October 2003 ASM3X2105A

rev 1.0


Alliance Semiconductor
2575, Augustine Drive • Santa Clara, CA • Tel: 408.855.4900 • Fax: 408.855.4999 • www.alsc.com
Notice: The information in this document is subject to change without notice.


Features
null FCC approved method of EMI attenuation.
null Generates a 1X or ½ X low EMI spread spectrum
clock of the input frequency.
null Input frequency range: 6MHz to 10 MHz.
null Internal loop filter minimizes external components
and board space.
null Frequency deviation: Maximum ± 1%.
null SSON# control pin for spread spectrum enable
and disable options.
null Low cycle-to-cycle jitter.
null 5.0V ± 5% operating voltage range.
null TTL or CMOS compatible outputs.
null Ultra-low power CMOS design.
null Available in 8-pin SOIC and TSSOP.

Product Description
The ASM3X2105A is a versatile spread spectrum
frequency modulator designed specifically for input clock
frequencies from 6MHz to 12MHz. The ASM3X2105A
can generate an EMI reduced clock from crystal, ceramic
resonator, or system clock. The ASM3X2105A offers
frequency deviation of ± 1%.

The ASM3X2105A reduces electromagnetic interference
(EMI) at the clock source, allowing system wide reduction
of EMI of down stream clock and data dependent
signals. The ASM3X2105A allows significant system cost
savings by reducing the number of circuit board layers
ferrite beads, shielding and other passive components
that are traditionally required to pass EMI regulations.

The ASM3X2105A uses the most efficient and optimized
modulation profile approved by the FCC and is
implemented in a proprietary all digital method.

The ASM3X2105A modulates the output of a single PLL
in order to “spread” the bandwidth of a synthesized clock,
and more importantly, decreases the peak amplitudes of
its harmonics. This results in significantly lower system
EMI compared to the typical narrow band signal produced
by oscillators and most frequency generators. Lowering
EMI by increasing a signal’s bandwidth is called ‘spread
spectrum clock generation’.

Applications

The ASM3X2105A is targeted towards EMI management
for high speed digital applications such as PC peripheral
devices, consumer electronics and embedded controller
systems.




Block Diagram
VSS
XIN
XOUT

Crystal
Oscillator


Frequency
Divider
Feedback
Divider
Modulation
Phase
Detector
Loop
Filter
VCO
Output
Divider
MODOUT
PLL
VDD
SSON#
DIV2
SR0