December 2003
P2040C
rev 1.0
Modulation Selection (Commercial) – Table 1
Spreading Range
54 MHz 65 MHz 81 MHz 108 MHz 162 MHz
MRA SR1
SR0
Modulation Rate
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
+/-1.4% +/-1.2% +/-1.0% +/-0.8%
+/-2.0% +/-1.9% +/-1.6% +/-1.2%
+/-1.1% +/-0.9% +/-0.5% +/-0.4%
+/-1.8% +/-1.5% +/-1.0% +/-0.6%
+/-1.3% +/-1.3% +/-1.3% +/-1.2%
+/-2.2% +/-2.1% +/-2.1% +/-1.9%
+/-1.4% +/-1.3% +/-1.4% +/-1.2%
+/-2.1% +/-2.1% +/-2.1% +/-2.0%
+/-0.4%
+/-0.8%
+/-0.3%
+/-0.4%
+/-1.1%
+/-1.8%
+/-0.9%
+/-1.4%
(Fin/80) * 62.49 KHz
(Fin/80) * 62.49 KHz
(Fin/80) * 62.49 KHz
(Fin/80) * 62.49 KHz
(Fin/80) * 20.83 KHz
(Fin/80) * 20.83 KHz
(Fin/80) * 20.83 KHz
(Fin/80) * 20.83 KHz
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: P2040C is designed for high resolution flat panel applications and is able to support panel frequencies
from 54MHz to 170MHz. For a 65MHz pixel clock frequency, a spreading selection of MRA=0, SR1=1 and SR0=1
provides a percentage deviation of +/-1.50% (see Table 1). This results in frequency on ModOUT being swept
from 64.03MHz to 65.98MHz at a modulation rate of 50.77KHz (see Table 1). This particular example (see Figure
below) 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.
P2040C Application Schematic for Mobile LCD Graphics
65MHz from graphics accelerator
Modulated 65MHz signal with
±0.75 deviation and modulation
1
2
3
4
8
7
6
5
VDD
CLKIN
rate of 56.24KHz. This signal is
connected back to the spread
spectrum input pin (SSIN) of the
graphics accelerator.
SR0
ModOUT
SSON#
MRA
SR1
VSS
+3.3V
0.1µF
Digital control for the SS enable
or disable
P2040C
LCD Panel EMI Reduction IC
3 of 9
Notice: The information in this document is subject to change without notice.
ALSC [ ALLIANCE SEMICONDUCTOR CORPORATION ]
