocketIO GTP
Category	Transceiver
Language	English