A new range of spread spectrum technology (SST) oscillators that can provide a low-cost means of reducing EMI radiation in electronic systems and are manufactured as drop-in replacements for standard clock oscillators are available from Euroquartz. The company's EQ-HM series oscillators provide EMI suppression of between 10 and 16 dB at source, and range from 8,0 MHz to 165 MHz.
Electronic devices must comply with electromagnetic radiation emission standards. Traditional EMI reduction techniques include the use of shielding, filtering, de-coupling, ground planes and ferrite beads. However, the current trend towards higher carrier frequencies, narrower bandwidth and lower operating voltages makes these traditional methods less effective and increasingly expensive. The present trend is to control EMI at its source, the system clock oscillator.
As system timing signals are usually synchronised to a reference clock oscillator, from the perspective of efficiency, an EMI suppressed reference signal at the clock oscillator stage eliminates the need for traditional EMI suppression measures. Spread Spectrum Technology (SST) serves this purpose, being a technique first used in World War II for RF jamming and anti-jamming tactics. By modulating the peak energy over a wide frequency bandwidth with a low frequency carrier, the amplitude of the fundamental frequency and its associated harmonics can be reduced by several dB, leaving the total amount of energy in the system remaining.
Using clock oscillators with SST technology has no detrimental impact on the system performance (for example CPU clock rate) as the modulation rate is very slow relative to the clock output frequency, making the SST technology transparent to the system. With the integration of SST, loop filter components and matched impedance layout, the Euroquartz EQ-HM series oscillators provide a highly cost-effective solution to many EMI problems.
As an example, the EQ-HM57 oscillator series is a 3,3 V supply part offering CMOS output logic and is housed in a standard 7 x 5 mm SMD package. Pin 1 options include modulation on/off, tri-state for all outputs and power down. Ageing is ±5 ppm/year maximum while jitter for all models is 250 ps typical.
For more information contact Kevin Murphy, Arrow Altech Distribution, 011 923 9600, [email protected].
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