May 2007
rev 0.3
Spread Spectrum Frequency Generation
The clocks in digital systems are typically square waves
with a 50% duty cycle and as frequencies increase the
edge rates also get faster. Analysis shows that a square
wave is composed of fundamental frequency and
harmonics. The fundamental frequency and harmonics
generate the energy peaks that become the source of
EMI. Regulatory agencies test electronic equipment by
measuring the amount of peak energy radiated from the
equipment. In fact, the peak level allowed decreases as
the frequency increases. The standard methods of
reducing EMI are to use shielding, filtering, multi-layer
PCS3P622S04J
PCBs etc. These methods are expensive. Spread
spectrum clocking reduces the peak energy by reducing
the Q factor of the clock. This is done by slowly
modulating the clock frequency. PCS3P622S04J uses
the center modulation spread spectrum technique in
which the modulated output frequency varies above and
below
the
reference
frequency
with
a
specified
modulation rate. With center modulation, the average
frequency is the same as the unmodulated frequency
and there is no performance degradation
Timing-Safe™ technology
Timing-Safe™ technology is the ability to modulate a
clock source with Spread Spectrum technology and
maintain synchronization with any associated data path.
Pin Configuration
CLKIN / XIN
XOUT
1
2
8
7
6
5
CLKOUT
VDD
CLK3
CLK2
PCS3P622S04J
CLK1
3
GND
4
Low Frequency Timing-Sage™ Peak EMI Reduction IC
Notice: The information in this document is subject to change without notice.
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PULSECORE [ PulseCore Semiconductor ]
