212.5[MHz] fundamental oscillator for fiber channel application

Abstract

As explosive growth of the Internet, a capacity of the server to distribute information has been increasing year by year and it is getting difficult for conventional interface (SCSI) to provide sufficient services. To solve the problem, the new method of fiber channel was developed and the transmission rate was speeded up. According to it, the frequency of the clock oscillator is required to become higher from 106.25[MHz] to 212.5[MHz]. To achieve high frequency, the PLL oscillator and the SAW oscillator are popular. The PLL oscillator has tight frequency stability, but the multiple of a frequency causes sub-harmonics and that deteriorates the jitter characteristics. On the other hand, the SAW oscillator has good jitter characteristics, but its frequency stability is worse. As the solution, we developed the single-seal type high frequency clock oscillator with fundamental oscillation in 7[mm] x 5[mm] package. For this oscillator, we designed the AT cut crystal unit with inverted mesa structure by etching in order to make crystal blank (quartz substrate) thinner to the limit. It enabled us to design high frequency crystal unit at higher than 200[MHz] by fundamental resonation. With this development, we can maximize the characteristics of the AT cut crystal unit. Now we can provide the oscillator at 212.5[MHz] with frequency stability of ±50[ppm] over 20 years in temperature range of –40[?] to +85[?]. Thanks to fundamental oscillation, the oscillator can also offer good jitter and phase noise characteristics.