SG-9101 Spread Spectrum Crystal to Reduce EMI Electromagnetic Interference Programmable Crystal

1. Using Spread Spectrum Clock Modulator to Reduce EMI

Essentially, spread spectrum is a modulation method measured by modulation percentage. For example, 0.5% modulation means that a 100MHz clock signal is modulated between 99.5MHz and 100.5MHz. Due to the fact that the fundamental frequency of 100MHz remains at the center frequency, it is called center 0.5% (б) modulation.

The spread spectrum method must also ensure that there are no conflicts in the minimum clock cycle. To avoid exceeding the maximum frequency of the system, the clock signal typically scans and varies between 99.5 MHz and 100 MHz, a method called down spread spectrum. In this case, the deviation of clock frequency is measured by a negative percentage, which is -0.5% (б) extension.

Spread spectrum is mainly used for system clocks. For the current 400MHz PC, specific electromagnetic radiation reduction measures are required due to the high-frequency clock. The spread spectrum clock crystal oscillator of SG-9101 provides several types of modulation methods, which can achieve modulation values of ± 0.5%, ± 0.75%, ± 1%, ± 1.5%, ± 2%, and 0.25%. Practice has shown that the introduction of spread spectrum clock crystal oscillator modulation results in minimal clock signal jitter.

2. What are the advantages of using Epson SG-9101 series spread spectrum adjustable crystal oscillator clock?

Compared to other EMI suppression technologies, the systematic characteristics of spread spectrum crystal oscillators are their main advantage. All clock and timing signals generated by the spread spectrum adjustable crystal oscillator are also modulated at the same ratio. This brings significant EMI improvement effects to the entire system. In EMC testing, changing only one capacitor or programmable digital input can adjust the frequency modulation degree (spread spectrum percentage). The programmable feature of the frequency display crystal oscillator simplifies the use of this technology in product design and EMC testing, and can also reduce the printed circuit board area used for EMI suppression, saving product costs and time to market. The establishment of holding time is only based on the rising edge of the timing signal as a reference. Due to the fact that the rise and fall times do not change when using spread spectrum technology, strict time limits can still be established and maintained. When using a central spread spectrum clock, the highest peak frequency will slightly increase, but downward spread spectrum clock modulation can be used to avoid this change. Another advantage of using a spread spectrum crystal oscillator is that it can further integrate programmable EMI suppression and timing functions into the same product, resulting in higher performance and lower cost. Another benefit is that it can accelerate the launch of wireless and portable application products into the market.

By dynamically changing the clock frequency, the electromagnetic radiation power can be effectively reduced, and the impact of EMI electromagnetic interference can be minimized. See the comparison chart of waveform output between Epson Extended Spectrum Clock Crystal and ordinary active crystal:

Internal block diagram of spread spectrum crystal oscillator: