The NJM2555 is a 622.08MHz VCXO (Voltage Controlled Crystal Oscillator) IC designed for optical fiber telecommunication systems，using NewJRC superior Bipolar technology，which consists of an oscillation amplifier，a variable capacitor diode，a quadruple (×4) frequency circuit，high pass filter，and limiter amplifier. The NJM2555 generate x4 frequency to add the only 155.52MHz crystal and LC filter，and the output is differential LVPECL equivalent. The recommended input crystal frequency is from 120 to 160 MHz. The jitter performance and phase noise is very low based on excellent oscillation circuit. This can be applied to optical communication，especially the WDM system.