In its simplest form, an oscillator consists of an amplifier and a filter/coupling network operating in a positive feedback loop. When Barkhausen’s criteria are met, the resulting oscillation can be used as a reference frequency for various circuit applications. The highly popular crystal clock oscillator (XO) on the market today consists of a leadless ceramic package, oscillator IC and quartz resonator. The crystal oscillator has a high Q, is self-compensating and designed to operate at specific stabilities over a given temperature range.