A 12MHz/38.4MHz Fast Start-Up Crystal Oscillator using Impedance Guided Chirp Injection in 22nm FinFET CMOS

Low power mobile and edge computing systems requires fast wakeup for pleasant end user experience and for efficient data processing. Fast start up oscillators are needed to enable system to periodically go to sleep state and wakeup. Oscillators implementing techniques like negative resistance (Rn) boosting [1] or external power injection [2 - 5] demonstrated sub-100 μs startup time. To boost Rn, either large bias current or multiple bias stages are required. Other techniques like Injection at start phase is proven to be highly efficient if the injected frequency matches the crystal frequency [4] or injected clock phase matches oscillation crossing phase [5]. However, it is difficult to maintain the injection frequency close to the crystal frequency across PVT variations and the efficiency drops sharply when there is a frequency mismatch [3]. Spreading the injection energy close to the target crystal using frequency dithering or chirp [2] can cover the crystal resonance frequency (f
₀
), however energy is not concentrated at f
₀
which degrades th e injection efficiency. To optimize th e injection efficiency and hence startup time, a new robust impedance guided chirp injection (IGCI) frequency locking technique for ultrafast startup of reference oscillators is demonstrated in an Intel 22FFL test chip achieving 6.5× reduction in start-up time at 38.4MHz. An impedance guided feedback network detects f
₀
and injects high energy only at resonance. As a result, both start-uptime and energy can be reduced significantly. Since the injection frequency is guided by the crystal impedance, a higher injection efficiency can always be guaranteed across PVT variations without accurate calibration of injection frequency and no highspeed (power) detection circuit is needed.