Shortening the startup time of a crystal oscillator is critical in improving the energy efficiency of the Internet of Things (IoT) sensor node. This article presents an investigative study on the application of adaptive chirping using zero-phase cross-detection to reduce the startup time of a crystal oscillator that is robust to voltage, temperature and even process variations without any costly trimming. Post-layout simulations on a 38.4 MHz crystal resonator with 1.0 V supply and 65-nm CMOS process confirms the feasibility of this approach and its ability to effectively reduce the startup time by correcting both phase and frequency mismatches. The results showcase the promising potential of zero-phase adaptive chirp as a viable variation-tolerant technique allowing for a high frequency mismatch tolerance of 1.1×10 ppm-Δf.