748-000
9
SPREAD SPECTRUM SELECTION
Table 1 illustrates the possible spread spectrum options. The optimal setting should minimize system
EMI to the fullest without affecting system performance. The spreading is described as a percentage
deviation of the center frequency (Note: the center frequency is the frequency of the external reference
input on CLKIN, Pin 1).
Example
: P2065 is designed for high resolution flat panel applications and is able to support XGA (1024
X 768) flat panel that operates on 65MHz (Fin) clock speed. A spreading selection of SR1=0, SR0=1 and
modulation rate selection MRA=1 provides a percentage deviation of +/-1.00% (see Table 1) of Fin. This
results in frequency on ModOUT being swept from 64.35 MHz to 65.65 MHz at a modulation rate of
33.85KHz (see Table 1). This particular example (see Figure 3) given here is a common EMI reduction
method for notebook LCD panel and has already been implemented by most of the leading OEM and
mobile graphic accelerator manufacturers.
Figure 3 – P2065 Application Schematic For Mobile LCD Graphics Controllers
P2065
This signal is
connected back to the
Spread Spectrum Input
Pin (SSIN) of the
Graphics Accelerator.
VDD
1
8
6
4
3
2
7
5
CLKIN
MRA
SR1
VSS
VDD
SSON
ModOUT
SR0
0.1uF
65 MHZ From Graphics Accelerator
Digital Control for SS
enable or disable
EMC SOFTWARE SIMULATION
By using PulseCore Semiconductor, Inc.’s proprietary EMC simulation software –
EMI-lator
, radiated
system level EMI analysis can be made easier to allow a quantitative assessment on PulseCore’s EMI
reduction products. The simulation engine of this EMC software has already been characterized to
correlate with the electrical characteristics of PulseCore EMI reduction IC’s.
Figure 4
below is an
example of the simulation result. Please visit our web site at
www.pulsecore.com
for information on how
to obtain a free copy and demonstration of
EMI-lator
.