EMI Reduction Spread Spectrum Clock Oscillators
3HM572 Series Group “R”
MERCURY
Since 1973
The most efficient way to reduce EMI (Electromagnetic Interference) is to reduce it from its
principle source – the clock oscillator. Mercury 3HM572, an integrated clock module
composed of a spread spectrum clock and a quartz crystal, reduces EMI by 9 dB or more
while providing the clock speed needed for the system. It is a drop-in replacement for
standard 5x7 mm non-SSC clocks, no need to change the board or the solder pad layout.
The 3HM572 series (1.4 mm height) replaces the 3HM57 series (1.8 mm height). They are
identical products, with the only difference being the package heights. The 3HM57 is obsolete.
Please refer to Mercury PCN-111004 “Change HM57 to HM572” .
Applications:
◘ Printers; Multiple function printers (MPCs)
◘ Digital copiers; PDAs
◘ Networking; LAN / WAN; Routers
◘ Storage systems (CD-ROM, VCD, DVD & HDD)
◘ Scanner; Modems; Projectors
◘ Hand-held ID Readers
◘ Embedded systems; Electrical Musical Instrument
◘ Automotive; GPS Car Navigation Systems
◘ LCD PC Monitors / LCD TVs
◘ ADSL; PCMCIA
◘ Still Digital Cameras (SDCs)
◘ Medical Devices
Modulation Types
DOWN or CENTER spread
Spread Spectrum Clock (SSC):
Down spread “D”. “D1” as an example
Center spread “C”. “C0.5” as an example
Unlike the conventional clock, the mode
energy of a spread spectrum clock is
spread (distributed) over a wider
bandwidth between two pre-defined
frequency boundaries by the frequency
modulation technique. The modulation
carrier frequency is in the KHz range
which makes the modulation process
transparent to the oscillator frequency.
This controlled modulation process can
be on all of one side of the nominal
frequency (down spread), which is
preferred if system over-clocking is a
concern, or 50% up and 50% down
(center spread).
Output amplitude (dB) vs frequency span (MHz)
Conventional
Clock
Conventional
Clock
dB
dB
EMI reduction
EMI reduction
Spread
spectrum
clock
Frequency
fo=fc
fo - (fo*0.5%)
fo + (fo*0.5%)
fc
fo - (fo*1%)
32.768 MHz non-SSC vs SSC at Center Spread 1.5%:
-9.9 dB
Center spread
1.5% (C1.5)
No modulation
-23.0 dB
13.1 dB
reduction
MERCURY www.mercury-crystal.com
Taiwan: TEL (886)-2-2406-2779, FAX (886)-2-2496-0769, e-mail: sales-tw@mercury-crystal.com
U.S.A.: TEL (1)-909-466-0427, FAX (1)-909-466-0762, e-mail: sales-us@mercury-crystal.com
MERCURY
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Oct. 18, 2011 Rev. 0