A 25-MHz Self-Referenced Solid-State Frequency Source Suitable for XO-Replacement

Recent trends in the development of integrated silicon frequency sources are discussed. Within that context, a 25-MHz self-referenced solid-state frequency source is presented and demonstrated where measured performance makes it suitable for replacement of crystal oscillators (XOs) in data interface applications. The frequency source is referenced to a frequency-trimmed and temperature-compensated 800-MHz free-running $LC$ oscillator (LCO) that is implemented in a standard logic CMOS process and with no specialized analog process options. Mechanisms giving rise to frequency drift in integrated LCOs are discussed and supported by analytical expressions. Design objectives and a compensation technique are presented where several implementation challenges are uncovered. Fabricated in a 0.25-$mu$m 1P5M CMOS process, and with no external components, the prototype frequency source dissipates 59.4 mW while maintaining ${pm} 152$ ppm frequency inaccuracy over process, ${pm} 10hbox{%}$ variation in the power supply voltage, and from ${-}$ 10 $^{circ}$ C to 80 $^{circ}$ C. Variation against other environmental factors is also presented. Nominal period jitter and power-on start-up latency are 2.75 ps$_{rm rms}$ and 268 $mu$s, respectively. These performance metrics are compared with an XO at the same frequency.