Product category:
Frequency Control Components
News Release from: Mercury United Electronics | Subject: 3HM57
Edited by the Electronicstalk Editorial
Team on 11 March 2004
Spread-spectrum oscillator reduces
system EMI
Mercury provides a clock oscillator drop-in replacement solution suitable for many products that fail EMI/EMC compliance testing.
Mercury provides a clock oscillator drop-in replacement solution for those products that fail at EMI/EMC compliance testing Traditional ways to deal with such problems include adding ferrite beads, metal shielding, EMI filters, ground planes etc
This article was originally published on Electronicstalk on 1 Jul 2005 at 8.00am (UK)
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However, the principal source of the radiated peak energy is from system clock signals.
Therefore, replacing the conventional clock oscillators with the low-EMI type can be the most economical and efficient route to compliance.
The advantages include reduced time to market and no board respinning.
Mercury has been producing low-EMI spread-spectrum clock oscillators for three years.
Packages include a 9.6 x 11.4 x 4.7mm FR4 based SMD leadless package and full- and half-size 4-pin DIPs.
To address the market need for a smaller package size for industries such as still digital cameras, wireless LANs and LCD displays, Mercury has begun volume production of its HM57 (5 x 7 x 1.8mm 4-pad ceramic leadless SMD package) spread-spectrum clock oscillators.
An even smaller package, HM53 (5 x 3.2 x 1.0 mm), is also in development.
The 3HM57 is available from 5.0 to 160.0MHz, produces a CMOS square-wave output with a supply voltage of +3.3V, a duty cycle of 50+/-5%, and spread types that include a down spread (-0.5, -1 and -3%) and centre spread (+/-0.25, +/-0.5 and +/-1.5%).
The typical cycle-to-cycle jitter is +/-250ps.
The modulation carrier frequency is 6.93kHz at 10MHz and 55.5kHz at 160MHz (frequency dependent).
The typical EMI reduction is 12dB.
Currently, sample lead times are 3 to 4 weeks with volume leadtime at 6 to 7 weeks.
Unlike conventional clocks whose mode energy has a narrow bandwidth and a sharp peak type, the mode energy of a spread-spectrum clock is spread over a wider bandwidth, resulting from the frequency modulation technique.
The modulation carrier frequency is in the kilohertz range, which makes the modulation process transparent to the oscillator frequency.
The controlled modulation process can be on all of one side of the nominal frequency (down spread) or 50% up and 50% down (centre spread).
The down spread is preferred if overclocking is a problem to the system.
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