May 2007

PCS5P23Z05B/09B

rev 0.2

Timing-Safe™ Peak EMI Reduction IC

2 of 14

Notice: The information in this document is subject to change without notice.

CLKIN

CLK2

1

2

3

4

5

6

7

8

CLK3

CLK4

CLKOUT

GND

PCS5P23Z05B

CLK1

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

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 )

Pin Configuration ( 16 Pin Device )

1

2

3

4

13

14

15

16

5

6

7

8

9

10

11

12

CLKA3

CLKA4

CLKB3

CLKB4

CLKOUT

GND

S1

S2

CLKA2

CLKB1

CLKB2

CLKA1

CLKIN

PCS5P23Z09B

GND