May 2007
rev 0.2
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
PCS5P23Z05B/09B
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. The PCS5P23Z05B/09B
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 ( 8 Pin Device )
CLKIN
1
8
7
6
5
CLKOUT
CLK4
V
DD
CLK3
CLK1
2
CLK2
3
GND
4
PCS5P23Z05B
Pin Configuration ( 16 Pin Device )
CLKIN
CLKA1
CLKA2
V
DD
1
2
3
4
16
15
14
CLKOUT
CLKA4
CLKA3
V
DD
GND
CLKB4
CLKB3
S1
PCS5P23Z09B
13
12
11
10
9
GND
5
CLKB1
6
CLKB2
7
S2
8
Timing-Safe™ Peak EMI Reduction IC
Notice: The information in this document is subject to change without notice.
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PULSECORE [ PulseCore Semiconductor ]
