Spread-Spectrum Clocking Introduction - Fujitsu MB86R02 Jade-D Application Note

2 Spread-Spectrum Clocking Introduction

Spread-spectrum clocking has become more popular in portable electronics devices because of faster
clock speeds and the increasing integration of high-resolution LCD displays in smaller and smaller
devices. As these devices are designed to be lightweight and inexpensive, passive EMI reduction
measures such as capacitors or metal shielding are not a viable option. This document briefly
describes the functionality and use of the Spread-Spectrum Clock Generation (SSCG) unit of the
MB86R02 'Jade-D' display controller device.
A configurable spread-spectrum clock generator unit is integrated in MB86R02 'Jade-D' in order to be
able to provide a modulated clock signal (as an alternative, parallel to the output of the internal PLL
unit), for use by the GDC's internal units. Actually, this means that a modulated clock signal can be
generated seperately for:
the internal circuitry
the output display controllers (also seperately for each)
The purpose of the SSCG is to spread the electromagnetic energy generated in a particluar bandwidth
over a frequency domain, resulting in a wider bandwidth, reducing the spectral density of the EMI
produced by the device. The radiated energy itself is not reduced, but simply distributed in a frequency
domain.
Version 1.30
Figure 1 Screenshot of EMI analysis using SSCG
Figure 2 EMI improvement using SSCG
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